Deformation-Induced Crystallization In Rubber-Like Materials

Deformation induced crystallization is crucial for determining the final mechanical properties of elastomers-rubber. Elastomeric networks show high upturn in the stress-strain curves with a significant hysteresis, this is attributed to the deformation induced crystallization phenomenon. Thermodynamics of rubber-like high polymers have been studied, and uniaxial extension with some approximations is discussed to obtain an overview of the proposed thermodynamic constitutive theory. A thermodynamical statistical model is presented for studying the stress-strain behaviour of elastomeric networks, and the dependence of the stress coefficients on the degree of crystallinity. This is based on the modified distribution of chains of finite length. A crystallization formulation based on irreversible thermodynamics is adopted to describe the crystallization taking into account the effects of strain rate and temperature. Mooney representation curves are introduced in this study to show the strong dependence of stress coefficients on the degree of crystallinity. Both uniaxial loading and unloading are investigated for a range of strain rates and temperatures, to explain the effect of molecular orientation and strain induced crystallization in polyisoprene rubber and ethylene-butene copolymers (thermoplastic elastomers). The effect of relaxation process, and the rate of deformation on crystallization has been illustrated. The hysteresis of the stress-strain relation and inelastic deformation behaviour is attributed to the deformation induced crystallites and their transformation; this is clearly shown at high strain rates and low temperatures (i.e. above the glass transition temperature). The model results show good agreement with experimental data that have been determined in this study