Effect of interfacial strength and energy absorption of plasma-modified UHMW-PE fiber/epoxy interface

The ability to tailor the interface in fiber-reinforced composite materials can provide the means of achieving an optimum balance of adhesion strength and energy absorbing properties. The poor adhesive nature in composites is largely attributed to the fiber's low surface energy and chemical inertness to the resin matrix. In efforts to enhance the adhesion strength between organic fibers and resins, surface modifications utilizing plasma treatments have been explored and pursued. The model system used in this study is an ultra-high molecular weight polyethylene (UHMW-PE) fiber and epoxy system. The fibers were subjected to a series of various plasma treatments, altering the plasma gas, exposure time, and gas flow-rate. Through the use of these plasma treatments, various reactive functional groups - hydroxyl, carboxyl, amine, and carbonyl groups as identified from X-ray Photoelectron Spectroscopy (XPS) can be created onto the surfaces of these fibers. The degree of functionality can be controlled with treatment parameters as higher uptake of specific chemical groups can be obtained. The interfacial shear strength (IFSS) and energy absorption at the fiber/epoxy interface before and after plasma treatments were assessed using a single-fiber microdroplet shear test. Results show that the plasma treatments aid in the adhesion of the fiber to the epoxy as a six-fold increase of the interphase shear strength was achieved along with increased energy absorption.