Interfacial adhesion assessment in flax/epoxy and in flax/vinylester composites by single yarn fragmentation test. Correlation with micro-CT analysis

Despite the academic interest in using plant fibres as reinforcement in polymer composites to replace glass fibres, the industrial exploitation of resulting composites in semi- or structural applications is still limited. This is mainly due to the poor adhesion at the plant fibre/polymer matrix interface dictated by their surface chemistry and strong hydrophilic behaviour. In the present work, an assessment of the interfacial adhesion at the yarn scale has been carried out. Fragmentation tests have been performed on flax/epoxy and flax/vinylester single yarn composites. High-resolution microtomography has allowed a 3-D reconstruction of the breaking area of the flax yarn. The flax/epoxy system has shown the lowest values of critical fragment length and interfacial debonding length, and the highest values of IFSS. For both epoxy and vinylester samples, it was found that the breakage of flax has been mainly concentrated in the peripheral zone of the yarn.