CONDUCTING RUBBER-LIKE COPOLYMER CARBON-FIBER COMPOSITES

Electrically conductive rubberlike copolymer-carbon fiber composites h ave been prepared by either a solution method or a concentrated emulsi on method. In the former procedure, carbon fibers were introduced with stirring in a copolymer-toluene solution, and the polymer-fiber compo sites were precipitated by extracting the solvent with methanol. In th e latter procedure, a pastelike concentrated emulsion of copolymer-tol uene solution in an aqueous solution of sodium dodecylsulfate (SDS) wa s first formed, and the carbon fibers were mechanically blended with t he concentrated emulsion. The polymer-carbon fiber composites were pre cipitated by extracting the toluene and water with methanol. Four kind s of rubberlike copolymers have been used: styrene/ethylene-butylene/s tyrene triblock copolymer (SES), styrene/butadiene/styrene triblock co polymer (SBS), ethylene/propene/ethylene triblock copolymer (EPE), and ethylene/vinylacetate copolymer (EVA). Short (L = 0.1 mm) - and mediu m (L = 5 mm) -length carbon fibers were employed. The composites were hot-pressed in a Laboratory Press to form a sheet. The effects of the two methodologies on the electrical conductivity and mechanical proper ties of the sheets were investigated by changing the type of polymer, the size of the carbon fibers, the volume fraction of the carbon fiber s in the composites, and the hot-pressing temperature. Composites with electrical conductivities in the range of 5-14 S/cm, tensile strength s in the range of 10-17 MPa, and elongations at break point larger tha n 200% were obtained. The conductivities of the composites prepared wi th the short fibers were by two orders of magnitude smaller than those prepared with medium-size fibers. (C) 1994 John Wiley & Sons, Inc.