International audienceThis papers aims to characterize the influence of moisture uptake on the mechanical behaviour of unidirectional flax fibre-reinforced epoxy laminates. Monotonic and cyclic tensile tests and free vibration characterization are carried out. Results show that LID flax-epoxy composites, when exposed to hygrothermal conditioning at 70 degrees C and 85% RH, exhibit a diffusion kinetic which follows a one dimensional Fickian behaviour. The mass uptake at equilibrium is approximately 3.3% and the diffusion coefficient 6.5 x 10(-6) m(2) s(-1). Water vapour sorption is shown to induce a significant change in the shape of the tensile stress-strain curve, a decrease in the dynamic elastic modulus of about 20% and a 50% increase in the damping ratio. Contrary to all expectations, water saturation does not degrade the monotonic tensile strength of such a flax-epoxy composites and leads to an increase in the fatigue strength for a high number of cycles. (C) 2016 Elsevier Ltd. All rights reserved

Alginate derived from seaweed is a natural polysaccharide able to form stable gel through carbohydrate functional groups largely used in the food and pharmaceutical industry. This article deals with the use of sodium alginate as an adhesive binder for wood fibres/textile waste fibres biocomposites. Several aldehyde-based crosslinking agents (glyoxal, glutaraldehyde) were compared for various wood/textile waste ratios (100/0, 50/50, 60/40, 70/30 and 0/100 in weight). The fully biomass derived composites whose properties are herewith described satisfy most of the appropriate requirements for building materials. They are insulating with a thermal conductivity in the range 0.078-0.089 W/m/K for an average density in the range 308-333 kg/m3 according to the biocomposite considered. They are semi-rigid with a maximal mechanical strength of 0.84 MPa under bending and 0.44 MPa under compression for 60/40 w/w wood/textile waste biocomposites with a glutaraldehyde crosslinking agent.

The use of biocomposites on a daily basis for industrial products brings to light the influence of environmental factors on the evolution of mechanical properties. This aging has a major influence in the lifetime of any product based on such materials. Among biobased composites, poly(lactic acid) reinforced with plant fibers are known to be sensitive to hydrothermal aging due to the intrinsic nature of their components. Although some papers studied the influence of temperature and water absorption on such materials, so far the difference between reversible and irreversible effects of aging has been hardly studied. This distinction is the purpose of this study. Poly(lactic acid) samples reinforced with various content of flax fibers (0%, 10%, and 30%) were immersed in water at different temperature (20, 35, and 50°C) up to 51 days. The physical and chemical phenomena responsible for the changes in the mechanical properties of biocomposites were evaluated. It was observed that these changes were mainly reversible. However, irreversible effects of aging turned out to increase drastically with the amount of fiber and the aging temperature. While hydrolysis drastically deteriorated PLA for longer aging times, the lifetime of biocomposites was significantly extended (+ 230% at 50°C from 0% to 10% in fiber content) by the presence of fibers which postponed the failure of PLA.2

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The development of composites based on vegetal fibers requires a good control of manufacturing process. The aim of this work is to determine the key parameters to produce high grade flax / epoxy unidirectional laminated composite by thermocompression. So, many processing parameters have been tested and ranked according to their influence on mechanical properties. Since variability can be high for this kind of materials, statistical analyses have been used to determine if properties variations were significant or not. Among all studied parameters, the three which have been identified as first rank influence on mechanical properties are: fibers conditioning, curing pressure and exit plate temperature.

In several industrial sectors, structural composite materials with good impact resistance are required to design parts submitted to crashes or falling objects. This work analyses the impact behaviour of short hemp fibres reinforced biocomposites through mechanical measurements, high speed imaging and finite element modelling. A drop-weight impact machine was instrumented with a high speed camera to measure the propagation of macro-cracks and correlate it to the force-displacement dynamic response at several impact energy levels. PP-hemp composites exhibit higher absorbed energies (up to 40%) than PP-glass composites due to higher strain at break. The video tracking analysis highlights that for a given cumulated crack length, PP-hemp composite absorbs much more energy, related to differences in failure mechanisms. The developed finite element model is in good agreement with the experimental measurements and the fracture growth pattern, thus constituting a useful tool to predict the impact response of biocomposite parts.

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