Kevlar and glass fiber treatment for thermoplastic composites by step polycondensation

Abstract Nylon‐6,6 was grafted at the surface of glass and plasma‐treated Kevlar fibers for use in nylon–Kevlar thermoplastic composites. Hydroxyl and, in the case of Kevlar, amine end‐groups occur at the fibre surface, either as defects or due to the plasma treatment. These were used as anchor points for nylon‐6,6 step polycondensation. Fibers were subjected to successive dipping in adipoyl chloride/CH₂Cl₂ and aqueous hexamethylenediamine solutions in order to attach and grow high molecular weight polymer on the fiber surface. Grafted nylon was characterized by Fourier transform infrared spectroscopy, proton nuclear magnetic resonance, differential scanning calorimetry and thermogravimetry. It was shown that no backbiting occurred during the first stage of the grafting process and that the polymer quantity increased linearly with number of passes, up to ∼50 passes for plasma‐treated Kevlar and 100 for glass fibers, after which polymer quantity remained constant, within experimental error, which was attributed to the onset of termination reactions. POLYM. COMPOS., 28:278–286, 2007. © 2007 Society of Plastics Engineers