On the separation of physical and chemical component of stress relaxation

This paper proposes a new method to separate physical and chemical components of stress relaxation. The stress relaxation measurements of tetrafluoroethylene-propylene rubber were carried out at various temperatures ranging from 200° to 310°C. A physical stress relaxation master curve could be generated from data of early period of time by the time-temperature superposition principle. The rate of physical stress decay at given temperatures was calculated from the master curve. The rate of chemical stress relaxation was given by subtracting the rate of physical decay from experimentally obtained rate at the corresponding temperatures. The activation energy was found to be 8.4 kcal mol^?1 for the rates of the calculated chemical stress relaxation, while it was found to be 5.7 kcal mol^?1 for the rates which were obtained in air. The results show that the physical component of stress decay should be subtracted from the measured stress relaxation curve to obtain the rate of chemical stress decay, especially at the low temperature.