Thermogravimetric studies of styrene-butadiene rubber (SBR) after accelerated thermal aging

Styrene-butadiene rubber was subjected to long-term thermal aging treatment at 80 A degrees C with aging period up to 180 days. The degradation kinetics of the aged sample was analyzed by thermogravimetric analysis. Multiple heating rate experiments were carried out in nonisothermal conditions and three isoconversional model-free methods (Friedman; Kissinger-Akahira-Sunose; Li and Tang methods) were employed. The results showed that the temperature for 5 % mass loss increased, whereas the maximum mass loss temperature decreased after aging. Activation energies (E (a)) derived from the three methods were found to be dependent on conversion degree (alpha). E (a) increased with increasing alpha in the whole range of conversion for samples aged for 0, 60, and 120 days, while the aged samples displayed higher E (a) values. However, samples aged for 180 days showed declining E (a) versus alpha. The changes on the degradation kinetics were associated with the modification on the chemical structure after thermal aging.