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International audience; Miscanthus biomass can be used to produce lightweight concrete. However, cell wall polymers leached in the alkaline cementitious medium can disturb cement setting. This is the case for grass lignin and grass arabinoxylan due to their specific alkali solubility. The main objective of this paper was to study the impact of lignin and of arabinoxylan from miscanthus biomass on the hydration of Portland cement and by electrical conductivity. To this end, dioxan lignin (DL) and arabinoxylan (AX) were extracted from miscanthus by methods preserving the main structural specificities of the native polymers. These DL and AX fractions were added to Portland cement (1-5% w/w in cement) and their impact on the electrical conductivity of cement/water mixtures was time-monitored. The novelty of this study lies in using polymers structurally similar to those of miscanthus fibers rather than commercially available ones, such as kraft lignin (KL). The addition of DL or of KL to cement/water mixture differently affected the electrical conductivity, which is most likely assignable to the severe structural degradation of KL during kraft process. The conductivity curves suggested that cement hydration was substantially delayed when DL % in cement was 3% or more while lower values had no impact. The results support the hypothesis that the access of water to cement grains was impeded by the adsorption of ionized lignin entities at their surface. When co-added to the cement (1.6 wt% each), the DL and AX fraction delayed cement hydration more substantially than when the same amounts were separately added. This unexpected synergy suggests that the miscanthus lignin and arabinoxylan polymers form lignin-carbohydrate complexes efficiently adsorbed on cement grains.

International audience; Due to an increasing demand for environmentally sustainable products, miscanthus and maize stover represent interesting lignocellulosic resources for conversion into biofuels and biomaterials. The overall purpose was to compare miscanthus and maize regarding cell-wall composition and stem anatomy for conversion into bioethanol and polymer composites using partial least squares regressions. For each of the two crops, six contrasted genotypes were cultivated in complete block design, and harvested. Internodes below the main cob for maize, and on the first aboveground internode for miscanthus, were analyzed for biochemistry and anatomy. Their digestibility was predicted using crop-specific near infrared calibrations, and the mechanical properties were evaluated in stem-based composites. On average, the internode cross-section of miscanthus anatomy was characterized by a thick rind (26.2 %) and few but dense pith-bundles (3.5 nb/mm²), while cell-wall constituted 95.2 % of the dry matter with high lignin (243.2 mg/g) and cellulose concentrations (439.7 mg/g). Maize internode-anatomy showed large cross-sections (397.5 mm²), pith with the presence of numerous bundles and non-lignified-pith fractions (22.3 % of the section). Its cellwall biochemistry displayed high concentrations of hemicelluloses, galactose, arabinose, xylose and ferulic acid. Cell-wall, lignin and cellulose concentrations were positively correlated with rind-fraction and pith-bundle-density, which explained strong mechanical properties as shown in miscanthus. Hemicelluloses, galactose, arabinose and ferulic acid concentrations were positively correlated with pith fraction and stem cross-section, revealing high digestibility as shown in maize. This underlines interesting traits for further comparative genetic studies, as maize represents a good model for digestibility and miscanthus for composites.

International audience; Belowground materials from two miscanthus species were ground into fragments for preparing polyethylene composites. Both species show a lot of similarities in terms of polysaccharides, lignin and cell wall-linked p-coumaric and ferulic acids contents. The structures of polysaccharides and of lignins are markedly different in the miscanthus belowground and aboveground biomass. The non-cellulosic fraction of the samples comprises a high level of xylose, with the arabinose to xylose ratio about twice as high as that observed for analogous stem samples, suggesting that belowground arabinoxylans are more substituted than stem ones. The mechanical properties of the belowground miscanthus-polyethylene composites correlate with several of their compositional traits, with similar trends as for plant stem-polyethylene composites with positive correlations for lignin and p-coumaric acid contents and negative correlations for most non-cellulosic sugars.

International audience; Concrete blocks prepared with Portland cement and miscanthus-based aggregates were prepared in order to check if the miscanthus genotype may influence their mechanical properties and to perform an environmental assessment. To produce lightweight, load-bearing concrete blocks using miscanthus stem fragments as aggregates in a single mixing method turned out to be impossible, although trying to optimize the concrete formulation. The results show that genotypes and size of miscanthus fragments controlled the mechanical properties of the final blocks. The lower was the amount of light elements such as leaves and sheath, the better were the mechanical properties of the blocks. When comparing genotypes with the same leaf/stem ratio, it was not possible to see a correlation between the biochemical composition of the stem and the compressive strength of the blocks. A probable explanation is the small variation of biochemical composition between genotypes. Using life cycle analysis tools, miscanthus block were not found to be competitive with conventional alternatives (concrete block and lightweight pumice block) when trying to increase compressive strength above 3 MPa. However, compared to non-load bearing alternatives (light clay brick), blocks integrating miscanthus had a better global environmental performance mainly due to a favorable climate change impact. The present work also points out the risk of decreasing the environmental performances when cultivating the crop on land in competition with food, because of the impacts of indirect consequences of Land Use Change.

