On toughness and stiffness of poly(butylene terephthalate) with epoxide-containing elastomer by reactive extrusion

To obtain a balance between toughness (as measured by notched impact strength) and elastic stiffness of poly(butylene terephthalate) (PBT), a small amount of tetrafunctional epoxy monomer was incorporated into PBT/ [ethylene/methyl acrylate/glycidyl methacrylate terpolymer (E-MA-GMA)] blends during the reactive extrusion process. The effectiveness of toughening by E-MA-GMA and the effect of the epoxy monomer were investigated. It was found that E-MA-GMA was finely dispersed in PBT matrix, whose toughness was significantly enhanced, but the stiffness decreased linearly, with increasing E-MA-GMA content. Addition of 0.2 phr epoxy monomer was noted to further improve the dispersion of E-MA-GMA particles by increasing the viscosity of the PBT matrix. While use of epoxy monomer had little influence on the notched impact strength of the blends, there was a distinct increase in the elastic stiffness. SEM micrographs of impact-fracture surfaces indicated that extensive matrix shear yielding was the main impact energy dissipation mechanism in both types of blends, with or without epoxy monomer, and containing 20 wt.-% or more elastomer.