Induction period in the aging of polypropylene

The ordinary methods for obtaining a rapid estimate of the useful life of a plastic, extrapolations from tests conducted at higher temperatures or at lower stabilizer concentrations than those of actual use, lead to serious errors in estimating the useful life of some stabilized polypropylene compositions. Two methods for obtaining more reliable rapid estimates of useful life have been explored and are reported here: (1) measurement of physical and chemical changes, such as weight loss, stabilizer loss, density increase, dyeability increase, and formation of carbonyl or hydroperoxide groups, which occur during the prefailure stages of oxidative deterioration at the temperature of interest (of these, measurements of stabilizer loss appear the most promising); (2) thermal development of the prefailure oxidative damage initiated at the temperature of interest. This method needs further exploration.