International audience; The thermal and dynamic mechanical properties of miscanthus stem fragments and differences between genotypes and positions along the stem are studied in relation with their biochemical and structural characteristics. The starting degradation temperature does not correlate to the biochemical composition. However, the first DTG peak temperature is negatively correlated to hemicelluloses content and positively correlated to lignin and p-coumaric contents. A pronounced genotypic effect is evidenced on fragments elastic moduli while limited effect of the position along the stem is found. This is mostly related to ferulic and p-coumaric acid contents of stem fragments for which a strong correlation to elastic moduli is evidenced. Our results highlight that genotypic effect, position along the stem, stem fragment dimensions and mechanical properties of miscanthus stem fragments are strongly interconnected in relation with their respective biochemical and structural characteristics. This opens interesting perspectives for identifying key biological traits that need to be optimized for a better selection of performing miscanthus genotypes targeted to polymer composite applications.

The prediction of the morphology of ternary polymer blends requires a good knowledge of the values of the three interfacial tensions. We selected three polymers, either biobased or biodegradable, PA, PBAT and PLA and we accurately measured their interfacial tensions using the retraction method, varying the molar mass or inverting the phases. The following values of interfacial tensions were obtained: = 3.3±0.7mN/m, = 5.6±0.3mN/m and = 3.0±0.4 mN/m. These values were used to calculate the spreading coefficients giving rise to two negative coefficients and one coefficient close to zero. Ternary blends with various compositions, two different levels of viscosity for the PBAT, different processing conditions were prepared. There was a very good agreement between the predictions of the spreading theory, when using the values of interfacial tensions in the right order of magnitude, and the observed morphologies, whatever the polymer serving as a matrix. When the PLA or PBAT was chosen as the matrix, the ternary blend morphology was composed of composite droplets, presenting a partial wetting morphology, dispersed in the polymer matrix. This morphology was observed whatever the composition, the viscosity level of the PBAT phase and the processing conditions. A further calculation of the free energy confirmed this 2 morphology. The formation process of this semi-encapsulated morphology was observed during blending.

International audience; A sea water wave tank fitted in an artificial UV light weathering chamber was built to study the behaviour of polypropylene (PP) injected pieces in close ocean-like conditions. In air, the same pieces sees a degradation in the bulk with a decrease of mechanical properties, a little change of crystal properties and nearly no change of surface chemistry. Weathering in the sea water wave tank shows only a surface changes, with no effect on crystals or mechanical properties with loss of small pieces of matter in the sub-micron range and a change of surface chemistry. This suggests an erosion dispersion mechanism. Such mechanism could explain why no particle smaller than about one millimeter is found when collecting plastic debris at sea: there are much smaller, eroded from plastic surfaces by a mechano-chemical process similar to the erosion mechanism found in the dispersion of agglomerate under flow.

International audience; This work aims to prepare composites of polyamide 66 with vegetal fibers from curauá, jute, and flax. Alkaline treatment was conducted followed by silanization, improving the thermal properties of treated natural fibers. To reduce the processing temperature of polyamide 66, a combination of LiCl and N-butylbenzenesulfonamide was added to pure polyamide 66. It is shown that plasticizing polyamide 66 is one way to prepare composites with natural fibers using this high temperature polymer. The increase in elastic modulus of polyamide 66 and the decrease in strain at break were observed.

International audience; The use of lignocellulosic fibers derived from renewable resources as a reinforcing phase in polymeric matrix composites provides positive environmental benefits with respect to ultimate disposability and raw material use. Despite the attractive properties, lignocellulosic fillers are used only to a limited extent in industrial practice due to the restriction to 200℃ in composites processing temperatures. Lignocellulosic materials start to degrade near 230℃. This limits the type of thermoplastics that can be used in association with polysaccharide fillers. To overcome these disadvantages, chemical treatments, i.e. alkaline treatment, were applied to curauá fibers to improve the thermal properties. Colorimetry was employed to evaluate the extension of darkening of composites prepared with treated curaua and Avicel. Fourier-transform infrared spectra of polyamide composites with treated curaua showed no differences when compared to pure polyamide. Moreover, no changes in molar mass were observed in microcrystalline cellulose processed in different temperatures.

Four processing tools (two twin-screw extruders, one being a mini-extruder, and two mixers) were used to prepare plasticized cellulose acetate with 20 wt% of glycerol triacetate. The goal was to deduce if the scale of the processing tool influences the dispersion of the plasticizer as estimated by the thermal, rheological, and mechanical properties of the obtained materials. The amount of polymer used ranged from 5 g for mini-extruder to a 10 kg/h for pilot-scale extruder. The specific mechanical energy was used to compare the thermal, rheological, and mechanical properties of cellulose acetate obtained with the four processing tools using different processing conditions. The measurement of the glass transition temperature was not able to discriminate the four tools used. Rheology shows differences, not as a function of small or large tools, but in terms of specific mechanical energy. The larger was the tool, the higher were the Young's moduli. This was ascribed to an overall better distribution and dispersion of the plasticizer. However, all variations were small, showing that small laboratory processing machines can prepare thermoplastic compounds with similar properties as pilot scale extruders, at least in what concerns cellulose acetate. POLYM. ENG. SCI., 2016. © 2016 Society of Plastics Engineers

