MECHANICAL-PROPERTIES OF THE RUBBER-TOUGHENED POLYMER BLENDS OF POLYCARBONATE (PC) AND POLY(ETHYLENE-TEREPHTHALATE) (PET)

The intrinsically impact-brittle PC / PET blends can be effectively to ughened, in terms of lower ductile brittle transition temperature (DBT T) and reduced notch sensitivity, by incorporating butylacrylate core- shell rubber. The rubber particles are distributed exclusively in the PC phase. Varying the PC melt flow rate (MFR) is more important than v arying the PET I.V. to vary the low temperature toughness of the blend s. PC with MFR = 3 is essential to produce the toughest PC / PET / rub ber blend. The presence of rubber slightly relieves the strain rate se nsitivity on yield stress increase. Lower MFR PC in the blend results in smaller activation volume and, therefore, higher strain rate sensit ivity, because a greater number of chain segments are involved in the cooperative movement during yielding. Two separate modes, localized an d mass shear yielding, work simultaneously in the rubber toughening me chanism. The plane-strain localized shear yielding dominates the tough ening mechanism at lower temperatures and brittle failure, while the p lane-stress mass shear yielding dominates at higher temperatures and d uctile failure. The critical precrack plastic zone volume has been use d to interpret the observed phenomenon. (C) 1994 John Wiley & Sons, In c.