Moisture effects on the transverse compressive behaviour of single flax fibres

Studying the effects of moisture on the mechanical behaviour of single flax fibres, particularly in the transverse direction, is of key importance for the reliable use of biobased composites exposed to varying humidity levels. In this study, the apparent transverse Young’s modulus evolution of single flax fibres is recorded through repeated compressive load/unload cycles conducted at three Relative Humidity (RH) levels— 40 %, 60 %, and 80 %. No significant changes in the apparent Young’s modulus, determined from the unloading, were observed during transverse compression cycling or under increasing humidity conditions. The absence of apparent softening with the rise in RH is attributed to the expression of two antagonistic mechanisms: wall softening due to plasticization and structural stiffening linked to fibre compaction. Intriguingly, a noteworthy transverse stiffening is recorded at 40 % RH following the humidification and drying of the fibre. This outcome is ascribed to a hornification phenomenon.