Fracture toughness of nylon 6 blends with maleated ethylene/propylene rubbers

The fracture of blends of nylon 6 and maleated ethylene-propylene rubber wa s examined by both the Izod impact test and a single-edge notch three-point bend (SEN3PB) instrumented Dynatup test. The effects of EPR-g-MA content, ligament length, method of fracture surface measurement, sample thickness a nd fracture position in the molded bar on the fracture behavior were invest igated. The data were analyzed by plotting the specific fracture energy (U/ A) as a function of ligament length. The blends containing a high portion o f EPR-g-MA in the rubber phase were found to be super tough over the whole range of ligament lengths and under all test conditions. However, a ductile -to-brittle transition was observed with ligament length for marginally tou gh blends which contained a low content of EPR-g-MA in the rubber phase and had a ductile-brittle temperature near or above room temperature; the spec imens with short ligament length fractured in a ductile manner, while the s pecimens with long ligaments showed brittle fracture. The transition ligame nt lengths were found to be dependent on the rubber particle size. The dual mode of fracture was rationalized by equations for ductile yielding and br ittle crack propagation; values of yield stress and critical intensity fact or were estimated from these model equations. The dissipative energy densit y, u(d), was more sensitive to rubber particle size, sample thickness and l ocation in the molded bar than the limiting specific fracture energy, u(o). There is a good correlation between the standard Dynatup impact strength a nd the parameter lid for the gate end specimens. (C) 2000 Elsevier Science Ltd. All rights reserved.