Improvement of the adhesion of Kevlar fiber to bismaleimide resin by surface chemical modification

Kevlar 49 fibers were surface-modified by chlorosulfonation and subsequent reaction of -SO2Cl with some reagents (allylamine, ethylenediamine, and deionized water) to improve the adhesion to 2,2-bis[4-(4-maleimidophenoxy)phenyl]propane (BMPP) resin. The change in fiber surface morphology and the surface functional groups introduced to the surface of the fiber were investigated by scanning electron microscopy (SEM) and electron spectroscopy for chemical analysis (ESCA), respectively. From the results of ESCA analysis, it was confirmed that the surface composition of the Kevlar fibers was significantly different from that of the bulk composition. After chlorosulfonation, the surface concentration of carbon was markedly decreased. The subsequent reaction with ethylenediamine, allylamine, and deionized water also changed the surface composition of the fiber; e.g. treatment with ethylenediamine and allylamine decreased the O/N ratio. On the other hand, the O/N ratio was increased by hydrolysis treatment. The synthesized 2,2-bis[4-(4-maleimidophenoxy)phenyl]propane (BMPP) resin was identified by FTIR, NMR, and differential scanning calorimetry (DSC). The microbond pull-out test was then used to measure the interfacial shear strength (IFSS) between Kevlar fibers and BMPP resin. The results showed that the IFSS increased by a factor of 1.07-1.62 after chemical treatments. The fracture surfaces of fibers from microbond pull-out specimens were examined by SEM.