Modification of epoxy resin by polysulfone to improve the interfacial and mechanical properties in glass fibre composites.: III.: Properties of the cured blends and their structures in the polymer/fibre interphase

Thermal and mechanical properties (linear expansion coefficient, glass transition temperatures, Young's modulus, tensile and bending strengths, and failure energies under quasistatic and impact loadings) of cured epoxy-polysulfone (PSF) blends, as well as their structures have been studied. It was shown that PSF incorporation did not lead to appreciable changes in the linear thermal expansion coefficients and glass transition temperatures of the cured blends. According to this observation, incorporation of PSF into the epoxy matrix should not result in a significant increase in the internal stresses in the system. No drop in the modulus and strength of the bulk blends was observed when compared with unmodified epoxy matrix. The failure energy of the epoxy-PSF matrices increased as the PSF content increased under all loading conditions, whereas the strength of the polymer blend matrices increased only under impact loading. Optimal PSF content was found to be 10 wt%. It was shown that all the blends investigated were homogeneous before curing and became heterogeneous after curing. For epoxy-PSF/fibre joints a mixed (interfacial-cohesive) failure mode was observed for all the samples investigated. The results from the rheology, wetting, thermal, mechanical and structural tests, described in a set of papers, are compared with each other to explain the reasons for the adhesion strength behaviour of epoxy-PSF/glass fibre joints. Based on the finding here, an epoxy-10% PSF matrix is recommended for composite production.