Hana Bouzit

Krusch Felix

Daniel Hermida-Merino

Eduardo Solano

Didier Cot

Jean Pierre Méricq

Stéphanie Roualdes

Mona Semsarilar

Damien Quémener

Karim Aissou
email: karim.aissou@umontpellier.fr

Double Stimuli-Responsive Perforated Lamellar Structure Formed by Linear ABC Triblock Terpolymer Monoliths

Keywords: PS-b-P2VP-b-PNIPAM, RAFT polymerization, thermo-sensitive, pH-responsive, membrane

Amphiphilic block copolymer (BCP) thick films with stimuli-responsive pores are promising candidates for the manufacturing of next-generation ultrafiltration (UF) membranes since their smart nanochannels facilitates the removal of fouling which is considered as one of the biggest challenges in membrane technology. In this work, a well-defined polystyrene-blockpoly(2-vinylpyridine)-block-poly(N-isopropylacrylamide) (PS-b-P2VP-b-PNIPAM) terpolymer was prepared for the first time via reversible addition-fragmentation chain transfer (RAFT) polymerization. The combination of the nonsolvent-induced phase separation (NIPS) process with a solvent vapor annealing (SVA) treatment was used to produce nanostructured pH-and thermo-double sensitive ABC-type BCP thick films. Here, the NIPS-made PS-b-P2VPb-PNIPAM thick film, comprising a microporous spinodal-type network substructure, topped by a dense thin layer of poorly defined nanopores is transformed into a monolith entirely composed of a well-ordered perforated lamellar (PL) phase upon exposure to a chloroform vapor during 6h. Such kind of PL-structured monoliths, showing a permeance value as high as 18 L.h -1 .m -².bar -1 at 46°C and pH = 7 with an excellent temperature cyclability, are highly desired to manufacture smart separation-based UF materials able to transit their pore state from hydrophilic to hydrophobic (and vice versa), thereby leading to much more efficient detachment of foulants during the cleaning process.

Introduction

Over the last decade, amphiphilic block copolymers (BCPs) have attracted extensive attention to manufacture ideal membranes combining high selectivity and good permeability for valuable ultrafiltration (UF) applications (e.g., water purification with complete rejection of virus, biopharmaceutical separations, etc.). [START_REF] Peinemann | Asymmetric Superstructure Formed in a Block Copolymer via Phase Separation[END_REF][START_REF] Abetz | Isoporous Block Copolymer Membranes[END_REF][START_REF] Nunes | Block Copolymer Membranes for Aqueous Solution Applications[END_REF][START_REF] Zhang | Block polymer membranes functionalized with nanoconfined polyelectrolyte brushes achieve sub-nanometer selectivity[END_REF][START_REF] Qiu | Selective Separation of Similarly Sized Proteins with Tunable Nanoporous Block Copolymer Membranes[END_REF] Such innovative materials with a better figure of merit compared to the state of the art membrane are based on the BCP self-assembly into wellordered nanofeatures leading to the formation of monodisperse pores in high areal density (up to 10 terapores per inch²) on the membrane top surface. [START_REF] Zhang | Nanoporous Membranes Generated from Self-Assembled Block Polymer Precursors: Quo Vadis ?[END_REF] However, in UF processes, the inevitable flux decline of membranes caused by the accumulation of foulants in the nanopores is particularly challenging to solve since low shear forces can be achieved in such small pores. [START_REF] Cetintas | Free-standing thermo-responsive nanoporous membranes from high molecular weight PS-PNIPAM block copolymers synthesized via RAFT polymerization[END_REF] One appealing approach to prevent the fouling effects (i.e., flux decline, high-energy consumption and material lifetime decreasing) is the nanodesign of smart membranes with an adjustable pore shape that can be controlled by external stimuli such as temperature, pH, ion concentration and redox potential. [START_REF] Liu | Thermoand pH-Responsive Graphene Oxide Membranes with Tunable Nanochannels for Water Gating and Permeability of Small Molecules[END_REF][START_REF] Chu | Negatively thermoresponsive membranes with functional gates driven by zipper-type hydrogen-bonding interactions[END_REF][START_REF] Zhang | Breathing Pores on Command: Redox-Responsive Spongy Membranes from Poly(Ferrocenylsilane)S[END_REF][START_REF] Liu | Bioinspired dual stimuli-responsive membranes with enhanced gating ratios and reversible performances for water gating[END_REF] In this way, one key feature of BCP membranes is the facile implementation of specific properties within the material since microphase-separated domains afford to overcome the dilemma between the mechanical strength of the material and a macromolecular dynamic under an external stimulus required for facilitating the cleaning process.

Following this strategy, several BCP membranes containing a stimuli-responsive block have been demonstrated by using a nonsolvent-induced phase separation (NIPS) preparation method. [START_REF] Mocan | Systematic variation of membrane casting parameters to control the structure of thermo-responsive isoporous membranes[END_REF][START_REF] Schacher | Self-Supporting, Double Stimuli-Responsive Porous Membranes from Polystyrene-Block-poly(N,N-Dimethylaminoethyl Methacrylate) Diblock Copolymers[END_REF][START_REF] Clodt | Double Stimuli-Responsive Isoporous Membranes via Post-Modification of Ph-Sensitive Self-Assembled Diblock Copolymer Membranes[END_REF][START_REF] Zhang | Dynamically Responsive Multifunctional Asymmetric Triblock Terpolymer Membranes with Intrinsic Binding Sites for Covalent Molecule Attachment[END_REF][START_REF] Algarni | Thermo-Responsive Membranes from Blends of PVDF and PNIPAM-b-PVDF Block Copolymers with Linear and Star Architectures[END_REF] For instance, asymmetric membranes with pH-responsive pores were achieved by using polystyrene-block-poly(2-vinylpyridine) (PS-b-P2VP) chains since the swelling/shrinking switches of the weak polyelectrolyte P2VP by protonation/deprotonation lead to a closing/opening state of the nanochannels. [START_REF] Jung | Structure Formation of Integral Asymmetric Composite Membranes of Polystyrene-Block-Poly(2-Vinylpyridine) on a Nonwoven[END_REF] In another example, thermoresponsive PS-b-poly(N-isopropylacrylamide) (PS-b-PNIPAM) membranes were produced due to the lower critical solution temperature (LCST) of PNIPAM occurring at 32°C. [START_REF] Cetintas | Free-standing thermo-responsive nanoporous membranes from high molecular weight PS-PNIPAM block copolymers synthesized via RAFT polymerization[END_REF] Here the effective porosity of nanochannels can be regulated according to changes in the water temperature since the PNIPAM block swells below its LCST, thus restricting the formation of large pores and vice versa. This behavior makes that an increase of the permeability by almost 400% was observed above the PNIPAM LCST. However, the formation of monodisperse PNIPAM-based nanochannels was not demonstrated for these single-responsive PS-b-PNIPAM membranes.

More recently, original linear and star-shaped PNIPAM-b-poly(vinylidene fluoride) (PNIPAMb-PVDF) membranes with a thermoresponsive character were produced by Algarni and coworkers. [START_REF] Algarni | Thermo-Responsive Membranes from Blends of PVDF and PNIPAM-b-PVDF Block Copolymers with Linear and Star Architectures[END_REF] Although some PNIPAM-b-PVDF membranes revealed an interesting zig-zag morphology at the micron scale, again monodisperse PNIPAM-based nanochannels in a high areal density were not generated during the NIPS process.

