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International audience; Fibre bundles are groups of elementary fibres glued together thanks to the middle lamella, and are the main fraction in plant fibre composites. In this study, relationship between the mechanical properties of flax fibre bundles, chemical composition and cellulose structure were investigated. To do so, a sequential biopolymer extraction was implemented. Fibre bundles were first depectinated by oxalate extraction, and then the hemicelluloses were extracted by LiCl/dimethyl sulfoxide (DMSO) and KOH. The oxalate extract consisted of homogalacturonans and type I rhamnogalacturonans, while the LiCl extract was composed mainly of glucomannans and the KOH extract of xyloglucans. The KOH stage resulted in the appearance of cellulose II in flax bundles. The extraction of pectin and hemicelluloses led to the disappearance of the middle lamella concomitant with a decrease in the tensile Young's modulus and maximum strength. Finally, the fibre bundle composition, ultrastructure and mechanical properties are discussed together in view of the thin middle lamella.

International audience; Injection moulded composite materials reinforced with wood fibres or particles can offer a credible alternative to other plant-derived fibres, particularly from an economic and environmental point of view. In this study, we compared the recycling behaviour of poly-(propylene) composites reinforced with ground wood particles versus wood and flax fibre reinforced composites. An experimental and numerical approach was used. In spite of the mechanical and morphological performances of fibres which were initially poorer than those of long fibres, the wood particles demonstrated their reinforcement potential (+84 % and +14 %, for the Young’s modulus and the strength at max, respectively, compared to the pure matrix), due to their good adhesion with the matrix and also to the stability of their aspect ratio after recycling (-24 % after 5 injection cycles against -66 % and -61 % for long flax and wood fibres, respectively). The numerical model developed and fed by the mechanical and morpho-logical measurements carried out on the reinforcements made it possible to compare the experimental and nu-merical values. Overall, a close match was obtained between the two sets of parameters. The small differences obtained can be explained by the increase in fibre dispersion as the recycling process progresses, as well as by the possible increase in wood stiffness after several processing cycles.

The paper describes an optimised strategy to measure the porosity in natural fibre composites. Particular emphasis is placed on thermoformed flax fibres reinforced poly-lactic acid (FFRPLA) laminates. Six different methods to measure the porosity were evaluated and compared: gravitometry in ethanol and in water, scanning electron microscopy (SEM), computed tomography (CT) scanning, optical microscope measurements and inverse identification from tensile tests. The measurements indicate porosity levels ranging from 3.5% to 21%. A measurement approach consisting of defining lower and upper bounds of porosity provided by CT-scanning and gravimetric measurements in water was identified. The lower bound of this interval represents the best approximation of the effective porosity, which is 8.3 ± 2.3% for the FFRPLA tested in this work. The approach could be also extended to other similar classes of natural fibre reinforced composites.

Pre-treatments for plant fibres are very popular for increasing the fineness of bundles, promoting individualisation of fibres, modifying the fibre-matrix interface or reducing water uptake. Most pre-treatments are based on the use of chemicals and raise concerns about possible harmful effects on the environment. In this study, we used physical pre-treatments without the addition of chemical products. Flax tows were subjected to ultrasound and gamma irradiation to increase the number of elementary fibres. For gamma pre-treatments, a 20% increase in the number of elementary fibres was quantified. The biochemical composition of pre-treated flax tows exhibited a partial elimination of sugars related to pectin and hemicelluloses depending on the pre-treatment. The hygroscopic behaviour showed a comparable decreasing trend for water sorption-desorption hysteresis for both types of pre-treatment. Then, non-woven composites were produced from the pre-treated tows using poly-(lactid) (PLA) as a bio-based matrix. A moderate difference between the composite mechanical properties was generally demonstrated, with a significant increase in the stress at break observed for the case of ultrasound pre-treatment. Finally, an environmental analysis was carried out and discussed to quantitatively compare the different environmental impacts of the pre-treatments for composite applications, the environmental benefit of using gamma irradiation compared to ultrasound pre-treatment was demonstrated.

Algerian palm groves, a key component of oasis ecosystems, generate significant volumes of natural waste. In the present study, leaflet and rachis derived date palm fibers (DPFs) produced from the pruning of date palm trees were used as an effective filler to reinforce composites consisting of polyvinyl chloride and high-density polyethylene (PVC-HDPE) (20:80). Composites with an untreated and treated DPFs loading of 30 wt.% were prepared using a twin-screw extruder and compression molding. The DPFs surface was modified using various treatments, including NaOH, 3-aminopropyltriethoxysilane, combined alkali-silane, bleaching with NaClO2, and H2O2+HNO3. The successful surface modification of the DPFs, including delignification and the extraction of cellulose microcrystals (CMCs), was verified using infrared spectroscopy (FTIR), scanning electron microscopy (SEM), X-ray diffraction (XRD), and thermogravimetric analysis (TG). The results revealed an improvement in the morphological, thermal, mechanical, dynamical-mechanical, rheological, and water uptake performance of the composites with the addition of the modified DPFs. It was concluded that it was the CMCs that primarily enhanced the thermo-physical properties of the PVC-HDPE composites, making them suitable for several industrial applications.

