Toughened blends of poly(butylene terephthalate) and BPA polycarbonate

Abstract

The toughening mechanisms of blends of poly(butylene terephthalate) (PBT) and bisphenol-A polycarbonate (PC) toughened with core/shell impact modifier have been studied by transmission electron microscopy, notched impact testing and uniaxial tensile dilatometry. It was found that in both toughened PBT and toughened PBT/PC blends, shear deformation is the major toughening mechanism. Brittleness at low temperatures is caused by a reduction in the ability of the matrix to undergo shear deformation. In tensile dilatometry this effect is indicated by an increase in the extent of internal cavitation of the impact modifier particles. The low-temperature impact toughness of toughened PBT/PC blends is significantly greater than that of toughened PBT. Modification of PBT with partially miscible PC appears to have a beneficial effect on the ability of PBT to undergo shear deformation. This effect has been attributed to the PC residing in the amorphous interlamellar regions of the PBT spherulites, thus facilitating interlamellar slip.