Fracture toughness of nylon-6 blends with maleated rubbers

The fracture toughness of blends of nylon-6 with maleated ethylene-propylene rubber and maleated styrene/hydrogenated butadiene/styrene triblock copolymer was investigated with a single-edge-notched three-point-bending instrumented Dynatup test. The blends for which the rubber particle size was less than 0.7 mum fractured in a ductile manner over the whole range of ligament lengths, whereas the blends with particles larger than 0.7 mum showed a ductile-to-brittle transition with the ligament length. In this regime, ductile fracture was observed for specimens with short ligaments, whereas brittle fracture was seen for those with long ligaments. The ductile fracture behavior was analyzed with the essential-work-of-fracture model, whereas linear elastic fracture mechanics techniques were used to analyze the brittle fracture behavior. The fact that the ductile fracture energy was larger for the blends with the styrene/hydrogenated butadiene/styrene triblock copolymer than for those with ethylene-propylene rubber was due to the larger dissipative energy density of the blends based on the styrene/hydrogenated butadiene/styrene triblock copolymer. Both the critical strain energy release rate (G(IC)) and the plane-strain critical stress intensity factor (K-IC) increased as the rubber particle size decreased for both blend systems. The G(IC) and K-IC parameters had similar values, regardless of the rubber type, when the rubber particle size was fixed. The transition ligament length was near the size criterion for plane-strain conditions for both blend systems. (C) 2004 Wiley Periodicals, Inc.