Vapor grown carbon fiber composites with epoxy and poly(phenylene sulfide) matrices

Vapor grown carbon fibers (VGCF, Pyrograf III(TM) from Applied Sciences, Inc.), with 100-300 nm diameters and similar to 10-100 mu m lengths, were formulated in various fiber volume fractions into epoxy (thermoset) and into poly(phenylene sulfide) (thermoplastic) composites. Increases in stiffness were observed as with previous VGCF/organic matrix composites. Large increases in flexural strengths were achieved in both systems demonstrating for the first time that discontinuous randomly oriented Pyrograf III(TM) can give strength increases and has substantial potential as a reinforcement in composites. Here-to-fore, addition of VGCF caused strength decreases. Voids, residual thermal strains (as the fiber surface area is similar to 35 times greater than 7 mu m-diameter PAN fiber), or uncertainties about fiber strength, fiber-matrix bonding and the degree of fiber dispersion, could cause losses of strength. Thermal conductivity properties of VGCF/ABS (acrylonitrile-butadiene-styrene from GE Plastics) and VGCF/epoxy composites with various fiber volume fractions were measured. Thermal conductivity increased with an increase in fiber volume fraction. However, these increases were not significant enough to make these VGCF fiber/organic matrix composites candidates for thermally conductive materials. (C) 1999 Elsevier Science Ltd. All rights reserved.