Temperature and pressure effects on the degradation of polypropylene tape yarns—depletion of antioxidants

Abstract

Polypropylene (PP) tape yarns with a specific antioxidant package consisting of hindered amine light stabilizers were used to evaluate the effects of high oxygen pressures on the depletion of antioxidants. In order to emphasize the pressure effects, relatively low temperatures at 35, 45, 55 and 65°C were utilized for the incubation. The high-pressure environments were created using air or oxygen at levels of 0.02, 1.3, 2.8, 4.9 and 6.3MPa. The depletion of antioxidants was effectively monitored using the high pressure oxidative induction (HP-OIT) test, whereas the oxidation of the polymer was evaluated using tensile and melt index tests. The test data indicate that the depletion of antioxidants was governed by the oxygen partial pressure, not the total pressure of the gas. The oxidation of the polymer did not start until the HP-OIT value dropped below 10% of the original when the antioxidant was essentially depleted.The reaction rate of antioxidant depletion increased with temperature according to the Arrhenius equation, whereas the rate increased exponentially with oxygen pressure. The antioxidant reaction was found to be a rate controlling mechanism. Analytical models were developed to predict the antioxidant depletion rate and antioxidant lifetime of this particular PP tape yarn.