ELECTRICAL AND THERMAL-CONDUCTIVITIES OF POLYETHYLENE COMPOSITES FILLED WITH BIAXIAL ORIENTED SHORT-CUT CARBON-FIBERS

Polyethylene composites filled with various types of carbon fiber were prepared for electrical and thermal conductivity measurements. By est imation of the anisotropic parameter (Hermans' parameter), the fibers were confirmed to be significantly biaxially oriented in the composite s. The critical volume fractions in the electrical conductivity of the se composites for the two oriented directions (X and Y) were equal to each other and smaller than that for a direction (Z) vertical to the a bove. The electrical anisotropy, i.e., ratio of electrical conductivit y of the composite for the Z direction to the X and Y directions varie d drastically with increase in filler content. The longer the length o f carbon fiber was, the higher became the electrical conductivity of t he biaxially oriented carbon fiber composites for all directions. But, the thermal conductivity of the composite was almost unchanged for th e Z direction, even if fiber length was sufficiently long. Our equatio n, previously proposed, proved adaptable to these thermal conductiviti es. The factors of C(p) and C(f) in the equation are kept unchanged, i n spite of increasing fiber length. (C) 1994 John Wiley & Sons, Inc.