Julien Peyrton

Luc Avérous
email: luc.averous@unistra.fr

Structure-properties relationships of cellular materials from biobased polyurethane foams

Keywords: Polyurethane, Foams, Biobased, Structure-properties, Sustainable

The polyurethanes (PU) are a very versatile family of materials mainly obtained by combinations of polyols and polyisocyanates. Based on their annual worldwide production of around 20 million tons and a global market of $50 billion (2016), PUs rank 6th among all polymers. Through their value chain, PUs involve different players: (i) the chemists producing most of PUs raw materials, (ii) the PUs producers from the raw materials, (iii) the compounders/assemblers who formulate PUs into their final products, and finally (iv) the end-users. Due to the multiplicity of their structures, PUs can be used in various forms and applications. Cellular materials are the largest part of this market (more than 60%) with segments including the furniture, automotive, bedding, insulation, building or construction markets. Two main types of foam can be fabricated: (i) flexible with open cells, stress and tensile properties, e.g., furniture or bedding, and (ii) rigid with closed cells, low thermal conductivity, low density and high dimensional stability mainly for thermal insulation, e.g., building industries. The formulation step significantly influences the microstructure or morphology of these cellular materials and impacts the final foam properties. Even if some partially biobased compounds (polyols) can be used, commercial PU cellular materials are till now mainly based on fossil resources. However, future materials will combine high performance with low environmental impact in order to

Introduction

The depletion of some resources from fossil-based refineries, the degradation of the environment and its connection with the climate is at the core of every recent international forums.

In 2015, the United Nations developed an agenda of action for people, planet, and prosperity regrouped in 17 establish goals. The "goal 12" entitled "Ensure sustainable consumption and production patterns" sets the sustainable management and efficient use of natural resources by 2030 [START_REF]Transforming our world: the 2030 Agenda for Sustainable Development[END_REF]. In this hot context, the development of new and/or greener polymer materials with higher performances and lower environmental impacts from cradle to cradle than the traditional fossilbased equivalent is a priority [START_REF] Manzardo | Life Cycle Assessment Framework To Support the Design of Biobased Rigid Polyurethane Foams[END_REF]. This recent trend is also driven by the development of innovative molecular architectures with new properties, which can be extracted or bioproduced from various types of biomass combining different disciplines such as biotech, chemistry, science and materials engineering.

The global production of plastics reached around 360 million tons in 2018 [START_REF]Plastics-the Facts[END_REF]. The bioplastics, defined as biobased or biodegradable polymers, represent less than 1% of this worldwide plastics production [START_REF] Garside | Production capacity of bioplastics worldwide from 2017 to 2024, by type[END_REF][START_REF]Bioplastic materials[END_REF]. Biobased polymers are defined as polymers obtained more or less directly from biomass, i.e., from all the living organisms, with a positive level of C 14 . The interest in biobased polymers knows an exponential growth in the last decades due to the desire to reduce the fossilbased products dependency [START_REF] Babu | Current progress on bio-based polymers and their future trends[END_REF] and the environmental impact. The production of biobased monomers for sustainable plastics was extensively developed to design common-like polymers such as polyamides [START_REF] Winnacker | Biobased Polyamides: Recent Advances in Basic and Applied Research[END_REF], polyesters [START_REF] Jiang | Enzymatic Synthesis of Biobased Polyesters and Polyamides[END_REF][START_REF] De Jong | Furandicarboxylic Acid (FDCA), A Versatile Building Block for a Very Interesting Class of Polyesters[END_REF], polyethylenes [START_REF] Aeschelmann | Biobased Building Blocks and Polymers in the World: Capacities, Production, and Applications-Status Quo and Trends Towards 2020[END_REF] or polyurethanes (PUs) [START_REF] Furtwengler | Renewable polyols for advanced polyurethane foams from diverse biomass resources[END_REF]. On the other hand, biodegradable plastics are defined as materials degraded into CO2 or/and CH4 and water mainly by the action of microorganisms [START_REF] Iwata | Biodegradable and Bio-Based Polymers: Future Prospects of Eco-Friendly Plastics[END_REF] in normalized conditions (time, temperature, media).

However, biodegradable polymers can also be produced from fossil-resource such as polycaprolactone. The development of biodegradable polymers is also linked to the vast and increasing problem of dispersion and accumulation of plastics in the environment. With the actual growth of microplastics accumulation in the ocean [START_REF] Cozar | Plastic debris in the open ocean[END_REF] and global warming, the urge is to design sustainable polymeric materials.

Although PUs can be obtained without isocyanates (Non-Isocyanate Polyurethanes or NIPU) by, e.g., the reaction between polycyclocarbonates and polyamines [START_REF] Carré | From the Synthesis of Biobased Cyclic Carbonate to Polyhydroxyurethanes: A Promising Route towards Renewable Non-Isocyanate Polyurethanes[END_REF], they are till now mostly obtained by polyaddition between polyisocyanates and polyols to obtain linear or crosslinked architectures. PU is the most versatile polymer family in terms of applications. This diversity originates from the myriad of chemical structures of the polyols and polyisocyanates and the particular property of the carbamate group. PUs rank 6 th among all polymers with a production of around 22 million tons [START_REF] Hicks | A review of the global PU industry 2016 and outlook for 2017[END_REF] and a global market of $50 billion (2016). The PU market is usually segmented in 5 uneven parts with the foams (65% of the market), the coatings (13%), the elastomers (12%), the adhesives (7%) and the others, including the biomedical field (3%) [START_REF] Akindoyo | Polyurethane types, synthesis and applications -a review[END_REF][START_REF] Wendels | Biobased polyurethanes for biomedical applications[END_REF]. Two main types of PU foams (PUFs) can be identified: the flexible foam (F-PUF) with an open cell structure and the rigid (R-PUF) one with a closed-cell structure. Of course, intermediate systems can also be developed, e.g., the spray foams are rigid with open-cell structures. PUFs structures and properties can be tailored by (i) the structure and quantity of the monomers, (ii) the catalysts, (iii) the surfactants and (iv) the blowing agents (BA). To this basic list, different other ingredients are also used, such as fillers, flame retardants (FR), pigments, or dyes. F-PUFs representing the main part of the foams market (60%) are synthesized by molding or slabstock process [START_REF] Randall | The polyurethanes book[END_REF]. As presented in Fig. 1, PUFs are classified into several categories depending on their properties. The high resilience foams provide resilience and buoyancy compared to viscoelastic foams, which respond slower to stress. Integral skin foams are composed of a highdensity skin and low-density core foam sandwich structure [START_REF] Ashida | Polyurethane and related foams: chemistry and technology[END_REF] obtained, e.g., by reaction injection molding (RIM). The foams formulation and processing are key points to obtain the required properties. The walls are melted after the cellular material synthesis to obtain very high consistency and controlled porosity for filter applications [START_REF] Randall | The polyurethanes book[END_REF]. F-PUFs are used in various everyday life applications, such as filters, automotive and furniture/bedding cushioning (Fig. 1).

The R-PUFs are classified into three categories (Fig. 1) such as (i) the sprayed foams which are produced on-site with a high-pressure gun, (ii) the boardstocks are flat sheet products made with flexible facings and (iii) the sandwich panels encased by rigid facings [START_REF] Randall | The polyurethanes book[END_REF]. The major R-PUFs are designed to be used as thermal insulation in appliances, construction, transport or pipe insulation.

Despite the emergence of new materials with low thermal conductivity [START_REF] Lang | Thermal Conductivity of Vacuum Insulation Materials for Thermal Energy Stores in Solar Thermal Systems[END_REF][START_REF] Vėjelis | Research on thermal conductivity of vacuum insulating materials[END_REF][START_REF] Zhan | Biomimetic Carbon Tube Aerogel Enables Super-Elasticity and Thermal Insulation[END_REF], the R-PUF remains a major material used as thermal insulation due to their low thermal conductivity and density, compared to mineral wool, polystyrene or lignocellulose product [START_REF] Abu-Jdayil | Traditional, state-of-the-art and renewable thermal building insulation materials: An overview[END_REF]. Thermal insulation is nowadays a major strategic field, e.g. in 2018, one third of the worldwide energy consumption was used for the heating or cooling of buildings [START_REF]World Energy Balances: Overview. IeaOrg[END_REF]. In this context, the development of new sustainable materials with better properties than their fossil-based counterparts is an actual fascinating challenge. The most significant variables to get the best environmental performances of PUF were linked to the low thermal conductivity and density of the biobased PUFs [START_REF] Manzardo | Life Cycle Assessment Framework To Support the Design of Biobased Rigid Polyurethane Foams[END_REF]. In the field of biobased PUs, different partial overviews can be found. Sustainable PUs were partially reviewed for adhesive applications [START_REF] Tenorio-Alfonso | A Review of the Sustainable Approaches in the Production of Bio-based Polyurethanes and Their Applications in the Adhesive Field[END_REF] or foams [START_REF] Furtwengler | Renewable polyols for advanced polyurethane foams from diverse biomass resources[END_REF][START_REF] Hayati | A simple methodology for improving the performance and sustainability of rigid polyurethane foam by incorporating industrial lignin[END_REF][START_REF] Agrawal | PU foam derived from renewable sources: Perspective on properties enhancement: An overview[END_REF]. The goal of this review is to complement, update and expand these previous states of the art. This work is also expected to provide a deep insight into the biobased PUFs field, especially in the study and analysis of the "structure-properties" relationships. The second section of this review gives an overview of basic information to know about PUFs, such as the isocyanate chemistry, the process of foam and the role of each component in the foam formation. The third section is focused on the renewable PUFs from biomass such as triglycerides, carbohydrates, polyphenols (lignins and tannins), wastes, and different molecules obtained by bioproduction as biobased building blocks for PUFs elaboration. The fourth section carefully reviews the relationships between these new biobased PU architectures, the cell morphology and the related properties such as the mechanical, thermal, fire resistance and acoustic behaviors. In the last section, very recent perspectives on the elaboration of foams from, e.g., NIPU, are analyzed and discussed.

PUF engineering and fundamentals

Isocyanate chemistry

The synthesis of urethane groups was first investigated in 1846 by Charles Adolf Wurtz (1817Wurtz ( -1884) ) with the study of the reaction between the cyanogen chloride and ethanol described in Scheme 1 [START_REF] Wurtz | Note sur la Formation de l'Urethane par l'Action du Chlorure de Cyanogène[END_REF]. Otto Bayer was a scientist in charge of finding a substitute for the Nylon 6.6 recently developed by Dupont when he discovered the PU by polyaddition between a diisocyanate and a polyester diol in 1937. The first thermoplastic PU (TPU) had elastic properties and was industrially developed during the Second World War as a rubber substitute from hevea in the USA. The development of isocyanate production and their fast reaction with hydrogen-labile groups helped the tremendous development of the urethane market [START_REF] Szycher | Szycher's handbook of polyurethanes[END_REF]. Scheme 1. The first synthesis of carbamate by Charles Adolf Wurtz. Adapted from [START_REF] Wurtz | Note sur la Formation de l'Urethane par l'Action du Chlorure de Cyanogène[END_REF].

Nowadays, the PU synthesis is still and mainly based on the polyaddition between polyisocyanates and polyols due to the high reactivity of the isocyanate groups with hydrogen-labile compounds, explained by the carbon electron deficiency. The isocyanate addition is a reversible reaction, exploited, for instance, to produce vitrimers called vinylogous urethane [START_REF] Denissen | Vinylogous Urethane Vitrimers[END_REF]. However, the cyclization of the product or the generation of gas inhibits the reversibility. Fig. 2 shows that the products of the isocyanate reactions can be classed according to the number of isocyanate additions (first, second and third) to yield it. The main PU synthesis results from the addition of isocyanate with an alcohol (A) yielding urethane group. This reaction is exothermic and releases 100 kJ/mol of heat [START_REF] Ionescu | Chemistry and technology of polyols for polyurethanes[END_REF]. Water has a similar reactivity as alcohol and, by reaction with isocyanate (B), produces unstable carbamic acid, which is instantaneously decomposed into CO2 and amine (C). The water-isocyanate reaction releases almost two times more heat (197 kJ/mol) than the alcohol-isocyanate system. The gases released due to the isocyanate additions are exploited to rapidly expand the polymer matrix for PUFs elaboration, mainly for soft foams with open cells. Analogously to the amine formation, the formation of amide by isocyanate and carboxylic acid addition (D) is accompanied by gaseous CO2 formation. For instance, when formic acid is used as carboxylic acid, the reaction produces an amine, CO2 and CO (E). Compared to the water-isocyanate addition, this particular reaction releases two moles of gas per mole of isocyanate. Furthermore, the amine formed by water or formic acid addition also reacts with isocyanate to form a disubstituted urea group (F). The isocyanate can also react with compounds without labile-hydrogen, such as epoxides (G). In this case, the oxygen atom from the epoxide ring attacks the carbon of the isocyanate; therefore, the reaction is less favored and requires high temperatures and specific catalysts to yield oxazolidone.

The high reactivity of isocyanate enables the 2 nd addition of isocyanate on the product resulting from a first addition. Both urethane and urea groups present labile hydrogens and can further react with isocyanate to synthesize allophanate (H) and biuret groups (I), respectively. Furthermore, isocyanate molecules can intermolecularly react and dimerize depending on the reaction conditions and catalysts into carbodiimide (J) or uretdione (K) [START_REF] Fink | Poly(urethane)s[END_REF]. Furthermore, the uretonimine group is irreversibly obtained after the third addition of isocyanate on carbodiimide (L).

The combination of three isocyanate groups also leads to a stable and six-membered ring isocyanurate group. It was demonstrated that allophanate (M), biuret (N), oxazolidone (O) and uretdione (P) are intermediates in the synthetic pathway to isocyanurate [START_REF] Gibb | The formation of high-purity isocyanurate through proazaphosphatrane-catalysed isocyanate cyclo-trimerisation: computational insights[END_REF][START_REF] Hoffman | Model System for a Urethane-Modified Isocyanurate Foam[END_REF][START_REF] Caille | Reaction of a diepoxide with a diisocyanate in bulk: I. Use of a tertiary amine catalyst[END_REF][START_REF] Nabulsi | Isocyanurate formation during rigid polyurethane foam assembly: a mechanistic study based on in situ IR and NMR spectroscopy[END_REF]. The polymerization of isocyanates with an appropriate catalyst was used to produce rigid foam exclusively composed of polyisocyanurate (PIR) network.

PUF Formulation

PUFs elaboration is a complex association of polyols, polyisocyanates, BAs, catalysts, surfactants and additives such as fillers or FRs. The general formulation quantities for PUFs in Table 1 are expressed in part by weight of polyol (pbw). The quantities of all components are calculated on a basis of 100 g of polyols to simplify the scale up or down. The BA quantity ranges from 3 to 30 pbw and depends on the targeted density and the BA structure. The dominant components in a PUF formulation are the polyisocyanate and polyol. Their contents, linked to the type of foam (R-PUF, F-PUF or PIR foam) and the targeted applications, are controlled by the NCO/OH index determined as the ratio between the isocyanate and the hydroxyl groups multiply by 100. promote the urethane group formation. As presented in Fig. 3, the PIR foam elaborated mainly from isocyanate is highly crosslinked and, consequently, highly brittle or friable [START_REF] Baumann | Isocyanurate Rigid Foam: Relationship Between Structure and Properties[END_REF]. However, the PIR foam has excellent thermal stability properties due to the isocyanurate group. In order to take advantage of the thermal stability of the isocyanurate and avoid the formation of a highly crosslinked network, hybrid PU-PIR foams were developed. They are formulated with NCO/OH index higher than 120 to form an isocyanurate group and lower than 600 to avoid high friability [START_REF] Reymore | Isocyanurate Foams: Chemistry, Properties and Processing[END_REF].

The PU-PIR foam combined the thermal stability of the PIR network with the flexibility of the PUF [START_REF] Nawata | Comparative Studies of Isocyanurate and Isocyanurate-Urethane Foams[END_REF]. They are classed among R-PUFs due to their similar mechanical properties and morphologies and consequently they are mainly used in thermal insulation. The PU-PIR foams are explicitly used when the fire hazard is high due to their higher thermal stability compared to R-PUFs. Several processes were developed industrially to produce PUFs, such as molding, slabstock, spaying, pour-in-place or frothing-in-place. In academic research, the two primary processes for the PUFs elaboration are the pour-in-place or molding method, described in Fig. 4. The foaming process is based on the one-shot method, where the polyol and polyisocyanate are intimately mixed. The components are usually separated into two parts with (i) the A-part containing the polyol, the BA, catalysts, surfactants and additives stirred vigorously to integrate air bubbles in the mixture and to obtain an emulsion (step 1 in Fig. 4) and (ii) the B-part composed of the polyisocyanate. Both parts are then mixed under stirring (steps 2 and 3 in Fig. 4). The reactive mixture is then poured into an open-cup for the pour-in-place process or in a closed mold with depending on the targeted application, an optional control of the temperature, for the molding process (step 4 in Fig. 4) where the polyaddition releases heat and forms the polymer network. The BA vaporizes and expands through the heat generated by the reaction, and the foam rises (step 5 in Fig. 4). In the end, a cellular material composed of gas-entrapping polymer cells is obtained (Step 6 in Fig. 4). Fig. 4. Detailed usual processes at lab scale for PUF elaboration: pour-in-place or molding process.

Polyisocyanate

Several pathways can be used to synthesize isocyanate groups such as the Curtius, Hofmann or Lossen rearrangements but also the phosgenation of primary amine [START_REF] Szycher | Szycher's handbook of polyurethanes[END_REF]. At the industrial scale, although toxic for human health, the phosgene is the preferred pathway for the production of isocyanate due to the difficulty of handling the unstable azide groups in the rearrangement reactions [START_REF] Knölker | A Novel Method for the Synthesis of Isocyanates Under Mild Conditions[END_REF][START_REF] Cotarca | Phosgenations -A Handbook[END_REF]. The main used isocyanates are the toluene diisocyanate (TDI), the methylene diphenyl 4,4'diisocyanate (MDI) and its polymeric form (pMDI) [START_REF] Szycher | Szycher's handbook of polyurethanes[END_REF], which is mostly used since it presents lower volatility and reduced toxicity compared to the monomer form. The pMDI superior functionality compared to the other polyisocyanates is also a key point for R-PUF elaboration, which require highly crosslink network. On the contrary to the aromatic monomer polyisocyanates, the pMDI is liquid at ambient temperature, facilitating the implementation at industrial scale. In addition to the aromatic polyisocyanates, some aliphatic polyisocyanates are used, such as the hexamethyleneisocyanate (HDI), the isophorone diisocyanate (IPDI), or the 4,4'-methylene bis cyclohexyl diisocyanate (H12 MDI). Their reactivities and structures are described in Table 2.

The stabilization of the mesomeric structures by the surroundings of the isocyanate group enhances the carbon electrophilic character and its reactivity. As shown in Table 2, the aromatic isocyanates are more reactive than the aliphatic or cycloaliphatic counterparts due to the delocalization of the negative charge on the aromatic ring. The reactivity of the aromatic TDI and MDI is two orders of magnitude higher than the aliphatic HDI, H12 MDI and IPDI.

Table 2 shows that the first addition of alcohol on a diisocyanate decreases the reactivity of the second addition. The foam elaboration requires high reactivity; therefore, aromatic polyisocyanates are used. Besides, the aromaticity brings several properties to the final products, such as, e.g., higher flame resistance and mechanical properties. In general, the MDI and TDI are used for F-PUFs and pMDI for R-PUFs. They are the primary polyisocyanates used in PUFs formulation. First, polyethers are produced from the alkoxylation with ethylene (EO) or propylene oxide (PO) from a simple starter molecule containing several OH or amine groups, primary and secondary. The polyolstarters can be pentaerythritol (f=5), sorbitol (f=6) or glycerol (f=3) and the polyamine starters can be ethylenediamine (f=4) or diethylenetriamine (f=5). From the starter to the corresponding oligomer, the IOH is decreased. Similarly, the polyester polyols are produced from controlled polycondensation or polyaddition between a dicarboxylic acid or an anhydride with a polyol-starter molecule. In general, polyether polyols generally present a lower viscosity and higher dispersity than polyester polyols, due to the flexible ether links. They also provide higher softness, hydrolytic and aging stabilities compared to polyester polyols [START_REF] Furtwengler | Renewable polyols for advanced polyurethane foams from diverse biomass resources[END_REF]. 3). On the contrary, the polyols used for F-PUFs have lower IOH and functionality. The higher the functionality of the polyols is, the higher the crosslinking density and rigidity of the foam should be. As depicted in Table 4, the reactivity toward isocyanate is mainly related to the nature of the H-labile group. The primary and secondary aliphatic amines, generally toxic for human health [START_REF] Greim | Toxicity of aliphatic amines: Structure-activity relationship[END_REF], are 1000 times more reactive than their OH aliphatic counterparts.

Water and primary aliphatic OHs have similar reactivities. Then, the reaction of water with isocyanate formed a primary amine, which reacts immediately due to its high reactivity compared to OH. The urea formed by the addition of the amine and isocyanate is half as reactive as a secondary aliphatic hydroxyl. Therefore, the formation of biuret is generally considered as a source of crosslinking in foams. The aromatic OH, usually found in phenolic resources (e.g., lignin), is around 300 and 1000 times less reactive than secondary and primary aliphatic OHs, respectively. This explains the need to chemically modified polyphenol molecules before their introduction in PUF as shown in a next section. The choice of the BA is crucial to determine essential properties and morphologies which are related to the applications. Two main types of BA are used: (i) Chemical, where BA reacts with a system component during the polymerization to generate the gas. As presented in Fig. 2, several H-labile compounds release gas by an exothermic reaction with isocyanates and, e.g., water or formic acid. (ii) Physical BA presents a phase change from liquid to gas during the polymerization using the energy released by the exothermic polyol-polyisocyanate reaction, with a strong and fast volume increase of the mix.

The key parameters of physical BAs are the molar mass, the boiling point, the heat of vaporization and conductivity in the gas phase. They are detailed in Table 5. Firstly, the molar mass of BA is essential for economic reasons. The quantity of gas and, by extension, the foam produced is inversely proportional to the molar mass. Therefore, in a formulation with a fixed mass of BA, the BA with a lower molar mass will generate a higher gas volume [START_REF] Singh | Blowing agents for polyurethane foams[END_REF]. To obtain foams with similar densities starting from the same formulation, a higher amount of, e.g., trichlorofluoromethane (137.4 g/mol) than n-pentane (72.2 g/mol) would be used. Secondly, the boiling point of BAs determines the temperature and then the time when the foam starts to rise. It is the main parameter for the fine-tuning of the foam expansion kinetic. In the case of one component-foam, the BA agent has a propellant role. It is common to use a BA with an ebullition temperature under 0 °C. Thirdly, the heat of vaporization represents the energy needed to phase change a liquid into gas. The quantity of heat released by the PU formation must be controlled to avoid attaining the critical degradation temperature of the PU. The endothermic vaporization of the BA consumes the heat released and decreases the temperature during the polymer formation, preventing degradation.

Finally, some BA properties are related to particular applications such as R-PUF for thermal insulation, where the thermal conductivity must be the lowest. The total thermal conductivity is related to the conduction through the polymer matrix, through the gas phase and the radiation. In this case, the gas contribution accounts for 65% of the total thermal conductivity [START_REF] Jarfelt | Thermal conductivity of polyurethane foam Best performance[END_REF][START_REF] Ferkl | Multi-scale modelling of heat transfer in polyurethane foams[END_REF]. The lower the conductivity in the BA gas phase, the lower the overall conductivity of the foam should be.