To take the concept one-step further, membranes showing both pH-and thermo-responsive behavior have also been manufactured. For instance, Clodt et al. have recently obtained this dual responsive behavior by coating an end-functionalized PNIPAM homopolymer on a pHresponsive PS-b-P4VP membrane via "grafting to" approach. [START_REF] Clodt | Double Stimuli-Responsive Isoporous Membranes via Post-Modification of Ph-Sensitive Self-Assembled Diblock Copolymer Membranes[END_REF] Generally, in the "grafting to" approach, the diffusion of the end-functionalized

Results and discussion

The Our approach was to start with (1) a bulk styrene polymerization using trithiocarbonate as RAFT agent and AIBN as the initiator, (2) followed by an extension with 2VP conducted in shows that the material top surface exhibits well-defined in-plane cylinders or out-of-plane lamellae arranged into large grains. The AFM topographic image presented in Figure 2a reveals that the equilibrium structure formed on the material top surface consists more precisely of an alternation of well-defined PS (bright) and P2VP/PNIPAM (dark) out-of-plane lamellae having a period of 37 nm, as extracted from the fast Fourier transform (FFT). The associated highresolution mapping obtained by using a Laplacian matrix deconvolution method allows distinguishing the presence of dark holes within the PS lamellae, which indicates that the nanostructure is rather a perforated lamellar (PL) phase (see Fig. 2b). In general, the perforation formed within the PL phase obeys either to a conventional hexagonal or tetragonal symmetry. [START_REF] Ji | Kinetic Pathways of Lamellae to Gyroid Transition in Weakly Segregated Diblock Copolymers[END_REF] As the symmetry of PS perforations extended through the P2VP/PNIPAM lamellae remains unclear from the AFM topographic image, grazing incidence blocks or could be due to the terpolymer chain architecture implying that P2VP and PNIPAM are the middle-and end-block, respectively, of the ABC-type BCP. In the last case, this makes that the P2VP conformation changes under pH variations could be impeded by the absence of a free chain-end and/or could be due to a partial deprotonation of P2VP since the middle-block cannot be directly in contact with the water at basic pH.

Conclusion

Synthesis procedures

Synthesis of the PS homopolymer macro-RAFT agent. In a typical experiment, a 100 mL round-bottomed flask was charged with 60 g of freshly purified styrene (0.57 mol), 0.26 g of CDPA (0.66 mmol) and 21 mg of AIBN (0.13 mmol). The sealed reaction vessel was purged with nitrogen and immersed in a preheated oil bath at 70 °C for 20h. The styrene bulk polymerization was stopped by cooling the reaction vessel in an ice bath, then an aliquot was withdrawn from the solution to determine the monomer conversion by 1 H NMR. By comparing the integrated aliphatic proton signals due to the PS groups at 1.88 ppm to those due to the styrene monomer at 5.77-5.83 ppm, the conversion was found to be 39%. The resulting PS macro-chain transfer agent (CTA) was precipitated three times in cold methanol and dried overnight in a vacuum oven at RT) to give a white-yellowish powder. The molecular weight of hPS was determined solely by SEC since the CTA chain-end protons are not visible from the NMR spectrum. [START_REF] Peinemann | Asymmetric Superstructure Formed in a Block Copolymer via Phase Separation[END_REF] H NMR (400MHz, CD2Cl2): δ = 6.59-7.05 (5H, m, Ph), 1.2-1.83 (3H,m,CH-CH2-). SEC in THF at 35°C using PS standard: the molecular weight (Mn) and dispersity (Đ)

values were found to be of 28.2 kg/mol and 1.09, respectively. 2D-DOSY-NMR (600MHz, CD2Cl2): D = 8.31 x 10 -11 m 2 .s -1 .

Synthesis of the PS-b-P2VP macro-RAFT agent.

In 200 mL round flask, hPS28.2k (5 g, 0.17 mmol) was mixed with 2VP (28.82 g, 0.27 mol), AIBN (5.8 mg, 0.035 mmol) and 1,4dioxane (54.9 mL). The solution was purged with nitrogen and then heated to 70°C by using a temperature controlled oil bath. Polymerization was allowed to proceed during 7h prior to stopping the reaction by immersing the vessel into an ice bath. An aliquot was withdrawn from the solution, then the brown mixture was concentrated, precipitated in heptane and dried promoted by exposing films during 6h to a continuous stream of CHCl3 vapor produced by bubbling nitrogen gas through the liquid solvent as described previously. [START_REF] Gotrik | Morphology Control in Block Copolymer Films Using Mixed Solvent Vapors[END_REF][START_REF] Aissou | Periodic Bicontinuous Structures Formed on the Top Surface of Asymmetric Triblock Terpolymer Thick Films[END_REF] This continuous flow system was used to control the CHCl3 vapor pressure in the chamber by dilution with a separate N2 stream so that a solvent vapor consisted of 32 sccm CHCl3 vapor and 8 sccm N2 (total 40 sccm). Note that the NIPS process was initially used to generate asymmetric terpolymer films after the SVA treatment. [START_REF] Aissou | Asymmetric Solvent-Annealed Triblock Terpolymer Thick Films Topped by a Hexagonal Perforated Lamellar Nanostructure[END_REF] However, a long SVA time (> 2h) was required to achieve well-defined nanopores on the material top surface, making that only symmetric terpolymer films entirely composed of the PL phase were finally considered in this work.

AFM, SEM and GISAXS characterizations

  homopolymers into the nanoscale pores is prevented by the polymer brushes already grafted on the membrane surface. Here, we have synthesized for the first time PS-b-P2VP-b-PNIPAM terpolymers via reversible addition-fragmentation chain transfer (RAFT) polymerization to produce asymmetric thick films endowed with thermo/pH dual responsive nanodomains. We show that the non-permeable NIPS-made PS-b-P2VP-b-PNIPAM thick film, consisting of a microporous (spinodal) network substructure and a dense top layer with a poorly-defined phase, is transformed into a permeable monolith entirely composed of a well-ordered perforated lamellar (PL) phase during the solvent vapor annealing (SVA) treatment. Water permeability tests were carried out to confirm the dual responsive behavior of the P2VP/PNIPAM nanopores formed within the PL-structured monolith as well as their good thermal cyclability. Such multifunctional monoliths with unique nanoscale properties provide prospect to the fabrication of efficient easy-to-clean separation based-materials.

Scheme 1 .

 1 Scheme 1. General route for RAFT polymerization of the (1) PS, (2) PS-b-P2VP and (3) PSb-P2VP-b-PNIPAM macro-RAFT agents.

1, 4 -

 4 dioxane in presence of AIBN and (3) then with NIPAM under similar conditions. According to the literature, this RAFT polymerization approach optimizes the synthesis of the PS-b-P2VPb-PNIPAM system since starting by a PNIPAM macroRAFT to prepare a PNIPAM-b-P2VPb-PS terpolymer may cause retardation of the styrene polymerization due to slow initiation, slow fragmentation of the intermediate radicals and possible irreversible termination reactions. 18 Figure S1 shows the size exclusion chromatography (SEC) traces of the PS homopolymer (hPS) (purple) and PS-b-P2VP BCP (red) macro-RAFT agents as well as the desired PS-b-P2VP-b-PNIPAM terpolymer (green) for which the synthesis preparation conditions are detailed in the experimental section. All SEC traces exhibit a narrow, unimodal distribution with no evidence of high molecular weight polymers that may justify uncontrolled polymerization or coupling reactions. Moreover, the shift of the SEC curves toward higher molecular weights, which comes from the difference in the hydrodynamic volumes of the hPS, PS-b-P2VP BCP and PS-b-P2VP-b-PNIPAM terpolymer, fully supports the successful preparation of targeted ABC triblock terpolymer chains with low dispersity (Đ < 1.32). Note that the molecular weight (Mn) of the hPS macroRAFT was found to be 28.2 kg/mol (Đ = 1.09) using PS standards. To determine the molecular weights of the P2VP and PNIPAM blocks, 1 H nuclear magnetic resonance (NMR) spectra of the AB-and ABC-type BCPs were used (see Fig. S2). By comparing the 1 H NMR integral ratios between the characteristic signal of PS at δ = 6.59-7.05 ppm and those of P2VP (δ = 8.25 ppm) and PNIPAM (δ = 3.99 ppm), the molar masses of the PS-b-P2VP and PS-b-P2VP-b-PNIPAM BCPs were calculated to be 34.6 kg/mol and 42.5 kg/mol, respectively. Therefore, the proton NMR spectroscopy indicates that PS-b-P2VP-b-PNIPAM chains consists of PS (28.2 kg/mol, PS = 0.68), P2VP (5.8 kg/mol, P2VP = 0.13) and PNIPAM (8.5 kg/mol, PNIPAM = 0.19) where  represents the different volume fractions (see

  As the presence of PS homopolymer or even PS-b-P2VP BCP within the ABC triblock terpolymer thick film can strongly affect the phase behavior of the PS-b-P2VP-b-PNIPAM chains, the powder purity was established by 2D-diffusion-ordered spectroscopy (DOSY)-NMR (see Fig. S3). The NMR experiment revealed that 1 H resonances belonging to the PS, P2VP and PNIPAM blocks are aligned with the same horizontal for the PS-b-P2VP-b-PNIPAM terpolymer, thereby indicating a good purity of the powder since all the signals arise from the same macromolecule having a diffusion coefficient of 5.01 x 10 -11 m 2 .s -1 . It is noteworthy that the diffusion coefficients of the PS and PS-b-P2VP chains are higher since they are found to be 6.60 x 10 -11 m 2 .s -1 and 8.31 x 10 -11 m 2 .s -1 , respectively. Thick film morphology formed by the PS-b-P2VP-b-PNIPAM terpolymer was also studied. Both the top view scanning electron microscopy (SEM) and atomic force microscopy (AFM) topographic images presented in Figure S4 reveal the representative top surface morphology of a PS-b-P2VP-b-PNIPAM thick film that was manufactured by NIPS from a 18 wt. % polymer solution in a di-solvent mixture of 1,4-dioxane and tetrahydrofuran (DOX/THF: 1/1w/w). These micrographs show that a dense top surface layer with poorly defined domains is produced when the mixture of di-solvents is allowed to evaporate from the PS-b-P2VP-b-PNIPAM thick film for 30s before immersing the material into a coagulation (water) bath to induce the phase inversion. To know more about the skin layer morphology and gain insight into the porosity generated by NIPS within the material, cross-sectional SEM views were also taken (see Fig.1).

