The effect of surface embrittlement on the mechanical behavior of rubber-modified polymers

An experimental study was conducted to better understand the mechanism of surface embrittlement in rubber-modified thermoplastics. Brittle polymer films were laminated onto acryionitnie-Duraaiene-styrene terpolymer and high-impact polystyrene to simulate either embrittlement due to environmental degradation or brittle paint systems. The effect of varying coating thickness and molecular weight was studied in tensile and impact testing. Results of this study suggest that the multiple crazing mechanism normally associated with the energy-absorbing capability of rubber-toughened polymers is severely restricted due to the formation of multiple surface cracks resulting from coating failure. This is particularly true when the coating thickness reaches a critical value at which a single surface crack is able to propagate across the coating/substrate interface in an unstable manner.