However, with the foam aging, the BA diffuses out of the cells and it is substituted by air. 1 Chlorofluorocarbon, 2 Hydrochlorofluorocarbon, 3 Hydrofluorocarbon, 4 Hydrocarbon, 5 Hydrofluoroolefin, 6 Hydrochlorofluoroolefin.

Historically, water was the only BA used until the 1950s and remains the primary chemical BA used today in F-PUFs. Foams developed only with water as BA faced several challenges: (i) high exothermic reaction causing scorching or fire, (ii) reduced flowability in mold due to higher viscosity, (iii) higher cost because water-blown foams consume more isocyanates. The water-blown R-PUF has high surface friability, high thermal conductivity, and poor dimensional stability. Furthermore, the higher amount of heat released by the urea induces a faster expansion of the foam. In consequence, some cell walls can be broken.

The development of the physical BA from 1970 to nowadays was conditioned by environmental concerns. The Montreal in 1987 and Kyoto in 1992 protocols banned chlorofluorocarbons, hydrofluorocarbons, and hydrochlorofluorocarbons due to their high ozone depletion activities [START_REF] Rowland | Chlorofluoromethanes in the environment[END_REF][START_REF] Shine | The global warming potential-the need for an interdisciplinary retrial: An editorial comment[END_REF]. Indicators to measure the impact of a molecule on the environment, such as the ozone depletion potential, were implemented, i.e., the Global warming potential (GWP).

Despite the ongoing utilization of forbidden substances by international protocols, the research turns toward new BAs more environmentally friendly such as hydrocarbons, hydrofluoroolefins or hydrochlorofluoroolefins (Table 5) [START_REF] Mateu-Royo | Thermodynamic analysis of low GWP alternatives to HFC-245fa in high-temperature heat pumps: HCFO-1224yd(Z), HCFO-1233zd(E) and HFO-1336mzz(Z)[END_REF][START_REF] Rigby | Increase in CFC-11 emissions from eastern China based on atmospheric observations[END_REF].

Surfactant

Fine and homogeneous cell structure cannot be obtained without surfactants. Fig. 5 details the principal surfactant structures used in PUFs formulation. The block and graft amphiphilic copolymers are based on hydrophobic siloxane groups and hydrophilic polyether grafted chains. The polyether/siloxane ratio, the EO unit content, the capping group (CAP in Fig. 5), the molar mass and the molecular architecture of the surfactant can be finely tuned to fit with the different polyols-BAs systems [START_REF] Hill | Siloxane Surfactants[END_REF].

Fig. 5. Representation of silicone surfactant. Adapted from [START_REF] Frey | New Silicone Surfactants for Rigid Polyurethane Foam[END_REF].

The surfactant has two main roles in the cell formation process: (i) the emulsification of the reagents and (ii) the stabilization of the formation of the bubbles [START_REF] Schmidt | The Effect of Surfactant Properties on a Rigid Foam System[END_REF]. Firstly, before the polyaddition starts, surfactants participate in the emulsification of the BA and the air in the monomers mixture, by reduction of the surface tension [START_REF] Hill | Siloxane Surfactants[END_REF]. Placed at the BA-polyol interfaces, the surfactant increases their miscibility and reduces the emulsion particle size. It was demonstrated that lower surface tension leads to higher bubble density in the A-part and, consequently, finer cell structure in the final foam [START_REF] Zhang | Role of Silicone Surfactant in Flexible Polyurethane Foam[END_REF].

The second role of the surfactant is the stabilization of the growing cells, along with the polymerization and foaming process. The cell growth is disrupted by two phenomena described in the left part of Fig. 6: (i) the Ostwald ripening and (ii) the cell drainage. The Ostwald ripening is controlled by the pressure difference between large and small bubbles. To equilibrate the pressure, the gas in small bubbles transfer into the larger ones (Fig. 6), and the exchange rate depends on the permeability of the cell walls [START_REF] Voorhees | The theory of Ostwald ripening[END_REF]. As shown in Fig. 6, this phenomenon tends to decrease the bubble density and to form coarser cells if not controlled. Surfactant molecules aggregated at the surface between air and foaming liquid limit the Ostwald ripening (Fig. 6). The surfactant packing increases the permeability of the cell walls. Therefore, by limiting the gas transfer between two cells, a homogeneous cell structure is formed [START_REF] Hill | Siloxane Surfactants[END_REF].

On the other side, cell drainage is governed by the pressure difference and the viscosity of the liquid phase [START_REF] Owen | The surface chemistry of polyurethane foam formation[END_REF]. Spherical bubbles collide when the gas volume fraction exceeds 70-75%, and distort into a multisided polyhedral [START_REF] Zhang | Role of Silicone Surfactant in Flexible Polyurethane Foam[END_REF]. The interface between two bubbles is described in the left bottom of Fig. 6. The liquid between two expanding bubbles is forced, due to capillary pressures, to flow toward the exterior forming the Plateau border and a thin film between bubbles. Once the polymerization is completed, the thin film between two cells is called cell wall, and the Plateau border is named cell strut (Fig. 6). Without surfactant, as shown in Fig. 6, the bubbles are open. The foam collapses if the cells are open too early in the foaming process.

The bubble expansion causes a gradient of surfactant concentration at the surface, as shown in Fig. 6. However, this surface tension gradient produces an antagonist effect on the film drainage, called the Marangoni effect. As shown in Fig. 6, surfactant molecules flow from the high to the low surfactant concentration to equally distribute the surfactant molecules at the interface. In this motion, surfactant drags along foaming liquid and delays the cell opening [START_REF] Obi | Foaming Processes[END_REF]. The transport rate from the bulk phase to the interphase and the absorption-desorption kinetics of the surfactant affects the efficiency against drainage [START_REF] Malhotra | Effects of surfactant adsorption-desorption kinetics and interfacial rheological properties on the rate of drainage of foam and emulsion films[END_REF][START_REF] Beneventi | Role of surfactant structure on surface and foaming properties[END_REF]. The cell drainage is fast without control, causing film ruptures, bubble coalescences, and very dense foams. In F-PUF formulations, cell rupture is wanted, and the surfactant controls the stage of cell opening. On the contrary, in R-PUF, the surfactant controls the film drainage to obtain closed cells.

Fig. 6. Illustration of the significant perturbations in foam cell formation, with or without surfactant.

The surfactant has critical roles in the formation and expansion of bubbles and, by extension, the properties of the material. The surfactant quantity is optimized to obtain a good performanceprice compromise. There were extensive researches to find the optimized quantity of surfactants to obtain the higher mechanical, thermal and morphological properties [START_REF] Lim | Effects of silicon surfactant in rigid polyurethane foams[END_REF][START_REF] Kang | Liquid nucleating additives for improving thermal insulating properties and mechanical strength of polyisocyanurate foams[END_REF][START_REF] Choe | Threshold cell diameter for high thermal insulation of water-blown rigid polyurethane foams[END_REF]. Between 1 and 1.5 pbw of the polyol are used in F-PUFs to control cell expansion and promote the cell opening.

However, too low quantity promotes collapsing, densification and splits of the foams [START_REF] Kaushiva | Structure-Property Relationships Of Flexible Polyurethane Foams[END_REF]. On the contrary, higher quantities are used in R-PUFs to obtain closed-cell structures. The average amount of surfactant used is between 1 and 3 pbw of the polyol (Table 1).

Catalyst

The main catalytic mechanisms for the PU formation described in the literature follow mainly two potential pathways: (i) The increase of the carbon electrophile character of the isocyanate group or (ii) the increase of the nucleophile character of the H-labile compound [START_REF] Silva | Recent Developments in Polyurethane Catalysis: Catalytic Mechanisms Review[END_REF]. In order to control the reaction kinetics, different catalysts presented in Fig. 7 The PUF catalysts are trapped inside the polymer matrix and released over time. Therefore, a new generation of catalysts is designed with an H-labile group in their chemical structures to react with isocyanate and be part of the polymer network, to avoid a catalyst release. However, to obtain similar foaming kinetics, the catalyst loading tends to be higher due to the decreased catalytic activity linked to the loss of mobility.

In any case, the catalyst role is to equilibrate the blowing and gelling reaction to get the optimal foam. In the case of a fast gelling compared to the blowing reactions, the polymer gels faster and thus, the cells would not expand to the optimum volume [START_REF] Banik | Water Blown Soy Polyol-Based Polyurethane Foams of Different Rigidities[END_REF]. Therefore, the density increase and all the properties related will be affected. On the contrary, a slow gelling produces a lower viscosity when the cells expand. In this case, the emulsion is destabilized. The gas blows the cell and the polymer gels later with big open cells [START_REF] Kim | Dynamic Film and Interfacial Tensions in Emulsion and Foam Systems[END_REF].

Other additives

A large range of additives is used on PUF formulations. Additives such as FRs, dyes, pigments, or fillers can be, for instance, added. As inert additive or reactive systems, FRs are used in PUFs. Inert additives are directly added during the formulation. They are mainly composed of halogen or phosphorous compounds, although melamine, aluminum trihydrate and magnesium hydroxide may also be used [START_REF] Wilkie | Fire retardancy of polymeric materials[END_REF]. Reactive systems are based on active groups that are chemically linked to the PUF network [START_REF] Wilkie | Fire retardancy of polymeric materials[END_REF], which are based on bromine or phosphorous atoms. Besides, more thermally stable groups can be introduced in the polymer network, such as isocyanurate, uretdione or carbodiimide [START_REF] Saiki | Carbodiimide-Modified Polyisocyanurate Foams: Preparation and Flame Resistance[END_REF].

PU can also be formulated with macro or nano-fillers to improve the mechanical properties, the fire resistance or the nucleation during the foaming steps. This specific domain was recently reviewed [START_REF] Agrawal | PU foam derived from renewable sources: Perspective on properties enhancement: An overview[END_REF][START_REF] Kausar | Polyurethane Composite Foams in High-Performance Applications: A Review[END_REF] and will not be further detailed in this review.

Evolution of the cells morphology during the PUF processing

Foam expansions are monitored by three characteristic times taken along the foam elaboration process. First of all, the cream time is defined as the moment where the foam changes color and starts rising. Secondly, the gel time related to the formation of the polymer network (gelation of the polymer) is usually determined when the formation of a continuous film or a fine string between the foam and a wooden stick occurs. The foam will continue to cure and reach the tack-free time when the surface of the foam will no longer have tacking properties. For a standard PUF formulation, the characteristic times are, for instance, 2-20 sec, 10-100 sec and 15-300 sec for the cream, gel and tack-free time, respectively.

The foam development was followed by instrumented setups, which record the foam height, the temperature, the pressure inside the mold and the dielectric polarization constant over time.

Equivalent characteristic times are determined from the corresponding-measured parameters. The cream time is characterized as when the foam reaches 15% of the maximum expansion rate.

Furthermore, 15% of the pressure derivative is defined as the gel time. Additional characteristic times are designated, such as the rise time when the 95-98% of the height is reached or the curing time when the dielectric polarization value is under 10% of the peak maximum. This curing time indicates the surface curing; the total curing time is proportional to the foam size. Generally, between 2 and 7 days at ambient temperature are sufficient.

Fig. 8 shows the different phases of the cell morphology evolution correlated with the temperature and viscosity evolution over time. Phase 1 is the mixing of the A-part before the start of the polymerization. Phase 2 is the cell nucleation where two theories are in competition, or can also be concomitant. First, the classical theory of nucleation is based on the generation of cells from BA droplets after dispersion. A microphases dispersion of BA in polyols is obtained due to the BA low miscibility into polyol. The high-speed stirring splits the dispersed bubbles until an equilibrium is reached. These small bubbles are expanded to form the final cells when the polyaddition can start [START_REF] Obi | Fundamentals of Polymeric Foams and Classification of Foam Types[END_REF]. A more recent theory is based on the effect of air pockets entrapped during the mixing stage (phase 1 in Fig. 8) [START_REF] Reignier | The morphology of rigid polyurethane foam matrix and its evolution with time during foaming -New insight by cryogenic scanning electron microscopy[END_REF]. In this case, the BA migrates through the matrix into the air bubbles during the expansion.

The phase 2 in Fig. 8 (expansion of the bubble) is controlled by the temperature and the viscosity of the mix. These two parameters are related to the kinetics of gelling and blowing steps and can be controlled by the catalyst. The temperature increase shown in Fig. 8 comes from the exothermic polyaddition of isocyanate with water and polyol. The temperature increase is caused by a small portion of water that rapidly reacts and releases twice more heat than the reaction with an hydroxyl. After the cream time, a slight increase in temperature is enough to make the gas bubbles to expand. The bubble expansion is followed by a viscosity increase shown in Fig. 8 since the bubbles act as thickener [START_REF] Mcclusky | Vibrating Rod Viscometer: A Valuable Probe into Polyurethane Chemistry[END_REF].

The immediate drop in viscosity after the expansion of the cell around 60 seconds in Fig. 8 is related to the thermal thinning of the reacting polymer. This drop in viscosity is beneficial for the cell expansion that starts to come into contact, forming the film, as shown in phase 4 of Fig. 8. The temperature stabilizes after 70-80 seconds inside the foam because of the increased viscosity and thermal insulating material property of the foam (Fig. 8). The increased concentration of urea groups formed by the reaction between isocyanate and water is responsible for a second viscosity rise. Urea groups strongly H-bond together and form hard domains in the polymer matrix, acting as reticulation points [START_REF] Mcclusky | Vibrating Rod Viscometer: A Valuable Probe into Polyurethane Chemistry[END_REF]. The next drop-in viscosity shown in Fig. 8 around 100 seconds is explained by the delay between hard segments formation and gelation of the urethane network. As explained in a previous Section, the cell wall drained by pressure difference is held by the surfactant until the network gelation occurs (phase 5 in Fig. 8). The drop in viscosity is beneficial for the film breakage if the gelation of the network is too slow. Finally, the polyol reaction conversion with polyisocyanate reaches the gelation point, and the viscosity becomes infinite. The network gelation fixes the cell morphology of the foam. The profiles of temperature and viscosity in Fig. 8 present a general case. Nevertheless, it can differ. For example, in PIR foams, catalysts for the trimerization are thermally activated [START_REF] Okuzono | New Polyisocyanurate Catalysts Which Exhibit High Activity at Low Temperature[END_REF].

Therefore, the viscosity profile changes due to the additional reticulation points formed by the trimerization. Furthermore, in F-PUF, the drainage of the cell walls is controlled until the film rupture to produce open-cell.

From renewable sources to biobased components for PUF

This chapter describes the different strategies recently developed to obtain the different renewable components to produce biobased PUFs from a large range of biomass, mainly from lipids, carbohydrates, polyphenols (lignins and tannins), and different others molecules from biorefinery obtained by biochemistry process, for instance. To a lesser extent than the polyols, the amines are used as raw materials in PU chemistry, either in the synthesis of polyureas or, in the case of low molar mass polyamines, as polyether polyol starters. As the production of biobased amines was recently reviewed [START_REF] Froidevaux | Biobased Amines: From Synthesis to Polymers; Present and Future[END_REF][START_REF] Pelckmans | Bio-based amines through sustainable heterogeneous catalysis[END_REF], the amines will not be incorporated in this review.

The biorefinery converts the biomass into different outputs such as fuels, energy, food, feed and/or chemicals through jointly applied conversion technology [START_REF] Cherubini | The biorefinery concept: Using biomass instead of oil for producing energy and chemicals[END_REF]. Biorefineries are classified according to different and successive generations depending on their feedstocks. The first generation consumes edible crops such as starch, for instance. The second generation uses industrial residues and non-edible crops such as lignocellulosic compounds from wood, without food competition.

Finally, the third one is based on algae and microalgae without arable land uses [START_REF] Moncada | Integrating first, second, and third generation biorefineries: Incorporating microalgae into the sugarcane biorefinery[END_REF]. The utilization of different biological systems, i.e., enzymes, cell extracts or whole microorganisms (biotechnology), is increasingly integrated into the biorefinery conversion processes. The development of white biotechnology, defined as the industrial production of chemicals, increases the availability of biobased building blocks, e.g., for PUFs synthesis [START_REF] Debuissy | Biotic and Abiotic Synthesis of Renewable Aliphatic Polyesters from Short Building Blocks Obtained from Biotechnology[END_REF]. The association between chemistry and biochemistry, also know as the chem-biotech approach, drives the evolution in the production of these renewable building blocks. Lipids are extracted from natural resources such as vegetables, seeds or micro-algae. They are composed of triglycerides, which can be decomposed in glycerol and three fatty acids per molecule, as shown in Fig. 9. On the contrary to plants oil, microalgae do not compete with food nor need arable land to grow [START_REF] Fabris | Emerging Technologies in Algal Biotechnology: Toward the Establishment of a Sustainable, Algae-Based Bioeconomy[END_REF][START_REF] Zappi | Microalgae Culturing To Produce Biobased Diesel Fuels: An Overview of the Basics, Challenges, and a Look toward a True Biorefinery Future[END_REF]. They are an interesting source of lipids due to a higher average length and a higher number of double bonds per fatty acid.

Lipids: Triglycerides and fatty acids

The diversity in fatty acids presented in Fig. 9 relies on the chain length (mainly till 24 carbons), position, configuration and types of unsaturation and additional substituents such as epoxide or hydroxyl groups along the aliphatic chain [START_REF] Gunstone | The Lipid Handbook with CD-ROM[END_REF]. The diversity of fatty acids distribution of lipids, which are species and growing conditions dependent, was used to develop various PU macromolecular architectures.

Taking into account the literature and the different previous reviews on this field [START_REF] Petrovic | Polyurethanes from Vegetable Oils[END_REF][START_REF] Pfister | Recent Advances in Vegetable Oil-Based Polyurethanes[END_REF][START_REF] Desroches | From Vegetable Oils to Polyurethanes: Synthetic Routes to Polyols and Main Industrial Products[END_REF][START_REF] Maisonneuve | Vegetable oils: a source of polyols for polyurethane materials[END_REF][START_REF] Ghasemlou | Polyurethanes from seed oil-based polyols: A review of synthesis, mechanical and thermal properties[END_REF][START_REF] Singh | Recent Advancement in Plant Oil Derived Polyol-Based Polyurethane Foam for Future Perspective: A Review[END_REF], the main highlights of this state of the art are mainly based on recent publications on the transformation of lipids into polyols, isocyanate or additives used in foam formulations. Esters and double bonds are the starting point of the oleochemistry described in Fig. 10 to access to different PUF components.

Fig. 10 shows the diversity of the oleochemistry with different pathways to obtain polyols. The particular case of castor oil, which contains an OH group, is described in the synthesis of an additive.

The epoxidation and further ring-opening are the main transformations and were used to produce both polyols and additives. Fig. 10. Overview of the main oleochemistry pathways for the elaboration of different PUF components.

Polyols

Polyols are the main PUF components elaborated from fatty acid, even at an industrial scale.

In this way, different approaches have been recently developed.

Epoxidation and ring-opening

The formation of epoxide is one of the most investigated ways to obtain polyols via double bonds modification. OH groups can be obtained in two steps from the double bonds with the epoxidation and the subsequent ring-opening synthesis. The electrophilic nature of the strained three-membered ring epoxide facilitates the nucleophilic attack to afford a beta-substituted OH group [START_REF] Fallah-Mehrjardi | Nucleophilic ring-opening of epoxides: trends in βsubstituted alcohols synthesis[END_REF]. Among the large variety of nucleophile used for ring-opening reaction, mono-alcohols [START_REF] Arbenz | Elaboration and Properties of Innovative Biobased PUIR Foams from Microalgae[END_REF][START_REF] Petrović | Polyols and Polyurethanes from Crude Algal Oil[END_REF][START_REF] Kahlerras | Elaboration and Characterization of Polyurethane Foams Based on Renewably Sourced Polyols[END_REF][START_REF] Peyrton | Biobased Polyurethane Foams Based on New Polyol Architectures from Microalgae Oil[END_REF][START_REF] Campanella | Polyurethane foams from soyoil-based polyols[END_REF], diols [START_REF] Borowicz | Biodegradable, Flame-Retardant, and Bio-Based Rigid Polyurethane/Polyisocyanurate Foams for Thermal Insulation Application[END_REF][START_REF] Pawar | Rigid polyurethane foams from cottonseed oil using bio-based chain extenders: a renewable approach[END_REF][START_REF] Zieleniewska | Preparation and characterisation of rigid polyurethane foams using a rapeseed oil-based polyol[END_REF][START_REF] Pawar | Synthesis and characterization of rigid polyurethane foams from algae oil using biobased chain extenders[END_REF][START_REF] Kurańska | Evaluation of application potential of used cooking oils in the synthesis of polyol compounds[END_REF][START_REF] Fan | Rigid polyurethane foams made from high viscosity soypolyols[END_REF][START_REF] Kurańska | Open-cell rigid polyurethane bio-foams based on modified used cooking oil[END_REF], and carboxylic acids [START_REF] Peyrton | Biobased Polyurethane Foams Based on New Polyol Architectures from Microalgae Oil[END_REF][START_REF] Pawar | Rigid polyurethane foams from cottonseed oil using bio-based chain extenders: a renewable approach[END_REF][START_REF] Pawar | Synthesis and characterization of rigid polyurethane foams from algae oil using biobased chain extenders[END_REF][START_REF] Herrán | Highly functional lactic acid ring-opened soybean polyols applied to rigid polyurethane foams[END_REF][START_REF] Contreras | Development of eco-friendly polyurethane foams based on Lesquerella fendleri (A. Grey) oilbased polyol[END_REF][START_REF] Fang | Development of High-Performance Biodegradable Rigid Polyurethane Foams Using Full Modified Soy-Based Polyols[END_REF] were the most investigated.

Weaker nucleophiles such as amines [START_REF] Yang | Thermal and Mechanical Properties of Polyurethane Rigid Foam Based on Epoxidized Soybean Oil[END_REF][START_REF] Biswas | Synthesis of Diethylamine-Functionalized Soybean Oil[END_REF][START_REF] Re | Osage Orange ( Maclura pomifera L.) Seed Oil Poly(α-hydroxydibutylamine) Triglycerides: Synthesis and Characterization[END_REF], water [START_REF] Campanella | Polyurethane foams from soyoil-based polyols[END_REF][START_REF] Testud | Hyperbranched polyesters by polycondensation of fatty acid-based ABn-type monomers[END_REF] or thiols [START_REF] Sharma | Synthesis of Hydroxy Thio-ether Derivatives of Vegetable Oil[END_REF] were also studied, but the ring-opening reaction was found to be slower. Nevertheless, polyols produced by ring-opening with secondary amines were demonstrated to have catalytic activity [START_REF] Peyrton | Biobased Polyurethane Foams Based on New Polyol Architectures from Microalgae Oil[END_REF][START_REF] Peyrton | New Insight on the Study of the Kinetic of Biobased Polyurethanes Synthesis Based on Oleo-Chemistry[END_REF]. Efficient ring-opening nucleophiles rarely investigated are the hydrogen halides [START_REF] Peyrton | Biobased Polyurethane Foams Based on New Polyol Architectures from Microalgae Oil[END_REF][START_REF] Guo | Structure and properties of halogenated and nonhalogenated soybased polyols[END_REF], even if they are used to quantitate epoxide groups on lipids since 1956 [START_REF] Durbetaki | Direct Titration of Oxirane Oxygen with Hydrogen Bromide in Acetic Acid[END_REF].

