SURFACE MODIFICATION OF DRAWN GEL-CAST ULTRA-HIGH-MOLECULAR-WEIGHT POLYETHYLENE FILMS

Gel-spun ultra-high molecular weight polyethylene (UHMWPE) fibers have superior properties but their use in composite material applications is limited by their poor adhesion to polymer matrices. Previous studie s have shown that etching improves the adhesion of epoxy to the fibers , but leads to a reduction in mechanical properties. The purpose of th is research was to use uniaxially drawn gel-cast UHMWPE films as a mod el system since both films and fibers have a highly oriented fibrillar structural hierarchy. Etching has detrimental effects on the mechanic al properties and crystallinity of these very thin films. The small am ount of carbonyl and carboxyl groups added to the surface through etch ing raises the film's surface tension and enhances wetting by epoxy. E ven though the unmodified film cannot be bonded with epoxy, the interl aminar shear strength between epoxy and the etched films approaches th e cohesive strength of the epoxy. A combination of interfacial and UHM WPE cohesive failures is observed. The increase in adhesion is attribu ted to the slight increase in surface oxygen.