International audience; This study was devoted to identifying specific biochemical traits that may be addressed in maize breeding programs for improving lignocellulosic composition for biomass utilization in the composites. To this aim, six maize contrasted genotypes were cultivated, harvested and compared in term of their capability to reinforce a low-density polyethylene (LDPE) matrix. Stem biochemical composition and histological pattern of a given internode were evaluated to determine the traits that impacted the mechanical properties of the maize-LDPE composites. Across genotypes, maize stems with higher concentrations of total cell wall residue, lignin, p-coumaric acids and cellulose in conjunction with lower concentrations of ferulic acids and hemicellulose yielded better composite performances. This strong influence of hydroxycinnamic acids is a new finding. Cellulose is found to be the component dominating the mechanical properties of the fragments since the effects of cell wall residue and cellulose are following the same pattern towards composite properties. Contrary to expectations, the correlations between the histological structure of stems and the mechanical properties of the composites prepared with stem fragments is complex and cannot be interpreted in a simple manner. The two most contrasted genotypes in terms of mechanical performances (Cm484 and F2bm3) have the most contrasted biochemical and histological parameters.

International audience; hree types of treatments of miscanthus were performed, alkali, silanization and the combination of both. There is a direct inverse relation between the amount of sugar-containing molecules extracted from miscanthus and the mechanical strength of the concrete blocks. The use of alkali treated stems as fillers increased remarkably the strength of the blocks, and this was even higher when the alkali treated fibers were coated with silica, with a compression strength of 11 MPa compared with an initial 2.2 MPa. The use of alkali-treated stems result in a faster cement hydration, compared to untreated ones suggesting that specific sugars or other components released from the alkali-treated plant may favor cement hydration. A remarkable decrease of the cellulose and xylose content is observed for the miscanthus pieces after being soaked in a cement-water-sand mixture, these two molecules being adsorbed on cement particles

International audience; Sorghum is expected to contribute significantly to the growing needs of ligno cellulosic biomass that will support the productions of renewable energy, biomaterials and innovative biorefinery approaches. The agronomic and genetic assets of sorghum will facilitate these contributions. Nevertheless, in order to fine tune the varieties to the expectations of the growers (agronomic behavior) and of the different value chains (quality parameters) there is a crucial need to i) optimize the production process of sorghum based derived products and ii) to accurately define the target ideotypes to consider in breeding programs depending on the end-products and contexts considered. As a first step, we considered three end products: methane, biocomposite and feed. For the first two targets, we optimized the process of production by adjusting the pre-treatments and fine tuning-the different steps of the processes. As a second step we aimed at identifying the sorghum traits that contributed to the final properties of the end products. To reach this objective, we characterized at the biochemical, histological and physical levels a panel of diversity that encompassed most of the chemical variability of sorghum biomass. This panel was also characterized for its feed and biocomposite properties and for its biomethane production potential. This allowed the identification of the sets of biomass properties to target for the different end-products. As a last step, specifically for the energy targets (methane and second generation ethanol), we performed a spatially based multicriteria analysis at the regional level (anchoring the analysis on the French Midi Pyrenées region) to assess the relevance of different types of crop management and end product value chains in accordance with the local constraints (i.e. water availability, technical context). These three steps provided us with a decision tool to orientate breeding efforts depending on the targeted end-product, the environmental and technical contexts.

International audience

International audience; Swollen softwood cellulose pulp in a DMAc/LiCl solvent system was compressed under elevated pressure (up to 900 MPa) in a Bridgman anvil press. The influence of high pressure on two cellulose systems was studied by measuring X-ray diffraction, mechanical and optical properties and observing scanning electron micrographs of the morphology. Compressed swollen cellulose, washed with distilled water, had lower elastic modulus and hardness compared to swollen cellulose washed with a combination of 2-propanol and deionized water. This work showed that material with lower mechanical properties will be affected more by compression and will result in higher mechanical properties after pressure treatment. Transmitted light in the visible range for both systems was increased after elevated pressure was applied. The XRD measurements revealed the decrease of the cellulose crystallinity after high pressure treatment for all swollen cellulose samples. The morphology of the compacted samples showed noticeable differences between the compact smooth surface and the layered core.

The articles belonging to the special issue are open access, all published articles are freely available online.; International audience; The dependence of cellulose solution shear viscosity as a function of temperature and measurements of solution activation energy are reviewed based on results obtained in our laboratory and elsewhere. Cellulose is not easy to solubilize. Solutions are often forming aggregates and are not stable in time and with temperature variations. This can be highlighted by the calculation of the activation energy of the shear viscosity, a parameter which is very sensitive to any change in the state of the solution during the shear experiments. Changes in the organization of the solution like gelation or cellulose or solvent degradation are phenomena which are strongly influencing the values of activation energy. Cellulose solutions in three classes of solvent, ionic liquids, N-methylmorpholine-N-oxide-monohydrate and (7-9)% NaOH-water with and without additives, were analyzed. Cellulose was of various molecular weights. The plot of the reduced activation energy versus cellulose concentration shows that most points fall within a narrow range of values, with a low downward curved shape, not in agreement of the predictions developed for flexible chains in semi-dilute regime.

