THE INFLUENCE OF PLASMA GAS SPECIES ON THE ADHESION OF THERMOPLASTIC TO ORGANIC FIBERS

Adhesion between organic fibers and thermoplastics in a composite material is usually weak because of the lack of chemical and mechanical bonding. This study investigated the influence of plasma gas species in a novel technique to improve interfacial adhesion of Kevlar 49 fibers to polycarbonate. Single Kevlar fibers were exposed to radio-frequency plasma discharge in atmospheres of argon, oxygen, and ammonia. Plasma treatment has been shown to generate reactive free radicals on polymer surfaces. The fibers that were coated immediately with a polycarbonate melt while still in the vacuum environment of a plasma reactor showed an increase in interfacial shear strength that was maximum at 4.1 s exposure and decreased at longer exposure times. At 4.1 s exposure, Ar and O2 plasma treatment increased shear strength by 20 and 18%, respectively. NH3 plasma treatment produced only a statistically insignificant increase at 4.1 s of exposure and a significant decrease in adhesion at 8.3 s of exposure. Fibers that were exposed to air for 1 h before coating showed no statistically significant increase or decrease in adhesion. The increase in adhesion of the directly coated fibers was attributed to free radical-initiated formation of covalent bonds between the Kevlar and the polycarbonate.