Thermoelastic and thermomechanical studies on natural rubber vulcanized in the swollen state

Three samples of natural rubber were crosslinked in n-decane solution. After the solvent had been removed, a thermodynamic investigation was made of the elastic behaviour of the samples in simple extension. Thermoelastic measurements at constant pressure and length were carried out on the first two samples. The third sample was subjected to a thermomechanical heat of extension study using a Calvet microcalorimeter. The experiments enabled the temperature coefficient of the mean-square unperturbed dimensions, 〈r²₀〉, to be derived. From the thermoelastic measurements average values for dln $\text{〈r}{}^2{}_0\text{d}\text{T}$ of (0.44 ± 0.08) × 10^?3deg^?1 and (0.38 ± 0.07) × 10^?3deg^?1 were obtained, whilst the thermomechanical measurements gave a value of (0.54 ± 0.04) × 10^?3deg^?1.