International audience; Miscanthus is a perennial grass which may be interesting for the composite industrial sector. When the cycle of the crop comes to the end, the biomass below ground need to be valorized. One never-studied topic is to evaluate its potential valorization as composites. Below-ground (rhizomes plus roots) biomass of Miscanthus × giganteus cultivated on three different blocks with three different nitrogen fertilization levels were collected, ground, sieved and used as fillers in a polyethylene matrix. Miscanthus rhizome plus roots fragments have a very low axial ratio around two, in contrast with stem fragments which are three to four times more elongated. The mechanical properties of composites filed with rhizome plus roots fragments are much below the ones of the composites filled with stem fragments. The tensile strength is about half the values of stem composites (7.4 MPa for rhizomes compared with 13 MPa for stems) and there is a very large drop of the Young’s modulus, down to 260 MPa compared with 900–1000 MPa for stems. Only impact strength has good values (6–7 kJ/m2). The very low aspect ratio of the rhizome fragments combined with the fact that there are twice more cellulose in stems than in rhizomes with a non cellulosic polysaccharides-cellulose ratio being twice larger for rhizomes (about 1 for rhizomes and 0.45 for stems) are both acting in the same direction of lowering the mechanical properties of rhizome fragment-based polymer composites. These low mechanical properties are restricting the use of such composites to applications were the low cost is the main factor of choice.

International audience; Composites prepared with whole sorghum stem fragments reinforcing a polyethylene matrix were studied using ten different sorghum genotypes. Using a robust processing protocol, it is shown that for a given sorghum genotype, the composition of the stem fragments varies depending on the size of the sieved fragments but with the genotype effect being larger than the sieving effect. There is a variation of mechanical properties between the genotypes (from 0.6 to 1 GPa for modulus, from 7.2 to 11.5 MPa for tensile strength and from 4.4 to 6.2 kJ/m2 for impact strength). The genotypes giving the best tensile mechanical properties are the ones which have the highest viscosity, which show during blending the largest energy dissipation and which have the less decrease of size after processing. There is a weak correlation between tensile mechanical properties and resistance to impact suggesting that it is not the same tissues or physical properties which contribute to these two tests.

International audience; Natural fillers composed of cellulose, lignin and fillers with a varying lignin/cellulose ratio (flax, jute, curauà fibers and miscanthus stem fragments) were used to prepare composites with polypropylene using the same procedure, with or without a maleic anhydride–grafted polypropylene (MA-g-PP) coupling agent. A clear acceleration of the crystallization kinetics was observed in the presence of miscanthus stem fragments. For non-coupled composites, the size and aspect ratio of fragments had no significant influence onto the crystallization kinetics of polypropylene. The presence of the MA-g-PP coupling agent increased even more the kinetics. A clear effect of the nature of the polymers present in the filler was observed. There is a direct relationship between the values of the Avrami kinetic constant k for the six fillers and their lignin content, the more effective to enhance crystallization kinetics being pure cellulose. Lignin has no effect onto the crystallization kinetics of polypropylene.

International audience; The hypothesis made is that thermal resistance of sorghum and miscanthus stem pieces taken at well-defined positions of the stem is simply related to their biochemical composition. For miscanthus, two different genotypes and two internode levels were selected. For each region, the stem was divided into three radial layers. For sorghum, two different genotypes were selected and the stem was divided into the same three radial layers. The results show that the thermal analysis is only sensitive to very large variations of compositions. But aside of such large composition differences, it is impossible to correlate thermal effects to biochemical composition even on very small size, well-identified pieces of plant materials. The interplay between sugar-based components, lignin and minerals is totally blurring the thermal response. Extreme care must be exercised when willing to explain why a given plant material has a thermal behaviour different of another plant material.

International audience; Three-dimensionally shaped cellulosic objects were produced via a two-step procedure: swelling of softwood pulp (93 % cellulose; 4.5 % hemicellulose; 54 % crystallinity) in DMAc/LiCl followed by moulding. Swollen cellulose pulp in the form of gel was solidified with two different anti-solvents: distilled water and a combination of 2-propanol and deionized water. The solid cellulose material was further moulded in a custom-built prototype mould. The role of the anti-solvent was to solidify the swollen cellulose fibres and prepare mouldable solid specimens. The anti-solvent was chosen based on the following criteria, viz., recoverability, stable chemical reactivity, availability, cost and previous research in the anti-solvent area. The choice of solidification solvent had a great influence on the structure and mechanical properties of the final cellulose material. Results of different characterisation techniques showed that when the cellulose gel was washed with distilled water, it had a significantly higher number of lithium cations (ICP-MS and Raman), amorphous structure (X-ray) and lower mechanical properties (nanoindentation) compared to samples washed with a combination of 2-propanol and deionized water. An increase in viscosity as previously reported and changes in the NMR and IR spectra of DMAc upon LiCl suggested the formation of an ion-dipol complex, where lithium cations reside adjacent to the oxygen of the carbonyl group of DMAc. The formed macrocation [DMAcn + Li]+ was preserved between cellulose chains in cellulose specimens washed with distilled water and had an essential role in the disruption of initial bonds, thus enhancing mouldability. Electron microscopy (FE-SEM) studies showed that the surface of cellulose after mechanochemical treatment was rough with no presence of fibres

International audience; Layered double hydroxide prepared with lignosulfonate (LDH/LS) can be easily dispersed down to the nanometric scale in thermoplastic starch, at concentration of 1 up to 4. wt% of LDH/LS. They can thus be used as a bio-based reinforcing agent of thermoplastic starch. Incorporation of LDH/LS in starch must be done using LDH/LS slurry instead of powder on order to avoid secondary particles aggregation, the water of the paste being used as the starch plasticizer. This reinforced starch was used for preparing a starch-polyolefine composite. LDH/LS-starch nanocomposites were mixed in a random terpolymer of ethylene, butyl acrylate (6%) and maleic anhydride (3%) at concentrations of 20. wt% and 40. wt%. With a 20% loading of (1. wt% LDH/LS in thermoplastic starch), the ternary copolymer is partially bio-based while keeping nearly its original processability and mechanical properties and improving oxygen barrier properties. The use of layered double hydroxides is also removing most odours linked to the lignin phase.

