Kinetics of degradation under non-isothermal conditions of a thermooxidative stabilized polyurethane

A flexible polyurethane (PU) foam prepared from a polyol and an isocyanate prepolymer was stabilized against thermooxidation with two types of compounds: 2,6-di-t-butyl-4-methyl-phenol (non-reactive) and, respectively, 3,5-di-t-butyl-4-hidroxy-benzyl alcohol (reactive). The TG were obtained at different heating rates: beta = 5, 7, 10, and 12 A degrees C min(-1) and the TG/DTG were processed with the following methods: Freidman, Flynn-Wall-Ozawa, Budrugeac-Segal, and, respectively, Non-Parametric Kinetics. By Freidman and Flynn-Wall-Ozawa methods it was observed a significant (more that 10%) variation of the activation energy, E, versus the conversion degree, this being an indication of a complex process. Therefore, the more sophisticated Budrugeac-Segal and NPK methods were used. The Budrugeac-Segal method presents a very good descriptive ability, so it is useful for simulations of the thermal behavior. The NPK method is the less speculative one and in the majority of cases the obtained values of the activation energy were in a rather good agreement with both Friedman and Flynn-Wall-Ozawa kinetic data. The value of the activation energy seems to be an appropriate parameter for the estimation of the thermal stability. In comparison with the unstabilized PU, the one stabilized with the reactive compound presented the best thermal stability.