Svitlana Nitiema-Yefanova

Romain Richard

Sophie Thiebaud-Roux

Brice Bouyssiere

Yvonne L Bonzi-Coulibaly
email: yvonne.bonzi@yahoo.fr.

Rh C N Ebie

Kevin Mozet

Lucie Coniglio
email: lucie.coniglio@univ-lorraine.fr.

Dry Purification by Natural Adsorbents of Ethyl Biodiesels Derived from Nonedible Oils

The purpose of this work is to analyze the efficiency of natural adsorbents (rice husk ash (RHA) versus corn husk ash (CHA)) for the dry purification of ethyl biodiesels obtained by transesterification via homogeneous catalysis of nonedible oils (Balagnites aegyptiaca, Azadirachta indica, and Jatropha curcas). The characterization of RHA and CHA was achieved by N 2 adsorption/Brunauer-Emmett-Teller analysis and by scanning electron spectroscopy with microanalysis by energy dispersive X-ray spectroscopy. The quality of the three biodiesels, before and after dry treatment on adsorbent, was evaluated by various analytical methods ( 1 H nuclear magnetic resonance, gas chromatography with a flame ionization detector, Karl Fischer titration, and inductively coupled plasma-atomic emission spectroscopy). Several operating conditions (presence of activated carbon in the ashes, temperature, contact time, and number of treatment cycles) were tested in order to define the best procedure. RHA combined with the selected procedure showed very satisfactory results for removal of impurities from the produced biodiesels (residual glycerides, free glycerin, water, catalyst, and metals introduced during the oil extraction) and thus may be an alternative to the conventional wet purification process (acidic water washing).

INTRODUCTION

Aiming for a sustainable energy supply and climate change mitigation, production of biodiesel fuel from nonedible vegetable oils (NEVOs) and bioethanol (derived from biomass residues) is an attractive alternative based on local and renewable use of agricultural resources. [START_REF] Bankovic-Ilic | Biodiesel production from non-edible plant oils[END_REF][START_REF] Brunschwig | Use of bioethanol for biodiesel production[END_REF][START_REF] Karmakar | Biodiesel production from neem towards feedstock diversification: Indian perspective[END_REF] Among the NEVOs, extensive attention has been devoted to Jatropha curcas (JC) during the past few years, [START_REF] Pandey | Jatropha curcas: A potential biofuel plant for sustainable environmental development[END_REF] but recent efforts for diversification of the feedstocks to secure biodiversity has directed scientific research toward oilseeds such as Balanites aegyptiaca (BA, Desert date), Azadirachta indica (AI, Neem), and Pongamia pinnata (PP, Pungam), etc. [START_REF] Karmakar | Biodiesel production from neem towards feedstock diversification: Indian perspective[END_REF][START_REF] Chapagain | Desert date (Balanites aegyptiaca) as an arid lands sustainable bioresource for biodiesel[END_REF] However, some impurities (such as free fatty acids (FFAs) naturally present in the NEVOs, especially water present both in bioethanol and the NEVOs) limit the use of these feedstocks in large-scale biodiesel production. Processes based on homogeneous catalysts (mainly alkali ones) are the most widely used for industrial biodiesel production, [START_REF] Leung | A review on biodiesel production using catalyzed transesterification[END_REF] despite important water consumption and catalyst loss in aqueous effluents during the purification stage. At laboratory scale, adsorptive treatments with Magnesol or rice husk ash (RHA) were reported to replace efficiently the wet-purification stage of biodiesel, [START_REF] Berrios | Comparison of purification methods for biodiesel[END_REF][START_REF] Sabudak | Biodiesel production from waste frying oils and its quality control[END_REF][START_REF] Berrios | Purification of biodiesel from used cooking oils[END_REF][START_REF] Stamenkovic | The production of biodiesel from vegetable oils by ethanolysis: Current state and perspectives[END_REF][START_REF] Schmitt Faccini | Dry washing in biodiesel purification: A comparative study of adsorbents[END_REF][START_REF] Manique | Rice husk ash as an adsorbent for purifying biodiesel from waste frying oil[END_REF][START_REF] Saengprachum | Glycerin removal in biodiesel purification process by adsorbent from rice husk[END_REF] and would therefore be attractive alternatives. Furthermore, the dry-purification method offers other benefits such as using local agricultural solid waste, [START_REF] Manique | Rice husk ash as an adsorbent for purifying biodiesel from waste frying oil[END_REF][START_REF] Saengprachum | Glycerin removal in biodiesel purification process by adsorbent from rice husk[END_REF][START_REF] Kratzeisen | Suitability of Jatropha seed shells as fuel for small-scale combustion units[END_REF] making the process even more environmentally friendly, while reducing substantially the total production time (as water-washing requires two treatment cycles and one centrifugation stage, which are long processes). [START_REF] Schmitt Faccini | Dry washing in biodiesel purification: A comparative study of adsorbents[END_REF] In accordance with the biorefinery concept inciting use of the entire resources, several authors illustrated the feasibility of using Jatropha husk activated carbon [START_REF] Namasivayam | Removal of anions, heavy metals, organics and dyes from water by adsorption onto a new activated Carbon from Jatropha husk, an agro-industrial solid waste[END_REF] or activated Neem leaf [START_REF] Ahmaruzzaman | Activated Neem Leaf: A Novel Adsorbent for the Removal of Phenol, 4-Nitrophenol, and 4-Chlorophenol from Aqueous Solutions[END_REF] as adsorbent for the removal of toxic pollutants from water (heavy metals [START_REF] Namasivayam | Removal of anions, heavy metals, organics and dyes from water by adsorption onto a new activated Carbon from Jatropha husk, an agro-industrial solid waste[END_REF] and phenolic compounds [START_REF] Ahmaruzzaman | Activated Neem Leaf: A Novel Adsorbent for the Removal of Phenol, 4-Nitrophenol, and 4-Chlorophenol from Aqueous Solutions[END_REF] ). RHA was evaluated with successful results as adsorbent for reducing FFAs of crude vegetable oils. [START_REF] Yoon | Deacidification effects of rice hullbased adsorbents as affected by thermal and acid treatment[END_REF] In another scope of applications, ashes from palm oil mill boilers [START_REF] Ho | Development and characterization of novel heterogeneous palm oil mill boiler ashbased catalysts for biodiesel production[END_REF][START_REF] Ng | Waste-to-wealth: Green potential from palm biomass in Malaysia[END_REF] or of rice husk [START_REF] Chen | Rice husk ash as a catalyst precursor for biodiesel production[END_REF] have been used as support of alkali heterogeneous catalyst for biodiesel production. Nevertheless, to the knowledge of the authors, no dry-purification test has been carried out for biodiesels produced by homogeneous acid-catalyzed ethanolysis or for removing biodiesel contaminants with corn husk ash (CHA) as adsorbent. In this work (exclusively based on experimental approach), RHA and CHA performances as natural adsorbents are tested for the dry purification of biodiesels obtained by ethanolysis of three NEVOs via homogeneous catalysis (with KOH for BA and AI oils and H 2 SO 4 for JC oils). The dry treatment procedure and the possibility of reusing the waste ashes obtained after biodiesel purification will also be assessed. Efficiency of RHA and CHA in the removal of specific impurities (glycerides, free glycerin, water, catalyst, and metals) without introducing supplementary contaminants (particularly Si, P, and Mg) will be evaluated via the characterization of biodiesel samples obtained before and after treatment. Structure and composition of RHA and CHA (before and after biodiesel purification, with characterization of the latter) will be investigated to provide guidance as to possible interpretation of the behavior observed for these materials. With the global results, it is intended to propose the optimal adsorbent material with the suitable treatment procedure.

METHODS

2.1. Materials. Solvents and other reagents were of analytical grade and were purchased with the chromatographic standards from Merck, Acros Organics, or Sigma-Aldrich. In addition to the biodiesels (i.e., fatty acid ethyl esters (FAEEs)) from NEVOs (BAEEs, AIEEs, and JCEEs), rapeseed ethyl esters (RSEEs) were also produced to compare the performance of the dry-and wet-purification methods.

2.1.1. Biodiesel Production. The BAEEs and AIEEs were obtained via alkali catalysis (KOH), and the JCEEs were obtained via acid catalysis (H 2 SO 4 ) according to a two-stage procedure based on intermediate addition of glycerol. [START_REF] Nitiema-Yefanova | Ethylic biodiesel production: Evaluation of twostage ethanolysis performances[END_REF] The RSEEs were produced in the same way as the BAEEs and the AIEEs. Alkali (acid) catalysis was operated at 35 °C (78 °C), with an ethanol to oil molar ratio equal to 8:1 (30:1), a catalyst concentration of 1 wt % (5 wt %) based on the initial mass of oil, and a reaction time of 50 min (26 h) while the addition of glycerol marking the start of the second step was carried out after 30 min (23 h) of reaction. The ester contents of the four FAEE products (BAEE, AIEE, JCEE, and RSEE) are respectively as follows: 97.4, 89.5, 85.7, and 92.0 wt %. The initial contents of contaminants in the FAEE products (unreacted glycerides, free glycerin, residual catalyst, water, FFAs, soaps, and metals) will be given when evaluating the dry-purification method in Results and Discussion.

2.1.2. RHA and CHA Production. Rice hulls and corn husks were collected from local production units (Burkina Faso), finely ground, then placed in crucibles made of porcelain covered with aluminum foil, and carbonized in a muffle furnace (MF4 Hermann Moritz Regulateur 2068, France). The operating temperature was set to 500 °C, as recommended in the literature to obtain ashes showing optimal adsorption properties. [START_REF] Yoon | Deacidification effects of rice hullbased adsorbents as affected by thermal and acid treatment[END_REF][START_REF] Chang | Rice hull ash structure and bleaching performance produced by ashing at various times and temperatures. JAOCS[END_REF][START_REF] Kim | Comparison of the adsorbent performance between rice hull ash and rice hull silica gel according to their structural differences[END_REF] The recommended ashing time of 10 h [START_REF] Yoon | Deacidification effects of rice hullbased adsorbents as affected by thermal and acid treatment[END_REF][START_REF] Kim | Comparison of the adsorbent performance between rice hull ash and rice hull silica gel according to their structural differences[END_REF] was reduced in this work to 8 h for practical reasons. After carbonization, the ashes were cooled to room temperature in a desiccator for 8 h minimum. Samples were placed in plastic screw-cap bottles and stored at room temperature.

