PLASMA SURFACE MODIFICATION OF ADVANCED ORGANIC FIBERS .3. EFFECTS ON THE MECHANICAL-PROPERTIES OF ARAMID VINYLESTER AND EXTENDED-CHAIN POLYETHYLENE VINYLESTER COMPOSITES

Aramid and extended-chain polyethylene fibres have been treated in ammonia and oxygen plasmas in order to enhance adhesion to vinylester resins and thereby improve fibre/resin interfacial properties in composites made from these materials. For both aramid/vinylester and extended-chain polyethylene/vinylester composites, the plasma treatments result in significant improvements in interlaminar shear strength and flexural strength. Extended-chain polyethylene/vinylester composites also exhibit increased flexural modulus. Scanning electron and optical microscopic observations have been used to examine the microscopic basis for these results, which are compared with results previously obtained for aramid/epoxy and extended-chain polyethylene/epoxy composites. It is concluded that the increased interlaminar shear and flexural properties of vinylester matrix composites are due to improved wetting of the surface-treated fibres by the vinylester resin, rather than covalent chemical bonding.