International audience; A commercial dissolving pulp was treated with aqueous solutions containing 3, 5 and 7 % of an organometalic complex (nitren) with the aim to selectively extract xylan and study its impact on the conventional physical-chemical properties of the pulp. The influence of these treatments on the pulp dissolution in a moderate solvent (8 % NaOH aqueous solution) was assessed by measuring the dissolution yields and the dissolution mechanisms. The results of this study show that nitren treatment has the effect of removing a large part of the xylan present in a dissolving pulp. It is also removing mannans and most important, it is influencing cellulose in two ways, (1) extracting it with more intensity when the nitren concentration increases, and (2) decreasing its mean molecular mass, also more evident with nitren concentration increase. The nitren extractions are favourable for the dissolution in cold NaOH-water, being more effective with higher concentrations. This chemical modification of the fiber surface leads to the disassembly of the primary wall. This allows an easier access of the NaOH reagent to regions not accessible on the initial fibres, which with the decrease of the cellulose molecular weight allows an easier dissolution and gives different dissolution mechanisms.

International audience; Dry and wet cotton linters were compressed under elevated pressure in a home-made Bridgman anvil press designed to reach 2.5 GPa and 180 °C. The structural organisation of cotton was changed under the joint action of temperature and pressure. Cotton having high moisture content shows that only a thin surface layer is partially destructured to a compact mat of nanofibres, while the initial cotton fibres are only deformed inside the sample. For dried cotton, the whole sample undergoes a destructuration into a compact mat of nanometre-sized fibres. The mechanical properties were studied by nano-indentation and dynamic mechanical analysis. Compressed dry cotton has higher modulus (10.3 GPa) than wet cotton (6.8 GPa). We postulate that the transverse elastic modulus of cotton microfibrils is around the value of 10 GPa. This work showed that nano-sized fibrils can also be separated in the solid state without flow, and re-compacted to form a solid object.

International audience; New organic inorganic layered double hydroxide (LDH) organoclays are assembled through coprecipitation with lignosulfonate (LS) interleaved inorganic host structure sheets. The biopolymer is found to accommodate the interlayer space adopting a bilayer molecular arrangement resulting in a basal spacing of 2.54 nm. However the crystallinity of the resulting bio-organoclay is weak, probably due to the difficulty of the inorganic sheets to be built on amorphous polymer chain, the latter inducing low structural ordering. An organoclay of composition Zn2Al/LS is subsequently used as filler in three bio-related polyesters, poly(lactic) acid (PLA), poly(butylene) succinate (PBS) and poly(butylene adipate-co-terephthalate) (PBAT). Melt polymer extrusion using 5 wt.% organoclay loading yields polyester nanocomposite with a nanocomposite structure largely intercalated for both PLA and PBS (Δd (expansion) > 6 nm) while a non miscible structure is obtained for PBAT. The incorporation of hydrophilic Zn2Al/LS platelets decreases the water/polymer contact angle of about 10° for the LDH/LS PBAT composite only. A strong increase of the complex viscosity |η*| is observed for both nanocomposites Zn2Al/LS PLA and PBS compared to the polyester itself. This is explained on the basis of a chain extender behavior of the intercalated Zn2Al/LS platelets towards polymer chains as evidenced on the Cole Cole representation showing an increase of the real viscosity in the low-ω region. In opposition a strong decrease in |η*| is observed for PBAT, underlining a plasticizing effect of the organoclay filler. Comparatively, the thermal stability of PLA is slightly enhanced with an increase of T0.5 value while PBS and PBAT bio-nanocomposites degrade at slightly lower temperature.

International audience; The production of ligno-cellulosic biomass-based composites requires the development of new methodologies to evaluate the reinforcement potential of a given biomass, such as miscanthus studied in the work. Miscanthus stems from thirteen genotypes were broken into elongated fragments and mixed with polypropylene composites in an internal mixer. The aim is to find the best protocol able to discriminate miscanthus genotypes for their reinforcement capability. The following process parameters were optimized in order to maximize the reinforcement effect of the stem fragment filler: mixing parameters (mixing time, rotor speed and chamber temperature), temperature, fragment content, size and length distributions and coupling agent. The relationship between the process parameters and the mechanical properties of composites were analyzed to evaluate the influence of genotype on reinforcement performance, showing the robustness of the protocol in effectively discriminating genotypes according to their reinforcing capacity.

