SURFACE MODIFICATION OF KEVLAR-149 FIBERS BY GAS PLASMA TREATMENT .2.IMPROVED INTERFACIAL ADHESION TO EPOXY-RESIN

Kevlar 149 fibers were surface-modified by NH3, O2, and H2O plasmas to improve the adhesion to epoxy resin. Poly(p-phenylene terephthalamide ) (PPTA) film prepared from Kevlar 149 fibers was also modified to est imate the changes in surface energy caused by the plasma treatments. T he interfacial shear strength (IFSS) between the fiber and epoxy resin was measured by the microbond pull-out test. The fracture surfaces of microbond pull-out specimens were examined by scanning electron micro scopy (SEM) to identify the failure mode of the microcomposites. The r esults showed that the IFSS of the Kevlar 149 fiber/epoxy resin system was remarkably improved (up to a factor of 2.42) by these plasma trea tments and the treatment time was the governing factor in improving th e IFSS. After the plasma treatments, the fracture mode of the microcom posites changed from failure at the interface to failure either in the fiber skin or in the epoxy resin. The surface free energy and the wor k of adhesion of water on the PPTA surface were markedly improved by t he plasma treatments. The polar component of the surface free energy a nd the acid-base (non-dispersion) component of the work of adhesion ma de an important contribution to the improvement. Some correlations bet ween the IFSS and the surface energies were found.