Interfacial compatibility and cyclic moisture durability of Flax/Polyamide 6 composites

Authors

Prapavesis A., Fuentes C.A., Sarlin E., Kallio P., Seveno D., van Vuure A.W.

Reference

Composites Part A Applied Science and Manufacturing, vol. 200, art. no. 109354, 2026

Description

Natural fibre composites are typically moisture sensitive, due to the hygroscopic nature of the fibres, leading to swelling and shrinkage inside the composite upon changes in environmental humidity. Long-term durability of flax fibre composites with a PA6 matrix was investigated to identify if a moisture susceptible matrix that can swell and shrink simultaneously in phase with the hydrophilic fibres can result in better mechanical performance. This improved performance arises from reduced hygroscopic stress concentration build-up compared to commonly used thermoplastic matrices, which are often considerably more hydrophobic than the fibres. First, the potential to overcome the thermal limitation by processing flax fibres alongside a PA6 matrix was examined, employing a fast processing method, thus reducing their overexposure to high temperatures required to melt the polymer matrix. The wetting behaviour was studied experimentally using the Wilhelmy technique and the thermodynamic work of adhesion between flax and PA6 was calculated and contrasted with the flexural unidirectional composite properties in longitudinal and transverse directions. The results suggest a good fibre/matrix adhesion due to a good interfacial compatibility, which explains the good properties achieved since fast processing often results in low impregnation quality. Furthermore, hygroscopic high-low humidity cyclic exposure was applied to the manufactured composites to assess the hypothesis that hygroscopic damage could be mitigated by the concurrent swelling and shrinking of both the fibre and matrix, owing to their similar hygroscopic characteristics. The findings indeed demonstrate a beneficial impact, suggesting that this composite type could rival the durability performance of conventionally employed epoxy matrix after long-term ageing.

Link

doi:10.1016/j.compositesa.2025.109354