FRACTURE-RESISTANCE OF POLYBLENDS AND POLYBLEND MATRIX COMPOSITES .2.ROLE OF THE RUBBER PHASE IN NYLON 6,6 ABS ALLOYS/

A comprehensive study was undertaken on the specific role of rubber on toughening when other rigid polymer or non-polymer phases were presen t. Nylon 6,6/SAN blends of various SAN concentrations ranging from pur e SAN to pure nylon 6,6 were investigated with and without fibre reinf orcements. These results could be compared with the toughness values o f unreinforced and fibre-reinforced nylon 6,6/ABS alloys from a previo us study in order to elucidate the role of rubber. Fracture behaviour was investigated rigorously by characterizing the fracture initiation toughness, J(IC), and the steady-state fracture toughness, J(ss). Thes e were then related to the microstructure and failure modes determined by microscopy and fractography methods. It was found that rubber incr eased both fracture initiation and propagation toughness in the presen ce of the rigid phase, while the rigid phase toughened the alloy only when the rigid phase/matrix interface was strong enough. The role play ed by glass fibres was found to be critically related to the fibre/mat rix interfacial strength. Toughening was generally observed, both in t he presence and absence of rubber, when the interface was strong. In a ll cases toughening could be related to the enhancement of plasticity in the crack tip by the presence of the rubber phase or the reinforcin g glass phase.