Impact strength and failure mechanisms of PBT/PC blends

Impact strength of a series of PBT/PC blends was tested at different strain rates. It was found that when fracture occurred under plane strain condition the impact fracture toughness of the PBT/PC blends with strong interface obeyed the rule of mixtures. But when fracture took place under non-plane strain condition, the toughness of the blends was much lower than that predicted by the rule of mixtures and negative blending effect was observed. Further study revealed that the PC domains of the blends are subjected to an additional plastic constraint imposed by the rigid neighboring PBT domains. Under this additional plastic constraint the PC domains have a tendency to undergo brittle fracture. Evidence from microscopic studies supports the failure mechanisms proposed.