Interface Enhancement of Aramid/Epoxy Composites

Abstract: The interfacial adhesion of para-aramid (Twaron® 2200 and Kevlar® 49) fibers and anhydride cured bisphenol-a epoxy resin was investigated. To evaluate the influence of the standart “oily” fiber surface sizing on the interfacial adhesion, a heat treatment at 220 °C for different times was conducted to remove the sizing and the interfacial shear strength (IFSS) was measured using a fiber-bundle pull-out test. It was shown that the IFSS increases in the absence of sizing for Twaron® 2200, while Kevlar® 49 did not show any significant improvement. The influence of moisture on the IFSS was investigated by exposing pull-out sample to a controlled humid environment prior to testing and it was shown that the sizing removal does lead to a decreased impact of moisture on the interfacial adhesion. Furthermore, the sorption behaviour of the fibers and laminates with and without fiber coating was analysed by moisture absorption tests at different conditions and a significant decrease for the moisture uptake of both fibers could be obtained as the finish was removed.