Charring processes in thermoplastic polymers: Effect of condensed phase oxidation on the formation of chars in pure polymers

Fifteen different pure polymers were studied by thermal methods under air, nitrogen, and nitrous oxide in order to determine their tendency to char in relation with their structure and the experimental conditions used. Styrene polymers and aliphatic polyolefines give chars under air and total volatilization without carbonization under nitrogen and nitrous oxide, showing the essential part played by oxygen in the charring process. On the opposite, ambient oxygen has some effect on the carbonization of polymers containing aromatic rings in their main chain. A schematic mechanism of the charring process is discussed in which condensed phase oxidation, formation of olefinic bonds and crosslinking, dehydrogenation–aromatization are postulated.