A thermodynamic study of viton elastomer

Abstract

AbstractThe temperature coefficients of the retractive force at successive fixed lengths were measured for a Viton fluoroelastomer sample. At each elongation the sample was held for at least 40 hr. before the tension measurement in order to minimize the relaxation effect. The range of elongations covered was confined to α values smaller than 1.65 because of the limited tensile strength of the sample. The results show departures from the predictions of simple gaussian theory of rubber elasticity in two respects. First, the tension f at 45°C. follows the Mooney equation with nonvanishing C2 values (2C1 = 3.324 kg./cm.2 and 2C2 = 2.865 kg./cm.2). Secondly, the internal energy makes a negative contribution to the elastic force, and moreover the ratio of the internal energy component to the total tension fe/f decreases with increasing α. The thermodynamic behavior of the Viton sample is thus qualitatively similar to that observed previously with a natural rubber network, except that the internal energy makes positive contribution in the latter. The experimental results were also compared with recent theories which purport to improve upon the simple Gaussian theory of rubber elasticity, but it is found that none of them can explain the results in satisfactory detail.