Résumé
Measuring and understanding the swelling and softening behaviour of plant fibres under controlled humidity as a function of their water content is essential for their use in composite applications. Indeed, this directly influences the processing and the in-service behaviour of biocomposites. The objective of this work is to characterize, under controlled hygro- and hydrothermal conditions (from 20% to 73% RH and in immersion), the moisture content, dimensional variations and mechanical behaviour of natural fibre bundles from various botanical origins with contrasting biochemical and structural characteristics. Automated laser scanning cross-sectional measurements [1] and micro-tensile tests in either a climate chamber or an immersion cell were used to measure the dimensional variations and tensile properties of fibre bundles as a function of their moisture content as measured by DVS and WRV. These analyses allowed the determination of the surface hygro- and hydroexpansion coefficients of the different natural fibre bundles in relation to the structural characteristics of the cell walls [2]. The softening effect of water on cell walls and the resulting loss of stiffness and strength of fibre bundles are also discussed in relation to water sorption and swelling [3]. These results provide key data for predictive modelling of the “in-service” mechanical behaviour of biocomposites.