2.2. RHA and CHA Characterization toward "Structure-Adsorption Efficiency" Relationship. Details of the equipment and operating conditions used to relate the efficiency of the potential adsorbent to its structural features are given in Table 1. Morphology was assessed by scanning electron microscopy (SEM), with elemental chemical composition informed by coupling SEM with microanalysis by energy dispersive X-ray spectroscopy (EDS). Surface area and porosity were evaluated through N 2 adsorption isotherms using Brunauer-Emmett-Teller (BET) method.

2.3. Biodiesel Characterization for Evaluation of the Purification Methods. Details of the equipment and operating conditions used to evaluate the performance of the dry-purification methods (adsorbent type and treatment procedure) are listed in Table 1. FAEE samples obtained before and after dry purification on RHA and CHA were characterized in terms of triacylglycerides (TG), diacylglycerides (DG), monoacylglycerides (MG), free glycerin, and ester contents by gas chromatography coupled with a flame ionization detector (GC-FID), in terms of water content by the volumetric Karl Fischer method, and in terms of potassium and heavy metals (resulting from the catalyst used and the oil extraction stage) by inductively coupled plasma atomic emission spectroscopy (ICP-AES). The comparative performance of the purification treatments with acidified water and with RHA was achieved on the basis of the soap content determined by an acidbase titration method. [START_REF] Van Gerpen | Biodiesel analytical methods[END_REF] 2.4. Biodiesel Purification. Dry purification via the natural adsorbents (RHA and CHA) was evaluated with the FAEEs obtained from the three NEVOs (BAEEs, AIEEs, and JCEEs). The comparative performance of the classical wet purification via an acid solution (H 3 PO 4 ) versus the dry purification via a natural adsorbent (RHA) was carried out with the FAEEs obtained from rapeseed oil (RSEEs). Two concentrations in H 3 PO 4 (1 and 5 wt % in distilled water 29 ) were tested.

2.4.1. Wet Purification with Acidic Water. Acid solution (30 wt % on the basis of the initial weight of FAEEs) was sprayed on the surface of an unpurified RSEE sample without mixing. The resulting mixture was then transferred in a separating funnel. After phase separation and removal of the aqueous phase (lower layer), the remaining FAEE product was washed twice identically. The washed FAEE product was then dried over anhydrous magnesium sulfate and next filtered off. The whole procedure was carried out at ambient temperature.

2.4.2. Dry Purification with RHA/CHA and Treatment Procedure. The dry-purification method proposed in batch mode by Manique et al. [START_REF] Manique | Rice husk ash as an adsorbent for purifying biodiesel from waste frying oil[END_REF] was selected as the "reference method" (one-stage treatment with 4 wt % RHA in the unpurified FAEE sample, stirred for 20 min and heated at 65 °C). In an attempt to optimize the treatment procedure, different values of the key variables were tested. Thus, dry purification was conducted in one or two stages (treatment cycles with freshly produced ashes as described in section 2.1.2 and intermediate filtration of the FAEE sample) with stirring by combining different processing temperatures (65 and 20 °C), purifying agents (RHA and CHA), and contact times between the purifying agent and the FAEE product to be purified (20 and 5 min). The possibility of reusing the ashes after FAEE purification has also been considered in the case of a dual treatment cycle. Nevertheless, unlike Manique et al., [START_REF] Manique | Rice husk ash as an adsorbent for purifying biodiesel from waste frying oil[END_REF] the same concentration of purifying agent was adopted for all tests (4 wt % was shown to be the optimal value by the same authors).

At the end of the required contact time, the purified FAEE product was filtered under vacuum through a Buchner funnel lined with filter paper and then stored for later analyses in a refrigerated (4 °C) and dry place away from direct sunlight.

In the following text, the treatment carried out at 20 °C during 5 min contact time will be referred as the "flash method".

RESULTS AND DISCUSSION

The 1 H NMR spectra of each of the three FAEE products before and after dry purification (Figure S.I.1, Supporting Information) were so similar that this method could not be used to evaluate the performance of the process (probably because of the high degree of TG conversion). All experiments and analyses were conducted in duplicate (or further in case of disagreement in the measurements). From each set of duplicates, an average value was then calculated to yield the given data.

3.1. Yields of the Incineration Process and Considered Ash Classes. Regarding rice husk, the mean yield of the incineration process (defined as the average value of the percent ratio of the mass of recovered ashes to the mass of initial rice husk) was 22 wt %. Nevertheless, incomplete carbonization of the rice husk led to a heterogeneous mixture consisting of light-gray, dark-gray, and black ashes (classification made on the basis of ash color), with respective mass fractions of 43, 10, and 47 wt %. Given the small recovered fraction of dark-gray ashes, these were mixed with the black ones to obtain a single batch of purifying agent containing activated carbon (on the basis of the ash color and results obtained in the literature [START_REF] Namasivayam | Removal of anions, heavy metals, organics and dyes from water by adsorption onto a new activated Carbon from Jatropha husk, an agro-industrial solid waste[END_REF] ). Thereby, only two classes of RHA respectively named as RHA-LG (for the light-gray ashes) and RHA-GB (for the grayblack ashes) have been considered. Furthermore, incomplete carbonization as observed here for the rice husk clearly shows that the applied operating conditions, particularly the temperature of carbonation (500 °C), are not adequate and should be optimized for the specific materials used.

By contrast, carbonization of corn husk conducted in the same conditions as those selected to produce the RHA has led to an apparently homogeneous mixture of finer ashes (named as CHA) and with a very low mean yield of around 1 wt %.

Incineration yields of used RHA (recovered after dry purification of the BAEEs) were around 41 wt % when the ashes had been used for a single treatment of esters but 26 wt % when the ashes had been used for a dual treatment of esters (instead of (41 wt %) 2 = 17 wt %), showing a decrease in adsorptive capacity of the used ashes. Furthermore, the resulting ashes became very similar to the RHA-LG (confirming that the initial dark-gray and black color ashes were due to incomplete carbonization). Regarding the used CHA (recovered after dry purification of the BAEEs), their incineration yield was around 57 wt %, revealing that this class of ashes has a significantly lower but not negligible adsorptive capacity.

For all of the preceding incineration yields, standard deviation was inferior to 1 wt %.

3.2. SEM/EDS Analysis of RHA and CHA. In accordance with the literature, [START_REF] Manique | Rice husk ash as an adsorbent for purifying biodiesel from waste frying oil[END_REF] the SEM/EDS analyses show that RHA and CHA are not homogeneous in morphology and composition (Figures 1 and2). Although both types of ashes globally contain a lot of Si, but K and P in equal proportion, the outer epidermis similar to a corncob is richer in Si while the other regions of the samples (inner part and cross-sections) are porous and richer in K, P, and Mg. Nevertheless, RHA (whatever the ash class, -LG or -DG) comprise a higher percentage of Si than CHA (Figure 1b vs Figure 2b 1 ).

Furthermore, SEM analyses of used RHA and used CHA obtained after one FAEE purification treatment followed by an additional carbonization showed differences in morphology. The same observation appeared for the used RHA as a function of the catalyst selected during ethanolysis (Figure 3). While the used RHA maintained the same morphology in the case of FAEEs obtained by alkali catalysis (Figure 3a,b), used CHA samples lost their corncob structure to become powder (Figure 2c). On the other hand, in the case of FAEEs produced via acid-catalyzed ethanolysis, larger pores appeared in the cross-sections of used RHA, revealing a predominantly macroporous structure that promotes the diffusion of species and their adsorption in this region (Figure 3a,c).

3.3. Textural Features of RHA and CHA from BET Analysis. For a high efficiency in the removal of contaminants, an adsorbent requires a porous structure with a high specific area. From Figure 4 showing the N 2 adsorption curves of RHAs (by distinguishing RHA-LG and RHA-GB) and CHA, it can be observed that the three ash classes have different adsorption profiles.

Although both classes of RHA show predominantly adsorption in high P/P 0 values (above 0.9), which is characteristic of a structure with large mesopores and macropores (of 50 nm diameter or more), [START_REF] Manique | Rice husk ash as an adsorbent for purifying biodiesel from waste frying oil[END_REF] RHA-GB can adsorb twice more matter than RHA-LG for the lowest P/P 0 values, indicating specifically in RHA-GB the occurrence of a higher fraction of micropores (with diameters lower than 2 nm).

By contrast, the CHA adsorption curve shows an extremely flat profile tending to zero, suggesting poor efficiency as adsorbent of this class of ashes (in agreement with observations of section 3.1).

From the N 2 adsorption isotherms, specific area and pore volume for the three classes of ashes were determined (Table 2). It is important to highlight that although both classes of RHA present quite close pore volumes, specific area of RHA-GB is almost twice as high. This result is in accordance with a higher fraction of micropores and a similar fraction of macropores observed for RHA-GB in comparison with RHA-LG (Figure 2). Actually, the slightly higher pore volume for RHA-GB compared to RHA-LG is probably due to this higher fraction of micropores, even though it corresponds globally to a low percentage of pore volume for the ash. RHA-GB samples should therefore have a better efficiency as adsorbent, probably due to their content of activated coal (section 3.1), which having low-volume pores increases thus the specific area of this class of ashes. By contrast, CHA presents a very low specific area, which is characteristic of a compact structure with a very low pore volume. Thus, this class of ashes should not be a suitable adsorbent for biodiesel purification. 3. The initial soap content of RSEEs was 527 mg/kg. By using a 5 wt % H 3 PO 4 solution, no soap residue could be detected in the RSEEs as soon as the first stage of acidic water washing was conducted. Nevertheless, a stable emulsion occurred during this treatment, leading to a difficult RSEEwater phase separation, and, thus, a decrease in the ester yield. The same trend was already observed with phosphorus catalyst, suggesting the use of lower concentrations. [START_REF] Sharma | A hybrid feedstock for a very efficient preparation of biodiesel[END_REF] Thereby, wet purification of RSEEs was conducted with a more dilute acidic solution (1 wt % H 3 PO 4 ), leading to a significant decrease in the soap content, but with an almost halved global yield in esters due to loss of matter via the two successive washing steps.

By contrast, the dry purification of RSEEs over RHA yielded better results than the water-washing method with H 3 PO 4 (solutions at 1 and 5 wt %). In addition to avoiding difficult phase separation, RHA showed better performance in removing soaps, with higher purification yield in FAEEs. Also, a second dry-purification stage over RHA (dual treatment "flash") reduced the amount of soaps below the detection limit of the quantification method.

Finally, it should be mentioned that RHA-LG and -GB had almost equivalent adsorptive capacities (yield of biodiesel dry purification: 92 and 93 wt % for a single ester treatment and 88 and 87 wt % for a dual ester treatment; Table S.I.1 in the Supporting Information).

