DEFORMATION AND TOUGHNESS OF POLYMERIC SYSTEMS .7. INFLUENCE OF DISPERSED RUBBERY PHASE

The deformation behaviour of ethylene-propylene-diene monomer rubber-m odified polycarbonate blends (PC/EPDM; where the EPDM is adhering to t he PC matrix) is studied and compared with non-adhering core-shell rub ber-modified polycarbonate blends (PC/CS) using slow-speed uniaxial te nsile testing and notched high-speed tensile testing. As expected, onl y the latter testing method reveals the existence of the critical thic kness of PC as a function of temperature. At a constant ligament thick ness the brittle-to-tough transition temperature (T(BT)) strongly incr eases upon replacing a hole (i.e. non-adhering rubber) by adhering EPD M rubbery particles. Electron beam irradiation is applied to selective ly crosslink the dispersed EPDM rubbery phase and, consequently, incre ase its cavitation stress (which is proportional to the dynamic shear modulus). The T(BT) proved to be highly influenced by the thus modifie d cavitation stress of the dispersed phase. In terms of the energy-bas ed criterion for the prediction of the critical thickness, this can on ly qualitatively be explained by (i) an increased strain energy densit y and/or by (ii) a change in the matrix volume involved in supplying t he stored elastic energy.