The secondary OH group was also formed by the reduction of the epoxide group with H2 and Nickel of Raney [START_REF] Petrovic | Polyurethanes from Vegetable Oils[END_REF][START_REF] Guo | Structure and properties of halogenated and nonhalogenated soybased polyols[END_REF][START_REF] Pillai | Polyurethane foams from chlorinated and non-chlorinated metathesis modified canola oil polyols: Research Article[END_REF]. Unfortunately, the method developed used an alkaline medium, which broke the ester, thus the triglyceride structure.

Miscellaneous double bond transformations

A recent trend in the modification of unsaturated triglyceride is the use of the "click" thiolene reaction where the double bond is transformed into thioether by radical addition of thiol under UV radiation. The mercaptoethanol was used to produced polyols for PUFs with castor, soybean or corn oil with high selectivity [START_REF] Ionescu | Highly functional polyols from castor oil for rigid polyurethanes[END_REF][START_REF] Alagi | Efficient and quantitative chemical transformation of vegetable oils to polyols through a thiol-ene reaction for thermoplastic polyurethanes[END_REF][START_REF] Ramanujam | Novel Biobased Polyol Using Corn Oil for Highly Flame-Retardant Polyurethane Foams[END_REF].

The cross-metathesis described in Scheme 2 is a reaction between the triglyceride double bond and an olefin yielding shorter monounsaturated fatty acid chains. The alkenes side products are hydrogenated to be suitable for diesel or jet propellant [START_REF] Yelchuri | Olefin metathesis of fatty acids and vegetable oils[END_REF][START_REF] Lutz | Shell higher olefins process[END_REF]. The previously developed double bond modification methods can be used to obtain polyols [START_REF] Pillai | Solvent-free synthesis of polyols from 1-butene metathesized palm oil for use in polyurethane foams[END_REF]. Another way to modify fatty acids is the 2+2 cycloaddition of oleic acid, and linoleic acid yields various six-membered cyclic diacids with long dangling chains, such as the theoretical structure shown in Scheme 2. OH groups can be introduced on this molecule by reduction or esterification of the carboxylic acid groups [START_REF] Ghosh | Biobased Multifunctional Macroglycol Containing Smart Thermoplastic Hyperbranched Polyurethane Elastomer with Intrinsic Self-Healing Attribute[END_REF]. Oleon and Croda developed diols based on the dimerization of fatty acids. As shown in Scheme 2, the cyclotrimerization of oleic acid was used to transform the flexible fatty acid chains into an aromatic core with dangling chains bearing carboxylic acids [START_REF] Lligadas | Polyurethane Networks from Fatty-Acid-Based Aromatic Triols: Synthesis and Characterization[END_REF].

Scheme 2. Metathesis and cyclization reactions.

The ozonolysis of the double bonds of triglycerides was investigated on several substrates such as canola oil, soybean or trioline [START_REF] Petrović | Structure and Properties of Polyurethanes Prepared from Triglyceride Polyols by Ozonolysis[END_REF][START_REF] Narine | Physical Properties of Polyurethanes Produced from Polyols from Seed Oils: II. Foams[END_REF]. This reaction reduces the chain length of the fatty acid, sets the functionality at three and forms primary OH group.

Ester modifications

To obtain polyols, ester modification chemistry is largely less developed than the double bonds modification. There are only two possible pathways, such as (i) the transesterification of oil and (ii) the saponification of the ester, followed by esterification with a small polyol. The first method was extensively applied to castor oil due to the high content in ricinoleic fatty acid. The transesterification of castor oil was investigated with glycerol [START_REF] Kaur | Addition of anti-flaming agents in castor oil based rigid polyurethane foams: studies on mechanical and flammable behaviour[END_REF][START_REF] Li | Preparation and properties of rigid polyurethane foam based on modified castor oil[END_REF][START_REF] Veronese | Rigid polyurethane foam based on modified vegetable oil[END_REF][START_REF] Bresolin | Polyurethane Foams Based on Biopolyols from Castor Oil and Glycerol[END_REF], ethylene glycol (EG) [START_REF] Sahoo | Synthesis of Vegetable Oil-Based Polyurethane: A Study on Curing Kinetics Behavior[END_REF] or triethanolamine [START_REF] Veronese | Rigid polyurethane foam based on modified vegetable oil[END_REF][START_REF] Sahoo | Synthesis of Vegetable Oil-Based Polyurethane: A Study on Curing Kinetics Behavior[END_REF]. An acceleration was noted in the urethane formation kinetic with the hydroxy ketone group due to the activation of the OH group via hydrogen bonding assistance [START_REF] Briou | Polyurethane Thermosets Using Lipidic Poly(α-Hydroxyketone)[END_REF].

The transesterification method was also applied to rapeseed [START_REF] Prociak | Effect of biopolyols with different chemical structures on foaming of polyurethane systems and foam properties[END_REF], soybean [START_REF] Campanella | Polyurethane foams from soyoil-based polyols[END_REF], coconut [START_REF] Paruzel | Rigid Polyurethane Foam Fabrication Using Medium Chain Glycerides of Coconut Oil and Plastics from End-of-Life Vehicles[END_REF] or andiroba oil [START_REF] Da Silva | Enzymatic synthesis of andiroba oil based polyol for the production of flexible polyurethane foams[END_REF].

The second method comprises one more step, but the polyols produced have higher molar masses compared to the transesterification method. As an example, the glycerol monostearate was oligomerized with glutaric acid and yield a polyol with an average molar mass superior to 3000 g/mol and thus a low IOH [START_REF] Ng | Preparation and modification of water-blown porous biodegradable polyurethane foams with palm oil-based polyester polyol[END_REF]. The esterification consumes OH groups, which could be used in PU networks formation, to form ester bond; therefore, the ester formation reduces the IOH. To avoid the reduction of IOH, a polyol was produced by esterification of polymerized glycerol with castor oil fatty acid that contains an OH. In this particular case, the obtained polyols had an IOH depending on the esterification time, around 550 mg KOH/g, suitable for PUFs synthesis [START_REF] Hejna | The influence of crude glycerol and castor oil-based polyol on the structure and performance of rigid polyurethanepolyisocyanurate foams[END_REF][START_REF] Hejna | Structure, Mechanical, Thermal and Fire Behavior Assessments of Environmentally Friendly Crude Glycerol-Based Rigid Polyisocyanurate Foams[END_REF].

Polyisocyanate

The most known diisocyanate produced from oleochemistry is the 2-Heptyl-3,4-bis(9isocyanatononyl)-1-pentylcyclohexane, commercialized by Cognis-BASF under the name DDI1410.

This biobased isocyanate was used in thermoplastic [START_REF] Charlon | Synthesis, structure and properties of fully biobased thermoplastic polyurethanes, obtained from a diisocyanate based on modified dimer fatty acids, and different renewable diols[END_REF] or thermoset PU materials [START_REF] Li | Property profile of poly(urethane urea) dispersions containing dimer fatty acid-, sugar-and amino acid-based building blocks[END_REF][START_REF] Calvo-Correas | Synthesis and Characterization of Polyurethanes with High Renewable Carbon Content and Tailored Properties[END_REF][START_REF] Zhang | High Biobased Carbon Content Polyurethane Dispersions Synthesized from Fatty Acid-Based Isocyanate[END_REF].

Other polyisocyanates were produced at a lower scale. Firstly, a dimer of oleic acid obtains by self-metathesis was transformed into diisocyanate by Curtius rearrangement [START_REF] Hojabri | Novel long chain unsaturated diisocyanate from fatty acid: Synthesis, characterization, and application in bio-based polyurethane[END_REF]. Secondly, sebacic acid and undecylenic acid derived from castor oil by alkali fusion and pyrolysis, respectively, were also transformed in diisocyanate via Curtius rearrangement [START_REF] More | Novel fatty acid based diisocyanates towards the synthesis of thermoplastic polyurethanes[END_REF]. Thirdly, soybean oil was transformed by allylic bromination with N-bromosuccinimide, followed by substitution with silver isocyanate salt [START_REF] Çaylı | Biobased polyisocyanates from plant oil triglycerides: Synthesis, polymerization, and characterization[END_REF]. This is the only report of polyisocyanates (f > 2) derived from lipids resources.

3.1.3. Some additives

Surfactant

Similarly to surfactant, lipids are constituted of long aliphatic and hydrophobic chains and a polar core with the ester groups. Linseed oil has been recently used as a renewable modifier in PUFs.

Mechanical and thermal properties improvement has been reported in PUFs containing linseed oil as a unique surfactant [START_REF] Członka | Linseed oil as a natural modifier of rigid polyurethane foams[END_REF]. The sodium sulforicinate obtained by sulfation of castor oil dispersed in water was used in foam formulations, both as BA and surfactant [START_REF] Arbenz | Advanced biobased and rigid foams, based on urethane-modified isocyanurate from oxypropylated gambier tannin polyol[END_REF].

FR

The modification of the lipids double bonds to enhance the thermal stability was achieved through the epoxidation and ring-opening process with phosphoric acid. The phosphorous compounds are known for their fire-retardant properties, especially in PUFs [START_REF] Chang | Novel sustainable biobased flame retardant from functionalized vegetable oil for enhanced flame retardancy of engineering plastic[END_REF]. Another strategy based on fatty acid as a modifier for a well-known FR: the 9,10-dihydro-9-oxa-10phosphaphenanthrene-10-oxide (DOPO) can be applied. The synthesis procedure introduced the terminal fatty reactive epoxide group on the DOPO molecule [START_REF] Lligadas | Synthesis and properties of thermosetting polymers from a phosphorous-containing fatty acid derivative[END_REF]. With this modification, the labile FR molecule is then attached to the polymer network.

Carbohydrates

Initially, carbohydrates were defined as molecules exclusively composed of carbon, oxygen and hydrogen atoms following the formula Cn(H2O)n [START_REF] Grunwald | Handbook of carbohydrate-modifying biocatalysts[END_REF]. However, the definition was enlarged to encounter the reduced, oxidized and heteroatoms (sulfur or nitrogen) containing molecules [153].

Carbohydrates are divided into two categories: (i) the monosaccharides composed of C5 or C6 molecules and numerous OH groups such as the sorbitol, sucrose and lactitol (Fig. 11). (ii) The polysaccharides obtained by condensation of monosaccharide building blocks, i.e., starch and chitosan (Fig. 11) [START_REF] Yarema | Handbook of Carbohydrate Engineering[END_REF]. The polysaccharides with a high molar mass such as starch, neat chitin or deacetylated chitin (chitosan) are largely used for polymers synthesis [START_REF] Halley | Starch polymers: from genetic engineering to green applications[END_REF][START_REF] Rinaudo | Chitin and chitosan: Properties and applications[END_REF][START_REF] Gandini | Progress of Polymers from Renewable Resources: Furans, Vegetable Oils, and Polysaccharides[END_REF].

The different pathways from carbohydrates (mono, di and long polysaccharides) to PUF components are described in Fig. 11. The esterification and the alkoxylation are the two main pathways for transforming mono, di and polysaccharides into polyols. The chitosan was slightly modified to be introduced as additives in PUFs. The isosorbide obtained from sorbitol was a platform for the biobased diisocyanates synthesis.

Polyols

The carbohydrates are multi-OH compounds that are of great interest to produce polyols for PUFs formulation. Unfortunately, most of the carbohydrates are solids at ambient temperature, so impossible to use without modification. Several strategies were developed to modify the carbohydrates to produce adequate polyols for PUFs.

Alkoxylation

The first strategy, commonly called alkoxylation, is based on the anionic ring-opening polymerization (ROP) of epoxides. This reaction initiated by small polyols (starters) forms polyether chains ended by OHs. The reaction product has a higher molar mass and the same functionality in OH as the starter. It was early shown that the alkoxylation of monosaccharides produced polyols with suitable properties for PUFs. BASF was the first company to patent PUFs based on alkoxylated carbohydrates [START_REF] Austin | Process for preparing a polyurethane foam from an oxyalkylated product[END_REF][START_REF] Austin | Polyurethane foam from an oxyalkylated product[END_REF]. The alkoxylation was successfully applied to sucrose [START_REF] Ionescu | High Functionality Polyether Polyols Based on Polyglycerol[END_REF], lactitol [START_REF] Wilson | Preparation and characterization of lactitol-based poly(ether polyol)s for rigid polyurethane foam[END_REF],

starch [START_REF] Lubczak | From starch to oligoetherols and polyurethane foams[END_REF], sorbitol [START_REF] Ugarte | Tailoring Mechanical Properties of Rigid Polyurethane Foams by Sorbitol and Corn Derived Biopolyol Mixtures[END_REF][START_REF] Jiang | Synthesis and characterization of polyurethane rigid foams from polyether polyols with isosorbide as the bio-based starting agent[END_REF] and reduced lactose [START_REF] Hu | Polyurethane Rigid Foam Derived from Reduced Sweet Whey Permeate[END_REF] to produce PUFs.

The major drawback of this reaction is the production of the epoxide reagents. 33 million tons of small epoxides such as EO, PO or, to a lesser extend, butylene oxide used for the alkoxylation are mainly fossil-based [START_REF] Herzberger | Polymerization of Ethylene Oxide, Propylene Oxide, and Other Alkylene Oxides: Synthesis, Novel Polymer Architectures, and Bioconjugation[END_REF]. However, epoxides could be bio-derived from ethanol, butanol or glucose, in a greener way [START_REF] Gandini | From monomers to polymers from renewable resources: Recent advances[END_REF][START_REF] Arbenz | Synthesis and characterization of fully biobased aromatic polyolsoxybutylation of condensed tannins towards new macromolecular architectures[END_REF][START_REF] Lee | A comprehensive metabolic map for production of bio-based chemicals[END_REF].

Esterification

Similarly to alkoxylation, the oligo-esterification increases the molar mass of monosaccharides with a reduction of the melting point and IOH. For example, sorbitol esterification was realized in one step with adipic acid and dioctanol mediated by enzymatic catalysis [START_REF] Gustini | Enzymatic synthesis and preliminary evaluation as coating of sorbitol-based, hydroxy-functional polyesters with controlled molecular weights[END_REF].

Polyester polyols from sorbitol, adipic acid and diols with various chain lengths produced in two steps were also reported [START_REF] Furtwengler | Synthesis and characterization of polyurethane foams derived of fully renewable polyester polyols from sorbitol[END_REF]. The resulting polyols based on two primary and four secondary OH groups were added in PUF and PU-PIR foams formulations [START_REF] Furtwengler | Elaboration and Characterization of Advanced Biobased Polyurethane Foams Presenting Anisotropic Behavior[END_REF][START_REF] Furtwengler | Novel Rigid Polyisocyanurate Foams from Synthesized Biobased Polyester Polyol with Enhanced Properties[END_REF].

The sorbitol was also transformed through dehydration, as described in Scheme 3, to form isosorbide. This product, commercialized by, e.g., Roquette (France), raised much interest due to the bicyclic rigid structure [START_REF] Dussenne | Synthesis of isosorbide: an overview of challenging reactions[END_REF]. Suitable polyols for the PUFs industry were also obtained by esterification with fatty acid dimers [START_REF] Khanderay | Fully biobased polyester polyols derived from renewable resources toward preparation of polyurethane and their application for coatings[END_REF]. The combinations between the rigidity of the isosorbide and the flexibility of fatty acids are an exciting way to obtain new properties. Neat Isosorbide was also directly added in PUFs with reduced thermal reversibility of the urethane bond [START_REF] Shin | Effects of Isosorbide Incorporation into Flexible Polyurethane Foams: Reversible Urethane Linkages and Antioxidant Activity[END_REF]. This reversibility at low temperatures was exploited to weaken the modulus of polymer located in the fragile thin wall. A decreased modulus combined with the heat increased the open-cell content.

Scheme 3. Isosorbide production pathway from sorbitol.

Miscellaneous transformations

Neat carbohydrates were used in the PU system in a pre-polymerization step with a default of diisocyanates [START_REF] Marín | Carbohydrate-based polyurethanes: A comparative study of polymers made from isosorbide and 1,4-butanediol[END_REF][START_REF] Konieczny | Green Polyurethanes from Renewable Isocyanates and Biobased White Dextrins[END_REF] or as crosslinkers [START_REF] Javaid | Utilization of waxy corn starch as an efficient chain extender for the preparation of polyurethane elastomers[END_REF][START_REF] Ugarte | Morphologyproperties relationship in high-renewable content polyurethanes[END_REF]. Furthermore, the integration of chitosans of different molar masses into a PUF formulation was tested with a higher reaction yield of chitosans with low molar masses [START_REF] Qin | Study on preparation and performance of PEG-based polyurethane foams modified by the chitosan with different molecular weight[END_REF].

Polyisocyanate

The too numerous OH groups of the carbohydrates limit the transformation into isocyanates.

Therefore, the isosorbide was a molecule of choice due to its two OHs and their transformation into isocyanate groups was achieved through a traditional amination-phosgenation route [START_REF] Bachmann | Synthesis of Novel Polyurethanes and Polyureas by Polyaddition Reactions of Dianhydrohexitol Configurated Diisocyanates[END_REF]. Another strategy was applied with succinic anhydride to form acid pending groups on isosorbide. The isocyanate groups were then formed by Curtius rearrangement [START_REF] Zenner | Polyurethanes from Isosorbide-Based Diisocyanates[END_REF].

Additives

Chitosan was introduced in PU formulations with phosphate derivatives to improve the char layer formation and the FR properties [START_REF] Liu | Preparation and characterization of chitosan derivatives and their application as flame retardants in thermoplastic polyurethane[END_REF][START_REF] Zhang | The novel application of chitosan: Effects of cross-linked chitosan on the fire performance of thermoplastic polyurethane[END_REF]. Furthermore, with the same goal, carbohydrates were modified with an alkyl chain to improve the mixing with the PUF components [START_REF] Malwitz | Fire-retardant Polyurethane Foam and Method and Resin for Preparing the Same[END_REF]. The synthesis of phosphorous-containing polyols with FR properties was achieved by the esterification of sorbitol and sucrose derivatives with dialkyl phosphonopropionate [START_REF] Quinn | Properties and Stability of Fire-Retardant Rigid Polyurethane Foams from Phosphonopropionate Polyols[END_REF] or the treatment of propoxylated starch with polyphosphoric acid [START_REF] Molotsky | Flame retardant polyurethane foams[END_REF].

Polyphenols (Lignins and tannins)

Lignocellulosic resources presented in Fig. 12 are primarily composed of cellulose (40-60%), hemicellulose (25-35%) and lignins (15-30%). Terpenes, alkaloids, or tannins are also accumulated by plants. Polyphenols such as lignins and tannins are then abundant. They are the first and second most abundant sources of aromatic biomolecules on earth, with an estimated worldwide production of 50 and 0.16 million tons per year, respectively [START_REF] Xu | Conversion of lignin into bio-based chemicals and materials[END_REF][START_REF] Laurichesse | Chemical modification of lignins: Towards biobased polymers[END_REF].

Fig. 12. Composition of lignocellulosic resources and classification of main polyphenols: tannins and lignins. Adapted from [START_REF] Isikgor | Lignocellulosic biomass: a sustainable platform for the production of bio-based chemicals and polymers[END_REF].

Lignins can be defined as amorphous polyphenolic materials arising from an enzymemediated dehydrogenative polymerization of three monolignols: coumaryl, coniferyl and sinapyl alcohols (Fig. 12) [START_REF] Dence | Introduction[END_REF]. In softwood such as spruce, the lignin is primarily composed of coniferyl alcohol, while in hardwood (e.g., birch), the coniferyl and sinapyl monolignols are dominant. The coumaryl alcohol is mostly found in compression woods or grasses. It is mainly extracted from lignocellulosic resources through various processes (e.g., kraft, sulfite, solvent or soda pulping). Until recently, the lignin was considered as a waste by-product of the paper and ethanol/fuel industries and burned for power and heat generation (black liquor) [START_REF] Xu | Conversion of lignin into bio-based chemicals and materials[END_REF].

Tannins are polyphenols defined as soluble compounds with a molar mass between 500 and 3000 g/mol or by their ability to precipitate protein. They present particular chemical and biological activities [START_REF] Hagerman | Tannin handbook[END_REF]. On the contrary to lignin, tannins are found in soft tissues and play a vital role, such as the defense against mushrooms or insects [START_REF] Roux | Condensed tannins. 13. Interrelationships of flavonoid components from the heartwood of Robinia pseudacacia[END_REF]. The main categories of tannins presented in Fig.

12 are the condensed tannins based on flavonoids structure, the hydrolyzable tannins composed of gallic esters derivatives and the phlorotannins [START_REF] Singh | Applications of Tannins in Industry[END_REF].

Lignins and tannins chemical structures depend mainly on the extraction methods, botanical sources, locations, and seasons. Nevertheless, for both resources, phenol, aliphatic OH and carboxylic acid are the primary chemical groups available for transformation. The chemical transformation of lignins and tannins has been extensively reviewed [START_REF] Laurichesse | Chemical modification of lignins: Towards biobased polymers[END_REF][START_REF] Pizzi | Tannins: Prospectives and Actual Industrial Applications[END_REF][START_REF] Arbenz | Chemical modification of tannins to elaborate aromatic biobased macromolecular architectures[END_REF][START_REF] Karunarathna | Valorization of Lignin as a Sustainable Component of Structural Materials and Composites: Advances from 2011 to 2019[END_REF][START_REF] García | Modification of condensed tannins: from polyphenol chemistry to materials engineering[END_REF]. Main modifications are summarized in Fig. 13 with a focus on the modifications for PUFs fabrication. The polyphenols sources were mainly divided into lignin and tannin structures. The liquefaction is one of the main pathways to obtain polyols from lignins, tannins or natural polyphenols sources. As shown in Fig. 13, the aromatic structure of tannin was investigated to produce additives. As described in Fig. 12, the plant cell walls are primarily composed of cellulose, hemicellulose and lignin. The solvolysis of this biomass in harsh conditions is called the liquefaction process and was recently reviewed [START_REF] Hu | Polyols and Polyurethanes from the Liquefaction of Lignocellulosic Biomass[END_REF][START_REF] Souza | Biomass Liquefaction and Alkoxylation: A Review of Structural Characterization Methods for Bio-based Polyols[END_REF][START_REF] Shao | Agricultural and Forest Residues towards Renewable Chemicals and Materials Using Microwave Liquefaction[END_REF]. This process was applied to produce polyols with lignins [START_REF] Mohammadpour | Effect of Liquefied Lignin Content on Synthesis of Bio-based Polyurethane Foam for Oil Adsorption Application[END_REF][START_REF] Xu | Preparation of polyurethane foams using fractionated products in liquefied wood[END_REF][START_REF] Gao | Improved mechanical property, thermal performance, flame retardancy and fire behavior of lignin-based rigid polyurethane foam nanocomposite[END_REF][START_REF] Xue | Producing Lignin-Based Polyols through Microwave-Assisted Liquefaction for Rigid Polyurethane Foam Production[END_REF][START_REF] Li | Polyurethane foams from alkaline lignin-based polyether polyol[END_REF][START_REF] Mahmood | Hydrolytic liquefaction of hydrolysis lignin for the preparation of bio-based rigid polyurethane foam[END_REF], woods [START_REF] Rastegarfar | Characterization of polyurethane foams prepared from liquefied sawdust by crude glycerol and polyethylene glycol[END_REF][START_REF] Yue | Liquefaction of waste pine wood and its application in the synthesis of a flame retardant polyurethane foam[END_REF][START_REF] Maldas | Liquefaction of Wood in the Presence of Polyol Using NaOH as a Catalyst and its Application to Polyurethane Foams[END_REF], barks [START_REF] Souza | Polyurethane foams made from liquefied bark-based polyols[END_REF][START_REF] Ge | Biodegradable polyurethane materials from bark and starch. I. Highly resilient foams[END_REF], celluloses [START_REF] Kosmela | The Study on Application of Biopolyols Obtained by Cellulose Biomass Liquefaction Performed with Crude Glycerol for the Synthesis of Rigid Polyurethane Foams[END_REF] or wattle tannins [START_REF] Ge | A novel biodegradable antimicrobial PU foam from wattle tannin[END_REF]. Furthermore, the direct hydrolysis of lignin with water under strong alkali conditions was investigated and afforded suitable polyols for PUFs formulation [START_REF] Mahmood | Production of polyols via direct hydrolysis of kraft lignin: Effect of process parameters[END_REF][START_REF] Xue | Hydrolytic depolymerization of corncob lignin in the view of a bio-based rigid polyurethane foam synthesis[END_REF][START_REF] Pérez | Quantitative analysis of products from lignin depolymerisation in hightemperature water[END_REF]. The liquefaction process is a fast and efficient way to obtain a mixture of aliphatic and aromatic polyols for PUFs.

