EFFECT OF OLIGOMERS AND ACRYLONITRILE CONTENT ON THE INTERFACIAL ADHESION BETWEEN PC AND SAN

The interfacial fracture toughness between polycarbonate (PC) and poly(styrene-co-acrylonitrile) (SAN) bilayers was measured using an asymmetric double cantilever beam geometry. The effects on fracture toughness of oligomer content and copolymer composition were investigated. Results showed that by removing residual oligomers from SAN, the fracture toughness of the PC/SAN interface was increased significantly. To study this effect in more detail, benzonitrile was used as a model oligomer and added in controlled amounts to pure SAN before attaching to PC and annealing. The PC/SAN interfacial fracture toughness in this case decreased monotonically with increasing benzonitrile content presumably due to migration of the small molecule to the interface. Interfacial toughness was also measured for five purified SAN materials with a range of 17-31 wt % acrylonitrile. A maximum in PC/SAN toughness was seen for a 24% AN material. Evidence of possible chain scission during fracture in purified SAN and PC was observed from x-ray photoelectron spectroscopy measurements. Optical microscopy showed that a single craze ahead of the crack is a possible failure mode during fracture of the SAN/PC interface. (C) 1993 John Wiley & Sons, Inc.