A FRACTURE STUDY OF A DUCTILE MATRIX BRITTLE DISPERSED PHASE POLYMER BLEND

In the relatively uncommon systems of brittle dispersed phase polymers in ductile matrix polymers, increases in both stiffness and impact st rength have been reported recently. In this investigation a semi-ducti le polyethylene matrix was studied containing crosslinked polystyrene particles (0.5 to 4 mu m) having carboxylic acid surface functionality ; Potential interfacial bonding was effected by the addition of varyin g amounts of a reactive polyethylene (with glycidyl methacrylate graft s) to the polyethylene matrix. Elastic-plastic fracture mechanics invo lving the J-integral test were used to determine the effects of disper sed phase particle size and volume fraction as well as the extent of r eactive matrix copolymer addition. The addition of brittle particles t o a non-reactive ductile matrix resulted in a significant drop in the fracture toughness of the blend, which was related to the surface-surf ace interparticle spacing. The fracture mechanism was primarily void n ucleation by interface decohesion at low strain. The addition of matri x reactivity causes some of the loss in toughness to be recovered. In the size range investigated, the larger particles cause a smaller toug hness drop when added to the matrix and show more significant improvem ents upon addition of matrix reactivity. The toughening effect was rel ated to covalent bonding at the interface and fracture was controlled by ductile yielding in the matrix.