Plasma surface modification of advanced organic fibres

Abstract

A marked improvement in the interlaminar shear strength and flexural strength of aramid/ epoxy composites is observed when the fibres are pretreated in an ammonia or ammonia/ nitrogen gaseous discharge (plasma) to introduce amine groups on to the fibre surface. Scanning electron and optical microscopic observations are used to examine the microscopic basis for these results. Scanning electron micrographs of shear fracture surfaces show clean fibre/matrix separation in composites made from untreated fibres, indicative of weak interfacial bonding. In contrast, shear fracture surfaces of composites containing plasma-treated fibres exhibit clear evidence of fibre fibrillation and matrix cracking, suggesting stronger interfacial bonding. Optical microscopic examination of flexure specimens shows that enhanced strength results mainly from reduced compressive fibre buckling and debonding, due to an increase in fibre/matrix interfacial bond strength. This increase is not accompanied by any significant change in the interlaminar fracture energy or flexural modulus of the composites, but there is an appreciable loss in transverse ballistic impact properties. These results are also examined in terms of the observed increase in fibre/matrix interfacial strength.