Effect of nanoclay grafting onto flax fibers on the interfacial shear strength and mechanical properties of flax/epoxy composites

The low fiber strength and high hydrophilic characteristics limit the wide acceptance of natural fiber-reinforced polymer (NFRP) composites in structural applications. In this article, to enhance the mechanical properties of flax fiber-based NFRP, flax fibers were tried to be grafted with organic nanoclay in assistance of a silane coupling agent. The effects of the nanoclay grafting on the interfacial shear strength between flax–epoxy resin and the tensile and flexural properties of the flax–epoxy composites were investigated. Through micrograph observation (scanning electron microscope [SEM] and atomic force microscope [AFM]), together with Fourier transform infrared (FTIR) and X-ray diffraction (XRD) analysis, nanoclay was confirmed to be successfully grafted onto the fiber surface through covalent bonds. The flax fiber-based NFRP plates were prepared with a vacuum-assisted resin infusion process. With the optimized nanoclay content (1.3 wt.%), an increase in the pull-out shear strength of flax yarn from epoxy block by 71% and short-beam shear strength by 17.9% were realized, respectively. Meanwhile, compared to the control samples, the grafted flax fiber-reinforced plates were enhanced in the flexural strength and tensile strength by 20.7% and 14.3%, respectively. POLYM. COMPOS., 40:3482–3492, 2019.