Thermal and thermo‐oxidative degradation of polystyrene in the presence of ammonium sulfate

Abstract Ammonium sulfate was compounded into polystyrene (PS) to modify thermal degradation of PS. At elevated temperatures, ammonium sulfate decomposes into ammonia, sulfuric acid and further into sulfur trioxide and water. The aim of the study was to investigate how these acidic and oxidizing compounds affect the thermal and thermo‐oxidative degradation behaviour of polystyrene. Thermal degradation was studied by thermochromatography (ThGC). In addition, isothermal pyrolysis at 340°C was carried out and the dissolved parts of the residues were analyzed by size exclusion chromatography (SEC). The random chain scission index S r (based on the components of evolving gases), the chain scission number S x (based on the number‐average molar mass), the oxygen effect K , and the synergistic effect Z were used to describe thermal and thermo‐oxidative degradation processes. The increases of S r and S x with the increase of ammonium sulfate imply that thermal degradation of PS is modified. The synergistic effect Z indicated that, at low addition levels, ammonium sulfate synergistically promotes thermo‐oxidative degradation with oxygen. At high addition levels, it promotes thermo‐oxidative degradation with oxygen.