Biocomposites have major advantage in term of weight saving thanks to lower densities compared to conventional materials; this property also allows a reduction of environmental impacts which is beneficial for the automotive industry. In addition, they maintain rather good mechanical properties after recycling cycles which makes possible to consider other end-of-life scenarios than incineration or landfill. In this work, we studied two potential routes for the recycling of moulding wastes from poly (propylene)-flax nonwovens. By representing close to 25%-wt, these wastes are a major industrial problem, inducing additional recycling or treatment costs. In a first step, the parts were grinded and reincorporated at different weight fractions into virgin nonwovens. Up to 30%-wt of reincorporated wastes, results showed good mechanical performances for recycled nonwovens, especially in bending mode. In a second stage, scraps were grinded and then compounded for injection moulding applications. Their good rheological behavior and ability to conserve fibre lengths during extrusion made possible to formulate competitive materials in terms of tensile performances. (C) 2017 Elsevier Ltd. All rights reserved.

International audience; The aim is to study the effect of the modification of the free surface energy of flax fibres by a thermal treatment on the mechanical behaviour of bio-based composites. It has been proved that this modification enhancesthe wettability of flax fibers by epoxy resin and resultsin a lower porosity amount in composites. Tests to evaluate mechanical properties of elementary fibres, yarns and composites have been performed. The main conclusion is that, even if elementary fibres and yarns have been embrittled and work of adhesion hasbeen lowered after thermal treatment, since the wettability of fibers has been improved, the mechanical behaviour of composites manufactured by LCM is better with treated fibers.; Le but de la présente étude est de prouver l’effet d’une modification d’énergie de surface de fibres de lin par traitement thermique sur le comportement mécanique de composites bio-sourcés. Il a été montré que ce traitement améliore le mouillage des fibres par de la résine époxy en réduisant le taux de porosité dans le composite. Des tests visant à évaluer les propriétés mécaniques des fibres élémentaires, des fils et du composite ont été menés. La conclusion est que, même si les fibres élémentaires et les fils ont été fragilisés et que le travail d’adhésion a diminué, comme le mouillage a été amélioré, le comportement mécanique des composites renforcés par des fibres traitées, élaborée par infusion, est meilleur.

International audience; In this work, the nonlinear properties of bio-based composite materials are derived for a thermomechanical loading. The thermo-elastic problem of the composite is firstly solved by a micromechanics approach. It accounts for the material anisotropy through the morphological and topological textures. Next, the nonlinear response is established in the framework of the J2plasticity. The obtained algorithmic tangent operator for each constituent is used as uniformmodulus for homogenisation purpose. Numerical results are compared with data from the open literature. Applications, which are conducted on a flax fibres/polypropylene PP composite, highlight the influence of the strain rate, and the volume fraction as well as the temperature on the effective properties.; Les propriétés non linéaires des composites bio-sourcés sous un chargement thermomécanique sont étudiées dans ce travail. L’approche, basée sur un formalisme micromécanique, dérive les propriétés thermoélastiques du bio-composite.Elle prend également en compte l’anisotropie du matériau par les textures morphologique et topologique de la microstructure. L’extension du modèle micromécanique au comportement non linéaire est obtenue de la linéarisation des équations constitutives locales. Celle-ci-est basée sur la théorie du J2en plasticité.Les modules tangents algorithmiques obtenus sont utilisés comme propriétés des phases dans d’homogénéisation micromécanique. Les résultats numériques sont comparés aux données de la littérature. Une application a été effectuée sur un composite de fibres de lin noyées dans une matrice polypropylène PP en fonction de la vitesse de déformation, la fraction volumique et la température.

