FORMATION OF GRAPHITE FIBER-POLYIMIDE PREPREGS BY ELECTRODEPOSITION

Nonaqueous electrodeposition of polyamic acid of pyromellitic dianhydr ide and 4,4'-diaminodiphenyl ether was carried out from an emulsion co ntaining a solvent, precipitant, emulsifier, and the polyamic acid. Th e amount of polyamic acid deposited onto the graphite fibers was depen dent on electrodeposition parameters such as the applied current, the amount of polyamic acid (solid content), precipitant/solvent (P/S) rat io, and the acid/base (COOH/TEA) mole ratio. The weight gain of fibers increased with increased current density, P/S ratio, solid content, a nd deposition time. A maximum weight gain of fibers of about 95% was o btained from an emulsion composed of 3 wt % solid content, P/S ratio o f 3 : 1, and TEA/COOH ratio of 1 : 1. The electrodeposit;ion of polyam ic acid onto graphite fibers proceeded in accordance with the Faraday' s law of electrolysis and a Coulombic efficiency of about 62.2 mg/C wa s attained. Thermal analysis shows that the cured polyimide coatings w ere thermally stable up to 500 degrees C. (C) 1996 John Wiley & Sons, Inc.