Effects of humidity conditions at fabrication on the interfacial shear strength of flax/unsaturated polyester composites

In comparison with carbon and glass fibres, natural fibres can readily absorb a substantial amount of moisture from the surrounding environment, leading to poor interfacial bond with polymer matrices. In this paper, we first present a single fibre microdroplet test procedure for measuring the interfacial shear strength in natural fibre composites. We then investigated the influence of relative humidity (RH) in composite fabrication on the interfacial shear strength and flexural properties of flax/unsaturated polyester composites. The interfacial shear strength of the flax/unsaturated polyester composite started to drop sharply at 70% RH and ended up with a more than sixfold reduction at 90% RH. The results highlighted the importance for air conditioning and dehumidification in natural fibre composite fabrication facilities.