Alkoxylation

Similarly to carbohydrates, the different and more or less accessible OH groups can be transformed into more active OH groups at the end of polyether grafted chains via alkoxylation reactions. Organosolv [START_REF] Arshanitsa | Two approaches for introduction of wheat straw lignin into rigid polyurethane foams[END_REF][START_REF] Cateto | Lignin-based rigid polyurethane foams with improved biodegradation[END_REF][START_REF] Nadji | Oxypropylation of Lignins and Preparation of Rigid Polyurethane Foams from the Ensuing Polyols[END_REF][START_REF] Cateto | Optimization Study of Lignin Oxypropylation in View of the Preparation of Polyurethane Rigid Foams[END_REF][START_REF] Li | Ethanol organosolv lignin-based rigid polyurethane foam reinforced with cellulose nanowhiskers[END_REF][START_REF] Kurańska | Synthesis of thermal insulating polyurethane foams from lignin and rapeseed based polyols: A comparative study[END_REF][START_REF] Li | Fractionation and oxypropylation of cornstover lignin for the production of biobased rigid polyurethane foam[END_REF], pyrolytic [START_REF] Saffar | Production of Bio-based Polyol from Oxypropylated Pyrolytic Lignin for Rigid Polyurethane Foam Application[END_REF], Kraft [START_REF] Cateto | Lignin-based rigid polyurethane foams with improved biodegradation[END_REF][START_REF] Nadji | Oxypropylation of Lignins and Preparation of Rigid Polyurethane Foams from the Ensuing Polyols[END_REF][START_REF] Cateto | Optimization Study of Lignin Oxypropylation in View of the Preparation of Polyurethane Rigid Foams[END_REF][START_REF] Wu | Engineering plastics from lignin. I. Synthesis of hydroxypropyl lignin[END_REF][START_REF] Mahmood | Preparation of bio-based rigid polyurethane foam using hydrolytically depolymerized Kraft lignin via direct replacement or oxypropylation[END_REF][START_REF] Li | Kraft Lignin-Based Rigid Polyurethane Foam[END_REF], Soda [START_REF] Cateto | Lignin-based rigid polyurethane foams with improved biodegradation[END_REF][START_REF] Cateto | Optimization Study of Lignin Oxypropylation in View of the Preparation of Polyurethane Rigid Foams[END_REF] lignins and tannins [START_REF] Arbenz | Advanced biobased and rigid foams, based on urethane-modified isocyanurate from oxypropylated gambier tannin polyol[END_REF][START_REF] Arbenz | Synthesis and characterization of fully biobased aromatic polyolsoxybutylation of condensed tannins towards new macromolecular architectures[END_REF] were transformed into suitable polyols by this way. Epoxide rings for the alkoxylation can be synthesized from double bonds presents in biomass products. Nevertheless, the propylene carbonate, a well-known and non-toxic O-alkylating agent of phenol was used to graft polyether chains originated from phenol groups. Similarly to the alkoxylation reaction, the average number of polyether units per chain increase with the excess of propylene carbonates [START_REF] Duval | Oxyalkylation of Condensed Tannin with Propylene Carbonate as an Alternative to Propylene Oxide[END_REF]. The investigation with several carbonates demonstrated the potential of this solvent-free, fast and quantitative reaction to transform non-reactive phenol into reactive primary or secondary OHs toward isocyanate groups [START_REF] Duval | Cyclic Carbonates as Safe and Versatile Etherifying Reagents for the Functionalization of Lignins and Tannins[END_REF]. The utilization of a kraft lignin polyol derived by this technique for PUFs production was realized using polyethylene glycerol (PEG) as a solvent [START_REF] Zhang | Rigid polyurethane foams containing lignin oxyalkylated with ethylene carbonate and polyethylene glycol[END_REF].

Neat Polyphenols

Contrary to polysaccharides, lignins with adapted extraction technics and also tannins can be used directly without modification, neat, in PUFs formulation. Nevertheless, the solid and powdery aspect of the extracted lignin is the major drawback for this utilization. The dissolution in different polyols such as di-(DEG), tri-ethylene glycol (TEG), PEG, alkoxylated sucrose or molasses circumvented this problem, and the mixture can be introduced in the formulations [START_REF] Hayati | A simple methodology for improving the performance and sustainability of rigid polyurethane foam by incorporating industrial lignin[END_REF][START_REF] Hatakeyama | Glass transition of rigid polyurethane foams derived from sodium lignosulfonate mixed with diethylene, triethylene and polyethylene glycols[END_REF][START_REF] Hatakeyama | Environmentally Compatible Hybrid-Type Polyurethane Foams Containing Saccharide and Lignin Components[END_REF][START_REF] Hatakeyama | Glass transition temperature of polyurethane foams derived from lignin by controlled reaction rate[END_REF][START_REF] Liu | Performance characterization of rigid polyurethane foam with refined alkali lignin and modified alkali lignin[END_REF]. The properties of the corresponding PUFs can be adjusted depending on the lignin content. The utilization of biobased fatty acid and glycerol to disperse lignins was also investigated [START_REF] Carriço | Production and characterization of polyurethane foams from a simple mixture of castor oil, crude glycerol and untreated lignin as bio-based polyols[END_REF]. On the contrary to some works where the lignin is used as fillers [START_REF] Thakur | Progress in Green Polymer Composites from Lignin for Multifunctional Applications: A Review[END_REF], the utilization of neat organosolv and kraft lignins as a polyol in PUFs formulations resulted in the integration of the lignin into the network architecture with covalent bonds [START_REF] Pan | Effect of replacing polyol by organosolv and kraft lignin on the property and structure of rigid polyurethane foam[END_REF]. The dispersion of tannin in polyols was also applied with alkoxylated fatty amine to act as a reticulation agent [START_REF] Basso | Flexible-elastic copolymerized polyurethane-tannin foams[END_REF]. Otherwise, the mildly-sulfided quebracho wood tannin was mixed with furfuryl alcohol to form aromatic PUFs [START_REF] Basso | MALDI-TOF and 13 C NMR Analysis of Tannin-Furanic-Polyurethane Foams Adapted for Industrial Continuous Lines Application[END_REF].

Miscellaneous transformations

The production of fully biobased polyol was achieved through the esterification of lignin with oleyl chloride and further epoxidation-ring opening of the oil double bonds [START_REF] Laurichesse | Original polyols based on organosolv lignin and fatty acids: new bio-based building blocks for segmented polyurethane synthesis[END_REF]. Another strategy was the utilization of the Mannich reaction with lignin, diethanolamine and formaldehyde. The ligninaminated was dissolved into PEG before the foaming process [START_REF] Huo | Crosslinking kinetics of the formation of ligninaminated polyol-based polyurethane foam[END_REF]. Otherwise, alkali lignins were modified by hydroxymethylation, epoxidation and phenolation and then introduced in polyols.

Despite the low portion of added lignin (1 wt%), the effect on the foam properties was notable [START_REF] Yang | Modification of renewable resources-lignin-by three chemical methods and its applications to polyurethane foams[END_REF].

Polyisocyanates

The pre-polymerization of lignin with a diisocyanate excess is the only strategy used to form polyisocyanate from neat phenolic biomass. The functionalization of lignin with pMDI was, for instance, realized [START_REF] Zhang | Effects of Surface Functionalization of Lignin on Synthesis and Properties of Rigid Bio-Based Polyurethanes Foams[END_REF]. This surface-functionalized lignin was further introduced into PUFs [START_REF] Zhang | Effects of Surface Functionalization of Lignin on Synthesis and Properties of Rigid Bio-Based Polyurethanes Foams[END_REF][START_REF] Zhang | Lab-scale structural insulated panels with lignin-incorporated rigid polyurethane foams as core[END_REF].

Additives

Lignins and tannins were widely investigated to form polyol thanks to the well-known increase of mechanical properties brought by the aromatic structure. However, aromatic structures are also known to be used as FR systems. The modified lignin contains primary OH groups to covalently linked to the PUFs network and phosphorous and aromatic compound for the FR properties [START_REF] Xing | Functionalized lignin for halogen-free flame retardant rigid polyurethane foam: preparation, thermal stability, fire performance and mechanical properties[END_REF]. Another strategy was the transformation of a tannin monomer, the gallic acid [START_REF] Howell | Phosphorus Flame Retardants for Polymeric Materials from Gallic Acid and Other Naturally Occurring Multihydroxybenzoic Acids[END_REF]. The production of industrial consumer goods inevitably generates wastes either from the production of non-compliant products or after the life of the product. This part is focused on the production of PUFs components based on three abundant wastes from industrial processes:

Products from industrial wastes

biobased PUs, crude glycerol, and lignocellulosic residues presented in Fig. 14.

Alkoxylation and liquefaction are the main pathways to develop polyols from lignocellulosic residues, biobased PUs or glycerol, as shown with polyphenol resources. Actually, there are no developed routes from industrial wastes toward isocyanates. and fast developments on the enzymatic degradation of PUs, there is still work to understand mechanisms and develop higher scale productions [START_REF] Magnin | Evaluation of biological degradation of polyurethanes[END_REF]. The chemical degradation of PUs is achieved through various processes such as hydrolysis, aminolysis, phophatation or alcoholysis. The two first methods yield amine, which can be further used in the epoxy resin formulation [START_REF] Xue | Preparation of epoxy hardeners from waste rigid polyurethane foam and their application[END_REF][START_REF] Dai | Effect of diaminotoluene on the decomposition of polyurethane foam waste in superheated water[END_REF],

and the third, based on phosphate reaction, will be detailed later. Aminolysis has been used on F-PUFs, followed by an alkoxylation reaction to produce polyols [START_REF] Der | New Chemical Recycling Process for Polyurethanes[END_REF]. However, the first process to obtain polyols from PUs wastes is the alcoholysis. The process was applied to numerous wastes such as RIM [START_REF] Modesti | Chemical recycling of reinforced polyurethane from the automotive industry[END_REF], foams [START_REF] Ulrich | Recycling of polyurethane and polyisocyanurate foam[END_REF][START_REF] Nikje | Glycolysis of Waste Polyurethane Integral Skin Foams from Steering Wheel[END_REF] or scrapped PUs [START_REF] Sendijarevic | Chemical Recycling of Mixed Polyurethane Foam Stream Recovered from Shredder Residue into Polyurethane Polyols[END_REF][START_REF] Shin | Sustainable rigid polyurethane foams based on recycled polyols from chemical recycling of waste polyurethane foams[END_REF]. Green chemistry can be obtained, for instance, using transesterified coconut oil for the alcoholysis of PUs [START_REF] Paruzel | Rigid Polyurethane Foam Fabrication Using Medium Chain Glycerides of Coconut Oil and Plastics from End-of-Life Vehicles[END_REF]. The major drawback of this strategy is the high-energy consumption, which is balanced by the valorization of "plastic" wastes.

Glycerol

The biodiesel produced from the transesterification of triglycerides generates a considerable amount of glycerol as side products. This crude glycerol contains sodium generally used as the catalyst for the transesterification, residue of oils and water, which can be removed to obtain high purity glycerol [START_REF] Thompson | Characterization of crude glycerol from biodiesel production from multiple feedstocks[END_REF]. This triol with a high IOH is introduced neat in a small portion as crosslinker with low IOH co-polyol in PUFs formulations [START_REF] Narine | Physical Properties of Polyurethanes Produced from Polyols from Seed Oils: II. Foams[END_REF][START_REF] Ng | Preparation and modification of water-blown porous biodegradable polyurethane foams with palm oil-based polyester polyol[END_REF][START_REF] Furtwengler | Synthesis and characterization of polyurethane foams derived of fully renewable polyester polyols from sorbitol[END_REF]. Glycerol can be polymerized to reduce the IOH value and obtain long polyol chains [START_REF] Ionescu | High Functionality Polyether Polyols Based on Polyglycerol[END_REF][START_REF] Piszczyk | Rigid polyurethane foams from a polyglycerol-based polyol[END_REF]. Recently developed, the formation of a ketal between glycerol and the methyl levulinate derived from wheat straw was reported. The methyl ester was further transesterified with EG to form a diol introduced up to 100% in PUFs [START_REF] Li | Efficient Synthesis of Biobased Glycerol Levulinate Ketal and Its Application for Rigid Polyurethane Foam Production[END_REF].

Liquefaction of waste from industrial process

Industrial processes such as sugar extraction from sugar cane generates biobased solid waste composed mainly of the solid part of plant cell walls (Fig. 12). It can be valorized into polyols for PUFs by the liquefaction process as detailed in the lignins and tannins section. This reaction was used with food industry wastes [START_REF] Amran | Polyols and rigid polyurethane foams derived from liquefied lignocellulosic and cellulosic biomass[END_REF][START_REF] Zhang | Open-Cell Rigid Polyurethane Foams from Peanut Shell-Derived Polyols Prepared under Different Post-Processing Conditions[END_REF][START_REF] Hakim | Preparation and characterization of rigid polyurethane foam prepared from sugar-cane bagasse polyol[END_REF][START_REF] Hakim | Preparation and characterization of rigid polyurethane foam prepared from sugar-cane bagasse polyol[END_REF][START_REF] Lee | Liquefaction of corn bran (CB) in the presence of alcohols and preparation of polyurethane foam from its liquefied polyol[END_REF][START_REF] Zhang | Optimization of preparation process to produce polyurethane foam made by oilseed rape straw based polyol[END_REF][START_REF] Zhang | Influence of NCO/OH ratio on preparation of four agricultural wastes liquefied polyols based polyurethane foams[END_REF][START_REF] Sendijarevic | Polyol from spent coffee grounds: Performance in a model pour-in-place rigid polyurethane foam system[END_REF][START_REF] Pavier | Oxypropylation of sugar beet pulp. 1. Optimisation of the reaction[END_REF], straws [START_REF] Jasiūnas | Mechanical, Thermal Properties and Stability of Rigid Polyurethane Foams Produced with Crude-Glycerol Derived Biomass Biopolyols[END_REF][START_REF] Hu | Production and characterization of biopolyols and polyurethane foams from crude glycerol based liquefaction of soybean straw[END_REF], digested sewage sludges [START_REF] Jasiūnas | Mechanical, Thermal Properties and Stability of Rigid Polyurethane Foams Produced with Crude-Glycerol Derived Biomass Biopolyols[END_REF] or microalgae biomass [START_REF] Hejna | Structure, Mechanical, Thermal and Fire Behavior Assessments of Environmentally Friendly Crude Glycerol-Based Rigid Polyisocyanurate Foams[END_REF].

Additives

As previously presented, the PU can be degraded by phosphate. This strategy was employed to produce urethane oligomers with high phosphorous content [START_REF] Troev | A novel approach to recycling of polyurethanes: chemical degradation of flexible polyurethane foams by triethyl phosphate[END_REF]. Otherwise, a glycerol derivative was transformed in FR via a Michael addition. The thioglycerol was added to diethyl allyl phosphonate to produce a polyol with low viscosity and intrinsic FR properties due to the phosphorous compound [START_REF] Bhoyate | Sustainable flame-retardant polyurethanes using renewable resources[END_REF].

Products from white biotechnology

This part is linked to Fig. 15. From different biobased molecules extracted from biomass mainly by biotechnology in biorefineries such as limonene, β-pinene, eugenol, malic and citric acid, furan, vanillic and syringic acid, oil cashew nut shell liquid (CNSL) or derived from amino acids, different PUFs components can be elaborated. One of the most common building blocks obtained by biotechnology for PU is the 1,4-butanediol. This diol is obtained industrially through hydrogenation of succinic acid obtained by biotechnology [START_REF] Debuissy | Biotic and Abiotic Synthesis of Renewable Aliphatic Polyesters from Short Building Blocks Obtained from Biotechnology[END_REF]. Genomatica developed another strategy by bioengineering an Escherichia coli strain to directly produce 1,4-butanediol from renewable carbohydrate feedstocks [START_REF] Yim | Metabolic engineering of Escherichia coli for direct production of 1,4-butanediol[END_REF]. The 1,3-propanediol is another important diol bioproduced either from glycerol or glucose [START_REF] Debuissy | Biotic and Abiotic Synthesis of Renewable Aliphatic Polyesters from Short Building Blocks Obtained from Biotechnology[END_REF]. In PUFs, these biobased diols are used as chain extenders [START_REF] Li | Fractionation and oxypropylation of cornstover lignin for the production of biobased rigid polyurethane foam[END_REF][START_REF] Rashmi | Development of water-blown bio-based thermoplastic polyurethane foams using bio-derived chain extender[END_REF] or through the synthesis of polyols [START_REF] Furtwengler | Synthesis and characterization of polyurethane foams derived of fully renewable polyester polyols from sorbitol[END_REF].

Polyols

Different compounds can be more or less directly extracted from biomass to produce polyols.

The processes are often integrated into biorefineries based on biotechnology and chemical steps.

For example, it is the case of the limonene, which is obtained, e.g., from orange peels or produced by microorganisms [START_REF] Jongedijk | Biotechnological production of limonene in microorganisms[END_REF]. Based on a cyclic structure with two double bonds suitable for chemical transformation, it can be transformed into a Mannich polyol with 1,3-N-hydroxyethyl oxazolidine [START_REF] Gupta | Synthesis of a Novel Limonene Based Mannich Polyol for Rigid Polyurethane Foams[END_REF]. Otherwise, limonene was mercaptanized with hydrogen sulfide and then reacted with glycerol-1-allyl ether via Michael addition to form a polyol for PUFs [START_REF] Zhang | Highly flame retardant and bio-based rigid polyurethane foams derived from orange peel oil[END_REF]. In another study, the malic acid, a dicarboxylic acid potentially obtained by microbial fermentation [START_REF] Kövilein | Malic acid production from renewables: a review[END_REF], was oligomerized with 1,6 hexanediol to produce a polyol which is used in PUFs formulation. The presence of one OH group on malic acid increases the IOH of the produced polyol [START_REF] Yang | Preparation, characterization and thermal degradation behavior of rigid polyurethane foam using a malic acid based polyols[END_REF].

As previously seen, carbohydrates are an important source for the elaboration of biobased molecules. The β-methyl-δ-valerolactone, a six-membered ester ring, was, for instance, synthesized from glucose with mevalonate as an intermediate [START_REF] Xiong | Scalable production of mechanically tunable block polymers from sugar[END_REF]. It was transformed into a polyol via acidcatalyzed ring-opening transesterification with trimethylolpropane ethoxylate [START_REF] Schneiderman | Chemically Recyclable Biobased Polyurethanes[END_REF].

Otherwise, alkoxylated [START_REF] Shrestha | Aliphatic-Aromatic Polyols by Thiol-Ene Reactions[END_REF] or not [START_REF] Hu | Synthesis of Eugenol-Based Polyols via Thiol-Ene Click Reaction and High-Performance Thermosetting Polyurethane Therefrom[END_REF] eugenol extracted from cloves was transformed through thiol-ene chemistry to produce polyols. In another study, the natural rubber was transformed through controlled oxidative degradation, followed by a reduction to obtain a OHterminated natural rubber [START_REF] Jaratrotkamjorn | Bio-based flexible polyurethane foam synthesized from palm oil and natural rubber[END_REF].

Another source of recent innovation in terms of new molecules is the CNSL, which is composed at 90% of anacardic acid, a particular lipid formed by a phenol with a carboxylic acid in the ortho position and an unsaturated carbon chain in the para position. The decarboxylation of anacardic acid by heating yields cardanol [START_REF] Quirino | Matrices from vegetable oils, cashew nut shell liquid, and other relevant systems for biocomposite applications[END_REF]. It was transformed into polyols via alkoxylation [START_REF] Reese | Polyether polyols based on cashew nutshell liquid and flexible foams[END_REF] or Mannich [START_REF] Ionescu | Polyols and Rigid Polyurethane Foams from Cashew Nut Shell Liquid[END_REF][START_REF] Gandhi | Mechanical, thermal and fire properties of sustainable rigid polyurethane foam derived from cashew nut shell liquid[END_REF][START_REF] Zhang | Synthesis and fire properties of rigid polyurethane foams made from a polyol derived from melamine and cardanol[END_REF] reaction. A hybrid polyol has recently been developed based on cardanol, composed of catalytic tertiary amine and polysiloxane chains similar to surfactants [START_REF] Huo | Preparation and properties of biobased autocatalytic polyols and their polyurethane foams[END_REF].

Additives

Cardanol was modified to obtain a FR molecule composed of 66% of cardanol and 3.4% of phosphorous [START_REF] Amarnath | Eco-Friendly Halogen-Free Flame Retardant Cardanol Polyphosphazene Polybenzoxazine Networks[END_REF]. The trimerization of vanillic acid, guaiacol and DOPO to form a FR containing phosphorous was developed for the epoxy resin, but it could be adapted to be used in PUFs formulation [START_REF] Liu | Facile synthesis of bio-based reactive flame retardant from vanillin and guaiacol for epoxy resin[END_REF]. Another example, the guanidine acetic acid (glycocyamine), which is derived from the hydrolysis of proteins (i.e., glycine), was modified to form a FR compound [START_REF] Wan | A novel guanidine ammonium phosphate for preparation of a reactive durable flame retardant for cotton fabric[END_REF].

Polyisocyanates

With lignin and tannins derivatives, aromatic isocyanates can be synthesized. Syringic and vanillic acid can be dimerized and further converted into isocyanate via Curtius rearrangement [START_REF] Kuhire | Poly(ether urethane)s from aromatic diisocyanates based on lignin-derived phenolic acids: Poly(ether urethane)s from aromatic diisocyanates[END_REF].

This method has the particularity to produced diisocyanate with a control chain length between the two aromatic moieties.

