Fracture resistance in rubber‐toughened polymers

The effects of rubber content, particle size and interparticle spacing on the fracture behaviour of toughened polymers over a range of strain rates and temperatures are discussed with particular reference to high‐impact polystyrene and rubber‐toughened nylons. It is concluded that the limiting factor in determining fracture resistance is a kinetic one: the rate at which the matrix polymer can respond to stress by forming oriented fibrils. Fibrillation can occur either by multiple crazing, in which case the preferred particle diameter D is about 1 μm; or as a result of cavitation within the rubber particles followed by shear yielding, which requires smaller inter‐particle spacings. An extension of the Argon‐Salama model for crazing is proposed to explain the interparticle spacing effect. Morphology is less critical in controlling fracture at low strain rates or higher temperatures.