A new semi-empirical equation for the thermal degradation of polymers is suggested. The proposed model starts from the recognition that the thermo-oxidative degradation occurs in both time and temperature and postulates a separation between the time and temperature dependence, based on the observation that both processes are described by sigmoid-like dependences (or superpositions of such sigmoids). This polymer was selected because atactic polystyrene is almost completely amorphous, thus removing the complications generated by the presence of amorphous domains, crystallites, and interphase(s). The actual fitting equation contained additionally the zero, slope, and second-order corrections. The experimental data are well fitted by the semi-empirical equation. TGA data on the degradation of atactic polystyrene, in a nitrogen atmosphere, and at various heating rates ranging from 1 oC to 40 oC were collected (see figure). Further, the TGA investigation is extended to the derivative of the thermograms (with respect to the temperature), with a detailed analysis of the dependence of the position and width of derivatives on the heating rate. It is demonstrated that the proposed approach (and equation) is consistent with Friedman's approximation.

Modelling the thermooxidative degradation of polymers: Polystyrene

ACS Spring 2022

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