3.4.2. Dry Purification, Adsorbent Type, and Treatment Procedure. Characterization results of the three FAEE products investigated in this work (BAEE, AIEE, and JCEE) before and after treatment are shown in Tables 4 and5 for all of the drypurification methods tested (involving different adsorbents with different treatment procedures). As mentioned previously, this characterization was achieved in terms of key component contents, i.e., esters and contaminants, the latter comprising molecules different in shape and size (TG, DG, MG, free glycerin, total glycerin, and water) as well as chemical elements (Si, K, S, Ca, Mg, Fe, and P). Also, efficiency of the dry-purification treatments was assessed as a function of the removal percentage of each contaminant calculated by the following equation:

η =×-xx x 100 ( )/ c f0 0 (1)
where η c is the efficiency of the dry-purification treatment and x 0 and x f are the contents of each contaminant before and after treatment, respectively. This class of results was also depicted in Tables 4 and5.

The key observations drawn from these entire results (Tables 4 and5) are discussed in the following text. It is important to note, however, that GC-FID analyses revealed that no residual triacylglycerides were remaining in the unpurified FAEE products, which moreover contained relatively high ester contents (around 97, 90, and 86 wt % for the BAEEs, AIEEs, and JCEEs, respectively). In addition, the observed iron, magnesium, and phosphorus contents in the initial FAEE products were mostly below detection limits of the analytical method used. These features of the initial material to be purified should also be considered as factors impacting the following observations. As it could be expected, results showed that the performance of the dry-purification process varies depending on the purifying agent (RHA-LG, RHA-GB, or CHA), the contaminant, the temperature, the contact time, and the number of cycles applied during treatment. CHA demonstrated a very different adsorptive efficiency according to the contaminants. While this purifying agent was successful in partly removing the organic compounds, very poor results were observed for the chemical elements, particularly K and mostly Si, whose level in the FAEE product increased significantly after treatment. This result can be explained by the SEM image of a sample of used CHA recovered after a purifying treatment and to which a supplemental incineration stage was applied (Figure 2c). The SEM image indeed reveals a radical change in the morphology of the ashes reduced to powder, with a complete destruction of the Si-based structures similar to corncobs. Thereby, CHA cannot be recommended reasonably as adsorbent for dry purification of biodiesel.

RHA-LG showed better efficiency in removing glycerides (DG and MG) than RHA-GB, while this purifying agent was more efficient for adsorbing small molecules such as water. These results are consistent with the SEM/EDS and BET analyses of RHAs, showing a macroporous structure with a higher fraction of micropores in RHA-GB than in RHA-LG.

When considering globally all the variables of the treatment procedure as a function of the contaminants, the efficiency of the dry-purification process is improved when increasing contact time (up to 20 min) and the number of treatment cycles (up to two). One exception is silicon whose level tends to increase with the treatment cycles, due to the ashes releasing gradually this element in the FAEE product (probably because of their high concentration in silicon, Figure 1). Furthermore, increasing the processing time in glass equipment may promote contamination by Si of the material processed. This may also explain the high initial level of Si in the JCEEs which were processed in a borosilicate glass reactor during a much longer reaction time (26 h) than the BAEEs and AIEEs (50 min). Regarding the last key variable of the treatment process, i.e., temperature (the nature of ashes, contact time, and number of treatment cycles have already been assessed previously), various effects were noted as significant according to the considered contaminant. While an increasing temperature (up to 65 °C) promotes retention of large molecules (MG and DG) as well as potassium, the other contaminants (i.e., free glycerin, sulfur, calcium, and particularly water) are removed more efficiently at ambient temperature (20 °C). To illustrate with the case of water as contaminant, the gradient in treatment efficiency over RHA-GB was around -36% by decreasing the operating temperature from 65 to 20 °C and around -25% by increasing the contact time from 5 to 20 min.

Thereby, the most efficient procedure of biodiesel dry purification has been the dual treatment [flash method (20 °C, 5 min) + reference method (65 °C, 20 min)] over RHA-GB. Under these conditions, the dry purification of FAEE products led to a larger reduction in water content: 47% for the JCEEs (obtained via acid catalysis); 38 and 25% respectively for the BAEEs and AIEEs (obtained via alkali catalysis). The levels of free glycerin and DG in the BAEEs and AIEEs were reduced by around 70 and 40%, respectively, but to a lesser extent in the JCEEs, i.e., around 27 and 4%, respectively.

The MG behavior over RHA-GB also appears to depend on the catalysis selected to produce the FAEEs, but more significantly here. Indeed, after the dry treatment over ashes, the MG content decreased in the BAEEs and AIEEs (by 34 and 22 wt %, respectively) but increased in the JCEEs (by 32 wt %). This increase in MG content in JCEEs went hand in hand with a a Efficiency of the dry-purification methods for the focused contaminants is also given in parentheses; the method efficiency was assessed as a function of removal percentage of each contaminant calculated by eq 1. b Standard deviation on esters, free glycerin, MG, DG, and total glycerin (wt %): 0.05. c All indications are limits, except for the ester content giving the maximum value.

supplementary production of esters. Indeed, while the drypurification process led to a reduction in the ester content for the BAEEs and AIEEs despite partial removal of contaminants (probably because of ester retention on the ashes), no reduction in the ester content was observed for the JCEEs. Furthermore, as already noticed in section 3.2, comparison of the SEM images of a sample of virgin RHA-GB with a sample of used RHA-GB (recovered after a purifying treatment of the JCEEs and a supplemental incineration stage) reveals clearly a change in the morphology of the ashes with the appearance of larger size pores in the cross-sections (Figure 3a,c). This phenomenon is not observed with the BAEEs (Figure 3a,b) and is thus due to the content in H 2 SO 4 of the JCEEs. Thereby, all of these results seem to suggest that chemical reactions such as DG ethanolysis to MG and esters occur inside the macropores of RHA-GB, where internal mass transfer resistance is decreased. Thus, RHA-GB seems to act as the support of the residual acid catalyst previously used for the JC oil ethanolysis and contributes to restart the acid activity through an heterogeneous catalysis process during the dry-purification treatment of the JCEEs. [START_REF] Suwannakarn | Biodiesel production from high free fatty acid content feedstocks[END_REF] Furthermore, K and Ca contents in JCEEs after treatment over RHA-GB are superior than they were before treatment, suggesting that the ashes released these chemical elements in the FAEE product during the treatment. Thereby, one might conclude that dry purification over RHA-GB should not be used for biodiesels obtained via acid catalysis.

Despite its demonstrated effectiveness, dry purification with dual treatment of FAEE products over RHA-GB has not been successful in leading to an acceptable range the contaminant levels in order to fulfill the EN 14214 Standard requirements, with the exception of water, potassium and sulfur (sulfur content of AIEEs being a specific case as will be discussed in subsequent text). Regarding silicon, although concentration in this element in most of FAEE products has been efficiently reduced after the purification process, it would be difficult to conclude whether this level is satisfactory or not since no standard-limiting Si content in biodiesel exists to date.

RHA did not succeed in bringing the sulfur level in the AIEEs below the EN 14214 Standard requirements due to the very high concentration of this element in crude AIEE product (before purification treatment). This very high concentration of sulfur (35 times higher than the limit imposed by EN 14214 [START_REF] Atabani | A comprehensive review on biodiesel as an alternative energy resource and its characteristics[END_REF] ) probably results from the presence of volatile organosulfur components in the initial lipidic resource. [START_REF] Balandrin | Biologically active volatile organosulfur compounds from seeds of the Neem tree, Azadirachta indica (Meliaceae)[END_REF][START_REF] Mubarak | Sulphur constituents of Neem seed volatiles: A revision[END_REF] Even higher sulfur concentrations were found by other authors 3 in AI oil (1990 mg/kg) and derived methyl biodiesel (473.8 mg/kg).

Similar performance to the dual treatment [flash method (20 °C, 5 min) + reference method (65 °C, 20 min)] was obtained with a single treatment cycle conducted at ambient temperature (20 °C) by increasing the contact time up 20 min. This procedure requiring no heating is more energy efficient. Moreover, its performance could be improved by operating under the ambient temperatures usually encountered in the original subtropical regions of the NEVOs (35-40 °C).

Whatever the class of RHA (-LG or -DG), ashes reused twice have shown poorer performance in removing contaminants than fresh ashes, except for water (probably because of a longer contact time promoting mainly water adsorption). This result prevents a priori the potential use of RHA as adsorbent in a continuous process by dry purification. a Efficiency of the dry-purification methods for the focused contaminants is also given in parentheses. The treatment efficency was assessed as a function of removal percentage of each contaminant calculated by eq 1; for a contaminant content below or equal to the observed ICP-AES detection limit, this latter value was used to evaluate the treatment efficiency. b Detection limits (mg/kg) of the analytical method used (ICP-AES): 0.2 for Ca, Mg, Fe, and P; 0.4 for Si; 1 for K and S. Maximum standard deviation (mg/kg): 0.01 for Fe; 0.03 for Mg and Ca; 0.06 for Si; 0.3 for K and S (with the exception of AIEEs with sulfur high contents, 1). c All indications are limits. d No specification exists regarding this species. e For (Na + K).

f For (Ca + Mg).

CONCLUSION AND OUTLOOK

Despite a clearly observed adsorptive capacity, CHA proved not to be efficient enough as purifying agent compared to RHA for the application focused on in this work. This different behavior might be ascribed to the difference in structure and composition of the two adsorbents: CHA has a compact structure with a very low specific area and a very low pore volume, while RHA is much richer in Si and has a micro-/macroporous structure with a high specific area. Thereby, the most efficient procedure of biodiesel dry purification was the dual treatment [flash method (20 °C, 5 min) + reference method (65 °C, 20 min)] over rice husk ash containing activated carbon (RHA-GB).

The impurity levels of biodiesels, such as organic materials (residual glycerides and free glycerin) or inorganic materials (water and metals), were significantly reduced, without however fulfilling the EN 14214 Standard requirements for most contaminants. Nevertheless, from the obtained results, better performance could be reached with a one-step procedure conducted in 20 min and at 35-40 °C, corresponding to the usual ambient temperatures of the subtropical regions where the considered NEVOs grow. Besides, the used ash loses efficiency as a purifying agent, preventing its application in a continuous process. However, the previously mentioned conclusions concern only the FAEE products produced by alkali-catalyzed ethanolysis of NEVOs. Indeed, although successful results were obtained in the literature for the removal of FFAs from vegetable oils with RHA, [START_REF] Yoon | Deacidification effects of rice hullbased adsorbents as affected by thermal and acid treatment[END_REF] poor performance was observed in this work for dry purification of JCEEs containing residual acid catalyst (H 2 SO 4 ). In such a case, liquid-liquid extraction with crude glycerol resulting from biodiesel production via alkali catalysis 9 might be a better solution. Moreover, during JCEE dry treatment over RHA-GB, some reactions still enhancing esters formation would occur via an acid heterogeneous catalysis inside the macropores of the adsorbent activated by residual H 2 SO 4 .