The amino acid lysine was transformed into diisocyanate by esterification with ethanol and phosgenantion of the amines. The ethyl ester (L) Lysine diisocyanate obtained is well known, especially in biomedical or coating applications [START_REF] Calvo-Correas | Thermally-responsive biopolyurethanes from a biobased diisocyanate[END_REF][START_REF] Li | Bio-based poly(urethane urea) dispersions with low internal stabilizing agent contents and tunable thermal properties[END_REF][START_REF] Gustini | Sustainable coatings from bio-based, enzymatically synthesized polyesters with enhanced functionalities[END_REF][START_REF] Acik | Synthesis and characterization of biodegradable polyurethanes made from cholic acid and l-lysine diisocyanate ethyl ester[END_REF]. Another synthetic route toward diisocyanate from β-pinene is described in Scheme 4. The β-pinene distilled from pine was transformed through several steps into a diamine and further in diisocyanate by phosgenation [START_REF] Kobilka | Pinene-Derived diisocyanates[END_REF].

Scheme 4. Synthesis of diisocyanate from β-pinene. Adapted from [START_REF] Kobilka | Pinene-Derived diisocyanates[END_REF].

The furan derivatives obtained by dehydration of monosaccharides could be good candidates for the replacement of aromatic structures. Extensive researches are conducted on the furan and a major component to produce PEF (equivalent to PET) the polyethylene 2,5-furan dicarboxylic acid [START_REF] De Jong | Furandicarboxylic Acid (FDCA), A Versatile Building Block for a Very Interesting Class of Polyesters[END_REF].

The furfuryl amine obtained from the biotransformation of furfural [START_REF] Zhang | Chemoenzymatic Conversion of Corncob to Furfurylamine via Tandem Catalysis with Tin-Based Solid Acid and Transaminase Biocatalyst[END_REF] was dimerized with acetone under mild conditions; the obtained difurfurylamine was transformed via phosgenation into diisocyanate [START_REF] Cawse | Polymers from renewable sources, 1. Diamines and diisocyanates containing difurylalakne moities[END_REF]. The reactivity of furan isocyanates was found to be similar to aromatic analogs (TDI) [START_REF] Belgacem | Urethanes and polyurethanes bearing furan moieties-3. Synthesis, characterization and comparative kinetics of the formation of diurethanes[END_REF][START_REF] Boufi | Urethanes and polyurethanes bearing furan moieties. 4. Synthesis, kinetics and characterization of linear polymers[END_REF][START_REF] Boufi | Urethanes and polyurethanes bearing furan moieties: 5. Thermoplastic elastomers based on sequenced structures[END_REF]. A novel strategy to develop foams from furan derivatives was based on the modification of two carboxylic groups of the bis(5-carboxyfurfuryl)ether into carboxylic-azide. This precursor was introduced with polyols and heated to induce the Curtius rearrangement to form isocyanate from azide. The nitrogen released by this reaction served as a BA for the foam network composed of the newly formed diisocyanate and the polyol [START_REF] Neumann | Water-Free Synthesis of Polyurethane Foams Using Highly Reactive Diisocyanates Derived from 5-Hydroxymethylfurfural[END_REF].

Study of "structure-properties" relationships in the case of biobased R-PUF.

The goal of this chapter is to study the relationship between the structure or morphology of the foams and some specific properties. This chapter is mainly focused on biobased R-PUFs, which are mainly used as insulation materials. The characterizations of these foams are then targeted and focussed on the application and largely less diverse than the F-PUFs. Besides, the processing and the additives differ from R-PUF to F-PUF, increasing the complexity to draw a general conclusion on the effect of the biobased components on all PUFs properties. R-PUFs are at least mainly based on six components, such as the polyisocyanate, polyol, BA, surfactant, catalyst and additives (Table 1). The conventional polyisocyanates and surfactants are usually pMDI and polyether siloxane, respectively. The BAs and catalysts structures evolve in the formulation to reach the optimum properties in accordance with the targeted application. The comparison between the data of the literature is often difficult due to the multiplicity of foam formulations with different NCO/OH indexes, catalysts/surfactant loadings and structures, foaming environments or BAs.

Morphological and structural data

In R-PUFs, the cells are generally defined by a polyhedron shape close to an honeycomb structure. The faces of the polyhedron are called the walls, and the thicker edges the struts. In a partially open system such as a cup often use as a mold, the cells are elongated in the vertical direction. This phenomenon was explained by the constraint expansion by the cup walls inducing a faster growth in the vertical direction than the horizontal direction [START_REF] Hawkins | Cell Morphology and Mechanical Properties of Rigid Polyurethane Foam[END_REF]. The cell morphology is defined by the density of the foam, the cells size and shape, and the closed-cell content. The related properties are affected by the foaming process and linked parameters (viscosity, surface tension, kinetics) and materials properties (phase separation).

Viscosity

Generally, the viscosity of polyols for R-PUFs is between 2 and 50 Pa.s (Table 3). Fig. 16 represents the dependence between cell size and viscosity. The data were compiled from the literature of foams made with a biobased sole polyol. As shown in Fig. 16, when the viscosity of the polyol is under 5 Pa.s, the produced foam presents dispersed cell sizes. On the contrary, the cells obtained with a moderately viscous polyol (5-25 Pa.s) are homogeneous and smalls, around 200 µm.

Finally, few examples of cell size from foams realized with highly viscous ( > 25 Pa.s) polyols are presented in Fig. 16. The size varies from 250 to 490 µm.

The high viscosity of biobased polyols can originate from triglycerides crystallization [START_REF] Ng | Preparation and modification of water-blown porous biodegradable polyurethane foams with palm oil-based polyester polyol[END_REF],

branched structure of phenolic compounds [START_REF] Hayati | A simple methodology for improving the performance and sustainability of rigid polyurethane foam by incorporating industrial lignin[END_REF][START_REF] Arbenz | Advanced biobased and rigid foams, based on urethane-modified isocyanurate from oxypropylated gambier tannin polyol[END_REF][START_REF] Xu | Preparation of polyurethane foams using fractionated products in liquefied wood[END_REF][START_REF] Carriço | Production and characterization of polyurethane foams from a simple mixture of castor oil, crude glycerol and untreated lignin as bio-based polyols[END_REF], solid residues in the polyol [START_REF] Hakim | Preparation and characterization of rigid polyurethane foam prepared from sugar-cane bagasse polyol[END_REF] or high molar masses [START_REF] Furtwengler | Elaboration and Characterization of Advanced Biobased Polyurethane Foams Presenting Anisotropic Behavior[END_REF][START_REF] Shin | Sustainable rigid polyurethane foams based on recycled polyols from chemical recycling of waste polyurethane foams[END_REF][START_REF] Ghaderian | Characterization of Rigid Polyurethane Foam Prepared from Recycling of PET Waste[END_REF]. Moderate viscosity is requested to reduce the cell-size due to the limitation of bubble coalescence and expansion [START_REF] Kurańska | Open-cell rigid polyurethane bio-foams based on modified used cooking oil[END_REF][START_REF] Arbenz | Advanced biobased and rigid foams, based on urethane-modified isocyanurate from oxypropylated gambier tannin polyol[END_REF]. For example, the cell diameters of foam obtained from alkoxylated glycerol (0.2 Pa.s) and tannin (6.9 Pa.s) were 440 and 290 µm in the rise direction, respectively [START_REF] Arbenz | Advanced biobased and rigid foams, based on urethane-modified isocyanurate from oxypropylated gambier tannin polyol[END_REF]. The authors attributed this decrease in cell size to the high viscosity and functionality of the alkoxylated tannin. Furthermore, the nucleation of cells is heavily affected by the viscosity of the foaming liquid. In more viscous polyols, the concentration of air bubbles is higher due to the limited diffusion and coalescence. The nucleation was enhanced by the branched and pendant chains of triglycerides polyols [START_REF] Fan | Rigid polyurethane foams made from high viscosity soypolyols[END_REF] or solid lignins dispersion in the polyol [START_REF] Hayati | A simple methodology for improving the performance and sustainability of rigid polyurethane foam by incorporating industrial lignin[END_REF][START_REF] Mohammadpour | Effect of Liquefied Lignin Content on Synthesis of Bio-based Polyurethane Foam for Oil Adsorption Application[END_REF]. The incorporation of 10 wt% of the unmodified lignin particles in the polyol improved the nucleation and can decrease the average cell size from 510 to 430 µm [START_REF] Hayati | A simple methodology for improving the performance and sustainability of rigid polyurethane foam by incorporating industrial lignin[END_REF]. The introduction of long aliphatic segments enhanced the flexibility and decreased the viscosity; therefore, coarser and more irregular cells were obtained [START_REF] Gaidukova | Polyurethane rigid foams obtained from polyols containing bio-based and recycled components and functional additives[END_REF]. However, too high polyol viscosity was also observed to cause coarser and less uniform cells. The polyols prepared with 40 wt% of lignin were highly viscous (16.7 Pa.s) and caused less uniform and coarser cells [START_REF] Pan | Effect of replacing polyol by organosolv and kraft lignin on the property and structure of rigid polyurethane foam[END_REF]. A similar trend was observed with soybean oil-based

polyol. An increase in viscosity from 7 to 23 Pa.s of the soybean-polyols clearly produced PUFs with coarser cells affecting the nucleation process [START_REF] Fang | Development of High-Performance Biodegradable Rigid Polyurethane Foams Using Full Modified Soy-Based Polyols[END_REF]. The high viscosity of polyols induces mixing drawbacks and therefore a higher dispersity in cell sizes, as shown in Fig. 16.

Surface tension

The surface tension was shown to play a crucial role in the formation of small cells. The growth of bubbles is closely related to the surface tension of the foaming mixture by the Laplace equation [START_REF] Furtwengler | Novel Rigid Polyisocyanurate Foams from Synthesized Biobased Polyester Polyol with Enhanced Properties[END_REF]. The increase in surface tension induced by the sorbitol polyester polyol slows down the growth of the cell. Cell size can be partially controlled by formulation, cells were reduced from 410 to 270 µm in the longitudinal direction by the addition of polyester polyol from 10 to 35 wt% [START_REF] Furtwengler | Novel Rigid Polyisocyanurate Foams from Synthesized Biobased Polyester Polyol with Enhanced Properties[END_REF].

Reaction kinetics

In the same study [START_REF] Furtwengler | Novel Rigid Polyisocyanurate Foams from Synthesized Biobased Polyester Polyol with Enhanced Properties[END_REF], the faster gelling of the polymer network was shown to help the generation of small cells. As previously explained, the expansion of bubbles is closely related to the equilibrium between blowing and gelling reaction. Significant modification in the formulation, such as the substitution of the polyol, alters the gelling/blowing balance. Fig. 17 represents the evolution of the temperature, viscosity and cell morphology over time in different cases: the balance is in favor of the blowing (Fig. 17A), equilibrium of the blowing/gelling balance (Fig. 17B) and the balance in favor of the gelling (Fig. 17C).

In the case of high blowing efficiency, the foam size increases rapidly due to a sudden temperature increase (Fig. 17A). Therefore, the cell size and elongation increase and the density decrease as represented in Fig. 17A in comparison with Fig. 17B. Moreover, fast cell expansion often induces breaks in the thin walls to form open cells (Fig. 17A). A decrease of density from 102 to 66 kg/m 3 attributed to the increased blowing efficiency was observed when the polytrimethylene ether glycol content was increased in the foam formulation [START_REF] Ugarte | Tailoring Mechanical Properties of Rigid Polyurethane Foams by Sorbitol and Corn Derived Biopolyol Mixtures[END_REF]. The hydrophilic character of the polyol and thus, its water content could explain this increased blowing activity, as it was observed with linseed oil used as a surfactant [START_REF] Członka | Linseed oil as a natural modifier of rigid polyurethane foams[END_REF]. Higher water content promotes the rapid and sudden release of CO2 producing larger cells with thinner walls [START_REF] John | Characterization of polyurethane foams from soybean oil[END_REF]. Furthermore, the closed-cell content decreased under 10% with higher foaming rate polyols [START_REF] Furtwengler | Elaboration and Characterization of Advanced Biobased Polyurethane Foams Presenting Anisotropic Behavior[END_REF]. Nevertheless, the primary effect observed, coupled with a higher blowing activity, is related to the decrease of the gelling activity. Fig. 17A represents the evolution of the viscosity over time when the gelling is lower than the blowing activity. In this case, the longer gel time is characteristic of a slow network formation around the growing bubbles; thus, cell drainage and Ostwald ripening get a longer time to deteriorate the closed-cell morphology (Fig. 17A). Therefore, the cells are coarser, and the closed-cell content decrease [START_REF] Furtwengler | Elaboration and Characterization of Advanced Biobased Polyurethane Foams Presenting Anisotropic Behavior[END_REF][START_REF] Li | Polyurethane foams from alkaline lignin-based polyether polyol[END_REF][START_REF] Mahmood | Hydrolytic liquefaction of hydrolysis lignin for the preparation of bio-based rigid polyurethane foam[END_REF][START_REF] Souza | Polyurethane foams made from liquefied bark-based polyols[END_REF][START_REF] Amran | Polyols and rigid polyurethane foams derived from liquefied lignocellulosic and cellulosic biomass[END_REF]. For example, the introduction of less reactive liquefied lignin compared to conventional polyols was observed to produce a broader cell distribution [START_REF] Li | Polyurethane foams from alkaline lignin-based polyether polyol[END_REF]. In another study, the introduction of liquefied biomass formed large and widely distributed cells. The coalescence of cells by Ostwald ripening explained the difference of the mean diameter between the reference foam made with PEG-glycerol (660 µm) and the biobased system (780 µm). The authors pointed out the low reactivity of phenols from the biobased aromatic polyols [START_REF] Amran | Polyols and rigid polyurethane foams derived from liquefied lignocellulosic and cellulosic biomass[END_REF].

The lower reactivity of the polymer network formation was also explained by lower IOH [START_REF] Ugarte | Tailoring Mechanical Properties of Rigid Polyurethane Foams by Sorbitol and Corn Derived Biopolyol Mixtures[END_REF][START_REF] Maldas | Liquefaction of Wood in the Presence of Polyol Using NaOH as a Catalyst and its Application to Polyurethane Foams[END_REF]. The OH density is related to the functionality of the polyol, and it is well known that the higher the functionality is, and the lower the conversion to reach the gel point will be [START_REF] Flory | Molecular Size Distribution in Three Dimensional Polymers. I. Gelation[END_REF][START_REF] Stockmayer | Theory of Molecular Size Distribution and Gel Formation in Branched Polymers II. General Cross Linking[END_REF].

Furthermore, with similar IOH, the decrease in gelling rates can be explained by the lower reactivity of the secondary [START_REF] Peyrton | Biobased Polyurethane Foams Based on New Polyol Architectures from Microalgae Oil[END_REF][START_REF] Fan | Rigid polyurethane foams made from high viscosity soypolyols[END_REF] or even phenolic OH groups [START_REF] Amran | Polyols and rigid polyurethane foams derived from liquefied lignocellulosic and cellulosic biomass[END_REF], compared to primary OHs. Furthermore, a high acidity of the polyols resulting from the biomass transformation can reduce the amine catalysis activity and forms coarser cells [START_REF] Peyrton | Biobased Polyurethane Foams Based on New Polyol Architectures from Microalgae Oil[END_REF][START_REF] Arshanitsa | Two approaches for introduction of wheat straw lignin into rigid polyurethane foams[END_REF]. The gel time was proved to increase from 200 to 510 s with the substitution of 50 wt% of the polyol by lignin. The authors explained that lignin contained free acetic/formic acid, which, once bonded with an amine catalyst, reduced its activity. This hypothesis was further supported by the decrease in density explained by the free carboxylic acid reaction with isocyanates forming amide and CO2 [START_REF] Arshanitsa | Two approaches for introduction of wheat straw lignin into rigid polyurethane foams[END_REF]. If the gelling is very low compared to the blowing, the cells burst, and the foam falls back before the polymer solidifies [START_REF] Campanella | Polyurethane foams from soyoil-based polyols[END_REF][START_REF] Fan | Rigid polyurethane foams made from high viscosity soypolyols[END_REF][START_REF] Hejna | The influence of crude glycerol and castor oil-based polyol on the structure and performance of rigid polyurethanepolyisocyanurate foams[END_REF].

On the contrary, when the gelling reaction is favored, the polymer solidifies faster than the gas expands. This is represented in Fig. 17C by a rapid increase in viscosity compared to Fig. 17B.

Therefore, smaller cell size, higher closed cell content and an increase in density are generally observed (Fig. 17C). Polyols with high IOH makes the polymer network gel faster because less conversion is required to form a crosslinked structure. For example, the transesterification of castor oil with crude glycerol produces polyols with lower IOH (350 mg KOH/g) than neat glycerol (540 mg KOH/g). The crude glycerol polyol formed lighter foams (95 vs 245 kg/m 3 ) with bigger cells (600 vs 400 µm) [START_REF] Bresolin | Polyurethane Foams Based on Biopolyols from Castor Oil and Glycerol[END_REF]. Similar results were observed on biobased polyols with high IOH produced with oils [START_REF] Riyapan | A Novel Rigid PU Foam Based on Modified Used Palm Oil as Sound Absorbing Material[END_REF], carbohydrates [START_REF] Furtwengler | Novel Rigid Polyisocyanurate Foams from Synthesized Biobased Polyester Polyol with Enhanced Properties[END_REF] or liquefied lignins [START_REF] Li | Fractionation and oxypropylation of cornstover lignin for the production of biobased rigid polyurethane foam[END_REF]. Furthermore, the shrinkage reduced from 4 to 0.4% and the collapsing from 2.3 to 0.1% within foam elaborated from 250 mg KOH/g polyol instead of 100 mg KOH/g [START_REF] Riyapan | A Novel Rigid PU Foam Based on Modified Used Palm Oil as Sound Absorbing Material[END_REF]. This is due to the thicker cell walls presented in Fig. 17C compared to Fig. 17B.

The higher content of more reactive primary OHs increased the gelling rate of foam [START_REF] Piszczyk | Rigid polyurethane foams from a polyglycerol-based polyol[END_REF][START_REF] Sendijarevic | Polyol from spent coffee grounds: Performance in a model pour-in-place rigid polyurethane foam system[END_REF]. As shown in Fig. 17C, a faster gelling form low cell size compared to Fig. 17B. A decrease in cell size of 150 µm was observed with the introduction of more reactive polyols obtained from liquefied spent coffee grounds. This phenomenon was explained by the reduction of the coalescence due to the faster polymerization [START_REF] Sendijarevic | Polyol from spent coffee grounds: Performance in a model pour-in-place rigid polyurethane foam system[END_REF]. Another way to increase the gelling activity of the polyol is the incorporation of catalytic sites inside the polyols structure. The introduction of a tertiary amine in model fatty ester alcohol was proved to increases the reaction rate between the OH group and isocyanate [START_REF] Peyrton | New Insight on the Study of the Kinetic of Biobased Polyurethanes Synthesis Based on Oleo-Chemistry[END_REF]. In PUFs, it was achieved with Mannich reaction on limonene based polyols [START_REF] Gupta | Synthesis of a Novel Limonene Based Mannich Polyol for Rigid Polyurethane Foams[END_REF],

triglycerides epoxidation and ring-opening with amine [START_REF] Peyrton | Biobased Polyurethane Foams Based on New Polyol Architectures from Microalgae Oil[END_REF] and modified cardanol [START_REF] Huo | Preparation and properties of biobased autocatalytic polyols and their polyurethane foams[END_REF]. However, this kind of polyol cannot substitute the standard polyol without a complete disequilibrium between the gelling and blowing balance. For example, the substitution of 25 wt% of conventional polyol by epoxidized microalgae oil ring-opened with diethylamine was proved to increase the kinetics of the foam and deteriorate the cell morphology [START_REF] Peyrton | Biobased Polyurethane Foams Based on New Polyol Architectures from Microalgae Oil[END_REF]. However, in the same study, the epoxidized soybean oil ring-opened by diethylamine was successfully used as a unique catalyst to form low-density foams (36 kg/m 3 ). Another strategy can balance blowing and gelling with a cardanol based "autocatalytic" polyol [START_REF] Huo | Preparation and properties of biobased autocatalytic polyols and their polyurethane foams[END_REF].

In some rare cases, the substitution of biobased polyols did not affect the foaming process (Fig. 17B). For example, the introduction of alkoxylated lignin produces foam with similar reactivity compared to fossil-based polyol. It was assumed that a similar structure composed of PO units plays a key role in similar kinetics [START_REF] Mahmood | Hydrolytic liquefaction of hydrolysis lignin for the preparation of bio-based rigid polyurethane foam[END_REF]. Despite the lower reactivity observed with an oil-based polyol, the foaming process and the cell morphology were not affected [START_REF] Borowicz | Biodegradable, Flame-Retardant, and Bio-Based Rigid Polyurethane/Polyisocyanurate Foams for Thermal Insulation Application[END_REF][START_REF] Herrán | Highly functional lactic acid ring-opened soybean polyols applied to rigid polyurethane foams[END_REF].

Microphase segregation

A particularity of the PU networks is the capacity to segregate into (i) strongly H-bonded hard segments and (ii) long flexible chains called soft segments. The microphase separation in PUFs generally explains a defect in the foam, such as irregular pores [START_REF] Arbenz | Elaboration and Properties of Innovative Biobased PUIR Foams from Microalgae[END_REF][START_REF] Ng | Preparation and modification of water-blown porous biodegradable polyurethane foams with palm oil-based polyester polyol[END_REF] or wrinkles [START_REF] Jiang | Synthesis and characterization of polyurethane rigid foams from polyether polyols with isosorbide as the bio-based starting agent[END_REF]. The activity of the soft segments formed by the long and flexible chain on the microphase separation is not yet fully understood. Some theories claimed that the higher flexibility of this soft segment allows a better migration of the surfactant with the formation of coarser cells and lower densities [START_REF] Borowicz | Biodegradable, Flame-Retardant, and Bio-Based Rigid Polyurethane/Polyisocyanurate Foams for Thermal Insulation Application[END_REF][START_REF] Contreras | Development of eco-friendly polyurethane foams based on Lesquerella fendleri (A. Grey) oilbased polyol[END_REF]. It was also noticed that the small molar mass molecules in liquefied bark polyols had a plasticizing effect increasing the drainage and open-cell content. Otherwise, the decline in the free volume of polymer with the gradual substitution of glycerol by lignin extended the density from 60 kg/m 3 to 115 kg/m 3 with 10 wt% and 40 wt% of lignin, respectively [START_REF] Carriço | Production and characterization of polyurethane foams from a simple mixture of castor oil, crude glycerol and untreated lignin as bio-based polyols[END_REF]. Nevertheless, these effects need to be further investigated with more in-depth analysis.

To summarize, the cell morphology is highly influenced by the structure of the biobased component via its reactivity, viscosity, nucleation capacity, surface tension or resulting microphase separation. In most cases, the foams are formulated by substitution of a weight portion of the fossilbased polyol by the biobased one, with every other parameters being constant. The advantage of this method is to show the influence of the biobased compound on the foaming process by the characterization of the density, cell size and closed-cell content. Formulation optimization should always complete this approach because the biobased polyol, by its structure difference, have certainly different interaction compared to the fossil-based. Furthermore, the morphology of the cell profoundly affects other properties such as mechanical, thermal or fire resistance. Consequently, the biobased compound impact on these properties is never really isolated and then determined.