Figure 1 .

 1 Figure 1. Cross-sectional SEM views of an asymmetric PS-b-P2VP-b-PNIPAM thick film generated by NIPS showing: (a) the full material having a thickness of 21 µm, (b) a 500 nm thick top layer (light gray) with a poorly defined phase topping the sponge-like substructure, and (c) the formation of a thin dense bottom layer without any pores.

Figure 2 .

 2 Figure 2. (a) AFM topographic view and (b) its associated high-resolution mapping obtained by using a Laplacian deconvolution matrix that show a 37 nm period fingerprint pattern formed on the top surface of a solvent-annealed (6h, CHCl3) PS-b-P2VP-b-PNIPAM thick film subsequently treated by a CF4 plasma. Insets: Magnified AFM topographic image and its corresponding high-resolution mapping showing the presence of lamellae with dots arising from PS perforations. Schematic representation of the PL phase showing the core-shell (green) PNIPAM-(red) P2VP lamellae perforated by (purple) PS protrusions connecting the adjacent PS lamellae.

  Figure S8showing the formation of a rhombic array with similar lattice parameters (a = 36 nm and b = 26 nm) extracted from the 2D-FFT. Note that the formation of a bicontinuous PL structure with perforations ordered into a rhombic array has been recently observed both from asymmetric poly(1,1-dimethyl silacyclobutane)-b-PS-b-P2VP thick films and their monolith homologs, depending on the SVA treatment duration.[START_REF] Aissou | Bicontinuous Network Nanostructure with Tunable Thickness Formed on Asymmetric Triblock Terpolymer Thick Films[END_REF] Here to highlight the fabrication of monoliths entirely composed of the phase after the SVA treatment, cross-sectional SEM images were taken from the top, middle and bottom regions of a PS-b-P2VP-b-PNIPAM film (see Fig.3). The cross-sectional SEM view presented in Figure3areveals that the PS-b-P2VP-b-PNIPAM material has densified during the SVA treatment to form a symmetric film exhibiting a well-developed PL structure (see FiguresS8 and S9) as attested by a strong decrease of the film thickness (14 µm). This phenomenon can be attributed to the growth of the nanoporous PL phase at the expense of the microporous spinodal-type network structure. Moreover, the cross-sectional images taken close to the top and bottom interfaces of the solvent-annealed (6h, CHCl3) PS-b-P2VP-b-PNIPAM thick film show both the presence of a self-assembled structure which clearly indicates the formation of a monolith entirely composed of a nanoporous PL phase (see Fig.3b,c).

Figure 3 .

 3 Figure 3. Cross-sectional SEM views of a solvent-annealed (6h, CHCl3) PS-b-P2VP-b-PNIPAM thick film generated by NIPS-SVA showing (a) the full symmetric material having a thickness of 14 µm as well as the formation of the nanoporous PL phase in the vicinity of the (b) top and (c) bottom interfaces.

Figure 4 .

 4 Figure 4. (a) Water fluxes, J, of the PS-b-P2VP-b-PNIPAM monoliths measured at different temperatures: (black squares) 20°C and viscosity corrected (red dots) 46°C. Uncorrected data (blue triangles) measured at 46°C are also given while error bars are the standard deviations of the mean relative permeance values calculated for two different samples. (b) Reversibility of the water permeance as a function of the temperature cycles (20°C and 46°C). Both uncorrected (blue triangles) and viscosity corrected (red dots) data are given. (c) J measured at 1 bar in acidic and basic water environments (pH = 3 and 9.5) for different temperatures: (black squares) 20°C and viscosity corrected (red dots) 46°C. (d) Schematic drawing of the PS-b-P2VP-b-PNIPAM terpolymer and illustration of the stimuli-responsive P2VP/PNIPAM nanopore behavior. The effective nanochannel porosity is regulated by the shape (i.e., a swollen or shrunken state) of the P2VP and PNIPAM blocks according to changes of temperature and pH. (1) and (2) correspond to the close and open channel state, respectively.

Figure 4b shows a

  Figure4bshows a good temperature cyclability of the symmetric PS-b-P2VP-b-PNIPAM film between 20°C and 46°C. Indeed, at each cycle (i.e., temperature switch), the permeance value matched with the previous one obtained at the same temperature. These results indicate that the well-defined PNIPAM-based nanochannels manufactured by NIPS-SVA have a fully reversible thermo-responsive character in accordance with a previous study reported by the Kamperman group on asymmetric single-responsive PS-b-PNIPAM membranes, however, endowed with short-range ordered nanopores.[START_REF] Mocan | Systematic variation of membrane casting parameters to control the structure of thermo-responsive isoporous membranes[END_REF] Note also that the permeability values of these asymmetric single-responsive AB-type BCP membranes, measured above and below the PNIPAM LCST, are in the same range as those obtained in this work from symmetric dual-responsive ABC-type BCP membranes.To go further in this study, the pH-sensitive character of the P2VP/PNIPAM nanoporous domains was also explored by measuring the viscosity corrected water fluxes under acidic and basic environments (at pH = 3 and 9.5) for two different temperatures (20°C and 46°C) (see Fig. 4c). The results revealed that the PS-b-P2VP-b-PNIPAM monolith generated by NIPS-SVA reaches various water flux values under the different conditions. This phenomenon occurs because the flux performance is closely related to the size of the adjustable porosity within the P2VP/PNIPAM nanochannels. The water channels are closed when the water flux test is conducted in an acidic environment (pH = 3) at 20°C (i.e., below the PNIPAM LCST). This close channel state illustrated by the sketch (1) in Figure 4d corresponds to the case where both the PNIPAM and P2VP blocks are swollen, thereby leading to a small water flux value (0.8 L.h -1 .m -² at 1 bar). Conversely, the highest water flux is achieved when the channel porosity is maximized by switching the pH environment to basic conditions (pH = 9.5) and increasing the temperature to 46°C (i.e., above the PNIPAM LCST). This open channel state illustrated by the sketch (2) in Figure 4d corresponds to the case where both the PNIPAM and P2VP blocks are shrunken, which allows for a corrected water flux value of 8.8 L.h -1 .m -² at 1 bar. Note that two partially open channel states can be reached when only one block shrinks within the P2VP/PNIPAM nanodomains. Therefore, an intermediate water flux value of 1.2 L.h -1 .m -² at 1 bar is measured when only the P2VP block shrinks (pH = 9.3 and T = 20°C). Interestingly, the corrected water flux value (5.1 L.h -1 .m -² at 1 bar) is substantially higher when only the PNIPAM block shrinks (pH = 3 and T = 46°C). This phenomenon could be attributed to the difference in size between the P2VP (5.8 kg/mol, P2VP = 0.13) and PNIPAM (8.5 kg/mol, PNIPAM = 0.19)

