Effect of finite extensibility on the viscoelastic properties of a styrene–butadiene rubber vulcanizate in simple tensile deformations up to rupture

Abstract

AbstractStress–strain and rupture data were determined on an unfilled styrene–butadiene vulcanizate at temperatures from −45 to 35°C and at extension rates from 0.0096 to 9.6 min−1. The data were represented by four functions: (1) the well‐known temperature function (shift factor) aT; (2) the constant strain rate modulus, F(t,T), reduced to temperature T0 and time t/aT, i.e., T0F(t/aT)/T; (3) the time‐dependent maximum extensibility, λm(t/aT); and (4) a function Ω(χ) where χ = (λ − 1)λm0/λm, in which λ is the extension ratio and λm0 is the maximum extensibility under equilibrium conditions. The constant strain rate modulus characterizes the stress–time response to a constant extension rate at small strains, within the range of linear response; λm is a material parameter needed to represent the response at large λ; and Ω(χ) represents the stress–strain curve of the material in a reference state of unit modulus and λm = λm. The shift factor aT was found to be sensibly independent of extension. At all values of t/aT for which the maximum extensibility is time‐independent, the relaxation rate was also found to be independent of λ. These observations indicate that the monomeric friction coefficient is strain‐independent over the ranges of T and λ covered in the present study. It was found that λm0 = 8.6 and that the largest extension ratio at break, (λb)max, is 7.3. Thus, rupture always occurs before the network is fully extended.