Wetting of oriented and etched ultrahigh molecular weight polyethylene

Highly oriented gel-spun ultrahigh molecular weight polyethylene (UHMWPE) f ibers possess many outstanding properties desirable for composite materials but their adhesion to such matrices as epoxy is poor. This article describ es the combined effects of drawing and surface modification on the bulk and surface properties of gel-cast UHMWPE films emphasizing the effects of etc hing on both undrawn and drawn films. Drawing the films yields a fibrillar structural hierarchy similar to UHMWPE fibers and a significant increase in orientation, melting point, modulus, and strength. The effects of drawing on bulk properties were more significant than those of etching. The poor ad hesion of epoxy to the smooth, fibrillar, and relatively nonpolar drawn fil m surface improves significantly with oxidization and roughening on etching . The interlaminar shear failure occurred cohesively in the UHMWPE, and thu s the interlaminar shear failure strength was greater for the drawn UHMWPE with its greater tensile strength. Nitrogen plasma etching yielded the best results, both removing any low molecular weight surface layer and etching the UHMWPE beneath. Oxygen plasma etching enhanced wetting but was too hars h, causing extensive surface degradation and a significant reduction in mec hanical properties. (C) 1999 John Wiley & Sons, Inc.