TOUGHENING OF SAN WITH ACRYLIC CORE-SHELL RUBBER PARTICLES - PARTICLE-SIZE EFFECT OR CROSS-LINK DENSITY

The effect of rubber particle size on fracture toughness and tensile p roperties have been investigated using styrene-acrylonitrile as a matr ix. Pre-formed particles with poly(butyl-acrylate) core and a poly(met hylmethacrylate) shell, ranging from 0.1 to 0.6 mu m in diameter, were used as a toughening agent. The morphology was checked by means of tr ansmission electron microscopy. The test methods involved an un-notche d uniaxial tensile test, notched Izod impact and notched tensile testi ng. The experiments were carried out with varying deformation rates an d temperatures. N.m.r. experiments were used to measure network densit ies in the rubber core of the various particles. Uniaxial tensile test s showed that elastic modulus and yield stress of the blends were inde pendent of particle size and network density of the rubber core. There were, however, some differences in cavitation resistance caused by th e differences in network density. Easily cavitating particles produced higher toughness in notched Izod impact and notched tensile test but a clear relation with particle size could not be established for the r ange studied. The brittle-tough transition temperatures were much high er than for materials based on poly(butadiene) core-shell rubbers. It is suggested that the mechanical properties of the rubber particle cor e are the key to the toughening efficiency. It was found that high tou ghness could only be achieved if the particles had a low cross-link de nsity (and a corresponding low modulus and low cavitation resistance). (C) 1998 Published by Elsevier Science Ltd. All rights reserved.