Effect of acrylonitrile content on the delamination toughness of PC/SAN microlayers

The effect of acrylonitrile (AN) content on the adhesion of poly(styrene-co -acrylonitrile) (SAN) to polycarbonate (PC) was examined by measuring the d elamination toughness of PC/SAN microlayers in the T-peel test. Experiments were carried out on microlayers with thin SAN layers, to ensure that delam ination would occur predominantly by an interfacial mechanism, and with PC layers that were thick enough to prevent the delamination crack from tearin g through the PC. Layer thicknesses of approximately 4.5 mu m/0.5 mu m (PC/ SAN) gave satisfactory results. A broad maximum in the interfacial toughnes s occurred at about 20% AN. When microlayers with thicker SAN layers were t ested, only SAN compositions with 15-25% AN crazed. This increased the dela mination toughness and greatly exaggerated the maximum at 20% AN. Crazing o nly occurred if the interfacial toughness of PC-SAN exceeded the SAN crazin g condition. When the crazing condition, which increased linearly with AN c ontent, was overlayed with the interfacial toughness, the intersections cor rectly predicted the AN content for transitions in failure mode. (C) 1999 E lsevier Science Ltd. All rights reserved.