Regarding the sulfur content of AIEEs (that dry purification over RHA-GB has not reduced successfully due to the very high initial concentration in this element in the crude AIEE product), it is planned to check the origin both in the initial lipidic resource and in the esters.

Apart from these positive results, dry purification on agricultural solid waste offers various benefits in addition to reducing water needs and aqueous effluent production during biodiesel processing. Indeed, this alternative could also be used to purify biodiesels obtained from other transesterification processes (via heterogeneous catalysis or noncatalytic supercritical route) as it has the potential of removing reaction residues as well as heavy metals resulting from the oil extraction stage or from the use of heterogeneous catalyst. A further option in agreement with the biorefinery concept would be to integrate the matter-heat-electricity cogeneration in the biodiesel production unit. This way, the agricultural solid waste combustion would be used to generate heat and power required in the unit operation, [START_REF] Pandey | Jatropha curcas: A potential biofuel plant for sustainable environmental development[END_REF][START_REF] Kratzeisen | Suitability of Jatropha seed shells as fuel for small-scale combustion units[END_REF][START_REF] Lim | A review on utilization of biomass from rice industry as a source of renewable energy[END_REF][START_REF] Luiz De Oliveira | Characterization and mapping of waste from coffee and eucalyptus production in Brazil for thermochemical conversion of energy via gasification[END_REF] while recovering combustion products (ash) for the purification stage (as natural adsorbent). Ultimately, used RHA-GB containing low amounts of metals could be recycled as a soil corrective [START_REF] Manique | Rice husk ash as an adsorbent for purifying biodiesel from waste frying oil[END_REF] due to its content of biodegradable organic matter (biodiesel, free glycerin, and residual glycerides) and potassium (when used as catalyst).

■ ASSOCIATED CONTENT

Figure 1 .

 1 Figure 1. SEM/EDS analyses of outer epidermis of a virgin RHA-GB sample (secondary electrons with gold-palladium coating): image (a) and EDS spectrum (b).

Figure 2 .

 2 Figure 2. SEM/EDS analyses of CHA (secondary electrons with gold-palladium coating): virgin CHA images (a) and EDS spectra (b), for the whole sample (a 0 ), for a corncob shaped region (a 1 ,b 1 ), and for a porous region (a 2 ,b 2 ); image of used CHA after purification of FAEEs produced via alkali catalysis and supplemental incineration (c).

Figure 3 .

 3 Figure 3. SEM analyses of RHA-GB (backscattered electrons without gold-palladium coating): virgin RHA-GB (a); used RHA-GB after purification and supplemental incineration, for FAEEs obtained via alkali (b) or acid (c) catalysis.

3 . 4 .

 34 Comparative Efficiency of the Purification Methods versus Biodiesel Characteristics. 3.4.1. Acidic Water Washing versus Dry Purification. The quality of the resulting FAEE products in terms of soap content and process yields per stage (Y I and Y II ) and globally (Y global ) are shown in Table

Figure 4 .

 4 Figure 4. N 2 adsorption isotherms of RHA-LG, RHA-GB, and CHA.

Table 1 .

 1 Equipment and Operating Conditions Selected

	objective	experimental technique	equipment	operating conditions
			RHA and CHA Characterization for Relating "Structure" and "Adsorption Efficiency"
	morphology	SEM	JEOL microscope; model JSM-6490 LV (Japan)	accelerated voltage, 5 or 20 kV; spot size, 60; magnification of up to 600×; second electrons analysis when sample metalized with gold-palladium; backscattered electrons analysis without sample gold-palladium coating
	elemental chemical composition	SEM-EDS	JEOL microscope; model JSM-6490 LV (microanalysis) (France) (Japan) + SAMX-IDFIX system	same as above
	surface area and porosity	N 2 adsorption isotherms + BET method	Sorptomatic 1990, ThermoQuest CE Instruments (Italy)	sample previously degassed for 16 h under vacuum with the temperature program of 1 °C/min from 30 to 120 °C; adsorption isotherms recorded at liquid nitrogen temperature (77.31 K)
			Biodiesel Characterization for Evaluation of the Purification Methods
	glycerides (TG, DG, MG), free glycerin, and FAEE contents	GC-FID	PerkinElmer Instrument (USA)	silica capillary column (CP-Sil 8 CB lowbleed/MS; 5% phenyl + 95% dimethylpolysiloxane; 15 m, 0.32 mm, 0.25 μm) from Varian (USA); carrier gas, helium (Air Liquide, France) at 15 psi at the head of the column; injector type and its temperature program, cool-on-column inlet at 55 °C (0.5 min)
				24,25
	water content	Karl Fischer titration (volumetric)	TIM 550 Titration manager by TITRALAB (France)

and 55-340 °C (200 °C/min, 43 min); oven temperature program, 55 °C (0.5 min), 55-80 °C (45 °C/ min), and 80-360 °C (10 °C/min, 16 min); detector temperature, 360 °C; automatic injections, 1 μL; silylation of the entire sample with a mixture of N-methyl-N-trimethylsilyl-heptafluorobutyramide and methylimidazole before GC-FID analysis; standard solutions prepared in cyclohexane (solvent); heptadecane used as internal standard (1 mg/mL) hydranal-medium K and hydranal-composite 5K used as solvent and titration reagent, respectively, with hydranal-water standard 10 (

10

mg of water/(g of solution)) potassium and other elements (Si, S, Ca, Mg, Fe, P) contents ICP-AES ARCOS by SPECTRO; Scott-type double-pass spray chamber combined with cross-flow nebulizer (Germany) plasma forward power, 1700 W; plasma argon (Ar) flow rate, 14 L/min; sample Ar flow rate, 0.65 L/min; auxiliary Ar flow rate, 1.9 L/min; pump speed, 15 rpm/min; calibration performed via a multielement oilbased standard (S-21 at 100 μg•g -1 ) diluted appropriately in xylene to prepare multielement working standard solutions ranging from 0.1 to 10 μg•g -1 ; quantification by external calibration with a test sample at 1 μg•g -126,27 FAEE and residual ethanol contents 1 H NMR Bruker 300 MHz analysis at 300 K in deuterated chloroform (99.8% D) solutions with naphthalene used as internal standard

Table 2 .

 2 Specific Areas and Pore Volumes of RHAs and CHA

	RHA-GB	0.191	202 ± 2
	RHA-LG	0.176	118 ± 2
	CHA	0.073	<1

adsorbent pore volume (cm 3 /g) specific area (m 2 /g)

Table 3 .

 3 Purification Yields and RSEE Product Quality before and after Treatment in Terms of Soap Content

		first stage		second stage	full process
	purification method	soap content (mg/kg) a	Y I (wt %) b	soap content (mg/kg) a	Y II (wt %) b	Y global (wt %) b
	wet purification with a 5 wt % H 3 PO 4 solution	undetectable	81	not determined c	not determined c	81
	wet purification with a 1 wt % H 3 PO 4 solution	68	70	18	61	43
	dry purification with RHA (flash treatment)	30	93	undetectable	94	87

a Milligrams of soap per kilogram of RSEEs; standard deviation, less than 2 mg/kg. b Yield of the ith purification process defined (per stage or globally) as Y i /(wt %) = (m i /m 0 ) × 100 where m i and m 0 are the masses of the RSEE sample before and after purification, respectively; standard deviation, less than 1 wt %. c This treatment was conducted in a single stage.

Table 4 .

 4 Characterization of FAEE Products with Regard to Their Molecular Components before and after Dry Purification with Different Adsorbent Agents and the Treatment Procedures a,b

	treatment procedure	esters (wt %)	free glycerin (wt %)	MG (wt %)	DG (wt %)	total glycerin (wt %)	water (mg/kg)
	Balanites aegyptiaca Fatty Acid Ethyl Esters (BAEEs)
	unpurified BAEEs of departure	97.35	0.13	3.14	0.48	1.00	466
	RHA-GB (20 °C, 5 min)	92.13	0.09 (-31)	2.40 (-24)	0.45 (-6)	0.77 (-23)	414 (-11)
	RHA-LG (20 °C, 5 min)	88.68	0.10 (-23)	2.26 (-28)	0.39 (-19)	0.73 (-27)	427 (-8)
	RHA-GB (20 °C, 20 min)	89.99	0.09 (-31)	2.79 (-11)	0.40 (-17)	0.86 (-14)	311 (-33)
	RHA-GB (65 °C, 20 min)	89.46	0.10 (-23)	2.72 (-13)	0.37 (-23)	0.85 (-15)	479 (+3)
	RHA-GB [(1) 20 °C, 5 min; (2) 65 °C, 20 min]	90.62	0.04 (-69)	2.06 (-34)	0.28 (-42)	0.61 (-39)	291 (-38)
	RHA-GB [(1) 20 °C, 5 min; (2) 20 °C, 5 min]	89.93	0.07 (-46)	2.27 (-28)	0.42 (-13)	0.71 (-29)	337 (-28)
	RHA-LG [(1) 20 °C, 5 min; (2) 20 °C, 5 min]	89.02	0.06 (-54)	2.15 (-32)	0.38 (-21)	0.66 (-34)	408 (-12)
	RHA-GB [(1) 20 °C, 5 min; (2) reused ashes from step 1, 20 °C, 5 min]	89.33	0.09 (-31)	2.49 (-21)	0.44 (-8)	0.79 (-21)	301 (-35)
	RHA-LG [(1) 20 °C, 5 min; (2) reused ashes from step 1, 20 °C, 5 min]	92.24	0.09 (-31)	2.44 (-22)	0.42 (-13)	0.77 (-23)	349 (-25)
	CHA (20 °C, 5 min)	89.17	0.09 (-31)	2.88 (-8)	0.45 (-6)	0.89 (-11)	429 (-8)
	Azadirachta indica Fatty Acid Ethyl Esters (AIEEs)
	unpurified AIEEs of departure	90.61	0.20	2.75	0.56	0.98	318
	RHA-GB (20 °C, 5 min)	90.36	0.08 (-60)	2.22 (-19)	0.40 (-29)	0.70 (-29)	303 (-5)
	RHA-GB [(1) 20 °C, 5 min; (2) 65 °C, 20 min]	87.63	0.06 (-70)	2.15 (-22)	0.35 (-38)	0.66 (-33)	240 (-25)
	Jatropha curcas Fatty Acid Ethyl Esters (JCEEs)
	unpurified JCEEs of departure	85.67	0.15	2.60	0.91	0.95	875
	RHA-GB (20 °C, 5 min)	83.80	0.13 (-13)	3.42 (+32)	0.93 (+2)	1.14 (+20)	918 (+5)
	RHA-GB [(1) 20 °C, 5 min; (2) 65 °C, 20 min]	85.81	0.11 (-27)	3.42 (+32)	0.87 (-4)	1.11 (+17)	467 (-47)
	specifications of EN 14214 c	96.5	0.02	0.80	0.20	0.25	500

Table 5 .

