Thermo oxidative stability of polyamide 6 films I. Mechanical and chemical characterisation

Unstabilised and stabilised polyamide 6 films were subjected to long-term oven ageing in ambient atmosphere at temperatures in the range of 100-120 degrees C. The strain at break of film strips showed a drop at a point of oxidation corresponding to a critical molar mass range of 15000-19000 g mol(-1). Embrittlement occurred at a molar mass of 40-50% of the original value of 27000 g mol(-1). The efficiency of a phenolic antioxidant such as Irganox 1098 was poor, extending the drop in strain at break only by a factor of 2. All investigated polyamide films showed a high rate of oxygen uptake at the beginning of oxidation followed by a gradual decline. The oxidation was accompanied by an autoretardant accumulation of peroxides as well as of carbonyl groups consistent with the oxygen uptake data. This behaviour is different from that reported for polyolefins, which show a well-defined induction period followed by a sigmoidal increase in the oxygen uptake, also in the presence of a phenolic antioxidant. It is unlikely that the rate of oxidation solely depends on the concentration of peroxides since, throughout the oxidation, peroxides were accumulating, while the rate of oxygen uptake was decreasing. (C) 1999 Elsevier Science Ltd. All rights reserved.