Wettability and adhesion studies of grafted poly(p-phenylene terephthalamide) fiber surfaces

Matrix-specific chemical modification of the poly(p-phenylene terephthalamide) [PPTA] fiber surfaces was carried out with the aim of enhancing adhesion, through covalent bonding, to selected thermoset matrix resins such as vinyl ester, unsaturated polyester and epoxy. Using a two-step grafting method [1], vinyl and epoxy groups were grafted onto PPTA fiber surfaces. The physical changes in the fiber surface were characterized by scanning electron microscopy and surface area measurement, and the chemical changes due to grafting were monitored by contact angle measurement and neutron activation analysis. The change in interfacial shear strength due to the surface grafting was measured by means of a single fiber pullout test. The results show a nearly twofold increase in the interfacial shear strength due to vinyl terminated grafts in the case of PPTA/ vinyl ester and PPTA/polyester composites. PPTA fibers containing the epoxy functionality on the surface had enhanced adhesion to epoxy matrix resin.