RUBBER ELASTICITY AT LARGE DEFORMATION (VIII)

Stress-strain Behavior of Polyurethane Elastomer

Abstract

A new rubber elastic equation derived from a uniform stress hypothesis was applied to analyze the stress-strain curves of polyurethane elastimers. Good applicability of the presented equation for many experimental data was obtained for both the extension and the retraction curve of hysteresis cycle as well as the ordinary bulk rubber vulcanizates. The parameters, such as vkT, b, C₁ and C₂ are obtained from this plot and Mooney-Rivlin plot. In general, b and C₂ terms harv larger values than those of bulk rubber vulcanizates. The fact can be explained by the network structure of polyurethane being composed of pseudo crosslink. The proportional relationship was obtained between vkT and C₁, b and C₂.
In the case of one-shot type polyurethane, these parameters increased with increasing concentration of urethane linkage.
On the other hand, for millable type polyurethane, vkT and C₁ increased, and b and C₂ decreased with increasing crosslinking density. Under elevated temperatuer, the values of b and C₂ became small. The apparent activation energy obtained from Arrhenius plot was within the values of 3-5Kcal/mol.
From these results, it can be considered that b and C₂ are the parameters concerned with internal viscous flow.