Large deformation tensile properties of elastomers. I. Temperature dependence of c1 and c2 in the mooney‐rivlin equation

Tensile stress‐strain data were determined at various extension rates and temperatures on unfilled butyl and silicone vulcanizates and on six hydrofluorocarbon (Viton A‐HV) vulcanizates that contain between 0.90 and 12.2 × 10−5 mole of effective network chains per unit volume of gel rubber. From 1‐min. isochronal data, values of C1 and C2 in the Mooney‐Rivlin equation were derived. For the butyl and silicone vulcanizates from, respectively, −20 to 150°C. and −45 to 200°C., C1 increases with temperature at a rate which is in reasonable agreement with published data from forcetemperature measurements. Because C2 is sensibly temperature independent over these extended temperature ranges, it is concluded that C2 is a finite quantity under equilibrium conditions. Time‐dependent behavior was observed on the Viton A‐HV vulcanizates between −5 and 230°C. For each vulcanizate between about 25 and 230°C., C1273/T is temperature independent, but it increases with decreasing temperature below about 25°C. Except at the lowest temperatures, C2273/T decreases with increasing temperature, the rate of decrease becoming progressively less with an increase in crosslink density. Above 25°C. the ratio C2/C1, which ranges from about 90 to 0.6, decreases with an increase in either temperature or crosslink density. The time‐dependent behavior of C2273/T appears to arise primarily from molecular processes whose relaxation times are considerably longer than the terminal relaxation time of individual chains.