THE SURFACE-TREATMENT OF CARBON-FIBERS BY ELECTRO-POLYMERIZATION AND PLASMA POLYMERIZATION

ENKA HTA-3000 carbon fibres have been subjected to surface treatments by electro-polymerization and plasma polymerization in order to bring about modifications to the level of interfacial bond strength between the fibres and an epoxide resin matrix. Treated fibres have been tensile tested in order to assess the effects of treatment on strength, and they have been used in single filament fragmentation tests to determine the fibre/matrix bond strength. Samples of composite containing larger quantities of fibre have also been subjected to tow tensile tests. and the appearance of treated fibre surfaces and composite fracture surfaces has been studied by scanning electron microscopy. The best of these treatments have been successful in raising the interfacial shear strength by some 52% above that for untreated fibres. and some 20-25% above the level for commercially oxidized and sized fibres. The shear strength increases with fibre surface oxygen and nitrogen contents. and it appears that the nitrogen/carbon ratio is the controlling compositional parameter. The strengths of the fibres are also raised to some extent by the surface treatments.