Mechanical properties

Cellular materials are a combination of excellent mechanical properties on lightweight materials [START_REF] Erjavec | Mechanical properties of cellular materials[END_REF]. In PUFs, the compression strength is the most common measurement to evaluate the mechanical properties of the material. The compression behavior of foams can be decomposed into several stages: First, the linear region is governed by the compression and bending of the cells struts, then the stretching of the cell walls and finally, the compression of the trapped gases [START_REF] Weißenborn | Modelling of the strain rate dependent deformation behaviour of rigid polyurethane foams[END_REF].

The effects of the cell morphology, the crosslink density and the structure of the biobased component on the compression strength properties of PUFs are given below.

Morphological structure of cells

The compression strength highly depends on the density of the material. The lower the density is, the lower the compression strength will be [START_REF] Yang | Thermal and Mechanical Properties of Polyurethane Rigid Foam Based on Epoxidized Soybean Oil[END_REF][START_REF] Ghaderian | Characterization of Rigid Polyurethane Foam Prepared from Recycling of PET Waste[END_REF]. Fig. 18A shows the evolution of the density and the compressive strength of foams with a gradual introduction of lignin-based polyol [START_REF] Li | Polyurethane foams from alkaline lignin-based polyether polyol[END_REF]. Fig. 18A shows that the increase in compressive strength follows directly the increase in density. Furthermore, the compression strength (σ) was correlated with the foam density (ρ) with a power-law model expressed in Equation 1.

) log( * log ) log( ρ σ B A + = (1)
Fig. 18B represents the compressive strength evolution over the density in logarithmic scales, modeled by Equation 1. The linear regression slope value was 1.5 in Fig. 18B for a series of waterblown foams realized with varying amounts of water. This value was in agreement with the literature value ranging between 1 and 2 [START_REF] Thirumal | Effect of foam density on the properties of water blown rigid polyurethane foam[END_REF]. The compressive strength can be normalized according to Gibson-Ashby [START_REF] Gibson | The mechanics of foams: Basic results[END_REF] equation, expressed in Equation 2 to compare foams with different densities.

2 ) 1 1 ( ) ( * s f s f m n X X ρ ρ ρ ρ σ σ + + = (2)
Where σn is the normalized compressive strength, σm the measured, ρf the measured density of the PUF, ρs the density of solid PU (1200 kg/m 3 ) and X the density of normalization [START_REF] Shin | Sustainable rigid polyurethane foams based on recycled polyols from chemical recycling of waste polyurethane foams[END_REF]. The compressive strength of the flexible cell foams relies on bending and cell wall axial deformation. On the contrary, in closed-cell foams, the air inside the cell and the walls contribute to the compressive strength [START_REF] Arbenz | Advanced biobased and rigid foams, based on urethane-modified isocyanurate from oxypropylated gambier tannin polyol[END_REF][START_REF] Souza | Polyurethane foams made from liquefied bark-based polyols[END_REF][START_REF] Gibson | The mechanics of foams: Basic results[END_REF]. It is worth mentioning that open-cell foams have higher compressive strength than closed-cell material with cell walls ruptured. The broken walls are unable to contribute to stress reinforcement and will initiate rupture when the cells are under load [START_REF] Narine | Physical Properties of Polyurethanes Produced from Polyols from Seed Oils: II. Foams[END_REF]. The homogeneity and cell size also affect the mechanical properties such as compression. R-PUFs with small and organized cells have higher compression strength due to homogeneous repartition of the load [START_REF] Fang | Development of High-Performance Biodegradable Rigid Polyurethane Foams Using Full Modified Soy-Based Polyols[END_REF][START_REF] Li | Preparation and properties of rigid polyurethane foam based on modified castor oil[END_REF][START_REF] Ng | Preparation and modification of water-blown porous biodegradable polyurethane foams with palm oil-based polyester polyol[END_REF][START_REF] Souza | Polyurethane foams made from liquefied bark-based polyols[END_REF][START_REF] Cateto | Lignin-based rigid polyurethane foams with improved biodegradation[END_REF][START_REF] Zhang | Rigid polyurethane foams containing lignin oxyalkylated with ethylene carbonate and polyethylene glycol[END_REF][START_REF] Pan | Effect of replacing polyol by organosolv and kraft lignin on the property and structure of rigid polyurethane foam[END_REF][START_REF] Amran | Polyols and rigid polyurethane foams derived from liquefied lignocellulosic and cellulosic biomass[END_REF].

Crosslink density

IOH represents the OH groups density of a given system. In the final material, OHs are transformed into urethane groups; therefore, the higher the IOH of the polyol is, the higher the density of urethane and crosslinking will be. This property indicates the strength of the polymer network and profoundly affects the mechanical properties. A high IOH gives high compressive strength [START_REF] Hayati | A simple methodology for improving the performance and sustainability of rigid polyurethane foam by incorporating industrial lignin[END_REF][START_REF] Ng | Preparation and modification of water-blown porous biodegradable polyurethane foams with palm oil-based polyester polyol[END_REF][START_REF] Hejna | Structure, Mechanical, Thermal and Fire Behavior Assessments of Environmentally Friendly Crude Glycerol-Based Rigid Polyisocyanurate Foams[END_REF][START_REF] Arbenz | Advanced biobased and rigid foams, based on urethane-modified isocyanurate from oxypropylated gambier tannin polyol[END_REF][START_REF] Mahmood | Hydrolytic liquefaction of hydrolysis lignin for the preparation of bio-based rigid polyurethane foam[END_REF][START_REF] Maldas | Liquefaction of Wood in the Presence of Polyol Using NaOH as a Catalyst and its Application to Polyurethane Foams[END_REF][START_REF] Kurańska | Synthesis of thermal insulating polyurethane foams from lignin and rapeseed based polyols: A comparative study[END_REF][START_REF] Hakim | Preparation and characterization of rigid polyurethane foam prepared from sugar-cane bagasse polyol[END_REF][START_REF] Riyapan | A Novel Rigid PU Foam Based on Modified Used Palm Oil as Sound Absorbing Material[END_REF][START_REF] Kosmela | Chemical structures, rheological and physical properties of biopolyols prepared via solvothermal liquefaction of Enteromorpha and Zostera marina biomass[END_REF] and vice-versa [START_REF] Ramanujam | Novel Biobased Polyol Using Corn Oil for Highly Flame-Retardant Polyurethane Foams[END_REF][START_REF] Ugarte | Tailoring Mechanical Properties of Rigid Polyurethane Foams by Sorbitol and Corn Derived Biopolyol Mixtures[END_REF][START_REF] Jiang | Synthesis and characterization of polyurethane rigid foams from polyether polyols with isosorbide as the bio-based starting agent[END_REF][START_REF] Pan | Effect of replacing polyol by organosolv and kraft lignin on the property and structure of rigid polyurethane foam[END_REF][START_REF] Amran | Polyols and rigid polyurethane foams derived from liquefied lignocellulosic and cellulosic biomass[END_REF]. For example, an increase in compressive strength from 26 to 81 kPa has been obtained with an increase of IOH from 100 to 250 mg KOH/g [START_REF] Riyapan | A Novel Rigid PU Foam Based on Modified Used Palm Oil as Sound Absorbing Material[END_REF]. Furthermore, the gradual substitution from 0 to 70 wt% of fossil-based by crude glycerol-based polyol demonstrated a constant increase in compressive strength in parallel and perpendicular directions [START_REF] Hejna | Structure, Mechanical, Thermal and Fire Behavior Assessments of Environmentally Friendly Crude Glycerol-Based Rigid Polyisocyanurate Foams[END_REF]. Finally, the compressive strength of foams realized with an increasing portion of liquefied biomass was shown to increase due to the larger crosslink density of the sample. The authors confirmed this hypothesis with the decrease of the soluble fraction in the foam elaborated with the highest IOH [START_REF] Kosmela | The Study on Application of Biopolyols Obtained by Cellulose Biomass Liquefaction Performed with Crude Glycerol for the Synthesis of Rigid Polyurethane Foams[END_REF]. However, the introduction of biobased polyol with lower IOH can be detrimental to the mechanical properties as Eceiza and coworkers showed with the introduction of 30 wt% of polytrimethylene ether glycol. The specific compressive properties decreased from 9.9 to 6.0 kPa.kg -1 .m 3 with the substitution of the fossilbased (444 mg KOH/g) by the biobased (80 mg KOH/g) polyol.

Molecular structure

The different biomass sources, previously described, present a large range of chemical structures. This variety of biobased components induces a multitude of new macromolecular architectures. The compression strength of the PUFs depends on the molecular level interactions in the studied system. The next part aims to detail the impact of the different biobased structures on the mechanical properties.

The triglycerides are composed of different long aliphatic chains. The corresponding increase of flexibility in the polyols gives higher elastic properties to the polymer network and then impacts the compression strength. The foam realized with 50 wt% of polyol synthesized from mercaptoethanol thiol-ene addition with corn oil had a compressive strength of 120 kPa [START_REF] Ramanujam | Novel Biobased Polyol Using Corn Oil for Highly Flame-Retardant Polyurethane Foams[END_REF]. This value was lower than foam with similar density realized by epoxidation and ring-opening with ethanol of microalgae oil (270 kPa) [START_REF] Peyrton | Biobased Polyurethane Foams Based on New Polyol Architectures from Microalgae Oil[END_REF]. This difference can be explained by the higher IOH due to the higher double bonds quantity of the microalgae compared to corn oil, for instance. Furthermore, the concentration of unfunctionalized long fatty chains called dangling chains higher in corn oil caused higher flexibility. Fig. 19. Effect of lignin addition on the compressive strength of R-PUF. The ratio of lignin to polyol, the molar ratio of the OH groups from lignin. Hardwood ethanol organosolv lignin (HEL) and hardwood kraft lignin (HKL). Reproduced with permission from [START_REF] Pan | Effect of replacing polyol by organosolv and kraft lignin on the property and structure of rigid polyurethane foam[END_REF].

As previously detailed, the liquefaction or alkoxylation of lignin was explored to introduce a higher lignin content into PUF. The liquefaction and alkoxylation products are a mixture of lignin with flexible chains bearing OH groups with unreacted low molar mass glycols. It is well-known that the alkoxylation generates free homopolymer chains of polyethers as by-products. This homopolymer can be removed by solvent extraction. However, to avoid extra steps, this by-product is often let in the mix [START_REF] Pavier | Oxypropylation of sugar beet pulp. 2. Separation of the grafted pulp from the propylene oxide homopolymer[END_REF]. These small polyols increase the flexibility of the polymer network and thus decrease the compression strength [START_REF] Li | Polyurethane foams from alkaline lignin-based polyether polyol[END_REF][START_REF] Cateto | Lignin-based rigid polyurethane foams with improved biodegradation[END_REF][START_REF] Li | Kraft Lignin-Based Rigid Polyurethane Foam[END_REF]. The introduction of 25 wt% of liquefied lignin polyol in PUFs decreased the compressive strength despite similar IOH and density. The authors explained this trend by the flexibility of PEG 400 used for the liquefaction of the lignin [START_REF] Li | Polyurethane foams from alkaline lignin-based polyether polyol[END_REF].

The addition of alkoxylated lignin as a unique polyol increased the compression strength of the network from 100 to 140 kPa due to the rigid aromatic and 3D structures of the lignocellulosic resources [START_REF] Li | Kraft Lignin-Based Rigid Polyurethane Foam[END_REF]. Furthermore, polyols made from rapeseed oil or lignin with similar IOH were gradually introduced up to 30 wt% in PUFs. The compressive strength of the lignin-based foams was always superior to the one realized with triglycerides. The authors explained this behavior by the presence of aromatic rings, which increase the rigidity [START_REF] Kurańska | Synthesis of thermal insulating polyurethane foams from lignin and rapeseed based polyols: A comparative study[END_REF]. Another example, the increase in mechanical properties in PUFs made with alkoxylated lignin could be related to the PPO chains, which enhance the miscibility of modified lignin in the network [START_REF] Saffar | Production of Bio-based Polyol from Oxypropylated Pyrolytic Lignin for Rigid Polyurethane Foam Application[END_REF].

Another possibility to produce biobased polyols with an aromatic structure is the alcoholysis of biobased PUs with small diols or triols. The capacity of the aromatic to stack added with a high crosslink density generates a highly rigid and brittle structure detrimental to the compressive strength. A polyol was obtained from liquefied aromatic wastes by transesterified coconut oil. The long and flexible chain of coconut oil avoided the excessive rigidity and brittleness of the PUFs.

Furthermore, the authors claimed that the combination of rigid aromatic and aliphatic flexible structure provided optimal block segregation [START_REF] Paruzel | Rigid Polyurethane Foam Fabrication Using Medium Chain Glycerides of Coconut Oil and Plastics from End-of-Life Vehicles[END_REF]. CNSL combined rigid aromatic structures like lignins and flexible aliphatic chains as triglycerides. The introduction of a higher portion into PUFs was found to increase the compression strength thanks to the rigid aromatic structure [START_REF] Ionescu | Polyols and Rigid Polyurethane Foams from Cashew Nut Shell Liquid[END_REF].

Thermal properties

R-PUFs are widely used as thermal insulation material in the building industry or for transportation where the thermal conductivity is a primary property [START_REF] Zhang | Experimental study of the thermal conductivity of polyurethane foams[END_REF]. The thermal insulation is related to the cell morphology, e.g., cell size, closed-cell content and density, the material properties, e.g., conductivity and complex index of refraction of the polymer and the conductivity of the gas entrapped in the cells [START_REF] Ferkl | Multi-scale modelling of heat transfer in polyurethane foams[END_REF]. From a physical point of view, the thermal conductivity (λ) of the foams is related to the total heat transfer (qt) passing through a thickness of foam (L) induced by a delta of temperature ΔT, as described by Equation 3.

T L q t ∆ = * λ (3)
Where qt is a sum of three components which are described in Equation 4 with the conduction through the polymer matrix (qPUR), through the gas phase (qgas) and the radiation (qrad).

The convection transfer is negligible for closed-cell porous materials with a cell size inferior to 3 mm [START_REF] Gibson | The mechanics of foams: Basic results[END_REF].

rad gas PUR t q q q q + + = (4)
The different contributions were physically examined and detailed in Equation 5, 6 and 7 [START_REF] Hilyard | Heat transfer in foams[END_REF].

dX dT A y kg y q N i N j ij j i i g ∑ ∑ = = - = 1 1 * δ With s f ρ ρ δ - ≈ 1 (5)
Where δ is called the void fraction, ρf the foam density and ρs the solid polymer density, yi is the mole fraction of the i th gas in the foam, N the number of gases in the foam, kgi the thermal conductivity of the pur i th gas and Aij a complex coefficient depending on the viscosity, molar mass and temperature of gases.

( )

dX dT b a f b a f k q s s p s       - + - - = 25 . 0 * ) 1 ( 2 * 3 1 δ (6)
Where kp is the conductivity of the polymer and a/b the cell aspect ratio. )

w s f s s f s K f f d K       - + = ρ ρ ρ ρ 1 * 10 . 4 (7)
Where d is the cell diameter, fs the solid fraction, σ is the Boltzmann constant and kW the extinction coefficient of the solid polymer. Equation 7 is known as the Rossland equation.

This equation shows the multitude of factors that affect the total thermal conductivity. Fig. 20A shows the evolution of the modeled thermal conductivity of R-PUFs over the closed-cell content.

The conductivity through the gas phase accounts for 70% of the total thermal conductivity. The conduction through the polymer matrix is 20%, and the radiation is 10% [START_REF] Ferkl | Multi-scale modelling of heat transfer in polyurethane foams[END_REF]. Fig. 20A demonstrates that the reduction of the total thermal conductivity with the porosity depends on the reduction of the conduction through the solid part of the foam.

The major contribution depends on the gas mixture enclosed in cells, which tends to flow out and be substituted by air over time. The thermal conductivity was measured on PUFs samples over 900 days to study the diffusion of the BA gases out of cells, and the results are shown in Fig. 20.B Within 100 days, the substitution of low conductivity BA gases (16.4 mW.K -1 .m -1 for CO2 and 12.8 mW.K -1 .m -1 for cyclopentane) by atmospheric air (25.6 mW.K -1 .m -1 at 20 °C) raise the initial 21 mW.K - 1 .m -1 thermal conductivity to almost 27 mW.K -1 .m -1 [START_REF] Santiago-Calvo | Longterm thermal conductivity of cyclopentane-water blown rigid polyurethane foams reinforced with different types of fillers[END_REF]. Fig. 20B shows the thermal conductivity value plateau around 29 mW.K -1 .m -1 after one year of aging. Therefore, the thermal conductivity must be analyzed in the utilization conditions and not considered as a constant property [START_REF] Berardi | Microstructural analysis and blowing agent concentration in aged polyurethane and polyisocyanurate foams[END_REF]. [START_REF] Ferkl | Multi-scale modelling of heat transfer in polyurethane foams[END_REF] and [START_REF] Santiago-Calvo | Longterm thermal conductivity of cyclopentane-water blown rigid polyurethane foams reinforced with different types of fillers[END_REF].

Effect of closed cell-content

Low closed cell content enhances the diffusion phenomenon and the substitution of BA gases by air; thus, decreasing the overall thermal conductivity of foams. As previously described, the utilization of biobased components directly impacts cell morphology. As a result, the decrease of the closed-cell content reduced the thermal conductivity [START_REF] Hayati | A simple methodology for improving the performance and sustainability of rigid polyurethane foam by incorporating industrial lignin[END_REF][START_REF] Borowicz | Biodegradable, Flame-Retardant, and Bio-Based Rigid Polyurethane/Polyisocyanurate Foams for Thermal Insulation Application[END_REF][START_REF] Hejna | The influence of crude glycerol and castor oil-based polyol on the structure and performance of rigid polyurethanepolyisocyanurate foams[END_REF][START_REF] Arbenz | Advanced biobased and rigid foams, based on urethane-modified isocyanurate from oxypropylated gambier tannin polyol[END_REF][START_REF] Piszczyk | Rigid polyurethane foams from a polyglycerol-based polyol[END_REF]. For example, the decline of closed-cell content from 95 to 85% implied an increase in thermal conductivity of 5 mW.K -1 .m -1 [START_REF] Hejna | The influence of crude glycerol and castor oil-based polyol on the structure and performance of rigid polyurethanepolyisocyanurate foams[END_REF]. The thermal conductivity decreased linearly with the closed-cell content [START_REF] Piszczyk | Rigid polyurethane foams from a polyglycerol-based polyol[END_REF].

Furthermore, it has been proved that the increase in average cell diameters from 250 to 600 µm caused an increase in the thermal conductivity coefficient by almost 50% [START_REF] Randall | The polyurethanes book[END_REF]. This variation is explained by the Rossland equation [START_REF] Winnacker | Biobased Polyamides: Recent Advances in Basic and Applied Research[END_REF], where the lower cell size (d) contributes to the reduction of the radiative transfers [START_REF] Arbenz | Advanced biobased and rigid foams, based on urethane-modified isocyanurate from oxypropylated gambier tannin polyol[END_REF][START_REF] Ugarte | Tailoring Mechanical Properties of Rigid Polyurethane Foams by Sorbitol and Corn Derived Biopolyol Mixtures[END_REF][START_REF] Furtwengler | Novel Rigid Polyisocyanurate Foams from Synthesized Biobased Polyester Polyol with Enhanced Properties[END_REF]. Besides, in denser materials, the heat transport passed through more quantity of solid; therefore, the contribution to the foam overall conductivity with the conduction through the polymer matrix (qPUR) is more important in denser materials [START_REF] Hejna | The influence of crude glycerol and castor oil-based polyol on the structure and performance of rigid polyurethanepolyisocyanurate foams[END_REF]. The thermal conductivity increases with the density of the material due to the increased quantity of solid material by which the heat must be transported [START_REF] Ugarte | Tailoring Mechanical Properties of Rigid Polyurethane Foams by Sorbitol and Corn Derived Biopolyol Mixtures[END_REF].

Effect of the chemical structure

To some extent, the thermal conductivity was directly correlated to the chemical structure of the biobased components. The addition of long dangling chain-end in the polymer network with triglycerides polyol seems to enhance the diffusion of heat in the material [START_REF] Borowicz | Biodegradable, Flame-Retardant, and Bio-Based Rigid Polyurethane/Polyisocyanurate Foams for Thermal Insulation Application[END_REF]. An increase in thermal conductivity from 20 to 25 mW.K -1 .m -1 with the increased substitution of fossil-based polyol by modified mustard oil was shown. Otherwise, the utilization of 2.5 to 5 wt% of kraft lignin as polyol was beneficial for the thermal conductivity, which was observed to decrease from 25.6 to 24.7 mW.K - 1 .m -1 due to the increased aromaticity, which reduces the gas transfer outward of the foam and therefore increases the thermal conductivity [START_REF] Hayati | A simple methodology for improving the performance and sustainability of rigid polyurethane foam by incorporating industrial lignin[END_REF].

Fire resistance

The test of the FR-based materials depends on the application and, thus, the corresponding fire risk scenario. In PUFs, the assessment of the enhancement or degradation of the fire resistance properties by a biobased material is performed with thermogravimetric analysis (TGA) measurement, burning test or determining the limiting oxygen index (LOI).

TGA is a dynamic measurement of material degradation. The weight of a material is followed over a determined temperature cycle, generally a rise at 10 or 20 °C/min. The degradation of PUFs samples takes place in two steps: (i) the urethane and urea bonds dissociation in the hard domain (200-300 °C) and (ii) the decomposition of the fragments and the isocyanurate structures (400-500 °C) [START_REF] Kurańska | Open-cell rigid polyurethane bio-foams based on modified used cooking oil[END_REF][START_REF] Furtwengler | Novel Rigid Polyisocyanurate Foams from Synthesized Biobased Polyester Polyol with Enhanced Properties[END_REF]. The burning test is the application of a flame, for 15 or 30 s depending on the test condition, on a foam specimen, and the flaming time is recorded (EN ISO 11925-2). The LOI is an international normalized test (ISO 4589-2). A candle-like flame is applied to the top of a specific PUFs specimen under a controlled atmosphere. The objective is to find the minimum oxygen concentration in nitrogen that will induce a combustion of at least 3 min [START_REF] Wilkie | Fire retardancy of polymeric materials[END_REF].

Thermal decomposition and degradation must be dissociated. The first one is the degradation of material properties due to exposure to heat, and the latter is related to the freeradical bond cleavage and subsequent pyrolysis of smaller molar mass fragments of a polymer upon exposure to heat [START_REF] Wilkie | Fire retardancy of polymeric materials[END_REF]. The relations between the enhancement or degradation of the FR properties of PUFs and the structure of the biobased polyol defined by the IOH, the rigidity, the molecular composition, the low molar mass compounds added through chemical transformation and the insoluble content are given below.

OH Index

In TGA analysis, characteristic temperatures are recorded at 5, 10 and 50% of weight loss to measure the FR of the related materials. Furthermore, the quantity of samples at the end of the measurement called char residue is also an indicator of the fire resistance of the foam. The evolution of the char residue, weight loss at 5, 10 and 50% over the average polyol IOH is represented in Fig. 21.