 5 Characterization of the Inorganic Composition of FAEE Products before and after Dry Purification with Different Adsorbent Agents and the Treatment Procedures a,b

	chemical element contents (mg/kg)

This work has been supported by the Fonds National pour l′Education et la Recherche (FONER) from Burkina Faso. Also, we express grateful acknowledgment to Olivier Fabre, Emilien Girot, Jean-Francois Reḿy, Fredeŕic Roze, and Corneĺius Schrauwen for their technical support and Professor Raphael Schneider for his helpful discussion during the work.


Philippe Evon
email: philippe.evon@ensiacet.fr

Justine Vinet

Laurent Labonne

Luc Rigal

Influence of thermo-pressing conditions on the mechanical properties of biodegradable fiberboards made from a deoiled sunflower cake

Keywords:

The objective of this study was to manufacture new biodegradable fiberboards by thermo-pressing. The starting material was deoiled cake (only 0.9% oil content), generated during the biorefinery of sunflower (Helianthus annuus L.) whole plant in a co-rotating twin-screw extruder. All fiberboards were cohesive mixtures of proteins and lignocellulosic fibers, acting respectively as binder and reinforcing fillers. The molding experiments were conducted using a 400 ton capacity heated hydraulic press. The influence of molding conditions on board density, mechanical and thermo-mechanical properties, thickness swelling, and water absorption was examined. Molding conditions included pressure applied (24.5-49.0 MPa), molding time (60-300 s), and mold temperature (156-204 • C), and these greatly affected board density and thus the mechanical and thermo-mechanical properties. Board density increased with increasingly extreme molding conditions, rising from 1162 to 1324 kg/m 3 . The flexural properties increased at the same time (from 12.2 to 27.7 MPa for flexural strength at break, and from 2183 to 5244 MPa for elastic modulus) and also Shore D surface hardness (from 69.6 to 79.0 • ). Conversely, Charpy impact strength was low and quite independent of thermo-pressing conditions. Statistical analysis of the Doehlert's experimental design was conducted to determine optimal thermo-pressing conditions for flexural properties, giving 49.0 MPa pressure applied, 300 s molding time, and 204 • C mold temperature. Density of boards molded under these conditions was 1267 kg/m 3 . Flexural strength at break, elastic modulus and Shore D surface hardness were 30.3 MPa, 5946 MPa, and 81.5 • , respectively, and these corresponded to the highest values for the entire study. Such boards largely complied with French standard NF EN 312, type P4 (i.e., load bearing boards for use in dry conditions) for flexural properties. However, thickness swelling (30%) needs to be slightly reduced to achieve the 21% recommended standard value.

Introduction

Twin-screw extrusion technology is an original and powerful solution for the biorefinery of sunflower (Helianthus annuus L.) whole plant. The latter is conducted in the presence of water, allowing the aqueous extraction of sunflower oil (Evon et al., 2010a). The twin-screw extruder produces highly effective, mechanical cell lysis in a single step and in continuous mode. The filtration section of the barrel allows an extract (filtrate) and a raffinate (cake) to be collected separately, and oil extraction yield attains 57% under optimal operating conditions. To simplify conservation, cake is first dried because it has a relatively high moisture content of at least 62%. Structurally, it is porous with a majority of lignocellulosic fibers (around 58% of the dry matter), although there is also cell debris from breakdown of the kernels. The soluble molecules (proteins, pectins. . .) and lipids have been partly removed, whereas the structural plant molecules have not been extracted. Because the cake is a mixture of proteins and lignocellulosic fibers, it has been the subject of new valorizations [START_REF] Orliac | Effects of additives on the mechanical properties, hydrophobicity and water uptake of thermo-moulded films produced from sunflower protein isolate[END_REF][START_REF] Orliac | Effects of various plasticizers on the mechanical properties, water resistance and aging of thermo-moulded films made from sunflower proteins[END_REF][START_REF] Rouilly | DSC study on the thermal properties of sunflower proteins according to their water content[END_REF][START_REF] Rouilly | Thermal denaturation of sunflower globulins in low moisture conditions[END_REF]Rouilly et al., , 2006a,b),b).

DSC (differential scanning calorimetry) analysis of the cake indicate that denaturation of proteins is almost complete, and the significant peak observed at high temperature (around 180 • C) in the DMTA (dynamic mechanical thermal analysis) spectrum obtained from a dried and ground sample is associated with the glass transition of proteins (Evon et al., 2010b). And as the cake is a mixture of proteins and lignocellulosic fibers, it can be processed by thermo-pressing into cohesive fiberboards, with the proteins acting as internal binder and giving the agromaterial's cohesion, and lignocellulosic fibers as reinforcing fillers (Evon et al., 2010a(Evon et al., ,b, 2012a(Evon et al., ,b,c, 2014a)).

Temperature, pressure, and length of time of thermo-pressing all increase fiberboard bending properties (Evon et al., 2010a(Evon et al., ,b, 2012b,c),c), and the highest elastic modulus (2.2 GPa) and highest flexural strength at break (11.5 MPa) are obtained with a cake having a dry matter residual oil content of 14.5%, using the following molding conditions: 500 mg/cm 2 cake quantity, 200 • C mold temperature, 31.4 MPa pressure applied, and 60 s molding time (Evon et al., 2010a,b). Fiberboard thickness is just 3.9 mm with quite a high density (1035 kg/m 3 ). A fiberboard with these flexural properties, could be used in the handling and storage industry as pallet inter layer sheeting, or for furniture manufacture and biodegradable, multi-board containers, e.g., composters, vegetable gardening crates (Evon et al., 2010b). Moreover, another industrial application of fiberboards with lower densities (from 500 to 858 kg/m 3 ) is heat insulation of buildings (walls and ceilings) (Evon et al., 2014a).

For dense boards, because of the high pressure applied, part of the cake residual oil is expressed through the sidewall vents of the mold during molding (Evon et al., 2010a(Evon et al., , 2012a,b,c),b,c). Logically, this molding oil expression decreases the fiberboard residual oil content (up to 8.7% of the dry matter for the highest pressure applied) (Evon et al., 2012c). Recuperation of this molding oil would mean filtering it, and then adding a refining step. Possible applications could be as a biolubricant, or transforming it into biodiesel (Amalia [START_REF] Kartika | Biodiesel production from jatropha seeds: solvent extraction and in situ transesterification in a single step[END_REF]Evon et al., 2014b). However, it is reasonable to suppose that oil expression during molding could reduce the mechanical resistance of fiberboards, due to defects appearing within the material as the oil escapes. Thus, an improvement in the molding process would be to use a deoiled cake as starting material for thermo-pressing.

This study aimed to manufacture new biodegradable fiberboards, by thermo-pressing from sunflower cake generated during the biorefinery of whole plant, which was then deoiled before molding using a Soxhlet extractor and n-hexane as extracting solvent. The influence of thermo-pressing conditions (pressure, time, and temperature) on the boards' mechanical (flexural properties, Charpy impact strength, and Shore D surface hardness) and thermomechanical properties, their thickness swelling and their water absorption, was then evaluated.

Material and methods

Material

Twin-screw extruder fractionation was applied to a batch of oleic type sunflower (Helianthus annuus L.) whole plant (Oxalliance, France) (Table 1), harvested at plant maturity, pre-dried in a ventilated oven (50 • C, 48 h) and then crushed with a hammer mill Table 1 Chemical composition of the sunflower whole plant used for the experiment and of the cake obtained, after its thermo-mechanical fractionation in the Clextral BC 45 twin-screw extruder and after its deoiling using n-hexane as extracting solvent (% of the dry matter). (Electra VS 1, France) through a 15 mm screen. Powdered plant moisture content was 8.9 ± 0.2% (French standard NF V 03-903).

Material

Analytical methods

The moisture contents were determined according to French standard NF V 03-903. The mineral contents were determined according to French standard NF V 03-322. The oil contents were determined according to French standard NF V 03-908. The protein contents were determined according to French standard NF V 18-100. The three parietal constituents (cellulose, hemicelluloses, and lignins) were estimated using the ADF-NDF method of Van Soest andWine (1967, 1968). Similarly, the water-soluble components were estimated by measuring the mass loss of the test sample after 1 h in boiling water. All determinations were carried out in duplicate.

Deoiled cake production by twin-screw extrusion plus deoiling

A Clextral BC 45 twin-screw extruder was used to conduct simultaneously at 80 • C the thermo-mechanical fractionation of whole plant and the aqueous extraction of sunflower oil, and the screw configuration was the same as that previously optimized (Evon et al., 2010a). Operating conditions for cake production were 67.4 rpm for the screw rotation speed, 5.5 kg/h for the inlet flow rate of the sunflower whole plant, and 20.5 kg/h for the inlet flow rate of the water. A filtrate was collected continuously from the filter section, and a cake was generated at the same time. Immediately after its production, and to facilitate conservation, it was dried in a ventilated oven (80 • C, 12 h). Then, residual oil inside the cake was extracted. Oil extraction was conducted for 5 h using a 1 L Soxhlet extractor and n-hexane as extracting solvent.

Particle size distribution

A 500 g test sample mass of deoiled cake was treated in a Retsch AS 300 (Germany) vibratory sieve shaker to determine particle size distribution. Sieve acceleration was 1.5 × g, and sieving time 10 min. For the apparent and tapped densities of the deoiled cake, which were also determined, the tapped density measurement used a Granuloshop Densitap ETD-20 (France) volumenometer.

TGA measurements

Thermogravimetric analysis (TGA) of the deoiled cake was performed with a Shimadzu TGA-50 (Japan) analyzer. Dynamic analysis was conducted under air at a heating rate of 5 • C/min, from 20 to 750 • C. The deoiled cake was first equilibrated in a climatic chamber (60% RH, 25 • C) for 3 weeks, and the test sample mass was about 5 mg. Sample weight was measured as a function of temperature, and the data used subsequently to plot the percentage of undegraded sample (1-D) (%) as a function of temperature,

D = W 0 -W W 0 (1)
where W 0 and W were the weights at the starting point and during scanning (mg). The measurement was carried out in duplicate.

