PHASE MORPHOLOGY OF INJECTION-MOLDED POLYCARBONATE ACRYLONITRILE BUTADIENE STYRENE BLENDS

The morphology of injection-moulded blends of polycarbonate (PC) and acrylonitrile-butadiene-styrene (ABS) has been examined across the entire composition range. Brittle fracture surfaces were etched to remove selectively the PC phase and viewed in the scanning electron microscope. Morphological features observed through the thickness of injection-moulded plaques were the basis for the identification of three composition ranges. In PC-rich blends, the ABS phase formed a bead-and-string structure oriented in the injection direction near the edge, while in the centre the ABS was dispersed as rubber domains and spherical particles of free styrene-acrylonitrile (SAN). A transition occurred between PC/ABS 70/30 and 60/40 wt% compositions from the bead-and-string structure with some interconnections to a coalesced, stratified morphology near the edge; while in the centre, the morphology changed from a dispersion of rubber particles and free SAN particles to thick coalesced ABS domains that created regions where ABS was co-continuous with PC. The ABS-rich blends had a conventional blend morphology with PC domains dispersed in ABS. Qualitatively, the solid-state morphology could be explained in terms of the melt morphology created by the melt flow pattern during mould filling, and subsequent relaxation during cooling prior to solidification.