  In this study, a well-defined linear PS-b-P2VP-b-PNIPAM triblock terpolymer was synthesized for the first time by RAFT polymerization. The combination of the NIPS process with a SVA treatment was used to produce thermo/pH dual-responsive PL-structured PS-b-P2VP-b-PNIPAM monoliths with an adjustable nanochannel porosity. It is showed that the smart P2VP/PNIPAM nanochannels truly adopt an open or close state depending on the temperature and pH of water. An excellent temperature-reversible performance was also demonstrated by switching the water temperature below and above the PNIPAM LCST. These easy-to-clean nanostructured monoliths with thermo-and pH-responsive channels are envisioned to have potential in smart separation-based applications.ExperimentalMaterialsN-isopropylacrylamide (NIPAM, >99%, Sigma-Aldrich) was purified by recrystallization in a mixture of toluene/hexane (50/50, v/v). Styrene (St, >98%, Sigma-Aldrich) was stirred with inhibitor removal resin about 30 min prior to use. 2-Vinylpyridine (2VP, >97%, Sigma-Aldrich) was passed throw a column of activated alumina in order to remove the tert-butylcatechol present in the monomer. 2,2′-Azobis (2-methylpropionitrile) (AIBN, >99%, Sigma-Aldrich) was purified by recrystallization from methanol before being used. 4-Cyano-4-[(dodecylsulfanylthiocarbonyl)sulfanyl]pentanoic acid (CDPA, >97%, RAFT agent, Sigma-Aldrich) was used without further purification. All the solvents: 1,4-dioxane (DOX, >99%), tetrahydrofuran (THF, >99%), heptane, diethyl ether (>99%) and NMR solvents (i.e., deuterated dichloromethane (CD2Cl2) and chloroform deuterated (CDCl3)) were purchased from Sigma-Aldrich and used as received.

Characterizations 1 H

 1 overnight under vacuum at RT (5.45 g, yield = 16 %). The PS-b-P2VP macro-RAFT agent conversion was calculated by[START_REF] Peinemann | Asymmetric Superstructure Formed in a Block Copolymer via Phase Separation[END_REF] H NMR to be 10.2 %, by comparing the integrated aromatic proton signals of the P2VP ring at 8.25 ppm to those of the 2VP monomer at 8.53 ppm.[START_REF] Peinemann | Asymmetric Superstructure Formed in a Block Copolymer via Phase Separation[END_REF] H NMR (400MHz, CD2Cl2): δ = 8.25 (1H,m Ph), 6.61-7.06 (8H,m,Ph) and 1.27-2.30 (6H,m,CH-CH2). The PS-b-P2VP molecular weight and its PS volume fraction were determined by 1 H NMR to be 34.6 kg/mol and 0.83, respectively. SEC in THF using PS standard: Mn= 41.8 kg/mol, Đ = 1.14. 2D-DOSY-NMR (600MHz, CD2Cl2): D = 6.60 x 10 -11 m 2 .s -1 .Synthesis of the PS-b-P2VP-b-PNIPAM terpolymer.The PS-b-P2VP34.6k macro-RAFT agent (4.5 g, 0.13 mmol), NIPAM (4.42 g, 0.03 mol) and AIBN (2.13 mg, 0.013 mmol) were dissolved in 23.4 mL of 1,4-dioxane. The solution was purged with nitrogen and then placed in preheated oil bath at 70°C for 5h. The polymerization was stopped by placing the reaction vessel into ice bath and an aliquot was afterwards withdrawn. 1,4-dioxane was removed with a rotary evaporator after which the PS-b-P2VP-b-PNIPAM chains were dissolved in a small amount of THF. The ABC triblock terpolymer was precipitated once from cold diethyl ether, in order to eliminate the unreacted NIPAM monomer, and heptane. To properly eliminate the undesired PNIPAM dead chains, a Soxhlet extraction was carried out with ethanol at 95°C for 96h. The PS-b-P2VP-b-PNIPAM terpolymer was then concentrated, precipitated in heptane and dried in vacuum oven at room temperature (RT). The conversion was calculated by 1 H NMR to be 56%, by comparing the integrated proton signals of the PNIPAM groups at 3.99 ppm to those of the NIPAM monomer at 4,01-4,13 ppm.[START_REF] Peinemann | Asymmetric Superstructure Formed in a Block Copolymer via Phase Separation[END_REF] H NMR (400MHz, CD2Cl2): δ = 3,99 (1H, s, CH), 1.13 (6H,m,CH3-).[START_REF] Peinemann | Asymmetric Superstructure Formed in a Block Copolymer via Phase Separation[END_REF] H NMR spectrum revealed that PS-b-P2VP-b-PNIPAM chains consisted of PS (28.2 kg/mol, PS = 0.68), P2VP (5.8 kg/mol, P2VP = 0.13) and PNIPAM (8.5 kg/mol, PNIPAM = 0.19). SEC in THF using a PS standard revealed a Mn value of 46.4 kg/mol (Đ = 1.32) which is close to the one obtained by NMR (42.5 kg/mol). 2D-DOSY-NMR (600MHz, CD2Cl2): D = 5.01 x 10 -11 m 2 .s -1 . NMR and SEC characterizations.[START_REF] Peinemann | Asymmetric Superstructure Formed in a Block Copolymer via Phase Separation[END_REF] H NMR spectroscopy were carried out on a Bruker Advance spectrometer operating either at 400 or 600 MHz using deuterated dichloromethane (CD2Cl2) or deuterated chloroform (CDCl3). SEC was carried out on a Viscotek device (Malvern Instruments, Worcestershire, U.K) with a triple detector array. The SEC apparatus was equipped with two PLgel 5µm 500Å columns, THF as eluent with a flow rate at 1mL/min at 35°C, PS standards were used for calibration of the column. Omnisec software using refractive index and light scattering signals was applied to calculate Mn and Đ of polystyrene synthesized. Mn of all block copolymers were calculated using the Mn of their PS macro-RAFT agent obtained from SEC and the block ratios obtained from 1 H NMR results.Fabrication of asymmetric PS-b-P2VP-b-PNIPAM thick films by NIPS: Freestanding 21 µm thick PS-b-P2VP-b-PNIPAM films were drawn onto (3 x 3 cm) silicon substrates by using a simple tape casting technique with 250 µm gap from a 18 % wt. terpolymer solution in a di-solvent mixture (DOX/THF: 1/1 by weight) (see Fig. S10). Solvents were allowed to evaporate during 30s at RT to form a dense air surface layer with a (kinetically trapped) poorly defined nanostructure, and then the PS-b-P2VP-b-NIPAM thick films were immersed into a deionized water bath at RT for 5 min to induce the polymer precipitation. In order to facilitate the removal of the terpolymer materials from the substrate, the silicon pieces were treated by an oxygen plasma in a home-made chamber (plasma conditions: 45 W, 75 mTorr O2, 10min) prior to their use, then a sacrificial poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) was inserted by spin-coating between the substrate and the PS-b-P2VP-b-PNIPAM thick films. It is noteworthy that the PS-b-P2VP-b-PNIPAM chains were solubilized in a large amount of THF (50 % wt.) in order to avoid their precipitation as observed in the commonly used DOX/THF: 4/1(by weight) mixture after several days. Fabrication of the PL-structured PS-b-P2VP-b-PNIPAM monoliths by SVA: The selfassembly of PS-b-P2VP-b-PNIPAM chains formed within the NIPS-made thick films was

:

  Atomic force microscopy (AFM Nano-Observer, CSInstruments) was used in tapping mode to characterize the surface morphology of PS-b-P2VP-b-PNIPAM thick films. Silicon cantilevers (PPP-NCH, Nanosensors) with a typical tip radius of 5 nm were used. The resonance frequency of the cantilevers was about 235 kHz. Prior AFM measurements, PS-b-P2VP-b-PNIPAM thick films were treated with a fluorine based plasma in a home-made chamber to improve the AFM topographic image contrast (plasma conditions: 45 W, 75 mTorr CF4, and 90s). Scanning electron microscopy (SEM, Hitachi S-4800) was used at an accelerating voltage of 5 kV to acquire top view and cross-section images of both asymmetric thick films and monoliths formed by PS-b-P2VP-b-PNIPAM chains. GISAXS experiments were performed on the Dutch-Belgian Beamline (DUBBLE) at the European Synchrotron Radiation Facility (ESRF) station BM26B inGrenoble.[START_REF] Portale | Polymer research and synchrotron radiation perspectives[END_REF] A monochromatic beam of 12 keV was set using a Si (111) double crystal monochromator. The sample (typical size of 150 mm 2 ) was shone with the X-ray beam with an angle of incidence of 0.2º, which is above the critical angle of the polymer, ensuring full penetration of the X-ray beam in the material and hence, analyzing the full volume of the sample. The 2D scattering patterns were collected with a PILATUS3 S 1 M detector. The scattering vector and the sample to detector distance were calibrated using silver behenate as standard, obtaining a sample-to-detector distance of 7500 mm.Water flux performances:The water permeability of the different PS-b-P2VP-b-PNIPAM thick films was measured in a 10 mL filtration cell (Amicon 8010 stirred cell) connected to a water reservoir and a compressed air line. The measurements were performed on 2.5cm diameter PS-b-P2VP-b-PNIPAM material discs supported by a high permeable hydrophilic PVDF material (water permeability of 2900 L h -1 m -2 bar -1 )[START_REF] Aissou | Asymmetric Solvent-Annealed Triblock Terpolymer Thick Films Topped by a Hexagonal Perforated Lamellar Nanostructure[END_REF] at pressures between 0.5 and 2 bar. The mass of water passing through the stacked materials (permeate) was recorded using a connected balance at regular time intervals for 10 min. Water temperature was maintained at 20°C and heated up to 46°C using a stainless steel electronic baths. Correction for the temperature dependence of water viscosity was obtained by multiplying the flux results with the relative change in dynamic viscosity of water at 46°C compared to that of water at 20°C. Hydrochloric acid and sodium hydroxide solutions were used for filtration experiments in acidic and basic conditions (pH = 3 and 9.5), respectively.