International audience; Miscanthus Giganteus – reinforced polypropylene composites have been prepared by internal mixing. The effect of the size of the miscanthus fragments used as fillers onto the thermal properties of composites has been evaluated by differential scanning calorimetry (DSC) and polarized light optical microscopy (POM). The kinetics of the crystallization processes have been evaluated by isothermal methods. The influence of the fiber-matrix interface onto the melting/crystallization processes has been evaluated by adding a maleic anhydride–grafted polypropylene (MA-g-PP) coupling agent. A clear acceleration of the crystallization kinetics was observed in the presence of miscanthus stem fragments. However, the results showed that, for non-coupled composites, the size and aspect ratio of those fragments had no significant influence onto the crystallization kinetics of polypropylene. The presence of the MA-g-PP coupling agent increased the kinetics and reduced the crystallization activation energy. Although relatively small, if a good fiber-matrix interface is achieved, the size of the filler plays a significant role onto the crystallization kinetics of the matrix, with smaller fragment leading to faster kinetics and reduced activation energy

National audience

International audience; The article is a critical review of all aspects of the dissolution of cellulose in NaOH-based aqueous solutions: from the background properties of the solvent itself, to the mechanisms of cellulose fibre swelling and dissolution, solution structure and properties and influence of additives and, finally, to the properties of various materials (fibres, films, aerogels, composites and interpenetrated networks) prepared from these solutions. A historical evolution of the research on this topic is presented. The pros and cons of NaOH-based aqueous solvent for cellulose are summarised and some prospects are suggested.

International audience; The use of plant biomass for developing energy efficient and low cost construction materials is an emerging field in building construction and civil engineering. Although the biomass-based cement and concrete composites have several advantages, such as low densities, low amount of CO2 gas emission, good thermal and acoustic insulation, there are also disadvantages or open questions like the durability of biomass in alkaline cement matrix, the high absorption of water and the cement-biomass compatibility, all deteriorating concrete mechanical properties, which are already intrinsically low due to the low mechanical properties of biomass-based fillers. This review gives the necessary basis in plant structure and composition for understanding how and why many treatments tested on biomass for overcoming the above-mentioned difficulties are acting. This paper reviews research papers and patents on the treatments tested to improve the mechanical properties, durability and compatibility of biomass for its use as concrete fillers for building materials.

International audience; The influence of ZnO as cellulose-8%NaOH-water solution stabilizer against gelation is studied. Cellulose intrinsic viscosity in 8%NaOH-water as a function of solution temperature is investigated in the presence and absence of ZnO. The addition of ZnO did not bring any improvement in terms of solvent thermodynamic quality. Non-dissolved ZnO particles were observed above 0.8-0.9% ZnO in 8%NaOH-water. Gelation of cellulose-8%NaOH solutions with and without ZnO are studied for various cellulose and ZnO concentrations (4-6% and 0-1.5%, respectively) in a wide range of temperatures (-5 °C to 50 °C). Gelation times were exponentially increasing with increasing ZnO concentration and with decreasing cellulose concentration and solution temperature. Gelation times of cellulose-NaOH-water-ZnO systems were found to follow a semi-empirical model correlating these three parameters. We suggest that ZnO is acting as water molecular "binder" stabilizing cellulose-NaOH-water solutions.

International audience; The swelling and dissolution mechanisms of dry, never-dried and re-wetted Lyocell fibers were investigated using mixtures of N-methylmorpholine N-oxide and water with various contents of water (from monohydrate to 24% w/w). A radial dissolution starting from the outer layers was observed. Dissolution kinetics was dependent on the water content, the drying state and the spinning conditions. A buckling of the core of dry fibers was observed during swelling. This phenomenon was attributed to the deformation of the unswollen core to accommodate the contraction of the swollen parts of the fiber. In purely swelling conditions with no dissolution, a huge swelling of a very thin skin layer was observed in the first stage, followed then by a progressive swelling of the inside of the fiber. We postulate that this mechanism arose from the fact that this skin is much less crystalline than the core.

The authors are grateful to the publisher, Elsevier, for letting the manuscript being archived in this Open Access repository. The final publication is available at http://www.sciencedirect.com/; International audience; Cellulose is a future major source of materials and biofuel but its extraction and its chemical or enzymatic treatments are difficult, polluting and inefficient tasks. The accessibility of the reagents to cellulose chains is indeed limited. Classical evocated reasons for this lack of accessibility are pore structure, tight hydrogen bond arrays, crystallinity and presence of resistant materials like lignin. Studying dissolution of cotton hairs and regenerated cellulose fibres in various solvents under uniaxial tension, we found that tension is preventing these fibres to dissolve in chemicals that would dissolve the same cellulose fibres tension-free. We show that what is controlling dissolution is not the degree of swelling since, at the same degree of swelling, fibres under tension do not dissolve while fibres without tension do. An important result is that when a fibre under tension (thus swollen but not dissolved) is breaking, it is immediately dissolving. Under tension, when the solvent is present around cellulose chains, it is activated to solvate the chains only when tension stress is released. A chemical reaction like acetylation of cellulose fibre under tension also gives an interesting result. The degree of substitution remains very low while the same experiment performed without tension leads to higher degree of substitution followed by the dissolution of the fibre (even increasing further the DS due to homogeneous reaction). We postulate that the lack of dissolution capacity or reacting activity under tension can be due to the hampering of local conformational movements, cellulose chains being not able to perform axial movements. The availability of performing local conformational movements could be a main component of cellulose activation.

