Effect of fiber surface modifications on the interfacial adhesion in kevlar fiber reinforced polymer composites

The weak interfacial properties of kevlar/epoxy composites are the main limitation in applications. This work focuses to improve interfacial adhesion in kevlar/epoxy composites by various concentrations of phosphoric acid (PA) pre-treatment followed by Epichlorohydrin (ECH) treatment with different time periods. The fiber surface modification was studied through X-ray diffractometer (XRD), energy dispersive X-ray (EDX), Fourier transform infrared spectroscopy (FTIR) and Field emission scanning electron microscopy (FESEM). The interfacial adhesion was investigated by conducting flexural, quasi-static indentation (QSI) and flexural after indentation (FAI) tests with acoustic emission (AE) monitoring. The results reveal that the crystallinity index was decreased by 20.35% with increased polar functional groups in treated kevlar fiber surfaces. However, the optimum treatment condition was confirmed from flexural properties and AE results. It was observed that 15% PA with 1 h ECH treatment is much effectively improving the resistance to debonding and delamination failure modes in comparison with untreated kevlar composites. It was also evidenced from the reduction in residual flexural of untreated and optimized treated composites by 56.36 and 48.35%, respectively. Moreover, acoustic emission results reveal that the percentage of hits corresponding to the failure modes such as debonding and delamination failure are significantly reduced in the case of optimized treated fiber composites.