Table 1

 1

	). Note that the PS-b-P2VP-b-PNIPAM chains were devised with a relatively low
	molecular weight in order to overcome the trade-off between the terpolymer chain mobility
	when exposed to a CHCl3 vapor and sufficiently good mechanical properties to generate non-
	brittle (freestanding) films.

Table 1 :

 1 Molecular weight and composition of the PS-b-P2VP-b-PNIPAM system used in this work.

Acknowledgements

This work was performed within the support of the ANR JCJC AFM_Ring project, grant ANR-18-CE09-00xx of the French Agence Nationale de la Recherche and through the project TAKCLE/AXE-Membrane du Futur/09-2020 founded by the Institut Européen des Membranes (IEM).


Yoann Jovet
email: yoann.jovet@insa-lyon.fr

Alexis Laurent

Nasrin Arjomand Kermani

Frédéric Lefevre

Brian Elmegaard

Marc Clausse

Environmental assessment of electrification of food industry for Denmark and France

Keywords: Sustainability, Environmental assessment, Planetary boundaries, Energy transition, Industrial systems Nomenclature BAU

To align energy demand with greenhouse gas emission reduction targets set by the COP21 or the EU Green Deal, electrification is one of the most promising options. Most studies on the electrification of industrial processes focus on energy and greenhouse gas emissions, while the other potential environmental impacts have often been overlooked. Hence, the proposed work aims to highlight the pros and cons of shifting to electricity thanks to a Life Cycle Assessment approach. Industrial heat productions for the Danish and French food industries are used as case study. The reference consists in heat production based on fossil fuel (i.e. gas and oil boilers mainly) while electrical boilers, mechanical heat pumps or mechanical steam recompression solutions are considered for shift to electricity. Different electrification scenarios are considered, including levels of electrification and technological development. To identify the most relevant environmental impacts, an assessment of the food industry sectors is performed. Different scenarios are evaluated according to the selected impact categories, allowing to assess the environmental trade-offs. Results show that an electrification of the food industry enables to meet a sustainable level for climate change in France and Denmark for the majority of industrial processes. However, several important drawbacks are identified with burden shifting to other impact categories that go beyond sustainable levels, e.g. particulate emissions impacting human health and mineral resource use. These findings highlight that it is difficult for one sector alone to be considered environmentally sustainable without looking at other sectors. Therefore, multi-sectoral studies should be carried out to assess the improvement potentials in each sector and identify the trade-offs between sectors in order to achieve sustainable industrial systems.

Introduction

The 2021 IPCC report highlights the scientific consensus on the anthropogenic origin of global warming [START_REF] Masson-Delmotte | IPCC, 2021: Climate Change 2021: The Physical Science Basis. Contribution of working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change[END_REF]. This report also emphasises that a massive reduction in greenhouse gases (GHG) emissions is required to limit the rise in temperature and its consequences for the environment and human life. This need to reduce the impact of human activity is currently at the centre of policy, such as the Paris Agreement signed by all UN parties in 2015. Despite recent attention to this issue, the current level of emissions is not sufficient to achieve the objective of limiting temperature increase to 2°C [START_REF]The emissions gap report[END_REF]. To achieve these goals in a European context, the EU strategy is based on several pillars such as process optimisation, the evolution of energy systems towards more virtuous systems and the circular economy. The reduction of industrial GHG emissions is one of the pillars of the European strategy to achieve its defined objectives [START_REF]Masterplan for a competitive transformation of EU energy-intensive industries enabling[END_REF]. Among these solutions, energy system transformation has been studied to assess the potential for reducing GHG emissions in industry [START_REF] Obrist | Long-term energy efficiency and decarbonization trajectories for the Swiss pulp and paper industry[END_REF], [START_REF] Bogdanov | Full energy sector transition towards 100% renewable energy supply: Integrating power, heat, transport and industry sectors including desalination[END_REF]. These studies show that achieving the targets depends on a variety of solutions depending on the constraints of each industry. However, electrification of heat production seems to be one of the most important options to achieve the reduction for two main reasons: (i) electrification represents the major part of the energy used in the compatible scenario [START_REF] Obrist | Long-term energy efficiency and decarbonization trajectories for the Swiss pulp and paper industry[END_REF], [START_REF] Bogdanov | Full energy sector transition towards 100% renewable energy supply: Integrating power, heat, transport and industry sectors including desalination[END_REF]; and (ii) electrification has a high technology readiness level [START_REF]Masterplan for a competitive transformation of EU energy-intensive industries enabling[END_REF]. Studies on the transformation of energy systems focusing on environmental impact are relatively recent and mainly focus on the potential reduction of GHG emissions [START_REF] Obrist | Long-term energy efficiency and decarbonization trajectories for the Swiss pulp and paper industry[END_REF], [START_REF] Furszyfer | Decarbonizing the glass industry: A critical and systematic review of developments, sociotechnical systems and policy options[END_REF]- [START_REF] Sovacool | Decarbonizing the food and beverages industry: A critical and systematic review of developments, sociotechnical systems and policy options[END_REF]. As shown by da Costa et al. [START_REF] Da Costa | Environmental comparison of forest biomass residues application in Portugal: Electricity, heat and biofuel[END_REF], the transformation of an energy system can have benefits in terms of reducing greenhouse gas emissions but at the same time an increased impact on other environmental indicators. Therefore, studies that focus solely on global warming may have blind spots and partial conclusions, ultimately leading to potential risk of environmental burden-shifting [START_REF] Laurent | Limitations of Carbon Footprint as Indicator of Environmental Sustainability[END_REF], [START_REF] Laurent | Potentials and limitations of footprints for gauging environmental sustainability[END_REF]. The aim of this study is to evaluate the environmental impacts of the electrification of industrial processes in order to highlight the ability of the change in energy system to achieve the GHG reduction objectives but also the trade-offs of such a change in the system on other environmental indicators. To evaluate these different environmental criteria, these values are put into perspective with the planetary boundaries [START_REF] Rockström | A safe operating space for humanity[END_REF] and thresholds for human health damages [START_REF] Vargas-Gonzalez | Operational Life Cycle Impact Assessment weighting factors based on Planetary Boundaries: Applied to cosmetic products[END_REF] as well as with the objectives set by the Paris Agreement. This assessment methodology is applied to the Danish and French food industry taken as illustrative cases. Finally, this work aims to classify the different environmental impacts in order to rank the criteria among themselves and thus facilitate decision-making between different technical solutions.