Thermo-pressing

The deoiled cake was dried in a ventilated oven (60 • C, 12 h) to minimize vapor generation during thermo-pressing thus reducing the risk of defects like blisters inside the fiberboards. Then, molding was by thermo-pressing inside an aluminum mold. A 400 ton capacity Pinette Emidecau Industries (France) heated hydraulic press was used to produce 150 mm × 150 mm fiberboards. The quantity of deoiled cake for all experiments was 150 g (i.e. 667 mg/cm 2 ). A Doehlert's experimental design with three variables was made to evaluate the influence of thermo-pressing conditions (including pressure applied, molding time, and mold temperature) on fiberboard properties. Statistical analysis of the results was by NEMROD software, which was also used to plot isoresponse curves.

The best-fit second-order response (Y) obtained to describe each of the fiberboard characteristics (including flexural properties, Charpy impact strength, Shore D surface hardness, thickness swelling, and water absorption) was given by the following formula:

Y = a 0 + (a 1 × X 1 ) + (a 2 × X 2 ) + (a 3 × X 3 ) + (a 12 × X 1 × X 2 ) +(a 13 × X 1 × X 3 ) + (a 23 × X 2 × X 3 ) + (a 11 × X 1 × X 1 ) +(a 22 × X 2 × X 2 ) + (a 33 × X 3 × X 3 ) (2)
X 1 , X 2 , and X 3 are the coding values of the experimental design, each varying from -1.0 to 1.0, and relative to the three molding conditions tested (pressure, time, and temperature, respectively), and a i (i varying from 0 to 3), and a ij (i and j varying from 1 to 3, and i ≤ j) the coefficients of the polynomial model. Three fiberboards were produced for all the thermo-pressing conditions. Immediately after molding, these were equilibrated in a climatic chamber (60% RH, 25 • C) for 3 weeks in order to assess their properties using equilibrated materials. A first fiberboard was used to assess thickness, mean apparent density, and mechanical properties for bending. After equilibration, four 30 mm wide test specimens were cut and their thickness measured at three points and their length at two points, with a 0.01 mm resolution electronic digital sliding caliper. Thickness and length mean values were recorded to calculate the specimen volume, and test specimens were all weighed to calculate their density. The thickness (t) and mean apparent density (d) of fiberboard were the mean values of measurements made on the four test specimens. A second fiberboard was used for measuring: Charpy impact strength, Shore D surface hardness, and finally thermo-mechanical properties. The third fiberboard was used for thickness swelling and water absorption.

Mechanical properties for bending

Measurement of the flexural properties of the 30 mm wide test specimens according to French standard NF EN 310 was undertaken using an Instron 33R4204 (USA) universal testing machine fitted with a 500 N load cell, and the three points bending technique. Test speed was 2 mm/min with 100 mm grip separation. Load was applied equidistant from the two supports, and the loading direction was perpendicular to the upper face of the test specimen. Properties covered energy-to-break (E), breaking load (F), flexural strength at break ( f ), and elastic modulus (E f ). An estimation of the energy-to-break for each specimen, using the area under the load deformation curve from zero to rupture, was calculated using the trapezium method. All determinations were carried out four times, i.e., from each of the four test specimens cut in each fiberboard.

Charpy impact strength

The impact strength of the unnotched test specimens according to French standard NF EN ISO 179 was assessed with a Testwell Wolpert 0-40 daN cm (France) Charpy machine, and this also covered absorbed energy (W), and resilience (K). After fiberboard equilibration, twelve test specimens, 60 mm long and 10 mm wide, were cut. To calculate their section, thickness was measured at three points with a 0.01 mm resolution electronic digital sliding caliper, and the mean value (t) recorded. Impact strength measurements were made at 23 • C using the three points bending technique, with 25 mm grip separation. Load was applied equidistant from the two supports, and the loading direction was perpendicular to the test specimen. All determinations were carried out twelve times, i.e., from each of the twelve test specimens cut in each fiberboard.

2.9. Shore D surface hardness Shore D surface hardness of the fiberboards was assessed using a Bareiss (Germany) durometer according to French standard NF EN ISO 868. The indentation direction was perpendicular to the upper face of the fiberboard. All determinations were carried out 48 times for each fiberboard (24 times for each board side).

Thickness swelling and water absorption

Four 50 mm × 50 mm samples were used to determine thickness swelling (TS) and water absorption (WA) of the fiberboards. To evaluate these, they were submerged in distilled water at 25 • C for 24 h. TS was determined according to the French Standard NF EN 317 and thickness of each sample was measured at four points, midway along each side 10 mm from the edge before and after soaking in distilled water. Each sample was also weighed to an accuracy of 0.01 g to determine WA values.

Dynamic mechanical thermal analysis (DMTA)

DMTA analysis was used to evaluate the thermo-mechanical behavior of fiberboards (boards 8, 14, and 7) produced at three different mold temperatures (160, 180, and 200 • C, respectively). DMTA experiments were on a Triton Technology Tritec 2000 (UK) machine. Fiberboards were analyzed using 10 mm wide and 30 mm long samples. Measurements were made using the two points bending technique: 1 Hz frequency, 50 m displacement, and a 3 • C/min heating rate over a 0-165 • C range. Distance between the two points was 10 mm. Curves for the storage modulus (E ′ ) and the loss modulus (E ′′ ) were plotted. Four samples were tested for each fiberboard.

Results and discussion

Physico-chemical characterization of the deoiled cake

The cake produced by twin-screw extrusion was a powder consisting of inhomogeneous particles, whose chemical composition is shown in Table 1. It revealed an oil content (17.3% of the dry matter) quite comparable to that of a cake used in a previous study for the manufacture of thermal insulation fiberboards (17.6%) (Evon et al., 2014a). Due to the fact that some lipids and proteins were partly extracted by water during the process, this meant that their residual contents in the cake decreased compared to initial whole plant values (Table 1). Similarly, with hemicelluloses and water-soluble components, the same tendency was also observed. On the other hand, cellulose and lignins were not extracted, because both these biopolymers are insoluble in water. Thus, in parallel, a significant increase relative to their initial values was observed.

Residual oil inside the cake was extracted before thermopressing to preserve fiberboard mechanical properties. As expected, the chemical composition of the deoiled cake (Table 1) revealed a large decrease in the oil content (0.9%), meaning that oil extraction using n-hexane was almost complete. Conversely, it logically showed an increase in the content of the other compounds like proteins, cellulose, and lignins. In conclusion, the chemical composition of the deoiled cake (Table 1) confirmed that it was a mixture of lignocellulosic fibers and proteins whose denaturation in the twin-screw extruder was almost complete (Evon et al., 2010b). Therefore, it could be considered to be a natural composite capable of being transformed into fiberboards by thermo-pressing. The particle size distribution inside the deoiled cake (Fig. 1) revealed the presence of large particles (above 1 mm), mainly composed of lignocellulosic fibers originating essentially from the sunflower stalk, and also smaller particles, mean diameter around 500 m. This second population contained not only smaller fibers but also spherical particles, from the kernel breakdown process. Most of the proteins contained in the deoiled cake were present within this population. Lastly, apparent and tapped densities of the deoiled cake were quite low (215 ± 3 and 233 ± 1 kg/m 3 , respectively). Thermogravimetric analysis of the deoiled cake was also conducted, and the TGA degradation curve is shown in Fig. 2. At 100 • C, there is an initial mass loss observed corresponding to water evaporation. After 3 weeks in a climatic chamber, the level of moisture in the deoiled cake was 7.5 ± 0.1%, and the TGA curve mass loss observed corresponded approximately to the same mass percentage. Then, thermal degradation of organic compounds took place essentially in one stage (between 220 and 375 • C) that lead to the loss of 70-75% of the sample dry matter. Finally, another degradation phenomenon was also observed between 425 and 500 • C, however this was associated with a lower mass loss (15-20% of the dry matter in sample).

Using data dealing with the thermal degradation of fibers and sunflower proteins, cited by some researchers in previous studies [START_REF] Beaumont | Pyrolyse Extractive Du Bois[END_REF][START_REF] Geneau | Manufacturing Process of Agromaterial Natural Composite by Twin-screw Extrusion and Injection Moulding from Sunflower Cake[END_REF][START_REF] Hatakeyama | Thermal Properties of Green Polymers and Biocomposites[END_REF][START_REF] Lalou | [END_REF][START_REF] Schaffer | Effect of pyrolytic temperatures on the longitudinal strength of dry Douglas-fir[END_REF], it was logical to infer that the main thermal degradation stage (220-375 • C) could be associated with the simultaneous breakdown of proteins, hemicelluloses, and cellulose. The subsequent stage, beginning about 425 • C, would in this case correspond to the thermal degradation of just the lignins. Following all the measurements, the undegraded sample accounted for less than 9% of the test sample mass, and represented the minerals contained in the deoiled cake.

Influence of thermo-pressing conditions on mechanical properties of fiberboards

Fourteen fiberboards were manufactured using different thermo-pressing conditions (Table 2). Conditions included pressure applied, molding time, and temperature of the aluminum mold. The pressure applied, in particular, varied from 24.5 to 49.0 MPa. This was comparable to values used in previous studies: up to 31.4 MPa (Evon et al., 2010b), from 31.4 to 35.3 MPa (Evon et al., 2012c), and from 24.5 to 49.0 MPa (Evon et al., 2012b), and the objective here was to manufacture dense fiberboards, i.e., with a density up to 1000 kg/m 3 . Molding time varied from 60 to 300 s, which was similar to values used in a previous study (Evon et al., 2012b), and was sufficient for sunflower proteins to reach a rubbery state during molding.

Mold temperature varied from 156 to 204 • C. The lowest temperature (156 • C) was chosen to be slightly higher than the protein glass transition temperature. A previous study using the DSC technique, showed that, for sunflower proteins, this temperature was clearly influenced by their water content [START_REF] Rouilly | DSC study on the thermal properties of sunflower proteins according to their water content[END_REF], with a large drop (from 181 to 5 • C) observed as this protein water content increased from 0 to 26.1% of the dry matter, confirming that water acted as a plasticizer for the proteins. Indeed proteins, like the main biopolymers (starch, pectins, hemicelluloses, and other polysaccharides), contain polar functions (amides) capable of linking the water molecules by hydrogen bonds. The presence of water separates the proteins and facilitates their movement [START_REF] Rouilly | Agro-materials: a bibliographic review[END_REF]. The thermal and rheological properties of proteins are therefore highly dependent on the amount of water, resulting in variations in their glass transition temperature according to their hydration. Because the cake moisture was only 2.8 ± 0.1% on molding, the glass transition temperature of proteins was therefore estimated to be close to 145 • C. On the other hand, the highest temperature (204 • C) corresponded approximately to that giving the best mechanical properties for bending in a previous study (200 • C) (Evon et al., 2010b). Finally, no temperature higher than 204 • C was tested because thermal degradation of most of the organic compounds in the cake occurs in the 220-375 • C temperature range (Fig. 2).