Automated fibre placement (AFP) has been used to manufacture flax/polypropylene biocomposites for the first time. This required preparation of tape with a calibrated width from impregnated fibre sheets. The unidirectional tapes showed polymer-rich zones on the surface. During manufacture the polypropylene (PP) is melted locally with a laser. A consolidation step in a hot press is then required to reduce void content. The flax fibres, composed of polysaccharides, have limited thermal resistance so optimization of the thermal cycle is necessary, but subsequent characterization of mechanical behaviour showed no evidence of property loss in spite of an additional melting cycle. AFP appears to be a promising manufacturing method for biocomposites. Keywords: Structural composites, AFP, Biocomposites, Flax, PP

The optimization of the processing method for poly-(propylene) (PP)/plant fibre composites compounding is a key point in the development of semi-structural parts, especially for automotive applications. The aim of this original and innovating work is to study, at different scales, the impact of extrusion equipment and fibre length on the composite's mechanical performances. Firstly, we studied the flax fibre morphology after compounding and injection as well as their individualization in injected specimens. Secondly, we focused on the effects they had on tensile properties. The impact of the processing tool was observed on fibre morphology and division; as well as the use of a BUSS system instead of a twin-screw extruder, which enhances the fibre individualization, however, the number of kneading areas should be reduced in order to preserve the reinforcement aspect ratio. We highlight the fact that the composite's mechanical performances are highly impacted by the fibre division and cell wall stiffness, as demonstrated by in-situ nanoindentation tests. Finally, the use of longer fibres is not a priority for the improvement of mechanical performances; it induces a more difficult fibre division and an increase in the compound viscosity, which could endanger the moulding process of the final part. Keywords: Injection moulding, Flax fibre, Poly-(propylene), Microstructure, Mechanical properties, Nanoindentation

The role of the main cell-wall polysaccharide-constituents of flax fibres on their mechanical behaviour has been investigated. One sample of scutched flax fibres underwent a successive sequence of extractions (boiling water, EDTA, HCl, NaOH), and tensile tests on elementary fibres were carried out after each step. Results indicated a role of the primary cell-wall in the tensile performance of the fibres. Indeed, an increase of the TIII mechanical behaviour proportion was observed after the boiling water extraction. Furthermore, after EDTA extraction, a significant decrease of the strength at the tangent modulus threshold (312–153 MPa) and a significant increase of the strain at rupture (2.3–2.9%), occurred. Additionally, it was highlighted that the strength at rupture and the Young’s modulus of flax fibres decreased after each extraction. In the secondary cell-wall, it was deduced that the matrix polysaccharides were involved in the load transfer whereas structuring polysaccharides enhanced the cohesion between cellulose microfibrils. At the end of the extraction sequence, fibres still had mechanical performances close to those of regenerated cellulose ones and exhibited a typical non-linear mechanical behaviour. Thus, it was hypothesized that microfibril reorientation phenomena can still occur after a NaOH extraction when fibres are mostly composed of cellulose.

International audience; Ultrasound-assisted synthesis of diglycidyl ethers of isosorbide (DGEI) with different epoxy equivalent weight (EEW) with isophorone diamine (IPD) hardener have been performed. Interestingly, it was found that one specific epoxy formulation exhibits high reactivity with amine hardener inducing high glass transition and indentation stiffness. Associated with flax fibres, this new bio-based resin has made it possible to develop performing and promising unidirectional biocomposites with characteristics comparable to commercial petroleum-based epoxy resins.

International audience; The purpose of this article is to understand the influence of typical composite parameters (interfacial bond strength, surface-area and fibre mechanical properties) on the tensile properties of nonwoven composite materials. The materials investigated were flax, hemp and Poly-(propylene) (PP) and Maleic Anhydride-grafted PP (MAPP), which provide different configurations in terms of fibre mechanical properties, bundle individualization and fibre/matrix interface. Whereas hemp fibres exhibit poorer tensile properties and lower bundle individualization than flax fibres, their higher lignin content evaluated by FT-IR analysis improves the interfacial shear strength (IFSS) with PP and MAPP. However, the tight interface developed with hemp fibres has only a weak effect at the scale of composites. With low-IFSS systems such as plant fibres associated with polyolefin matrices, mechanical properties at the macroscale are governed by the fibre mechanical properties and bonding area rather than by the interfacial bond strength.

International audience; In this study, the impregnated fibre bundle test, a common method used by carbon and glass fibre manufacturers to determine the properties of fibres used in composites, was adapted for natural fibres and validated by a round robin test on one type of natural fibres, namely flax fibres. Five European laboratories have carried out in parallel the impregnated fibre bundle test, on the same batch of hackled flax (long fibres), to check the applicability and reliability of this modified method on natural fibres. The results were compared to the more traditional single fibre test on elementary fibres. The back-calculated fibre stiffness shows a very low scatter between the five laboratories of less than +/- 5% (59.8 +/- 2.4 GPa, as measured between 0 and 0.1% strain). The fibre ultimate tensile strength of 527 +/- 138 MPa has a higher scatter, compared to stiffness values, as this property is highly sensitive to imperfections and flaws.