Methods and Material

Assessment framework

The methodology used aims to define the environmental impact of three scenarios based on the study of the electrification of the Danish food industry by Elmegaard et al. [START_REF] Elmegaard | Electrification of processes and technologies for Danish Industry[END_REF] on the basis of the work of Bülher et al. [START_REF] Danmarks | Energy efficiency in industry: a study of the methods, potentials and interactions with the energy system[END_REF]. The first scenario, called "business as usual" (BAU), represents the current state of the industry. This scenario is complemented by two electrification scenarios: the Li scenario includes a massive electrification of the processes with the use of heat pumps for temperatures up to 150°C and the Hi scenario goes further by assuming a technological improvement allowing the use of heat pumps for temperatures up to 300°C. Following the methodology developed by Bülher et al. [START_REF] Danmarks | Energy efficiency in industry: a study of the methods, potentials and interactions with the energy system[END_REF], each industry is broken down by process type and temperature level in order to define the appropriate process electrification technology. These scenarios assess for each process and temperature which technology is the most appropriate. Mechanical heat pump (MHP) are used when the process is compatible and below the scenario temperature threshold except for mechanical vapor recompression (MVR), which is used for evaporation processes. Above the temperature threshold, heat is produced with electric boilers and if this is not possible with gas boilers as a last option. However, the sitespecific integration constraints cannot be integrated and the study is based on standard integration. This assessment considers marginal process for the evaluation of both energy and environment. Marginal process are defined by Hauschild et al. as "the changes to the economy caused by the introduction of the studied product system, i.e. the product system's consequence" [START_REF]Life Cycle Assessment[END_REF]. For the proposed application, namely the food industry, which represents a significant share of the energy market, the change of energy system will lead to a change in electricity production to satisfy this new demand. Considering marginal process requires to study the impact of the new sources of electricity production. For the environmental part, the so-called "consequential" approach as embedded in the ecoinvent database (i.e. consequential version) is considered.

Energy model description

Energy efficiency

The energy model is based on the current energy consumption of the industry. Assessing the total energy consumption (EcT) of the process requires considering the efficiency of the heat generation technology and the system losses, which depends on the type of fuel and the temperature level of the process as described in eq. ( 1).

Ec T = Ep x,T Seff ,x,T . (1 -𝜂) ( 1)
Where Epx,T is the heat requirement of the industry for a specific process at temperature T, Seffx,T the system efficiency for a fuel x and a process temperature T and η the thermal losses of the system, presented in Tab. 1, which represent the heat losses to the environment of the heat generation technology as defined by Bülher et al. [START_REF] Danmarks | Energy efficiency in industry: a study of the methods, potentials and interactions with the energy system[END_REF].

Tab. 1 -System efficiency by fuel and temperature level from [START_REF] Danmarks | Energy efficiency in industry: a study of the methods, potentials and interactions with the energy system[END_REF] Range The system efficiency depends on both the type of technology and the process temperature. The efficiency used is this work are from [START_REF] Danmarks | Energy efficiency in industry: a study of the methods, potentials and interactions with the energy system[END_REF]:

1. Mechanical heat pump (MHP) are assumed to be transcritical CO2 heat pump with an efficiency

𝐶𝑂𝑃 MHP = 𝜂 𝐿𝑜𝑟𝑒𝑛𝑧 𝑇 ̅ 𝑙𝑚,𝑠𝑖𝑛𝑘 𝑇 ̅ 𝑙𝑚,𝑠𝑖𝑛𝑘 -𝑇 ̅ 𝑙𝑚,𝑠𝑜𝑢𝑟𝑐𝑒 ( 2)
where 𝜂 𝐿𝑜𝑟𝑒𝑛𝑧 is a Lorenz efficiency and a value of 0.45 is assume in this study. 𝑇 𝑙𝑚,𝑠𝑖𝑛𝑘 and 𝑇 𝑙𝑚,𝑠𝑜𝑢𝑟𝑐𝑒 are defined in eq ( 3) and ( 4): 𝑇 ̅ 𝑙𝑚,𝑠𝑖𝑛𝑘 = 𝑇 𝑠𝑖𝑛𝑘,𝑜𝑢𝑡 -𝑇 𝑠𝑖𝑛𝑘,𝑖𝑛 𝑙𝑛(𝑇 𝑠𝑖𝑛𝑘,𝑜𝑢𝑡 ) -𝑙𝑛(𝑇 𝑠𝑖𝑛𝑘,𝑖𝑛 )

𝑇 ̅ 𝑙𝑚,𝑠𝑜𝑢𝑟𝑐𝑒 = 𝑇 𝑠𝑜𝑢𝑟𝑐𝑒,𝑖𝑛 -𝑇 𝑠𝑜𝑢𝑟𝑐𝑒,𝑜𝑢𝑡 𝑙𝑛(𝑇 𝑠𝑜𝑢𝑟𝑐𝑒,𝑖𝑛 ) -𝑙𝑛(𝑇 𝑠𝑜𝑢𝑟𝑐𝑒,𝑜𝑢𝑡 )

Where 𝑇 𝑠𝑖𝑛𝑘,𝑖𝑛 and 𝑇 𝑠𝑖𝑛𝑘,𝑜𝑢𝑡 are respectively the input and output temperatures of the sink, 𝑇 𝑠𝑜𝑢𝑟𝑐𝑒,𝑖𝑛 and 𝑇 𝑠𝑜𝑢𝑟𝑐𝑒,𝑜𝑢𝑡 are respectively the input and output temperatures of the source.

2.

A mechanical vapour recompression (MVR) COP of 5 is assumed. 3. Electric, gas, oil or coal boilers have an efficiency of 1.

Danish & French consumption scenarios

The BAU, Lo and Hi scenarios are based on energy consumption per energy source of the Danish food industry; the data are from the Danish Energy Agency (Energistyrelsen) [START_REF] Sørensen | Kortlaegning af energiforbrug i virksomheder[END_REF] corrected with efficiency of eq. ( 1). The energy distribution of the Danish food industry is presented in Fig. 1Erreur ! Source du renvoi introuvable.. The main energy consumption of the current food industry is gas following by oil and coal. After electrification, electricity can cover all the demand except for slaughterhouses and the share of MHP depends on the electrification scenario. The category "other food industry" includes all industries not covered by the other four categories and will be the focus of this study because it is composed of a number of different processes to be representative of the average performance.

The details of energy demand by energy source of the French food industry, presented in Fig. 2Erreur ! Source du renvoi introuvable., are taken from the French statistical office (INSEE) [START_REF] Agreste | Consommation d'énergie dans les industries agroalimentaires et les scieries en 2019[END_REF]. Due to lack of detailed data of the distribution between the different processes and their temperature within a sector for French industry, we assume that this distribution is the same as the Danish industry. However, the type and quantities of energy are country specific.

Energy mix

The environmental impact assessment for the electricity is correlated to the electricity production mix for each country. As the French and Danish electricity production systems are different, the study considers the specificities of each type of production. The marginal electricity mix for Denmark comes from the consistent Ecoinvent 3.7.1 database and is allocated as follows: less than 0,1 % from hydro river production, 61.0 % from wind power and 39.0 % from biomass [START_REF] Wernet | The ecoinvent database version 3 (part I): overview and methodology[END_REF]. For the marginal electricity mix for France, we have chosen to consider three different scenarios from the French Transmission System Operator (RTE) whose allocation is described in Tab. 2 [START_REF] Rte | Futurs énergétiques 2050 : les scénarios de mix de production à l'étude permettant d'atteindre la neutralité carbone à l'horizon 2050 -Chap[END_REF], [START_REF] Rte | Futurs énergétiques 2050 : les scénarios de mix de production à l'étude permettant d'atteindre la neutralité carbone à l'horizon 2050 -Chap[END_REF]. The values used here are medium-high voltage electricity mixes, which explains the absence of solar, which is mostly low voltage and therefore used by industry to a negligible extent. These three different scenarios propose variants of a low GHG emission mix with a highly variable share of nuclear and renewable energy, ranging from nuclear-free production (scenario M0) to a maximum share of 56.8 % (scenario N03) and an intermediate scenario N1. The French electricity projections is used to assess the sensitivity of the electricity mix to environmental impacts. Storage to regulate the grid, which is essential for scenarios with a high share of renewable energy, is included in the model. RTE has carried out scenarios including the storage required to the French electricity grid [START_REF] Furszyfer | Decarbonizing the ceramics industry: A systematic and critical review of policy options, developments and sociotechnical systems[END_REF]. As only marginal processes are considered here, the main contributor to electricity storage is the battery, in the absence of a significant increase in pumping station storage in the scenarios. Other changes are the increase in demand flexibility, interconnection between countries, the addition of new decarbonised thermal installations and storage in electric cars. Only the impact of batteries is considered in this work. This choice was made because electricity storage is the main type of storage in the scenarios and is the only type of regulation which has a direct impact on national electricity. Others flexibility factors like flexibility or interconnection have an impact that is accounted elsewhere. Assuming a daily storage cycle and a discharge time of a few hours, an energy-to-power ratio of 10 and a life time of 10 years can be assumed [START_REF]Handbook on Battery Energy Storage System[END_REF]. Therefore, with a density of 300 Wh/kg, a ratio of battery mass per unit of electric energy can be calculated as presented in Tab.

