The Effects of Di-T-Butylperoxide on the Oxidative Stability of Polypropylene II.

The oxidative embrittlement of polypropylene film 5 mil has been studied by measuring stress-strain behavior, molecular weight changes, and development of carbonyl concentration in the infrared spectrum. Oxidation was conducted both in air and in peroxide in the temperature range of 50-90C. The mechanical measurements show the effects of oxidation in the most responsive way the embrittlement can be clearly seen as a sudden decrease in the elongation at break. Only a small decrease in average molecular weight has taken place at embrittlement, and the development of carbonyl concentration progresses even more slowly. After 6 hours at 70C in peroxide the elongation has decreased from 900 to 20. To obtain a comparable decrease without peroxide, the film must be exposed for 6 days in the air oven at 70C. The molecular weight is not nearly as sensitive as the mechanical property effects. The use of infrared carbonyl concentration to follow degradation effects has been found to be ineffective. The cause of the drastic change in mechanical properties is believed to be the scission of tie molecules in the amorphous phase which interconnects crystalline regions. Author, modified-PL