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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.

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

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.

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