Environmental model description

The environmental assessment is based on a life cycle assessment of the energy systems including energy consumption, refrigerant characteristics, and the heat production technology. This analysis is performed using the Ecoinvent 3.7.1 LCI database for modelling background processes [START_REF] Wernet | The ecoinvent database version 3 (part I): overview and methodology[END_REF], based on the marginal process defined in the assessment framework. The life cycle impact assessment methodology used to assess the environmental impact is the EF 3.0 methodology [START_REF]Supporting information to the characterisation factors of recommended EF Life Cycle Impact Assessment methods: new methods and differences with ILCD[END_REF]. The assessment boundaries are set from cradle-tograve including transport and conversion losses for the life cycle of energy and the equipment life cycle with the exception of materials needed to adapt the system to the new technology like the connections to the existing current grid. For the refrigerant, a charge by power unit ratio of 2.0 kg/kW [START_REF] Metz | Safeguarding the Ozone Layer and the Global Climate System: Issues Related to Hydrofluorocarbons and Perfluorocarbons[END_REF], an annual leakage rate of 5 % [START_REF] Metz | Safeguarding the Ozone Layer and the Global Climate System: Issues Related to Hydrofluorocarbons and Perfluorocarbons[END_REF] and an end of life leakage rate of 15 % [START_REF] Yang | The life cycle climate performance evaluation of low-GWP refrigerants for domestic heat pumps[END_REF] are considered.

Sustainability assessment

The life cycle assessment is expanded to include the sustainability assessments of the proposed transition scenarios. Sustainable limits are based on the carrying capacities of the whole Earth system in the face of various anthropogenic pressures based on planetary boundaries and extended with human health [START_REF]Life Cycle Assessment[END_REF]. Sustainable levels are defined using equation ( 5) on the basis of the current impact, which is corrected with a reduction factor from Vargas et al. [START_REF] Vargas-Gonzalez | Operational Life Cycle Impact Assessment weighting factors based on Planetary Boundaries: Applied to cosmetic products[END_REF].

𝑆𝑙 𝑥 = 𝐼 𝐵𝐴𝑈,𝑥 𝑅𝑓 𝑥 ( 5
)
Where Slx is the sustainable level of the studied entity for environmental impact x, IBAU,x the impact of the studied entity for environmental impact x using BAU as a reference, Rfx the reduction factor presented in Tab. 4 to reach a sustainable level of environmental impact x. Ix units depend on the category x. A sustainable level of less than 1 means that the impact is within the threshold (planetary boundary or human health damage threshold) and therefore is considered sustainable. For example a reduction factor of 9.4 is estimated by Vargas et al. [START_REF] Vargas-Gonzalez | Operational Life Cycle Impact Assessment weighting factors based on Planetary Boundaries: Applied to cosmetic products[END_REF] for climate change impacts. This value can be compared to the work by Bjørn and Hauschild [START_REF] Bjørn | Introducing carrying capacity-based normalisation in LCA: framework and development of references at midpoint level[END_REF] who estimated the steady-state emissions of greenhouse gases to stay below 2°C at 6.8 Gt-CO2eq/yr, hence a reduction factor of 8.2 compared to the EF 3.0 reference value [START_REF]Supporting information to the characterisation factors of recommended EF Life Cycle Impact Assessment methods: new methods and differences with ILCD[END_REF]. The sustainability ratio (Srx) defined in eq. ( 6) is use to assess the gap between the process and the sustainable level for each impact category.

𝑆𝑟 𝑥 = 𝐼 𝑥 𝑆𝑙 𝑥 [START_REF] Furszyfer | Decarbonizing the glass industry: A critical and systematic review of developments, sociotechnical systems and policy options[END_REF] Where Slx is the sustainable level defined in eq. ( 5) and Ix the contribution of BAU, Lo or Hi scenarios for impact category x. A value of less than 1 implies that the level of the evaluated solution is sustainable and the lower the value, the greater the margin. Conversely, a value greater than 1 implies a level higher than the level defined as sustainable.

Tab. [START_REF] Obrist | Long-term energy efficiency and decarbonization trajectories for the Swiss pulp and paper industry[END_REF]

Share of the contribution in the global economy

To put food industry emissions into perspective with respect to global emissions, a downscaling methodology is used to compare the emission of the different scenarios with the current global environmental impact. There are many principles of downscaling, i.e. moving from global to process level impacts [START_REF] Ryberg | Downscaling the planetary boundaries in absolute environmental sustainability assessments -A review[END_REF], [START_REF] Bjørn | Review of life-cycle based methods for absolute environmental sustainability assessment and their applications[END_REF]. The sharing principle used in this work is the economic value added (EVA), which has been the most used sharing principle until now [START_REF] Ryberg | Downscaling the planetary boundaries in absolute environmental sustainability assessments -A review[END_REF]. Although many biases may distort this coupling, this approximation allows the share of environmental impact for each industry to be estimated. As these data are readily available, it makes the study reproducible and transferable to other sectors. To define whether a process has a significant impact within an impact category, we use eq. ( 7). The economic share of global value added (GVA) of this process is compared to its share of emissions for that impact category relative to global emissions for that same category. The higher the share of environmental impact in relation to the share of GVA, the more significant the contribution of the sector studied to this impact category. On the contrary, when the value is low, it means that the sector is not a contributor to the global impact.

𝐶𝑙 𝑥 = 𝐼 𝑥 𝐼 𝑡𝑜𝑡 . 𝐸𝑉𝐴 𝑡𝑜𝑡 𝐸𝑉𝐴 𝑥 ( 7)
Where Clx is the contribution level of the studied entity for the environmental impact x, Ix/Itot the share of impact of the studied perimeter for environmental impact x in relation to total emissions (%), EVAx/EVAtot is the share of economic value added of the studied perimeter for category x in relation to total economic value added (%). Data for Denmark are from [START_REF]Production and generation of income (117-grouping) by transaction, industry and price unit[END_REF], data for France are from [START_REF] Agreste | Consommation d'énergie dans les industries agroalimentaires et les scieries en 2019[END_REF] and the world data are from [START_REF]Gross value added at basic prices (GVA)[END_REF]. As the Danish GVA value includes several "Production of compound feed", " Production of Sugar" and " Other food industry", the distribution of the GVA is made in proportion to the energy consumption between these 3 sectors. A value of 1 represents a share of emissions equivalent to the share of GVA created, implying a contribution to GVA aligned with the process impact. On the contrary, a low or high value implies an environmental contribution that is not aligned with the value created, which leads to an insignificant or predominant environmental contribution of the process on the impact category respectively.

Results and discussion

Environmental impact analysis

As presented using logarithmic scale in Fig. 3(a) for France and Fig. 3(b) for Denmark, the two electrification scenarios can be compared to the sustainable level, and it can be observed that the "climate change" indicator is within the sustainable threshold for both countries. However, the reduction of the climate change indicator through electrification leads to the unsustainability of some other categories concerning human health or resource use. The assessment of these indicators shows that electrification reduces the impact of 7 indicators for France and 8 for Denmark, but only reaches the sustainable threshold for the indicators "climate change" and "resource use, fossils" for Denmark. On the other hand, 9 impact categories show higher impacts for France and 8 for Denmark. Of these, two impact categories pertaining to chemicals toxicity impacting human health and ecosystems become unsustainable as well as the water use indicator for Denmark.

Fig. 3 -Results of the different impact categories for the other food industry scenarios for (a) France and (b)

Denmark using logarithmic scale. The level defined as sustainable is represented with a green line for each impact category; the current share of GVA (

𝐸𝑉𝐴 𝑥 𝐸𝑉𝐴 𝑡𝑜𝑡
) value is represented with the blue line.

