Effect of polycarbonate molecular weight and processing conditions on mechanical behaviour of blends with a core-shell impact modifier

Abstract

Morphology, tensile properties and impact strength behaviour of blends of three different molecular weight (or viscosity) grades of polycarbonate (PC) and a core-shell type impact modifier (3–18 wt%) were prepared in a single screw extruder with an intensive mixing head and in a co-rotating, fully intermeshing twin screw extruder at different conditions. The morphology of these blends were quantitatively analysed from transmission electron photomicrographs. Tensile properties and Izod impact strength, as a function of temperature for 3.13 mm specimens, were also measured. All mechanical properties were found to be very sensitive to the degree of dispersion of the impact modifier in the PC matrix. Blends made in the twin screw extruder consistently showed better dispersion and mechanical properties: higher tensile modulus, yield strength and elongation at break; higher notched Izod impact strength and lower ductile-brittle temperature. Blends with higher molecular PC show better impact properties reflecting the matrix properties. A subsequent paper explores a more complete analysis of the fracture toughness of such blends and the modes of deformation they undergo during fracture.