The data were compiled from the literature of foams made without FR additive. The general trend observed in Fig. 21 is an increase of the characteristic temperature with IOH augmentation. The char residue presented in Fig. 21A is close to 0% when the IOH is inferior to 200 mg KOH/g. Such polyols are often used in F-PUFs (Table 3), producing open-cells morphology. As discussed previously, low closed cell content decreases the thermal insulation properties. Therefore, the heat transfer is facilitated, and the material burns completely. In the case of higher closed-cell content, the heat transfer toward the center is hindered by the numerous cells wall. Fig. 21A shows an increase in char residue after 200 mg KOH/g. This is linked to the foam structure formed by a higher crosslink density, which limits heat transfers [START_REF] Riyapan | A Novel Rigid PU Foam Based on Modified Used Palm Oil as Sound Absorbing Material[END_REF]. Besides, a crosslinked network requires higher activation energy to initiate chain movement and decomposition compared to less branched polymers [START_REF] Ugarte | Tailoring Mechanical Properties of Rigid Polyurethane Foams by Sorbitol and Corn Derived Biopolyol Mixtures[END_REF][START_REF] Rastegarfar | Characterization of polyurethane foams prepared from liquefied sawdust by crude glycerol and polyethylene glycol[END_REF]. Fig. 21B, Fig. 21C and Fig. 21D present a high distribution of value directly linked to the difference in foam formulations. However, the general trend observed is the increase in the temperature at 5, 10 or 50% weight loss with the average IOH of polyol increase. The thermal decomposition of PUFs starts with the urethane bond dissociation around 250 °C. The high density of OH groups will be transformed into urethane groups in the final materials. Therefore, a polyol with high IOH will produce a material that will take an extended time to dissociate [START_REF] Furtwengler | Novel Rigid Polyisocyanurate Foams from Synthesized Biobased Polyester Polyol with Enhanced Properties[END_REF][START_REF] Huo | Preparation and properties of biobased autocatalytic polyols and their polyurethane foams[END_REF]. Finally, the increase of FR properties with the IOH presented in Fig. 21 is low, and other factors such as the molecular energy, the molar mass and the structure of the polyol affect the fire resistance of the foam.

Activation energy

The activation energy of materials decomposition is directly related to the mobility of the chains. A very stable alkane structure forms the dangling chains in lipids-based polyols. Therefore, PUF realized with similar IOH, but different dangling chain quantities had different thermal stability.

The polyol prepared via ozonolysis, which reduced by 60%, the end chains had the fastest first loss at 335 °C compared to castor oil or epoxidized and ring-opened soybean oil-polyol (380 °C) [START_REF] Narine | Physical Properties of Polyurethanes Produced from Polyols from Seed Oils: II. Foams[END_REF]. On the contrary, the rigid structure formed by isosorbide polyol needs higher energy to initiate decomposition [START_REF] Jiang | Synthesis and characterization of polyurethane rigid foams from polyether polyols with isosorbide as the bio-based starting agent[END_REF]. The 3D structure of lignin, liquefied or alkoxylated, is stiffer than fossil-based polyol and degraded at higher temperatures [START_REF] Li | Polyurethane foams from alkaline lignin-based polyether polyol[END_REF][START_REF] Saffar | Production of Bio-based Polyol from Oxypropylated Pyrolytic Lignin for Rigid Polyurethane Foam Application[END_REF].

Low molar mass compounds

Low molar mass polyols such as PEG or glycerol are introduced into foams via biobased polyols synthesis (e.g., alcoholysis of wastes, lignin liquefaction or dispersion) or as an additional polyol. Their thermal stability was also investigated; for example, PEG is known to enhance the thermal stability of foams due to the thermally stable ether bonds and the increase in crosslink density [START_REF] Li | Preparation and properties of rigid polyurethane foam based on modified castor oil[END_REF][START_REF] Ng | Preparation and modification of water-blown porous biodegradable polyurethane foams with palm oil-based polyester polyol[END_REF][START_REF] Rastegarfar | Characterization of polyurethane foams prepared from liquefied sawdust by crude glycerol and polyethylene glycol[END_REF]. For example, the temperature of 50% weight loss shifted from 379 to 370 °C, with the integration of 0 to 100% of palm oil polyester polyol. The authors explained this trend by the decrease in PEG added as co-polyol [START_REF] Ng | Preparation and modification of water-blown porous biodegradable polyurethane foams with palm oil-based polyester polyol[END_REF]. In another study, foam realized with 40 wt% of EG had a higher LOI value (25%), than without (20%) [START_REF] Li | Preparation and properties of rigid polyurethane foam based on modified castor oil[END_REF]. Furthermore, the addition of crude glycerol increased the onset temperature in TGA measurements from 210 to 223 °C with 0 and 70 wt% of crude glycerol, respectively [START_REF] Hejna | Structure, Mechanical, Thermal and Fire Behavior Assessments of Environmentally Friendly Crude Glycerol-Based Rigid Polyisocyanurate Foams[END_REF].

Molecular architecture

As introduced in the last section, the polyol structure plays a key role in the degradation of cellular materials. For instance, the presence of sulfur in the chemical structure of the mustard oil polyol increases the LOI value from 23 to 26% and thus, the thermal stability of the PUFs. Sulfur has several oxidation levels and is transformed into SO2 and SO3 acids in the decomposition process. This oxygen consummation, combined with the catalytic activity of these acids for the decomposition of a fire intermediate (ionic peroxide), inhibited the chain reaction of oxidation [START_REF] Borowicz | Biodegradable, Flame-Retardant, and Bio-Based Rigid Polyurethane/Polyisocyanurate Foams for Thermal Insulation Application[END_REF].

The epoxidation and further ring-opening reactions produced numerous lipids based polyols was previously detailed. To reduce the synthesis steps, 25 wt% of epoxidized oil were directly introduced in PUFs formulations and compared to polyols formed one step further. The weight loss for the first degradation peak was improved from 45 to 40% with a polyol and with epoxidized oil, respectively. Some authors hypothesized the enhancement to originate from the formation of thermally stable oxazolidone groups [START_REF] Arbenz | Elaboration and Properties of Innovative Biobased PUIR Foams from Microalgae[END_REF]. However, the oxazolidone formation was not evidenced in PUFs with epoxidized oils.

Otherwise, polyester polyol based on sorbitol had a low onset temperature (170 °C) compared to conventional PUFs (200-250 °C). The authors explained that the ester scissions happen at lower temperatures than ether groups. Therefore, the decomposition of the soft segment is detected at a lower temperature in TGA [START_REF] Furtwengler | Elaboration and Characterization of Advanced Biobased Polyurethane Foams Presenting Anisotropic Behavior[END_REF].

Aromatic structures are well known to improve the thermal degradation with smoke production, which expands the char layer. This expanded layer is denoted as intumescent and protects the material from flame exposition and limits the transfer of oxygen toward the flame [START_REF] Duquesne | Mechanism of fire retardancy of polyurethanes using ammonium polyphosphate[END_REF].

The improvement of thermal stability by an increased aromatic content was observed with tannins [START_REF] Arbenz | Advanced biobased and rigid foams, based on urethane-modified isocyanurate from oxypropylated gambier tannin polyol[END_REF], lignins [START_REF] Souza | Polyurethane foams made from liquefied bark-based polyols[END_REF][START_REF] Li | Fractionation and oxypropylation of cornstover lignin for the production of biobased rigid polyurethane foam[END_REF], PUFs wastes [START_REF] Paruzel | Rigid Polyurethane Foam Fabrication Using Medium Chain Glycerides of Coconut Oil and Plastics from End-of-Life Vehicles[END_REF][START_REF] Shin | Sustainable rigid polyurethane foams based on recycled polyols from chemical recycling of waste polyurethane foams[END_REF] and CNSL [START_REF] Ionescu | Polyols and Rigid Polyurethane Foams from Cashew Nut Shell Liquid[END_REF], for instance. Foam realized with oxypropylated tannin had a lower peak of heat released and propagation of the flame rates than oxypropylated glycerol. The authors explained that the aromatic structure of the tannin is coke forming. This hypothesis was supported by the measurement of the total smoke release, which was higher with tannin than glycerol-based polyol [START_REF] Arbenz | Advanced biobased and rigid foams, based on urethane-modified isocyanurate from oxypropylated gambier tannin polyol[END_REF]. With 15 and 30 wt% of fractionated and alkoxylated lignin, the maximum loss rate was lower than without. Furthermore, the temperature at half mass loss and the residual mass at 800 °C was also higher than the reference foam. This degradation profile seems to be linked to the higher density of the aromatic structure.

It is well-known that the presence of thermally stable fillers increases the overall thermal stability of the foams by increasing the residue amounts [START_REF] Delucis R De | Thermal and combustion features of rigid polyurethane biofoams filled with four forest-based wastes[END_REF]. The evolution of the foam flammability over the content of insoluble residue in the liquefaction mixture of the polyol is represented in Fig. 22. The trend was clear; the flammability decreased with the increase of insoluble residue (Fig. 22). The recalcitrant liquefaction residue of lignin improved the FR properties of the PUFs made thereof. This improvement is explained by the inorganic components present in liquefied bark polyol [START_REF] Ge | Biodegradable polyurethane materials from bark and starch. I. Highly resilient foams[END_REF]. The glass transition temperature (Tg) of a polymer is critical information to know the network better. In thermosets like PUFs, the α-transition temperature determined by temperature-dependent dynamic mechanical analysis in temperature is linked to the Tg determined by differential scanning calorimetry. Transition temperatures depend on the isocyanate index, cross-link density, aromaticity, plasticizer and PIR content in PUFs [START_REF] Wu | Rheology Study in Polyurethane Rigid Foams[END_REF]. When phase separation occurred, two Tg are identified, the first one for the soft segment around -50 °C and the second for the hard segment found between 50 and 80 °C in R-PUFs. The substitution of fossil-based polyol by a biobased one induces a change in the network structure, which can be seen by a Tg shift. The dangling chains and the long flexible structure of lipids based polyols are responsible for a plasticizing effect and a decrease in Tg [START_REF] Kahlerras | Elaboration and Characterization of Polyurethane Foams Based on Renewably Sourced Polyols[END_REF][START_REF] Zieleniewska | Preparation and characterisation of rigid polyurethane foams using a rapeseed oil-based polyol[END_REF]. The small reactants present for the polyglycerol formation are also plasticizers of the PUFs network [START_REF] Piszczyk | Rigid polyurethane foams from a polyglycerol-based polyol[END_REF].

Furthermore, the Tg heavily depends on the PEG length used to plasticize lignins [START_REF] Hatakeyama | Glass transition of rigid polyurethane foams derived from sodium lignosulfonate mixed with diethylene, triethylene and polyethylene glycols[END_REF]. The other effect observed with biobased polyols is the correlation between the Tg increase and the augmentation in crosslink density explained by the reduced chain motions [START_REF] Hayati | A simple methodology for improving the performance and sustainability of rigid polyurethane foam by incorporating industrial lignin[END_REF][START_REF] Pawar | Synthesis and characterization of rigid polyurethane foams from algae oil using biobased chain extenders[END_REF][START_REF] Narine | Physical Properties of Polyurethanes Produced from Polyols from Seed Oils: II. Foams[END_REF][START_REF] Kosmela | Chemical structures, rheological and physical properties of biopolyols prepared via solvothermal liquefaction of Enteromorpha and Zostera marina biomass[END_REF]. 4.5.2. Acoustic property R-PUFs are principally used in thermal insulation, and their acoustic properties are often overlooked because open cell structures are considered good sound absorbers. It was proved that lower closed cell content resulted in higher sound absorption [START_REF] Zhang | Correlation between the acoustic and porous cell morphology of polyurethane foam: Effect of interconnected porosity[END_REF]. However, foams based on palm oil with closed cell structure has been elaborated for such applications. High sound absorption coefficients (< 90%) defined as the ratio of the acoustic energy absorbed by the foam to the incident acoustic energy, were obtained. They explained that the damping effect from the increased urethane group content and network density dissipated sound energy into heat [START_REF] Riyapan | A Novel Rigid PU Foam Based on Modified Used Palm Oil as Sound Absorbing Material[END_REF].

The R-PUFs properties can be affected by numerous factors represented in Fig. 23, and the structure of the components and the cell morphology are the dominant effects.

Perspectives on Biobased PUF

Polyols are one of the main biobased compounds used in PUFs formulations. However, it represents often less than 50 wt% of the PUF (Table 1). Another major component are the polyisocyanates, which are more rarely biobased. Besides, the toxicity for human health [START_REF] Peters | Studies of isocyanate toxicity[END_REF][START_REF] Brugsch | Toluene Di-Isocyanate (TDI) Toxicity[END_REF] of the isocyanate group is highly problematic. Moreover, their industrial synthesis is based on hazardous compounds (e.g., phosgene). The isocyanate reduction and elimination in the foam elaboration join the sustainability approach discussed in this review. In the next part, NIPU and other chemistries are outlined to produce greener biobased foams without isocyanate for a more sustainable and safe future.

Non-isocyanate polyurethane

Urethane groups are usually formed by addition of isocyanate and hydroxyl groups. However, several alternative pathways presented in Fig. 24 to form NIPU can be developed [START_REF] Suryawanshi | Advances in the synthesis of non-isocyanate polyurethanes[END_REF][START_REF] Guan | Progress in Study of Non-Isocyanate Polyurethane[END_REF][START_REF] Rokicki | Non-isocyanate polyurethanes: synthesis, properties, and applications: Non-Isocyanate Polyurethanes: Synthesis, Properties, and Applications[END_REF][START_REF] Kreye | Sustainable routes to polyurethane precursors[END_REF][START_REF] Maisonneuve | Isocyanate-Free Routes to Polyurethanes and Poly(hydroxy Urethane)s[END_REF].

Carbamoyl chloride, ring-opening polymerization, chloroformate, aziridine and alkyl-carbonate routes presented in Fig. 24 involve precursors synthesized via toxic phosgene derivatives, or the precursor itself (e.g., aziridine) is hazardous [START_REF] Ghasemlou | Bio-based routes to synthesize cyclic carbonates and polyamines precursors of non-isocyanate polyurethanes: A review[END_REF]. Furthermore, all theses routes require elevated temperatures. The polyaddition between cyclocarbonates and amines forming polyhydroxyurethane (PHU) networks can be carried out at ambient temperature, and no toxic phosgene is involved.

Moreover, PHU precursors have manageable toxicity and can be conveniently obtained from a wide range of renewable and sustainable resources [START_REF] Carré | From the Synthesis of Biobased Cyclic Carbonate to Polyhydroxyurethanes: A Promising Route towards Renewable Non-Isocyanate Polyurethanes[END_REF][START_REF] Suryawanshi | Advances in the synthesis of non-isocyanate polyurethanes[END_REF][START_REF] Ghasemlou | Bio-based routes to synthesize cyclic carbonates and polyamines precursors of non-isocyanate polyurethanes: A review[END_REF]. In the green chemistry frame, the cyclic carbonate route is the most sustainable pathway to obtain NIPU. Fig. 24. Overview of the main synthetic routes to NIPU. Fig. 24 shows that polyamines and 5 or 6-membered cyclic carbonates are the main building blocks toward a biobased PHU network. Although very few natural amines are available (i.e., chitosan and lysine), sustainable amines can be produced through various chemical processes from carbohydrate, lignins or oleochemical sources [START_REF] Froidevaux | Biobased Amines: From Synthesis to Polymers; Present and Future[END_REF][START_REF] Pelckmans | Bio-based amines through sustainable heterogeneous catalysis[END_REF]. One promising route toward sustainable diamines was recently highlighted as dianiline was recovered from the enzymatic recycling of PUs [START_REF] Magnin | Enzymatic recycling of thermoplastic polyurethanes: Synergistic effect of an esterase and an amidase and recovery of building blocks[END_REF].

Cyclocarbonates were initially synthesized from the reaction between diol and phosgene [START_REF] Nemirowsky | Ueber die Einwirkung von Chlorkohlenoxyd auf Aethylenglycol; vorläufige Mittheilung[END_REF]. However, the current and industrial common pathway transforms epoxide into cyclocarbonates with high pressure of sustainable and naturally occurring CO2 [START_REF] Carré | From the Synthesis of Biobased Cyclic Carbonate to Polyhydroxyurethanes: A Promising Route towards Renewable Non-Isocyanate Polyurethanes[END_REF], for instance from fermentation process. The production of fully biobased carbonates was achieved through the carboxylation of epoxidized oil [START_REF] Pérez-Sena | Aminolysis of cycliccarbonate vegetable oils as a non-isocyanate route for the synthesis of polyurethane: A kinetic and thermal study[END_REF][START_REF] Mann | Synthesis of Carbonated Vernonia Oil[END_REF].

In PHU synthesis, no difference in reaction conditions, kinetics, products, nor side reactions was observed between structurally similar biobased and fossil-based monomers [START_REF] Carré | From the Synthesis of Biobased Cyclic Carbonate to Polyhydroxyurethanes: A Promising Route towards Renewable Non-Isocyanate Polyurethanes[END_REF]. Similarly to conventional PUs, the nature of the renewable source directly impacts the properties of the PHU.

Therefore, the development of innovative molecular architectures extracted or bioproduced from various biomass types can bring new properties for the PHU networks. Very recently, the synthesis of the PHU network from carbonated biobased triglycerides and glycine was patented. The authors claimed similar mechanical properties as conventional PUs [START_REF] Dong | Renewable Polymers and resins and methods of making the same[END_REF].

Figvosky patented the first NIPU solution to substitute conventional PUFs in 2004. In this study, acrylic NIPU was foamed by radical polymerization of acrylate with pentane as BA [START_REF] Figovsky | Foamable photo-polymerized composition[END_REF]. The first foam realized with the reaction between cyclic carbonate and diamine to obtain PHU networks was recently developed by Caillol and coworkers. The reagents were mixed with polymethylhydrogenosiloxane, which H2 release after reaction with diamine and heated at 80 °C [START_REF] Cornille | A new way of creating cellular polyurethane materials: NIPU foams[END_REF]. The corresponding foams were dense (200-300 kg/m 3 ) compared to conventional PUFs. The method was improved by adding thiourea as a catalyst; therefore, the curing temperature was reduced until ambient [START_REF] Cornille | Room temperature flexible isocyanate-free polyurethane foams[END_REF]. The resulting foams were still dense (270-300 kg/m 3 ). Furthermore, the open cells of the NIPU foams were coarser (300-1300 µm) compared to conventional PUFs (350-850 µm). Due to the bigger open-cells, the thermal conductivity was higher (100 vs. 67 mW.K -1 .m -1 ), and the thermal stability was slightly inferior compared to the conventional PUFs.

The synthesis of closed and small cells NIPU foams was achieved with supercritical CO2 at high temperature or high pressure. The samples were foamed by fast depressurization of the cell leading to a density of 110 kg/m 3 with small pores (10 µm) and high thermal conductivity (50 mW.K - 1 .m -1 ) [START_REF] Grignard | CO2 -blown microcellular non-isocyanate polyurethane (NIPU) foams: from bio-and CO2 -sourced monomers to potentially thermal insulating materials[END_REF]. Mulhaupt and coworkers used a liquid hydrofluorocarbon to produce NIPU foams at 80 °C [START_REF] Blattmann | Flexible and Bio-Based Nonisocyanate Polyurethane (NIPU) Foams[END_REF]. The authors produced dense foams (142 kg/m 3 ) with cell size similar to R-PUFs (171 µm).

Pizzi and coworkers developed self-blowing NIPU foams. The reaction was performed between a synthesized glucose-NIPU with maleic acid and glutaraldehyde as a crosslinker. The soft foam was formed within 5 hours at ambient temperature [START_REF] Xi | Preparation and Evaluation of Glucose Based Non-Isocyanate Polyurethane Self-Blowing Rigid Foams[END_REF]. Recently, self-blowing NIPU foams were elaborated by amine and thiol reaction with cyclo-carbonates catalyzed by 1,8diazabicyclo [5.4.0]undec-7-ene [START_REF] Monie | Chemo-and Regioselective Additions of Nucleophiles to Cyclic Carbonates for the Preparation of Self-Blowing Non-Isocyanate Polyurethane Foams[END_REF]. As the reaction thiol-cyclocarbonate reaction forms hydroxythioether and carbon dioxide, thiol is used as chemical blowing agent. Unfortunately, as most of the other, these NIPU foams are slow to form, mainly open cells and flexible. In order to improve the mechanical properties of NIPU foams by aminolysis, rigid cyclocarbonate such as lignin could be used [START_REF] Salanti | Chemical modifications of lignin for the preparation of macromers containing cyclic carbonates[END_REF]. Another development axis toward green foams, could be the adaptation of new chemical BAs, a subject recently reviewed [START_REF] Coste | From gas release to foam synthesis, the second breath of blowing agents[END_REF], to new polymers or formulations. However, the route toward a large substitution of R-PUF and F-PUF by NIPU foams or equivalents is still long.

