Effect of styrene-butadiene-styrene block copolymer on the kinetics of thermooxidative degradation of high-impact polystyrene

The stability of polyolefins and their blends is very important for their practical use under high temperatures. The effect of styrene-butadiene-styrene block copolymers on the intensity of the thermooxidative degradation of HIPS can be followed through kinetic parameters. In styrene-butadiene copolymers soft, polybutadiene phase (PB), and hard, polystyrene phase (PS) have a different sensibiltiy on thermal degradation. The thermooxidative stability of high impact polystyrene (PS-HI) and blends of PS-HI and styrene-butadiene-styrene copolymer, (SBS) were investigated. The investigation was done by isothermal DSC analysis. The kinetic parameters of the thermooxidative degradative process, i.e., the reaction rate constants, the reaction orders, and the activation energies have been determined. The total area under the exothermic curve was used to calculate the isothermal heat of degradation. On the basis of the heat of the thermooxidative degradation the conversion ( alpha ) and the rate of the thermooxidative degradation (d alpha /dt) have been obtained. The experimental data have been tested with kinetic model for autocatlytic reactions: d alpha /dt (k alpha exp m (1-( alpha ) exp n . The activation energy has been determined by Arrhenius equation. On the basis of the calculated kinetic parameters the order of thermooxidative stability of the investigated system has been obtained. The experimental data have a good agreement with the autocatalytic model.