Novel aligned hemp fibre reinforcement for structural biocomposites: Porosity, water absorption, mechanical performances and viscoelastic behaviour

This paper examines the thermal and mechanical behaviour as well as moisture absorption of aligned hemp composites using hemp/PLA wrap spun yarns. Uniaxial composites were fabricated with 30 mass% hemp using compression moulding. The properties of composites in terms of hemp fibre orientation (aligned and random), off-axis angle and alkali treatment were investigated. It was found that the testing direction influenced the mechanical properties of the composites. Compared with all the fabricated composites, the aligned alkali hemp/PLA yarn composite possessed the best mechanical properties, including tensile, flexural and impact strengths, lower porosity and water absorption. The water absorption for all composites was higher than for neat PLA, both at room temperature and 80 °C. The PLA in its treated composites had higher crystallinity, which was attributed to effective heterogeneous nucleation induced by hemp. Based on SEM observation and theoretical analysis of DMTA data, there was a favourable interfacial adhesion in all composites.