Deoiled cake quantity for all the experiments was 667 mg/cm 2 , and this led to the manufacture of fiberboards with thicknesses after climatic chamber conditioning (at least 5.0 mm, and up to 5.8 mm) (Table 3) comparable to those of other materials from sunflower cake described in previous studies (Evon et al., 2010b(Evon et al., , 2012b,c),c). All fiberboards were cohesive. Proteins acted as an internal binder within the fiberboards, and they contributed to ensuring cohesion of the agromaterial. In addition, the entanglement of lignocellulosic fibers also acted as reinforcement.

The density of the equilibrated fiberboards was clearly influenced by the thermo-pressing conditions used, increasing with increasing conditions (Table 3). This was illustrated by the positive values obtained for the a 1 , a 2 , and a 3 coefficients of the corresponding best-fit second-order response (Table 4). At the same time, a ij coefficients were negative but their absolute values were all much lower than a i coefficients. Therefore, logically an increase in pressure applied and/or molding time led to fiberboard densification. But it was the mold temperature that most affected fiberboard density, as shown by the a 3 coefficient which was higher (59.5) than the a 1 and a 2 coefficients (43.7 and 40.9, respectively). And such an evolution, explained the decrease in the moisture content of equilibrated fiberboards with the increase in pressure, molding time, and especially temperature (Table 3). Indeed, water uptake during climatic chamber conditioning was less for denser boards, due to their lower porosity.

The mechanical properties for bending of fiberboards were also clearly influenced by the thermo-pressing conditions. And it was still the mold temperature that most affected the energy-to-break, and especially the breaking load, the flexural strength at break and the elastic modulus (Table 4). Moreover, the higher the fiberboard density, the higher its flexural properties (Table 3). And the most mechanically resistant fiberboard (board 7) was also the densest board. The NEMROD software analysis of the isoresponse curves for flexural strength at break (Fig. 3) and elastic modulus (Fig. 4), perfectly the increase in mechanical properties for bending of fiberboards with increasing thermo-pressing conditions, especially the mold temperature. Similarly, the Shore D surface hardness increased slightly with increasing thermo-pressing conditions (Tables 3 and4). Conversely, Charpy impact strength was low and relatively independent of thermo-pressing conditions, and such fragility could be explained by the high rigidity of the boards manufactured (Tables 3 and4).

Since the mold temperature was always higher than the protein glass transition temperature, this change occurred systematically during molding and proteins were thus always in a rubbery state. However, because the protein-based resin became less and less viscous with increasing mold temperature, this meant that the fiber wetting improved progressively. This could explain why the mechanical properties of fiberboards increased as the mold temperature increased, the 200 • C mold temperature logically leading to the most resistant fiberboards of the study (Table 3).

Thickness swelling (TS) and water absorption (WA) of fiberboards were also dependent on thermo-pressing conditions, decreasing as they increased (Table 3), with the greatest effect from mold temperature (Table 4) which, at 200 • C gave the least water-sensitive boards. At such a temperature, TS and WA were only 61-100 and 43-69%, respectively (Table 3). Moreover, as previously observed for flexural properties, thickness swelling, and water absorption were correlated to the board density, and both tended to decrease with its increase. Indeed, an increase in board density resulted in a reduction of its internal porosity, and this contributed to making it less water-sensitive.

DMTA analysis of fiberboards was conducted on boards 8, 14, and 7 (Fig. 5). They were molded at 160, 180, and 200 • C, respectively, and the higher the mold temperature, the higher the storage modulus (E ′ ). This confirmed that fiberboards' internal cohesion increased with increasing mold temperature. Moreover, no significant transition occurred between 0 • C and 118 • C for board 8, up to 129 • C for board 14 and 140 • C for board 7. Thus, no phase a The optimal response is the maximal one for fiberboard mechanical properties (including flexural properties, Charpy impact strength, and Shore D surface hardness), and the minimal one for thickness swelling and water absorption. change took place in these temperature ranges, and proteins still ensured panel cohesion in all three cases. Then, a rapid decrease in the storage modulus was observed, and at the same time a peak appeared in DMTA loss modulus (E ′′ ) curves (Fig. 5). This transition was associated with the protein's glass transition, and the corresponding temperature was around 120 • C for board 8, 131 • C for board 14, and 142 • C for board 7. These differences can be explained by the decrease in moisture content of equilibrated fiberboards with increasing mold temperature (Table 3), thus re-illustrating the plasticizing effect of water for proteins. And logically, because panel cohesion was no longer ensured by the protein-based resin beyond the protein's glass transition temperature, the storage modules were negligible at higher temperatures. Polynomial models were used to determine the optimal responses for each fiberboard characteristic analyzed, i.e., mechanical properties for bending, resilience, Shore D surface hardness, thickness swelling, and water absorption. All optimal responses are given in Table 5, as well as relevant thermo-pressing conditions. The X 3 coding value was always 1.00, i.e., 204 • C mold temperature, confirming that this was the thermo-pressing condition that most affected fiberboards' mechanical properties, thickness swelling, and water absorption. Moreover, optimal flexural strength at break (31.9 MPa) and elastic modulus (6526 MPa) were both obtained under the same thermopressing conditions, i.e., 49.0 MPa pressure applied, 300 s molding time, and 204 • C mold temperature. Such conditions were considered as the optimal ones. So, a fifteenth fiberboard was molded using these conditions, and Table 6 shows fiberboard characteristics calculated from bestfit second-order equations, plus experimental data. The board obtained (Fig. 6) was a little less dense (1267 kg/m 3 ) than expected from the polynomial model. However, flexural strength at break and elastic modulus were 30.3 and 5946 MPa, respectively, relatively close to the expected values. Shore D surface hardness was 81.5 • instead of the 81.6 • expected value, and the fiberboard molded under optimal thermo-pressing conditions was indeed the strongest board of the entire study for bending stress and surface hardness. The only significant difference between the model and the experiment was Charpy impact strength where excessive panel rigidity significantly altered its impact resistance. Conversely, thickness swelling and water absorption (30 and 23%, respectively) were better than expected, meaning that the optimal board was not very water-sensitive.

Therefore, this optimal fiberboard largely complied with French standard NF EN 312, type P4 (i.e., load bearing boards for use in dry conditions) for flexural properties (recommendations of 16 and 2200 MPa for flexural strength at break and elastic modulus respectively, for boards with a thickness of between 4 and 6 mm) but not exactly for thickness swelling (recommendation of 21% after 24 h immersion in water). An additional process such as preheating, chemical, or steam treatment would probably improve this dimensional stability parameter [START_REF] Halvarsson | Manufacture of non-resin wheat straw fiberboards[END_REF][START_REF] Okuda | Chemical changes of kenaf core binderless boards during hot pressing. I: influence of the pressing temperature condition[END_REF][START_REF] Saadaoui | Characterization of date palm lignocellulosic by-products and self-bonded composite materials obtained thereof[END_REF][START_REF] Widyorini | Manufacture and properties of binderless particleboard from bagasse. I: effect of raw material type, storage methods, and manufacturing process[END_REF].

Another fiberboard was molded using the optimal thermopressing conditions with sunflower cake before deoiling, retaining cake quantity at 667 mg/cm 2 . Part of the oil was expressed during molding, due to pressure applied, representing 66% of the oil inside the cake. Nevertheless, the resultant fiberboard still contained oil (7.1 ± 0.1% of the dry matter). It remained cohesive like the others, but its mechanical properties were particularly low compared with those of the optimal board from deoiled cake (Table 6): 10.1 ± 0.7 MPa for flexural strength at break, 2163 ± 153 MPa for elastic modulus, 1.32 ± 0.15 kJ/m 2 for Charpy impact strength, and 67.5 ± 3.1 • for Shore D surface hardness. At the same time, thickness swelling and water absorption were higher (54 ± 5% and 45 ± 5%, respectively). Thus, oil expression during molding reduced both board mechanical and water resistance, due to defects appearing within the material as the oil escaped.

To conclude, all fiberboards from deoiled cake were self-bonded composite materials, entirely derived from a renewable resource and also biodegradable. The proteic resin ensured the board's cohesion and lignocellulosic fibers further acted as reinforcement. Moreover, the use of the deoiled cake for thermo-pressing significantly improved the molding process, leading to more resistant a The number in parentheses in the second column is the ratio of the response calculated from the best-fit second-order equation to the associated optimal response (Y optimal ) (%).

b The number in parentheses in the third column is the ratio of the fiberboard characteristic obtained from the experiment to the one calculated from the best-fit second-order equation (%). c 4.95 ± 0.16 mm for the thickness of the equilibrated fiberboard. d 115 ± 10 mJ for absorbed energy.

and less water-sensitive boards compared with those produced from sunflower cake before deoiling. Fiberboards produced under optimal thermo-pressing conditions (49.0 MPa pressure applied, 300 s molding time, and 204 • C mold temperature) largely complied with the French standard NF EN 312, type P4 regarding mechanical properties for bending, while this was slightly less valid for thickness swelling. However, these optimal boards had low dimensions (150 mm × 150 mm). Therefore, significant work is still needed to produce commercial products, i.e., with a width from 1 to 4 m, while maintaining the same properties.

When comparing the optimal boards to most conventional ones, there was no necessity to add any external binder such as a thermosetting resin in order to obtain a cohesive panel. Further, the inclusion of lignocellulosic fibers revealed a promising ability for mechanical reinforcement. Essentially originating from the byproducts of sunflower culture, i.e., the stalks and heads, these fibers are not commercially available for the moment, the sunflower harvest concerning only the seeds. Thus, this could, in the future, justify their harvest in the field and provide farmers with the potential benefits from an additional source of income.

Conclusion

New biodegradable and cohesive fiberboards were manufactured using a heated hydraulic press, from a deoiled cake generated during the biorefinery of sunflower whole plant in a twin-screw extruder. Proteins acted as an internal binder, and entanglement of lignocellulosic fibers also acted as reinforcement. The thermopressing conditions had an important influence on board density and on mechanical properties for bending. Statistical analysis of the Doehlert's experimental design revealed that the optimal thermopressing conditions for flexural properties corresponded to the highest values of pressure applied (49.0 MPa), molding time (300 s), and mold temperature (204 • C). Density of the fiberboard produced under these conditions was 1267 kg/m 3 . Flexural strength at break and elastic modulus were 30.3 and 5946 MPa, respectively, and these values were the highest for the entire study. At the same time, thickness swelling and water absorption were 30% and 23%, respectively. Such boards largely complied with French standard NF EN 312, type P4 (i.e., load bearing boards for use in dry conditions) for flexural properties but not entirely for thickness swelling. It is anticipated that one additional process such as preheating, chemical, or steam treatment could achieve the recommended thickness swelling value, i.e., 21%.

