Potential of Recent Rubber-Elasticity Theories for Describing the Tensile Stress-Strain Dependences of Two-Phase Polymer Networks

摘要

The potential of recent rubber-elasticity theories for giving a well-founded, molecularly based and as-precise-as-possible description of experimental tensile stress-strain dependences of two-phase polymer networks (such as block polymers of the polyurethane and styrene-butadiene-styrene type) up to the break has been explored. Theoretical arguments lead to the conclusion that the rigorous theory of the high-strain hardening effect based on Langevin statistics (Arruda and Boyce, 1993) is to be preferred to the slip-link and extended-tube theories in view of the approximations involved in their derivation. None of the existing theoretical treatments of the low-strain softening was found suitable for the purpose of the study. Therefore, a semiempirical solution had to be chosen by combining the Langevin-theory-based term with an empirically modified C_2 term of the Mooney-Rivlin equation, similarly to the treatment used previously for unfilled and filler-reinforced networks (Meissner and Matejka, 2000, 2001). A very good data description is obtained for networks with different contents of hard blocks, up to 50%, provided that yield does not appear. The parameter values of the proposed equation have been determined for a number of two-phase networks and their relations to structural parameters are discussed. The experimental high-strain behavior strongly suggests the presence (absence) of topological changes on increasing (decreasing) elongation, of the same kind as observed previously for unfilled and filler-reinforced networks. Thus, a unified picture of the tensile stress-strain behavior of rubbery networks of all kinds emerges.