The authors are grateful to the publisher, Springer, for letting the manuscript being archived in this Open Access repository. The final publication is available at http://www.springerlink.com; International audience; Four wood pulps and a microcrystalline cellulose were dissolved in a NaOH 8%-water solution. Insoluble fractions and clear solution fractions were isolated by centrifugation and were observed by optical microscopy and transmission electron microscopy. Molecular weight distribution, carbohydrate composition and cellulose II content were measured. The dissolution of wood cellulose fibres in NaOH 8%-water solutions occurs by successive dismantlement and fragmentation steps governed by the swelling and the shearing of the original structure. The cellulose from insoluble and clear solution fractions is in both case converted in cellulose II and the insoluble fractions contain embedded mannans. Besides, the molecular weight distributions of cellulose from insoluble and clear solution fractions reveal the existence of heterogeneities in dissolution capacity of the cellulose chains, independent to the degree of polymerization, which are related to the chemical environment of the chains in the fibre structure.

International audience

International audience; Hydroxyethyl cellulose (HEC) fibers with low degree of substitution were prepared by wet spinning of solutions in 8 wt% aqueous NaOH solvent. The spinning solution had a classical shear-thinning behavior and a good stability towards gelation according to its rheological behavior. The influence of drawing conditions on the structural characteristics and tensile properties of the resultant HEC fibers was investigated using synchrotron X-ray measurements, scanning electron microscope and tensile tests. HEC fibers exhibited circular cross-sections with soft and deformable surface layer as well as relatively uniform and dense inner structure. Regardless of the different jet stretch or post-drawing conditions, most of the structural features and the tensile properties of HEC fibers were improved as the drawing ratio increased. Post-drawing was confirmed to be the key factor in controlling the fiber structure and tensile properties due to plastic deformation. Excellent tensile properties were found for HEC fibers prepared at relatively low jet ratio associated with high post-drawing ratio.

The articles belonging to the special issue are open access, all published articles are freely available online.; International audience; Hydroxyethyl cellulose (HEC) with low molar substitution has better solubility in 8%NaOH-water solution than pure cellulose. The thermal behavior of ternary HEC/NaOH/water mixtures was investigated by DSC, and the results are compared with those of cellulose/NaOH/water solutions, aiming at providing better understanding about cellulose dissolution mechanism in NaOH-water. At low polymer concentrations and below 0°C, HEC and cellulose solutions exhibit a similar thermal behavior with ice, eutectic and/or melting and recrystallization peaks, showing that the overall interactions between NaOH, water and cellulose or HEC are identical. However, when the concentration increases above 2%, the eutectic peak of HEC solutions disappeared, leaving only the ice peak, which is different from previous results for cellulose where the disappearance of the eutectic peak was related to the maximum solubility of cellulose (around 8 wt%). This implies that the dissolution behavior of HEC in NaOH solution is changed due to possible changes of chain flexibility and/or increased attractions to water caused by the hydrophilic hydroxyethyl groups. The melting and recrystallization peaks visible only at low concentrations of HEC or cellulose in solution also support the conclusion that dissolution of cellulose and HEC at low concentrations bears features which are not yet understood.

International audience; The shear rheology of a microcrystalline cellulose dissolved in a 9% NaOH aqueous solution was studied in the steady and oscillatory modes. The cellulose-(9% NaOH-H2O) mixtures show not to be true solutions. In the dilute regime, with cellulose concentration below 1%, the rheological behavior is typical of the one of suspensions. The formation of cellulose aggregates is favored when temperature is increased. In the semidilute regime, an irreversible aggregate-based gelation occurs, being faster with increasing temperature.

The curing of a homogeneous mixture of a nematic liquid crystal and an acrylate UV curable prepolymer was studied by small angle light scattering, varying temperature and UV intensity. For all the conditions except at elevated temperature, the phase separation occurs with a spinodal decomposition which phases can be more or less easily recognised. Whatever the temperature below the clearing point of the liquid crystal and the UV intensity, the isotropic-to-nematic transition that occurs in the liquid crystal rich region is easily seen as a strong decrease of the light scattering intensity. For all the conditions tested, the final morphology is in the form of a droplet morphology. At high UV intensity, there are two scattering peaks that are appearing in the scattering pattern which was tentatively interpreted as a double spinodal decomposition.

International audience; The rheological properties of hydroxyethyl cellulose (HEC) with a low molar substitution (MS) dissolved in 8 wt% NaOH–water were studied as a function of solution temperature, polymer concentration and molar substitution. Special attention was paid to gelation kinetics. Similar to cellulose dissolved in alkali or ionic liquids, the intrinsic viscosity of HEC decreased with temperature increase, indicating a decrease of solvent thermodynamic quality. The gelation time of HEC solutions decreased exponentially with temperature but the kinetics is much slower than the gelation of microcrystalline cellulose solutions in the same solvent. Higher molar substitution leads to slower gelation. The small amount of introduced hydroxyethyl groups prevented cellulose aggregation thus increasing solution stability.

