Craze initiation during the environmental stress cracking of polymers

The environmental stress cracking behaviour of polycarbonate in ethanol was studied with the aim of critically evaluating craze initiation criteria. A combination of constant strain-rate tensile tests and creep tests were conducted in air and ethanol. The onset of crazing was determined by the use of departure points, which were shown to correlate well with the formation of optically visible crazes. Samples with different states of physical ageing and hence different relaxational behaviour were used to test out various initiation criteria. It was found that crazing occurred when the slower relaxations had accumulated a certain amount of strain, in this case, 0.1%, and that a criterion based on critical inelastic strain was the most appropriate. Post-immersion tests showed that the development of craze precursors occurs independently of the environment.