Enhancing with glass-fibre hybridization the interlaminar fracture toughness of water-aged flax/epoxy composites

The benefits of using materials from renewable resources are now well established. Plant fibre composites in particular are increasingly common in various industrial sectors, due to their attractive characteristics (specific strength and modulus, availability, cost) [1]. However, their development may be limited due to their high sensitivity to the moisture absorption. In addition, the low interfacial properties between hydrophilic reinforcement and hydrophobic matrix can result in delamination and thus lowering the mechanical properties. Although numerous works have studied the effect of water absorption on the mechanical properties of natural fibre composites, the study of their interlaminar properties in a wet environment remains limited [2]. It is within this context that Flax, Glass and Hybrid flax-glass Fibre Reinforced Epoxy (referenced by FFRE, GFRE and HFRE) laminates were investigated. Three twill weave fabric laminates were manufactured by a compression moulding process and subjected to ageing by immersion in 20°C water until saturation. Double cantilever beam test was performed to evaluate the mode I critical energy release rate as well as the corresponding resistance curve. Table 1 summarises the initiation fracture toughness GIc of the composites. For unaged composites, the results highlight that more energy is needed for the initiation of the cracks for FFRE, compared with HFRE and GFRE. After the water ageing, the drop of GIc is severe for the FFRE by about 60%. With the replacement of half flax layers with glass layers, the drop in HFRE become very lower (4% compared to its non-aged corresponding, 16% compared to unaged 100% flax). The reached value is comparable to the unaged 100% glass composite.