International audience; The paper deals with the influence of surface treatment of olive husk flour (OHF) by trimethox-yoctadecylsilane (TMOS) on the morphology and physical properties of bio-composites based on poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV). Biocomposites based on PHBV/OHF: 80/20 (w/w) before and after filler treatment were prepared by melt compounding, while the modification of OHF surface by TMOS was performed by thermo-chemical vapor deposition. Scanning electron microscopic observations showed that modification of OHF by TMOS led to homogeneous and finer dispersion of the filler particles in PHBV matrix, indicating improved compatibility between the two components. Further, TGA data revealed an increase in thermal stability of treated PHBV/OHF biocomposites. An increase in the crystalline index determined by DSC was also observed due to the nucleating effect of OHF in the polymer matrix, however more pronounced for the treated biocomposites. The latter exhibited better tensile properties, as confirmed by DMA results, showing higher reinforcing effect of OHF for the treated biocomposites. This study highlighted significant improvements of the properties of PHBV/OHF biocomposites through silane treatment of OHF. (C) 2017 Elsevier Ltd. All rights reserved.

International audience; The purpose of the present article is to evaluate the real fibre surface involved in the practical adhesion of a flax/epoxy system. The difference in practical adhesion evaluated by microbond tests between Hermes (τapp = 22.5 ± 1.5 MPa) and Electra (τapp = 13.2 ± 3.2 MPa) flax fibres varieties/epoxy systems could not be explained by their superficial surface chemistry evaluated by XPS. FTIR spectroscopy highlights a difference in biochemical composition and Laser Confocal microscopy evidences a resin penetration for the two flax fibres systems (1.7 ± 0.7 μm for Hermes and 2.2 ± 0.8 μm for Electra). Thus the effective surface or complex interphase will be by consequence the overall area where the resin and fibre are in contact, i.e. the entire area penetrated by resin.

Flax fibres are increasingly used as polymer reinforcement as an alternative to glass fibres. Indeed, flax has attractive assets (low density, low environmental footprint, high tensile mechanical properties, etc.) but also some limits that need to be investigated. This study gives a comparison between the in-plane shear behaviour of flax/epoxy and glass/epoxy unidirectional laminates. For equivalent volume fractions, the shear stiffness of biocomposites is significantly lower than glass ones. This result is explained by the microstructure and anisotropic properties of flax fibres wall components. However, the micromechanical analytical model of in-plane shear strength demonstrates that the low shear modulus of flax fibres (Gf LT =2500 and 29,700 MPa for flax and glass fibre, respectively) is an advantage since it limits strain concentration within plies by reducing potential cracking. Finally, due to the low failure strain of flax composites, our study show that a 2% strain limit must be chosen for a suitable comparison of flax and glass composites shear strength.

International audience; Many works deal with the mechanical properties of flaxfibers cultivated for textile applications and today used for the reinforcement of polymers. Nevertheless, quantities of oleaginousflaxfiber are obtained each year and not promoted. The aim of this work is to study the mechanical properties of single linseed flaxfiber as a function of variety, culture year, dew-retting degree and agronomic factors. Five varieties of oleaginousflax have been characterized by tensile tests on elementary fibers and compared to four varieties of textile flax. These tensile experiments have been carried out on with the same equipment, experimental protocol and environmental conditions. The results show that interesting mechanical properties were obtained with the oleaginous variety and are close of those of textile varieties, such as Agatha or Electra. Considering the diameters and specific properties of these oleaginousfibers, we evidenced that they are good candidates for the substitution of glass fibers in composite materials. To increase the development of flaxfibers, it is important to have a better control of the spread of their mechanical properties. This point could be observed with the Everest variety cultivated for 4 years and no conclusion could be made. We have evidenced that the retting degree has no influence on the diameters and mechanical properties of the fibers; the same conclusion is obtained with agronomic factors such as seeding rate and plant height.

International audience; The present article reports a study of oxidative degradation under eBeam irradiation of neat PHBV, neat PLA and PHBV/PLA blend (50/50 w/w) with and without Cloisite 30B (C30B) (3 wt%) at absorbed doses of 1 and 10 kGy. The changes in the chemical structure, the molecular weight, the thermal, mechanical and barrier properties as well as the morphology were evaluated. The data showed that eBeam irradiation of PHBV/PLA blend leads to oxidation reactions involving ester groups in both neat PLA and neat PHBV resulting in the formation of hydroperoxides groups. The presence of C30B in the polymer blend has no influence on the nature of the degradation process. However, the good dispersion of C30B nanoparticles provides more stability to the molar mass and the thermal, mechanical and barrier properties of PHBV/PLA blend. At absorbed dose of 10 kGy, the irradiated samples are completely safe. Furthermore, ecotoxicity testing of both non irradiated and irradiated samples clearly showed no toxicity