Interface tailoring between flax yarns and epoxy matrix by ZnO nanorods

To improve plant fibres/polymer matrix adhesion, the surface of flax yarns was modified by zinc oxide (ZnO) nanorods, which were synthesized through a hydrothermal treatment. Several parameters were analysed in order to obtain a uniform and homogeneous ZnO interphase, such as the number of seeding cycles, growth times and the replacement of the growth solution. The results showed that it is possible to obtain highly oriented ZnO nanostructures (by FE-SEM), with an hexagonal wurtzite structure (by XRD) and a high degree of coverage along the whole yarn (by TGA), by reducing the number of the seed cycles, with rather long growth times (5 h) and refreshing the growth solution. The optimized synthesis preserved the breaking force of the yarns, while Single Fibre Fragmentation Tests (SFFT) highlighted a better interfacial adhesion of ZnO-modified flax yarns with epoxy matrix, confirmed by a 29% reduction in average debonding length relative to untreated yarns.