International audience; The 3rd EPNOE International Polysaccharide Conference (EPNOE 2013) with the title “Polysaccharides and polysaccharide-derived products. From basic science to applications” was held in Nice (France) from 21 to 24 October 2013. This conference was jointly organised by EPNOE (European Polysaccharide Network of Excellence) and the Cellulose and Renewable Materials Division of the American Chemical Society (ACS). Patrick Navard from the Materials Processing Center of Mines ParisTech was the chairman of the local organising committee. EPNOE 2013 was a great success. More than 450 participants from 45 countries gathered in the newly refurbished Nice Acropolis Convention Center, a perfect location for a scientific meeting with rooms for oral communications, posters and lunch being in the same place. It was also a wonderful site since the Congress Hall is situated in the heart of the old Nice city, close to the Mediterranean sea side. The EPNOE 2013 conference was a forum for bringing together academic, industrial, and government scientists and students dealing with polysaccharides and polysaccharide-derived products. Scientists from many disciplines were present, including biologists, chemists, physicists, food specialists, technologists, and environmentalists. In total, 236 oral communications were presented in four parallel sessions and 200 posters were permanently displayed throughout the conference, catalysing numerous discussions and providing good visibility of the exhibited work.

International audience; Calorimetry, small-angle X-ray scattering, and viscometry were used to study the structure of NaOH-water and cellulose-NaOH-water solutions in the range of 0-20% NaOH and 0-5% cellulose concentrations in the low-temperature region of -60 to 0 °C. Pure NaOH-water solutions show a pseudoeutectic behavior with three phases: free water that crystallizes and melts at a certain melting temperature which decreases with the increase of NaOH concentration; a NaOH hydrate that melts at -35 °C; water bound to hydrates that does not crystallize. The addition of cellulose does not change the amount of the free water. The cellulose chains are located in the hydrate region, one to two hydroxyl groups of the glucopyranose unit being bound to a soda hydrate.

International audience; Concentrated suspensions of swollen-in-water polyelectrolyte gels are shown to behave a new electro-rheological fluid. Without electric current the suspension apparent viscosity is high, while upon switching current the apparent viscosity drastically decreases. The change of apparent viscosity is due to the reversible contraction of the gel in the presence of an electric current. Under a 20-100 mA current, a suspension of sodium polyacrylate gel particles can decrease its apparent viscosity by more than 100 times.

International audience; We have studied by in situ microscopy the flow of a lyotropic liquid crystal polymer, hydroxypropylcellulose (HPC) in water, around an obstacle placed in a rectangular flow channel. The obstacle separates the flow into two parts which rejoin downstream of the obstacle, resulting in the formation of a `weld-line'. Measuring the velocity field in the vicinity of the weld-line beyond the obstacle, we find as expected a positive elongational strain (acceleration) along the weld (parallel to the flow direction). For an anisotropic (concentrated) HPC solution we observe in addition a significant shear strain in the weld-line region, there being an important velocity gradient perpendicular to the plane of the weld line. Isotropic (lower concentration) solutions of the same polymer demonstrate no visible weld line, a larger elongational strain rate near the obstacle, and no shear component of strain downstream of the obstacle. These results are similar to observations reported for fluids reinforced by macroscopic fibres. Polarised light observations of the anisotropic solution show that the strain field generates a generally increased degree of orientation of the liquid crytalline polymer near the weld (generally reduced crossed-polariser transmitted intensity when the polariser is parallel to the flow direction), however there is also a striking fine birefringent colour variation in the weld-line region, reminiscent of the structure observed at the channel side walls in rectangular channel flow (Haw and Navard 2000). The results show that the simple concept of weld-line structure as confined to an enhanced alignment along the weld due to elongational strain is incomplete; the two-dimensional shear strain field must also be taken into account for the anisotropic fluid.

Epoxy resins with mesogenic groups were prepared from diglycidyl ether of 4,4'-biphenol (DGEBP) as rigid block and 4,4'-diaminodiphenylsulphone (DDS). Curing kinetics were investigated using size exclusion chromatography in the 155-175°C range above the melting temperature. It was found that the ratio R=k 2 /k 1 or secondary to primary amino hydrogen rate constants displays unusual values higher than unity and decreased on increasing the temperature. This effect was assumed to be due to the neumatic structure in which polymerization takes place before reaching the gel point.

International audience; The rheology of rigid rod cellulose whisker suspensions has been investigated. The isotropic-at-rest suspension flow curves show two plateaus, one at low shear rates and another at high shear rates, that reflect the flow of isotropic (at low shear rates) or oriented (at high shear rates) suspensions. From the low shear rate viscosity plateau vs concentration, we see that the system is in the semidilute region above 0.02 wt %, in agreement with the theoretical predictions. From the same curve, we can estimate a maximum packing concentration of whiskers rods that corresponds to the experimentally measured isotropic-to-anisotropic transition. The high shear rate plateau viscosity data show that the. suspension is still in the dilute state above 0.6 wt %. The critical concentration at the dilute-semidilute transition is thus strongly dependent on the state of order, which suggests that care has to be taken when measuring parameters extracted from flowing solutions or suspensions, as for example occurring with Ubbelhode viscometry. Above a certain critical concentration, the suspensions become anisotropic at rest. The viscosity vs concentration curve has a maximum that vanishes at high shear rates as for liquid crystalline polymer solutions. Rheological and rheo-optical observations show fast inception and relaxation of both the rheological functions and the texture, in complete contrast with liquid crystalline polymer solutions.