The main differences between France and Denmark for the studied sector after electrification stem from the electricity mix, due to the presence of nuclear power in France and biomass in Denmark. This leads to an unsustainable contribution of the "ionising radiation" impact, which is almost zero in Denmark, and of the "resource use fossil" impact in France, while the Danish electricity mix achieves the targets. At the same time unsustainable contributions are more critical for Denmark than for France for the impact categories "land use" and "particulate matter". The methodology used has two main limitations: (i) for the category "resource use, minerals and metals" recycling is not considered in the definition of the [START_REF] Owsianiak | Identification of dissipative emissions for improved assessment of metal resources in life cycle assessment[END_REF], [START_REF] Schulze | Abiotic resource use in life cycle impact assessment-Part II -Linking perspectives and modelling concepts[END_REF]. The sustainable level is therefore underestimated because it only considers the reserve present in the ground; (ii) the reduction factor is based on global level emissions and these factors are applied to BAU impacts. Therefore, for sectors with a (a)

(b)

low contribution, the reduction target may not be appropriate, e.g. gas production for land use indicator is probably the most efficient solution, so it is not possible to reduce for equal consumption.

In order to assess the environmental impact of a solution, it is interesting to go beyond the study of the sustainable level itself by integrating the share of the contribution of the process in relation to the global economy. Fig. 4 evaluates the contribution of environmental impact for the category "other food industry" for France and Denmark in 2 electrification configurations, namely BAU and Lo. It can be noted that the differences between Lo and Hi scenarios remain limited for this industry category.

Four trends emerge from Figure 4: (i) The low-left zone where the impacts are at (or have reached) a sustainable level and are associated with an impact share below the GVA share of the sector, e.g. "ozone depletion". The impact categories in this zone are sustainable and the considered sector is not a major contributor for these impact categories in the global economy and is hence of less importance. Even if this sector grows in the global economy, it is not expected to have a major significance on this impact category. (ii) The bottom-right zone where the impacts are at (or have reached) a sustainable level and are associated with an impact share greater than the GVA share of the sector. Even if these categories are sustainable, their relative importance in the global economy implies to consider them. While no impact category is

Sustainability

Contribution present in this zone for France, some can be found for Denmark because the importance of the agri-food sector has a larger share of GVA. (iii) The upper left-hand area is for impacts that are unsustainable, but where the impact share is less than the economic share of the sector. While this impact must be considered, any change (growth or decline) in this economic sector is not expected to lead to a major change in the compliance with global sustainability thresholds for this environmental impact. Water use for both country and land use for France are in this configuration. (iv) The impact categories on the top-right have an unsustainable level and a share of impact higher than the economic share of the sector. Categories such as "resource use, minerals and metals" are the most critical as they are not sustainable while the sector in question is proportionally very impactful. For Denmark, land use is also in this case due to the high share of biomass in the electricity mix.

Fig. 4 shows that there is not a general improvement in all environmental impact categories related to electrification: some indicators reflect impact decreases while others demonstrate impact increases. Therefore, to achieve GHG emission reduction targets, trade-offs have to be made with other environmental indicators such as land use or mineral and metal use. This impact/contribution classification highlights which categories need to be considered more specifically. In particular, impact categories located in the top-right zone are estimated to be within unsustainable ranges and may limit the growth of one sector and/or require a trade-off with other sectors of the economy to achieve economy-wide environmental sustainability.

Influence of electricity grid mix

A sensitivity analysis was carried out on the French electricity grid mix in order to study its influence on the results (see Figure 5). Results show a large variability in the sensitivity of the impact indicator scores to the electricity grid mix and in particular to the share of nuclear power and renewable energy sources (see also Methods, Section Erreur ! Source du renvoi introuvable.; share of biomass not considered here because not reported as predominant source in the French scenarios). Regarding the use of mineral resources and metals, which is associated with the largest impact share, the electricity mix may play a predominant role due to a strong increase in several impacts when assuming a completely renewable energy mix resulting from the use of metals in the manufacture of renewable energy technologies, e.g. wind power, batteries, etc. It should be noted for this specific point that, as for the previous part, recycling is not considered in the method, which overestimates the share of this impact category. This means, however, that there will be a large quantity of metals available in this sector and that it is essential to make progress on recycling these materials. The second indicator with a high degree of uncertainty is the use of fossil resources, including uranium ore, which leads to an increase in this impact if nuclear power is used.

The impact categories "climate change" and "resource use, fossils" are found to be the only impact categories where the impact scores may exceed or remain below the sustainability thresholds depending on the electricity mix. For the use of fossil resources, the shift to a 100 % renewable mix enables to reach a sustainable level. This trend could be seen in Fig. 5 (a) with the sustainable level represented with a green line. The variability, which can be defined as the difference between the maximum value and the minimum value (upper and lower bounds in Fig. 5) divided by the reference value, shows a high magnitude for this indicator with a value of 219 % due to the low use of fossils for the 100 % renewable mix and a high use for the mix with a high nuclear share. For the climate change indicator, however, the electricity mix with 100 % renewable exceeds this threshold as shown in Fig. 5 (b). For the climate change indicator, the variability remains limited with a value of 63 %. This low variability is explained by the fact that both solutions result from low GHG emissions strategy.

Conclusions and recommendations

This study proposes a methodology for analysing the environmental impacts of an energy transformation with respect to sustainable levels based on planetary limits and the impact on human health. The methodology applied to the case of the electrification of the food industry assesses environmental externalities that are expected to happen when reducing the GHG emission to achieved targets. These environmental counterparts exist for both French electricity grid mix based on a renewable and nuclear mix as well as for the Danish mix composed of renewable and biomass energy sources. Electrification reduces the environmental impacts of 7 out of 16 categories studied in France and 8 in Denmark. Of these categories, climate change is the only one that remains potentially below sustainable levels. At the same time, electrification will increase the impact of several impact categories and notably some categories related to human health which might then exceed their thresholds.

The study of sustainability thresholds is not sufficient to show the impact of the transformation on the global system. To assess the overall impact of a system and its future evolution, it is important to evaluate its contribution from a global perspective. The greater the contribution of a sector to an impact category, the greater the impact of reducing it at the global level. In the study, we have identified and classified impact categories into 4 groups based on their threshold crossing and relative contribution. This classification indicates that for the industry studied, there is a large disparity between the different impact categories. This suggests that a breakdown using another indicator than GVA might be more relevant to allow for the assessment of the relative critical impact categories (i.e. strongly above or below the threshold) of each industry.

When changing the energy consumption of an industry, the identification of the most sensitive impact categories can help in the decision-making process. In order to plan a global transformation of industrial energy systems, it would therefore be necessary to assess the environmental externalities of each process within a broader perspective, accounting for sectoral interactions. Once these externalities have been assessed, the ability of industrial systems to remain within the planetary boundaries and below acceptable human health damage thresholds could be evaluated in terms of technical and political choices.

Fig. 1 -

 1 Fig. 1 -Danish food industry energy consumption by source

Fig. 4 -

 4 Fig. 4 -Level of environmental impact category and contribution of the environmental indicators studied for the scenarios (a) BAU-France, (b) BAU-Denmark, (c) Lo-France, (d) Lo-Denmark

Fig. 5 -

 5 Fig. 5 -Environmental impact sensitivity to different electricity generation scenarios for France; (a) full scale (b) focus on lower value. The green lines indicate the sustainable level for climate change (b) and "resource use, fossils" impact categories (a).

Acknowledgement:

  This work was supported by the French Ministry of Higher Education and Research.

[°C] Direct electrical heating [%] Other fuel efficiency (gas, oil or coal) [%]

	≤ 120	0	0
	120 -380	10	15
	≥ 380	25	30

  3.

	Tab. 3 -Electricity storage assumptions with batteries for France
		Battery storage	Battery mass /energy
		capacity (GW)	(kg/GWh)
	Sc. N03	1	0.05
	Sc. N1	9	0.45
	Sc. M0	26	1.22

  -Reduction factor for all environmental categories in the EF 3.0 methodology

	change	Ozone depletion	Ionising radiation	Photochemical ozone	formation	Particulate matter	Human toxicity, non-cancer	Human toxicity, cancer	Acidification	Eutrophication, freshwater	Eutrophication, marine	Eutrophication, terrestrial	Ecotoxicity, freshwater	Land use	Water use	Resource use, fossils	Resource use, minerals and metals
	9.36	0.28 0.01 0.54 5.97 0.90 0.26 0.30 3.22	-a 0.30 0.85 9.33 0.51 4.08 4.08

a Value not given in Vargas et al.

[START_REF] Vargas-Gonzalez | Operational Life Cycle Impact Assessment weighting factors based on Planetary Boundaries: Applied to cosmetic products[END_REF]