Interface modification and the influence on damage development of flax fibre – Epoxy composites when subjected to hygroscopic cycling

The moisture sensitivity of natural fibre composites limits their use in structural applications. Degradation of the fibre–matrix interface is likely to occur when the material is subjected to variable moisture conditions. This study investigates the damage development in unidirectional flax fibre reinforced epoxy composites during hygroscopic cycling. It is expected that the insertion of a silicone interphase increases interfacial toughness and therefore postpones or avoids interface degradation. Various silicones and a silane coupling agent were used in an attempt to enhance the long-term behavior of the composite. Hygroscopic cycling was performed by varying the relative humidity between approximately 25 and 80% at 80 °C. When examining the flax-epoxy reference composite, regression analysis showed a significant decline of the transverse strength during six consecutive wet-dry cycles. The degradation of the mechanical properties is attributed to fibre–matrix debonding and to cohesive failure in the fibre bundles. Both damage mechanisms are visualized in a unique three-dimensional model. Contrary to the hypothesis, the insertion of a silicone interphase led to an accelerated decrease of the transverse strength. Computed tomography analysis confirmed the weakening of the fibre–matrix interphase. Although the damage development was altered, the composites having a thin silicone interphase did not show a significant decrease in longitudinal stiffness and strength. This result is promising as it suggests that stress transfer is not significantly hindered. ispartof: pages:S273-S279 ispartof: Materials Today: Proceedings vol:31 pages:S273-S279 ispartof: 4th International Conference on Natural Fibers - Smart Sustainable Materials (ICNF) location:Porto, Portugal date:1 Jul - 3 Jul 2019 status: published