Deeper insights into the moisture-induced hygroscopic and mechanical properties of hemp reinforced biocomposites

This article provides deeper insight into moisture sorption over a wide range of relative humidity (RH), from 9% to 98%, and its effect on the evolution of the tensile behaviour and performance of hemp/epoxy unidirectional biocomposites. Moisture sorption is associated with orthotropic hygroscopic expansion which is also related to the influence of fibre reinforcement distribution and the generation of residual stresses due to manufacturing. Tensile behaviour is significantly modified by moisture content, with a non-linear behaviour becoming more evidenced. The increase of moisture content causes exponential decay of tensile modulus, but a non-monotonic evolution of tensile strength and strain at break shows optimal properties at about 3%. The hygroscopic property evolution observed is responsible for the creation of compressive radial stresses at the fibre/matrix interface, which promotes load transfer and benefits the interface performance.