Effect of blending sequence on the morphology and impact toughness of poly(ethylene terephthalate)/polycarbonate blends

The morphology of PET/PC/E-GMA-MA blends made by different mixing sequences was studied by transmission electron microscopy (TEM). The results suggest that migration of the E-GMA-MA copolymer from the PET phase to the PC phas e occurred during the mixing of the (PET/E-GMA-MA) pre-blend with the PC at 10% copolymer content. As a result of the migration, the E-GMA-MA particle s are located in the PC phase rather than in the PET phase. This finding is not in agreement with the prediction made previously by others based on th e possible reaction between the epoxy group of GMA and carboxyl group of PE T. Core-shell (PC/E-GMA-MA) particles formed in situ during blending and th e size of the core-shell particles was controlled by the blending sequence used. Mechanical properties of the ternary blends were tested at various te mperatures. Although the blending sequence does not have a noticeable effec t on the yield strength and modulus of the blends, it has a strong influenc e on the morphology formed, which determines the impact toughness. For blen ds made under optimum processing conditions, the brittle-ductile transition occurred at a lower temperature and lower elastomer content. A study of th e toughening mechanism suggested that the major toughening events were cavi tation plus matrix sheer yielding. It is postulated that the very high impa ct toughness found with the (PC/E-GMA-MA)/PFT blend (at 10% E-GMA-MA) origi nated from the bimodal particle size distribution of the core-shell particl es formed in situ.