CRAZING PHENOMENA IN PC SAN MICROLAYER COMPOSITES/

The crazing behavior of coextruded microlayer sheets consisting of alt ernating layers of polycarbonate (PC) and styrene-acrylonitrile copoly mer (SAN) was investigated as a function of PC and SAN layer thickness es. In this study, the total sheet thickness remained essentially cons tant and the PC and SAN layer thicknesses were changed by varying both the total number of layers from 49 to 1857 and the PC/SAN volume rati o. Photographs of the deformation processes were obtained when microsp ecimens were deformed under an optical microscope. Three different typ es of crazing behavior were identified: single crazes randomly distrib uted in the SAN layers, doublets consisting of two aligned crazes in n eighboring SAN layers, and craze arrays with many aligned crazes in ne ighboring SAN layers. The transition from single crazes to doublets wa s observed when the PC layer thickness was decreased to 6 microns. Cra ze array development was prevalent in composites with PC layer thickne ss less than 1.3 microns. It was concluded that SAN layer thickness wa s not a factor in formation of arrays and doublets; formation of craze doublets and craze arrays was dependent only upon PC layer thickness. (C) 1994 John Wiley & Sons, Inc.