Kevlar 49 fibers were surface-modified by NH3-, O-2-, and H2O-plasma etching and chlorosulfonation and subsequent reaction with some reagents (glycine, deionized water, ethylenediamine, and l-butanol) to improve the adhesion to epoxy resin. After these treatments, the changes in fiber topography, chemical compositions of the fiber surfaces, and the surface functional groups introduced to the surface of fibers were identified by SEM, XPS, and static SIMS. Interlaminar shear strength (ILSS) and T-peel strength between the fiber and epoxy resin, as measured by the short-beam test and T-peel test, were remarkedly improved by gas plasma and chlorosulfonation (0.1% and 0.25% ClSO3H at 30 s). However, from the results of similar G(IC) values of the treated and untreated fiber composites, it is clear that the fiber/matrix interfacial bond strength is only a minor contributor to G(IC). SEM was also used to study the surface topography of the fracture surfaces of composites in T-peel test. It could be seen from SEM observations that the improvement of fiber/matrix interfacial bond strength often accompanied a change in fracture mode from the interface of fiber/epoxy resins to the fiber fibrillation and the resins. (C) 1996 John Wiley & Sons, Inc.
