DEVELOPMENT OF COVALENT BONDING PROCESSES FOR THERMOPLASTIC COMPOSITES

THERMOPLASTIC POLYMERS, WITH CHARACTERISTICS OF HIGH STRAIN-TO-FAILURE, RAPID FORMABILITY AND REPROCESSING CAPABILITY, ARE ATTRACTIVE AS MATRIX MATERIALS FOR COMPOSITE MATERIAL SYSTEMS. A MAJOR LIMITATION IS THAT THERMOPLASTIC COMPOSITES EXHIBIT LOW FIBER/MATRIX ADHESION. CONTRIBUTING FACTORS INCLUDE POOR MATCHING OF SURFACE ENERGETICS COMPONENTS, THEREBY REDUCING SECONDARY BONDING FORCES, AND NON-REACTIVITY, PREVENTING COVALENT BOND FORMATION. POLYARAMID/THERMOSET RESIN COMPOSITES HAVE FACED SIMILAR PROBLEMS. SUBSTANTIAL IMPROVEMENTS IN INTERFACIAL BOND STRENGTH HAVE BEEN OBTAINED BY DEPOSITING REACTIVE GROUPS ON FIBER SURFACES THROUGH A GLOW DISCHARGE PLASMA PROCESS. WITH REACTIONS TO THE THERMOSETTING RESIN, COVALENT BONDS ARE DEVELOPED, SIGNIFICANTLY INCREASING FIBER/MATRIX ADHESION. IT APPEARS FEASIBLE TO ADAPT THIS PROCESS TO THERMOPLASTIC COMPOSITES, THE MAJOR MODIFICATION BEING THE SIMULTANEOUS MODIFICATION OF THE SURFACE CHEMISTRY OF FIBER AND MATRIX CONSTITUENTS. PLASMA TREATMENT PROCESSES FOR DIRECT REACTIONS TO PRODUCE COVALENT OR ACIDBASE BONDING ARE PROPOSED FOR INVESTIGATION AS ARE TWO-STEP REACTION PROCESSES CAPABLE OF COVALENT BONDING THROUGH THE USE OF AN INTERMEDIATE FUNCTIONARY BETWEEN THE PLASMA TREATED SURFACES. QUESTIONS TO BE ADDRESSED ARE: ABILITY TO ACHIEVE ADQUATE REACTIVE GROUPS CONCENTRATION DENSITY, MOBILITY/STEREO CHEMISTRY OF REACTIVE GROUPS, DIFFUSION OF REACTIVE GROUPS UNDER THERMOPLASTIC COMPOSITE PROCESSING CONDITIONS, AND ATTAINMENT OF COVALENT BONDS.