Other potential approaches

The question linked to the future of the foams could be not only related to PU macromolecular architectures. As previously described, the formation of reactive foams needs an exothermic and fast reaction associated with a BA. The development of the well-known epoxide chemistry with epoxidized oil was widely investigated to produce foams [START_REF] Negrell | New bio-based epoxy materials and foams from microalgal oil: Agal oil epoxy materials and foams[END_REF][START_REF] Dworakowska | Formulation of bio-based epoxy foams from epoxidized cardanol and vegetable oil amine: Cardanol-based epoxy foams[END_REF][START_REF] Huang | Bio-based thermosetting epoxy foams from epoxidized soybean oil and rosin with enhanced properties[END_REF][START_REF] Khundamri | Bio-based flexible epoxy foam synthesized from epoxidized soybean oil and epoxidized mangosteen tannin[END_REF]. Furthermore, some recent investigations raised some exciting new pathways toward biobased foams. The modification of soybean oil was achieved to introduce alkoxysilane groups. They were subsequently used in a Piers-Rubinsztajn reaction, which released methane to expand the polymer and produce foams. PDMS added as chain extender controls the density and Young's modulus of the produced foams [START_REF] Gale | Silicone Structurants for Soybean Oil: Foams, Elastomers, and Candles[END_REF]. Carbon-Michael chemistry has been investigated as a new way of foam elaboration. First, they quickly transformed polyols used in PUFs into poly-acetoacetate, a Michael donor, via transesterification. These new molecules were added into a mix of polyacrylates (Michael acceptor), surfactants, catalysts and physical BAs. The foams had entirely raised in less than 5 minutes, with more than 80% of closed cells and a low density of around 35 kg/m 3 comparable to conventional PUFs [START_REF] Sonnenschein | From rigid and flexible foams to elastomers via Michael addition chemistry[END_REF]. Another approach has been recently developed. A fully biobased foam with closed-cell was developed by Pelletier and coworkers, based on fungal mycelium. It was found to be promising fully biobased alternatives for acoustic shielding to the traditional fossil-based polymer based on synthetic fibers [START_REF] Pelletier | Acoustic evaluation of mycological biopolymer, an all-natural closed cell foam alternative[END_REF]. [START_REF] Arbenz | Elaboration and Properties of Innovative Biobased PUIR Foams from Microalgae[END_REF][START_REF] Campanella | Polyurethane foams from soyoil-based polyols[END_REF][START_REF] Borowicz | Biodegradable, Flame-Retardant, and Bio-Based Rigid Polyurethane/Polyisocyanurate Foams for Thermal Insulation Application[END_REF][START_REF] Kurańska | Evaluation of application potential of used cooking oils in the synthesis of polyol compounds[END_REF][START_REF] Herrán | Highly functional lactic acid ring-opened soybean polyols applied to rigid polyurethane foams[END_REF][START_REF] Contreras | Development of eco-friendly polyurethane foams based on Lesquerella fendleri (A. Grey) oilbased polyol[END_REF][START_REF] Kaur | Addition of anti-flaming agents in castor oil based rigid polyurethane foams: studies on mechanical and flammable behaviour[END_REF][START_REF] Briou | Polyurethane Thermosets Using Lipidic Poly(α-Hydroxyketone)[END_REF][START_REF] Paruzel | Rigid Polyurethane Foam Fabrication Using Medium Chain Glycerides of Coconut Oil and Plastics from End-of-Life Vehicles[END_REF][START_REF] Ng | Preparation and modification of water-blown porous biodegradable polyurethane foams with palm oil-based polyester polyol[END_REF][START_REF] Wilson | Preparation and characterization of lactitol-based poly(ether polyol)s for rigid polyurethane foam[END_REF][START_REF] Lubczak | From starch to oligoetherols and polyurethane foams[END_REF][START_REF] Shin | Sustainable rigid polyurethane foams based on recycled polyols from chemical recycling of waste polyurethane foams[END_REF][START_REF] Zhang | Highly flame retardant and bio-based rigid polyurethane foams derived from orange peel oil[END_REF][START_REF] Gandhi | Mechanical, thermal and fire properties of sustainable rigid polyurethane foam derived from cashew nut shell liquid[END_REF][START_REF] Ghaderian | Characterization of Rigid Polyurethane Foam Prepared from Recycling of PET Waste[END_REF]. [START_REF] Gao | Improved mechanical property, thermal performance, flame retardancy and fire behavior of lignin-based rigid polyurethane foam nanocomposite[END_REF] and [START_REF] Erjavec | Mechanical properties of cellular materials[END_REF]. Fig. 19. Effect of lignin addition on the compressive strength of R-PUF. The ratio of lignin to polyol, the molar ratio of the OH groups from lignin. Hardwood ethanol organosolv lignin (HEL) and hardwood kraft lignin (HKL). Reproduced with permission from [START_REF] Carriço | Production and characterization of polyurethane foams from a simple mixture of castor oil, crude glycerol and untreated lignin as bio-based polyols[END_REF]. Compilation of data from literature [START_REF] Arbenz | Elaboration and Properties of Innovative Biobased PUIR Foams from Microalgae[END_REF][START_REF] Borowicz | Biodegradable, Flame-Retardant, and Bio-Based Rigid Polyurethane/Polyisocyanurate Foams for Thermal Insulation Application[END_REF][START_REF] Pawar | Rigid polyurethane foams from cottonseed oil using bio-based chain extenders: a renewable approach[END_REF][START_REF] Kurańska | Evaluation of application potential of used cooking oils in the synthesis of polyol compounds[END_REF][START_REF] Kurańska | Open-cell rigid polyurethane bio-foams based on modified used cooking oil[END_REF][START_REF] Herrán | Highly functional lactic acid ring-opened soybean polyols applied to rigid polyurethane foams[END_REF][START_REF] Contreras | Development of eco-friendly polyurethane foams based on Lesquerella fendleri (A. Grey) oilbased polyol[END_REF][START_REF] Kaur | Addition of anti-flaming agents in castor oil based rigid polyurethane foams: studies on mechanical and flammable behaviour[END_REF][START_REF] Briou | Polyurethane Thermosets Using Lipidic Poly(α-Hydroxyketone)[END_REF][START_REF] Paruzel | Rigid Polyurethane Foam Fabrication Using Medium Chain Glycerides of Coconut Oil and Plastics from End-of-Life Vehicles[END_REF][START_REF] Ng | Preparation and modification of water-blown porous biodegradable polyurethane foams with palm oil-based polyester polyol[END_REF][START_REF] Wilson | Preparation and characterization of lactitol-based poly(ether polyol)s for rigid polyurethane foam[END_REF][START_REF] Lubczak | From starch to oligoetherols and polyurethane foams[END_REF][START_REF] Shin | Sustainable rigid polyurethane foams based on recycled polyols from chemical recycling of waste polyurethane foams[END_REF][START_REF] Thompson | Characterization of crude glycerol from biodiesel production from multiple feedstocks[END_REF][START_REF] Zhang | Highly flame retardant and bio-based rigid polyurethane foams derived from orange peel oil[END_REF][START_REF] Gandhi | Mechanical, thermal and fire properties of sustainable rigid polyurethane foam derived from cashew nut shell liquid[END_REF][START_REF] Ghaderian | Characterization of Rigid Polyurethane Foam Prepared from Recycling of PET Waste[END_REF].

Figures captions

Table captions

Table 1. General foam formulation with quantities expressed in part by weight of the polyol. Table 2. Relative reactivity of isocyanates with alcohol groups for the 1 st and the 2 nd additions.

Adapted from [START_REF] Szycher | Szycher's handbook of polyurethanes[END_REF].

Table 3. Main requirements on polyols properties for F-PUF and R-PUF. Adapted from [START_REF] Furtwengler | Renewable polyols for advanced polyurethane foams from diverse biomass resources[END_REF][START_REF] Ionescu | Chemistry and technology of polyols for polyurethanes[END_REF]. Table 4. Relative reactivity of hydrogen active compounds without catalyst. Adapted from [START_REF] Ionescu | Chemistry and technology of polyols for polyurethanes[END_REF]. Table 5. BA structures, name physical properties and global warming potential (GWP). Data from literature [START_REF] Singh | Blowing agents for polyurethane foams[END_REF][START_REF] Bobbo | Low GWP halocarbon refrigerants: A review of thermophysical properties[END_REF][START_REF] Gil | Efficiency Evaluation of the Ejector Cooling Cycle using a New Generation of HFO/HCFO Refrigerant as a R134a Replacement[END_REF][START_REF] Lai | Thermodynamic properties of HFO-1243zf and their application in study on a refrigeration cycle[END_REF][START_REF] Mateu-Royo | Thermodynamic analysis of low GWP alternatives to HFC-245fa in high-temperature heat pumps: HCFO-1224yd(Z), HCFO-1233zd(E) and HFO-1336mzz(Z)[END_REF][START_REF] Rapra | Blowing agents & foaming processes[END_REF][START_REF] Yaws | Thermophysical properties of chemicals and hydrocarbons[END_REF][START_REF] Yaws | Handbook of Thermal Conductivity: Organic Compounds C1 to C4[END_REF].

Scheme captions

Scheme 1. The first synthesis of carbamate by Charles Adolf Wurtz. Adapted from [START_REF] Wurtz | Note sur la Formation de l'Urethane par l'Action du Chlorure de Cyanogène[END_REF]. Scheme 2. Metathesis and cyclization reactions. Scheme 3. Isosorbide production pathway from sorbitol. Scheme 4. Synthesis of diisocyanate from β-pinene. Adapted from [START_REF] Gustini | Sustainable coatings from bio-based, enzymatically synthesized polyesters with enhanced functionalities[END_REF].

Fig. 1 .

 1 Fig. 1. Examples of F-PUF (Left) and R-PUF (right) applications.

Fig. 2 .

 2 Fig. 2. Main isocyanate reactions with H-labile groups.

  Fig. 3 presents the effect of the NCO/OH molar ratio on the chemical architectures of PUFs,

Fig. 3 .

 3 Fig. 3. Effect of the NCO/OH index on the chemical architectures of PUF, PU-PIR and PIR foam networks.

  can be used. Catalysts activities can favor the urethane network formation (gelling) or the generation of gas generally via the water-isocyanate reaction (blowing)[START_REF] Van Maris | Polyurethane Catalysis by Tertiary Amines[END_REF]. The tin salts, i.e., stannous octoate and dibutyltin dilaurate, have higher gelling activity compared to hindered amine such as 1,4-diazabicyclo [2,2,2]octane (DABCO). The dibenzylamine, tetramethylethylenediamine and N,N-dimethylcyclohexanamine (Fig.7), which are less hindered tertiary amines than DABCO, are classified as balanced catalyst because they promote both gelling and blowing reactions. Catalysts containing ether bonds close to the tertiary amine group such as 2,2' dimorpholinodiethylether or 2,2'-oxybis (N,N-dimethylethan-1-amine) promote the blowing reactions. The carboxylate-potassium salts for PIR foams favor the trimerization that actively participates in the molecular crosslinking. Therefore, they are ranked in the gelling activities of Fig.7.

Fig. 7 .

 7 Fig. 7. Catalysts structures ranked according to their main activities in the foam formulation. Adapted from [70].

Fig. 8 .

 8 Fig. 8. Viscosity profile associated to the cell bubbles formation.

Fig. 9 .

 9 Fig. 9. Triglyceride structure and the most abundant fatty acids in vegetables, seeds and microalgae oil.

Fig. 11 .

 11 Fig. 11. Overview of the transformation of main carbohydrates into different PUF components.

Fig. 13 .

 13 Fig. 13. Overview of the transformation of lignins and tannins into PUF components.

Fig. 14 .

 14 Fig. 14. Overview of the transformation of wastes from industrial processes into PUF components.

3. 4 . 1 .

 41 Polyols 3.4.1.1. Biobased PUF One way to obtain biobased components for PUFs, such as polyols, is to use compounds obtained from recycling biobased PUs, such as chemical or biological recycling. Despite the recent

Fig. 15 .

 15 Fig. 15. Overview of the transformation of products from biotechnology into the PUF component.

Fig. 16 .

 16 Fig.[START_REF] Akindoyo | Polyurethane types, synthesis and applications -a review[END_REF]. Viscosity of polyol vs. the cell size for PUF. Compilation of data from literature[START_REF] Kahlerras | Elaboration and Characterization of Polyurethane Foams Based on Renewably Sourced Polyols[END_REF][START_REF] Pawar | Rigid polyurethane foams from cottonseed oil using bio-based chain extenders: a renewable approach[END_REF][START_REF] Zieleniewska | Preparation and characterisation of rigid polyurethane foams using a rapeseed oil-based polyol[END_REF][START_REF] Kurańska | Open-cell rigid polyurethane bio-foams based on modified used cooking oil[END_REF][START_REF] Fang | Development of High-Performance Biodegradable Rigid Polyurethane Foams Using Full Modified Soy-Based Polyols[END_REF][START_REF] Yang | Thermal and Mechanical Properties of Polyurethane Rigid Foam Based on Epoxidized Soybean Oil[END_REF][START_REF] Veronese | Rigid polyurethane foam based on modified vegetable oil[END_REF][START_REF] Paruzel | Rigid Polyurethane Foam Fabrication Using Medium Chain Glycerides of Coconut Oil and Plastics from End-of-Life Vehicles[END_REF][START_REF] Ng | Preparation and modification of water-blown porous biodegradable polyurethane foams with palm oil-based polyester polyol[END_REF][START_REF] Hejna | Structure, Mechanical, Thermal and Fire Behavior Assessments of Environmentally Friendly Crude Glycerol-Based Rigid Polyisocyanurate Foams[END_REF][START_REF] Ugarte | Tailoring Mechanical Properties of Rigid Polyurethane Foams by Sorbitol and Corn Derived Biopolyol Mixtures[END_REF][START_REF] Jiang | Synthesis and characterization of polyurethane rigid foams from polyether polyols with isosorbide as the bio-based starting agent[END_REF][START_REF] Piszczyk | Rigid polyurethane foams from a polyglycerol-based polyol[END_REF][START_REF] Yang | Preparation, characterization and thermal degradation behavior of rigid polyurethane foam using a malic acid based polyols[END_REF][START_REF] Huo | Preparation and properties of biobased autocatalytic polyols and their polyurethane foams[END_REF][START_REF] Luo | Synthesis and Characterization of Polyols and Polyurethane Foams from PET Waste and Crude Glycerol[END_REF].

Fig. 17 .

 17 Fig. 17. Effect of the gelling/blowing balance vs. temperature, viscosity and foam cell morphology in three typical cases: (A) mainly blowing, (B) equilibrium and (C) mainly gelling.

2

 2

Fig. 18 .

 18 Fig. 18. (A) Effect of the introduction of lignin-based polyol on the density and compressive strength of PUF. (B) Dependence of the compressive strength on density. Reproduced with permission from[START_REF] Li | Polyurethane foams from alkaline lignin-based polyether polyol[END_REF] and[START_REF] Thirumal | Effect of foam density on the properties of water blown rigid polyurethane foam[END_REF].

Fig. 20 .

 20 Fig. 20. (A) Dependance of the heat conductivity on porosity modeled with cell size of 300 µm and filled with air (B) Thermal conductivity evolution over 900 days of PUF and PUF modified with 1.5% of talc. Reproduced with permission from[START_REF] Ferkl | Multi-scale modelling of heat transfer in polyurethane foams[END_REF] and[START_REF] Santiago-Calvo | Longterm thermal conductivity of cyclopentane-water blown rigid polyurethane foams reinforced with different types of fillers[END_REF].

Fig. 21 .

 21 Fig. 21. Dependence of the char residue (A), weight loss at 5% (B), 10% (C) and 50% (D) on the IOH of

Fig. 22 .

 22 Fig. 22. Effect of the amount of insoluble bark residue on the flammability of PUF. Reproduced with permission from [213][211]

Fig. 23 .

 23 Fig. 23. Overview of the different factors affecting several properties (cell morphology, mechanical, thermal and fire resistance behaviors).

Fig. 1 .

 1 Fig. 1. Examples of F-PUF (Left) and R-PUF (right) applications.

Fig. 2 .

 2 Fig. 2. Main isocyanate reactions with H-labile groups.

Fig. 3 .

 3 Fig. 3. Effect of the NCO/OH index on the chemical architectures of PUF, PU-PIR and PIR foam networks.

Fig. 4 .

 4 Fig. 4. Detailed usual processes at lab scale for PUF elaboration: pour-in-place or molding process.

Fig. 5 .

 5 Fig. 5. Representation of silicone surfactant. Adapted from [57].

Fig. 6 .

 6 Fig.6. Illustration of the significant perturbations in foam cell formation, with or without surfactant.

Fig. 7 .Fig. 8 .

 78 Fig. 7. Catalysts structures ranked according to their main activities in the foam formulation. Adapted from [70]. Fig. 8. Viscosity profile associated to the cell bubbles formation.

Fig. 9 .

 9 Fig. 9. Triglyceride structure and the most abundant fatty acids in vegetables, seeds and microalgae oil.

Fig. 10 .

 10 Fig. 10. Overview of the main oleochemistry pathways for the elaboration of different PUF components.

Fig. 11 .

 11 Fig. 11. Overview of the transformation of main carbohydrates into different PUF components.

Fig. 12 .

 12 Fig. 12. Composition of lignocellulosic resources and classification of main polyphenols: tannins and lignins. Adapted from [189].

Fig. 13 .

 13 Fig. 13. Overview of the transformation of lignins and tannins into PUF components.

Fig. 14 .

 14 Fig. 14. Overview of the transformation of wastes from industrial processes into PUF components.

Fig. 15 .

 15 Fig. 15. Overview of the transformation of products from biotechnology into the PUF component.

Fig. 16 .

 16 Fig. 16. Viscosity of polyol vs. the cell size for PUF. Compilation of data from literature

Fig. 17 .

 17 Fig. 17. Effect of the gelling/blowing balance vs. temperature, viscosity and foam cell morphology in three typical cases: (A) mainly blowing, (B) equilibrium and (C) mainly gelling.

Fig. 18 .

 18 Fig. 18. (A) Effect of the introduction of lignin-based polyol on the density and compressive strength of PUF. (B) Dependence of the compressive strength on density. Reproduced with permission from

Fig. 20 . 98 Fig. 21 .

 209821 Fig. 20. (A)Dependance of the heat conductivity on porosity modeled with cell size of 300 µm and filled with air (B) Thermal conductivity evolution over 900 days of PUF and PUF modified with 1.5% of talc. Reproduced with permission from[START_REF] Ferkl | Multi-scale modelling of heat transfer in polyurethane foams[END_REF] and[START_REF] Zhang | Experimental study of the thermal conductivity of polyurethane foams[END_REF].

Fig. 22 .

 22 Fig. 22. Effect of the amount of insoluble bark residue on the flammability of PUF. Reproduced with permission from [211].

Fig. 23 .

 23 Fig. 23. Overview of the different factors affecting several properties (cell morphology, mechanical, thermal and fire resistance behaviors).

Fig. 24 .

 24 Fig. 24. Overview of the main synthetic routes to NIPU.

Table 1

 1 General foam formulation with quantities expressed in part by weight of the polyol.

	Foam component	Polyisocyanate Polyol BA	Surfactant Catalyst Additives
	Quantity (pbw 1 )	100-300 2

Table 2 Relative

 2

	Isocyanate	Structure	1 st addition	2 nd addition
	TDI		702	58
	MDI		561	193
	HDI		1.8	0.9
	IPDI		1.1	0.4
	H12 MDI		1	0.7
	2.2.2. Polyol

reactivity of isocyanates with alcohol groups for the 1 st and the 2 nd additions. Adapted from

[START_REF] Szycher | Szycher's handbook of polyurethanes[END_REF]

.

Since PUF are mainly crosslinked networks and since polyisocyanates are mainly bifunctional, polyols must present, on average, a functionality (f) higher than 2. Polyol mixes are often used to obtain the suitable requirements. Polyols are usually viscous liquids containing at least two or more hydroxyl (OH) groups per molecule. They are characterized by their OHs density (IOH) expressed in mg KOH/g. Both main types of polyols are oligomers of polyether and polyester with OH ending chains.

Table 3 Main

 3

	PUF type	IOH (mg KOH/g)	Functionality (f)	Molar mass (g/mol)	Viscosity (Pa.s)
	Rigid	200-800	2-8	300-1000	2-50
	Flexible	15-100	2-3	3000-6500	0.2-20

requirements on polyols properties for F-PUF and R-PUF. Adapted from

[START_REF] Furtwengler | Renewable polyols for advanced polyurethane foams from diverse biomass resources[END_REF][START_REF] Ionescu | Chemistry and technology of polyols for polyurethanes[END_REF]

.

Polyols properties have a profound impact on the behaviors and structures of the final cellular materials. Polyols for R-PUF have IOH ranging between 350 and 800 mg KOH/g, with between 3 and 8 OH groups per molecule (Table

Table 4

 4 Relative reactivity of hydrogen active compounds without catalyst. Adapted from[START_REF] Ionescu | Chemistry and technology of polyols for polyurethanes[END_REF].

	Hydrogen active compound	Structure	Uncatalyzed relative reactivity at 25 °C
	Primary aliphatic amine		3300
	Secondary aliphatic amine		650-1650
	Primary aromatic amine		6.5-10
	Primary aliphatic OH		3.3
	Water		3.3
	Carboxylic acid		1.3
	Secondary aliphatic OH		1
	Urea		0.5
	Tertiary aliphatic OH		0.0017
	Phenolic OH		0.003-0.017
	Urethane		0.0033
	2.2.3. Blowing agent

Table 5

 5

	BA structures, name physical properties and global warming potential (GWP). Data from literature

Acknowledgment

This study was funded by the Programme d'investissements d'avenir (PIA) of Bpifrance (Trans'alg Project).

The increasing portion of dangling chains is said to plasticize the network, reducing the compression strength [START_REF] Zieleniewska | Preparation and characterisation of rigid polyurethane foams using a rapeseed oil-based polyol[END_REF][START_REF] Pillai | Solvent-free synthesis of polyols from 1-butene metathesized palm oil for use in polyurethane foams[END_REF][START_REF] Narine | Physical Properties of Polyurethanes Produced from Polyols from Seed Oils: II. Foams[END_REF][START_REF] Ng | Preparation and modification of water-blown porous biodegradable polyurethane foams with palm oil-based polyester polyol[END_REF]. Narine and coworkers studied the effect of the dangling ends in PUFs. They used different polyols with similar IOH synthesized by various methods. The authors found that the compressive strength of soybean polyol realized by epoxidation and ringopening was the lowest with the plasticizing effect of the dangling ends [START_REF] Narine | Physical Properties of Polyurethanes Produced from Polyols from Seed Oils: II. Foams[END_REF]. The PUF realized with rapeseed oil-based polyol had compression strength 15% lower than the fossil-based reference due to the plasticizing effect of dangling chains-ends [START_REF] Zieleniewska | Preparation and characterisation of rigid polyurethane foams using a rapeseed oil-based polyol[END_REF].

As previously explained, the epoxidation followed by ring-opening is one of the most popular ways to obtain polyols from vegetable oil. The ring-opening reaction is often accompanied by side reactions such as epoxide polymerization, which can modify the final properties. Then, an unexpected increase of compressive strength was obtained for foams with 30 to 50 wt% of epoxidized soybean oil ring-opened by EG. The authors hypothesized that the polyether network formed by this polymerization supported the network [START_REF] Fan | Rigid polyurethane foams made from high viscosity soypolyols[END_REF].

Lignins produced with different extraction methods are often a powder. Unfortunately, the foam processing is not adapted for the integration of solid polyols at high content. This is shown in Fig. 19, by the compressive strength evolution over the lignin/polyol ratio. The introduction of a small portion (25 wt%) of raw lignin instead of the polyol made the compressive strength drop from 500 to 250 kPa without significant change in density [START_REF] Pan | Effect of replacing polyol by organosolv and kraft lignin on the property and structure of rigid polyurethane foam[END_REF]. In Fig. 19, the gradual introduction of lignins into PUFs showed a plateau in compressive strength from 25 to 60 wt%. However, after 60%, the poor dispersion of lignin into the matrix results in a ruin of mechanical properties (Fig. 19).

Curiculuml Vitae Julien Peyrton

Julien Peyrton obtained his Master's degree in chemistry with a specialization in polymer engineering in 2017 in the European Engineering School of Polymers, Chemistry and Materials in Strasbourg, France. He earned his Ph. D. in polymer science in 2020 at the Institute of Chemistry and Processes for Energy, Environment and Health -University of Strasbourg/CNRS in Strasbourg, France, under the supervision of Prof. L. Avérous. His interests cover several aspects of biobased chemicals and renewable polymer materials. During his doctoral studies, his research focuses on the synthesis of new biobased building blocks coming from micro-algal resources in order to develop cellular materials with new macromolecular architectures. Collaboration with the national institute for research and development in chemistry and petrochemistry in Romania led to the development of new olive oil based flexible polyurethane foams. He co-authored a publication in Molecules investigating the kinetics of the oil modifications toward the utilization in polyurethane synthesis and a publication in ACS Sustainable studying the impact of modified microalagae oil on rigid polyurethane foam.

Luc Avérous

Prof. Luc Avérous is a Group Leader (BioTeam), Head of the Polymer Research Department and former Lab Director at the ICPEES (UMR CNRS 7515) -Univ. of Strasbourg (France). In 2003, he became a full Professor at the ECPM (Strasbourg-France), where he teaches biopolymer science, biomaterials, composites, plastic processing & polymer characterization. Over the past two decades, his major research projects have dealt with biobased and/or biodegradable polymers. As a leading international expert in these fields, he has developed strong collaborations with several foreign labs (Australia, Brazil, Canada, Spain) and major companies. He serves as a member of research advisory boards for several different companies. In France and overseas, he is regularly invited to co-organize conferences, to chair symposia, and to give plenary/keynote lectures. He has co-edited 4 books (2 Wiley, 1 Elsevier & 1 Springer). He is a member of the editorial board and/or guest Editor for several scientific journals. He is also a referee for many scientific journals, books and international projects. He has published hundreds of scientific communications such as 16 review articles, with more than 11,000 citations (H-Index = 48 -Scopus data).