Thermal Degradation of Polystyrene, Poly(1,4-butadiene) and Copolymers of Styrene and 1,4-butadiene Irradiated Under Air or Argon with 60Co-γ-rays
Polymer Degradation and Stability
60Co-γ-irradiated samples of polystyrene (PSt), poly(1,4-butadiene), (PBD), and two poly(styrene-co-butadiene)s containing 25 and 75% BD were subjected to thermogravimetric analysis (TGA), in the presence and absence of O2. In the case of PSt the irradiation caused a significant shift in Tonset, the onset temperature for mass loss, to higher temperatures, whereas in the cases of the BD-containing polymers irradiation caused a decrease in Tonset (oxic irradiation) or had little or no effect on Tonset (anoxic irradiation). The amount of non-volatile residue formed in the cases of BD-containing polymers was augmented by γ-irradiation. The improved thermal stability of PSt is attributed to radiation-generated unsaturations acting as depolymerization retardants and/or agents in thermal crosslinking. Radiation-induced crosslinks do not affect the thermal behavior of PSt. In the cases of BD-containing polymers the thermal behavior is predominated by reactions of the carbon–carbon double bonds (crosslinking and cyclization). Radiation-induced chemical alterations, therefore, play a minor role during the thermal decomposition.