Hygroscopic and Mechanical Properties of Hemp Fibre Reinforced Biocomposites

Mainly used for the paper industry, hemp fibres present a high potential for valorisation in new industrial of semi-structural or structural composites material applications. To reach certain markets, it is inevitable to certify their behaviour and durability in humid environment which is currently lacking in the literature. This article provides a better insight into the moisture sorption, on a wide range of relative humidity (HR), from 9 % to 98 %, and its effect on the evolution of the tensile behaviour and performances of hemp/epoxy unidirectional biocomposites. Tensile behaviour is significantly modified by moisture content with nonlinear behaviour becoming more evidenced. Increase of moisture leads to an exponential decay of tensile modulus but a non-monotonic evolution through an optimum of tensile stress and strain at break. Complex compressive hygroscopic stress state at the fibre/matrix interface is hypothesised so that load transfer is kept until a moisture content threshold is reached and moisture induced degradation triggered.