Thermal initiation of the oxidation of thermoplastic polymers (Polyamides, Polyesters and UHMwPE)

•Thermal initiation can play an important role in the auto-oxidation mechanism of polymers•Thermal initiation is more important for aliphatic polyamides than for semi-aromatic polyamides and polyesters and of minor importance for polyolefins For polyolefinic materials it is shown that thermal initiation of the auto-oxidation is of minor importance. Since the auto-oxidation mechanism of all other polymeric materials is derived from that of polyolefins, it is assumed that for other polymers thermal initiation is unimportant too. However, recent literature data suggested that for polycondensates thermal initiation might be important. Using luminescence measurements, the relevance of initiation for the oxidation of aliphatic and semi-aromatic polyamides and polyesters was determined and compared to that of a polyolefin, UHMwPE. In contrast to what has been widely assumed, thermally alkyl radicals are formed, that initiate oxidation. This is more important for aliphatic polyamides than for semi-aromatic polyamides and polyesters and of minor importance for polyolefins. Generally thermal initiation becomes more prominent at higher temperatures.