Fig. 1 .

 1 Fig. 1. Particle size distribution in the deoiled cake.

Fig. 2 .

 2 Fig. 2. TGA degradation curve of the deoiled cake.

  table correspond to the mean values ± standard deviations. a HFB is the moisture content of the fiberboard. Fiberboards were equilibrated in a climatic chamber (60% RH, 25 • C) for 3 weeks before moisture measurements.

Fig. 3 .

 3 Fig. 3. Isoresponse curves for flexural strength at break ( f ) of fiberboards at 180 • C mold temperature (a), at 36.8 MPa pressure applied (b), and for 180 s molding time (c).

Fig. 4 .

 4 Fig. 4. Isoresponse curves for elastic modulus (E f ) of fiberboards at 180 • C mold temperature (a), at 36.8 MPa pressure applied (b), and for 180 s molding time (c).

Fig. 5 .

 5 Fig. 5. DMTA curves of boards 8, 14, and 7: storage modulus (E ′ ) (a) and loss modulus (E ′′ ) (b).

Fig. 6 .

 6 Fig.6. Photograph of test specimens from fiberboard produced under optimal thermo-pressing conditions.

Table 3

 3 Mechanical properties, thickness swelling, and water absorption of the fourteen fiberboards manufactured by thermo-pressing.

			0.12	0.26	31	12	4	0.7	258		18	0.17		2.6
	14		0.04 6.98 ±	0.19 5.30 ±	20 1275 ±	9 171 ±	2 122 ±	0.4 21.7 ±	283 3719 ±		11 161 ±	0.21 3.03 ±		3.5 74.9 ±
	13		0.07 6.96 ±	0.12 5.32 ±	12 1257 ±	21 184 ±	10 112 ±	1.9 19.8 ±	312 3258 ±		10 168 ±	0.38 3.15 ±		2.4 74.2 ±
	12		0.01 6.84 ±	0.23 5.24 ±	40 1280 ±	20 181 ±	5 131 ±	0.9 23.8 ±	248 4212 ±		10 172 ±	0.19 3.28 ±		1.7 76.4 ±
	11		0.10 6.66 ±	0.25 5.12 ±	28 1299 ±	12 164 ±	7 134 ±	1.2 25.5 ±	121 4978 ±		15 153 ±	0.26 2.98 ±		2.4 77.8 ±
	10		.09 7.37 ±	0.24 5.49 ±	44 1234 ±	11 172 ±	7 103 ±	1.0 17.0 ±	270 2911 ±		17 166 ±	0.31 3.03 ±		3.1 72.0 ±
	9		0.02 7.92 ±	0.25 5.54 ±	39 1215 ±	17 143 ±	7 92 ±	1.1 15.0 ±	226 2673 ±		14 145 ±	0.25 2.62 ±		2.7 70.6 ±
	8		0.05 8.00 ±	0.20 5.80 ±	17 1162 ±	13 132 ±	8 82 ±	3.1 12.2 ±	461 2183 ±		12 158 ±	0.24 2.73 ±		1.7 69.6 ±
	7		0.00 6.94 ±	0.21 4.98 ±	43 1324 ±	14 183 ±	9 137 ±	1.6 27.7 ±	209 5244 ±		17 146 ±	0.33 2.94 ±		2.6 79.0 ±
	6		0.01 6.96 ±	0.20 5.27 ±	34 1280 ±	14 207 ±	8 142 ±	1.4 25.6 ±	284 4262 ±		16 169 ±	0.30 3.21 ±		3.3 76.2 ±
	5		0.03 7.25 ±	0.24 5.41 ±	37 1247 ±	24 193 ±	8 118 ±	1.1 20.1 ±	75 3316 ±		12 152 ±	0.22 2.81 ±		3.2 72.9 ±
	4		0.04 7.46 ±	0.22 5.71 ±	50 1182 ±	15 160 ±	12 104 ±	2.2 15.9 ±	323 2717 ±		10 164 ±	0.19 2.87 ±		2.1 71.3 ±
	3		0.06 7.06 ±	0.21 5.22 ±	38 1287 ±	16 201 ±	7 134 ±	2.1 24.6 ±	151 4220 ±		10 164 ±	0.17 3.15 ±		2.8 77.1 ±
	Board number 1 2	Mechanical properties for bending	HFB a (%) 7.71 ± 0.11 7.44 ±	t (mm) 5.18 ± 0.28 5.63 ±	d (kg/m 3 ) 1299 ± 33 1200 ±	E (mJ) 210 ± 8 174 ±	F (N) 136 ± 3 114 ±	f (MPa) 25.4 ± 0.6 18.0 ±	E f (MPa) 4505 ± 452 3177 ±	Charpy impact strength	W (mJ) 147 ± 11 147 ±	K (kJ/m 2 ) 2.84 ± 0.21 2.61 ±	Surface hardness	Shore D ( • ) 73.7 ± 1.6 71.4 ±	Thickness swelling and water absorption	TS (%)

Table 4

 4 Coefficients of the best-fit second-order response for each of the fiberboard characteristics analyzed, and corresponding correlation coefficient (R 2 ).

	Coefficient	a0	a1	a2	a3	a12	a13	a23	a11	a22	a33	R 2
	Mechanical properties for bending
	d (kg/m 3 )	1265.9	43.7	40.9	59.5	-33.4	-5.3	-10.1	-16.3	-17.1	-11.9	0.99
	E (mJ)	177.4	16.2	15.8	16.4	-22.6	12.3	-30.6	14.8	12.1	-29.0	0.99
	F (N)	116.9	7.9	14.6	25.6	-12.7	0.6	-8.3	8.2	7.1	-9.5	0.98
	f (MPa)	20.7	2.9	3.9	6.7	-3.0	0.7	-0.6	1.0	0.8	-1.3	0.98
	E f (MPa)	3488.7	496.0	729.7	1361.0	-370.0	-6.7	194.2	352.1	69.3	211.7	0.98
	Charpy impact strength
	K (kJ/m 2 )	3.1	0.0	0.2	0.2	0.0	0.0	-0.3	-0.4	0.0	-0.2	0.89
	Surface hardness
	Shore D ( • )	74.5	1.2	2.5	4.3	-0.4	0.2	0.9	-2.0	0.4	-0.1	1.00
	Thickness swelling and water absorption
	TS (%)	144.8	-11.2	934.2	-94.6	8.7	5.6	-18.3	14.1	18.7	6.4	0.99
	WA (%)	104.6	-20.3	-45.5	-111.6	38.0	5.4	17.7	16.3	37.3	48.4	0.99

Table 5

 5 Optimal thermo-pressing conditions for each of the fiberboard characteristics analyzed, and corresponding optimal response (Y optimal ).

	Thermo-pres-sing conditions	X1	Pressure applied (MPa)	X2	Molding time (s)	X3	Mold tempe-rature ( • C)	Y optimal	a
	Mechanical properties for bending
	d (kg/m 3 )	1.00	49.0	-0.08	171	1.00	204	1336
	E (mJ)	1.00	49.0	-1.00	60	1.00	204	258
	F (N)	1.00	49.0	-1.00	60	1.00	204	163
	f (MPa)	1.00	49.0	1.00	300	1.00	204	31.9
	E f (MPa)	1.00	49.0	1.00	300	1.00	204	6526
	Charpy impact strength
	K (kJ/m 2 )	0.00	36.8	-1.00	60	1.00	204	3.31
	Surface hardness
	Shore D ( • )	0.26	39.9	1.00	300	1.00	204	82.7
	Thickness swelling and water absorption
	TS (%)	-0.11	35.4	1.00	300	1.00	204	23
	WA (%)	0.25	39.8	0.25	209	1.00	204	36

Table 6

 6 Fiberboard characteristics calculated from best-fit second-order equations for 49.0 MPa pressure applied (1.00 for X1), 300 s molding time (1.00 for X2), and 204 • C mold temperature (1.00 for X3), and obtained from the experiment under these conditions.Results obtained from the experiment (right column in the table) correspond to the mean values ± standard deviations.

	Fiberboard characteristic	Calculated from best-fit second-order equation a	Obtained from the experiment b
	Mechanical properties for bending
	d (kg/m 3 )	1316 (99%)	1267 ± 25 c (96%)
	E (mJ)	183 (71%)	190 ± 13 (104%)
	F (N)	150 (92%)	149 ± 9 (99%)
	f (MPa)	31.9 (100%)	30.3 ± 2.6 (95%)
	E f (MPa)	6526 (100%)	5946 ± 272 (91%)
	Charpy impact strength
	K (kJ/m 2 )	2.62 (79%)	2.33 ± 0.21 d (89%)
	Surface hardness
	Shore D ( • )	81.6 (99%)	81.5 ± 0.8 (100%)
	Thickness swelling and water absorption
	TS (%)	40	30 ± 4
	WA (%)	90	23 ± 2


A Skarlatos

G Pichenot

Cea List

D Lesselier

Marc Lambert

Bernard Duchêne

Numerical Modeling of Eddy Current Nondestructive Evaluation of Ferromagnetic Tubes via an Integral Equation Approach

• Additional inspection configuration studies • Conclusion and perspectives

Riveted structures

The CIVA Software

• The CIVA software is an expertise platform dedicated to non destructive testing.

• It is composed of simulation, imaging and analysis modules that allow to conceive or to optimize inspection techniques and to predict their performances upon realistic NDT configurations.

• CIVA includes Ultrasonic (UT) and Eddy Current techniques (ET).

• Until now the CIVA Eddy Current module was limited to non-magnetic materials.

Tilted coils CAD defined geometries Cylindrical configurations

Multi-coil probes with ferrites

Primary Field Calculation

Coaxial Coil

Off-axis Coil

Semi Analytical Solution (Dodd -Deeds)

• Interpolation Algorithm using Splines

Green

  the existing models to treat Planar multilayered ferromagnetic configurations -Tubes with support plates (nuclear applications) -Tubes in expanded zone (nuclear applications) -Ferromagnetic tubing inspection with surface ridding probes Perspectives

Off-centering Effect in Case of a Hole

Validation: Remote Field Probe