Combined deformation- and temperature-induced scission in a rubber cylinder in torsion

When an elastomeric material is deformed and subjected to temperatures above some characteristic value TcrTcr (near 100∘C for natural rubber), it undergoes time and temperature dependent chemical changes consisting of scission and crosslinking of its macromolecular structure. The process continues until the temperature decreases below TcrTcr. Experiments carried out in uniaxial extension have shown that the chemical changes are independent of stretch ratio within moderate stretches. It is reasonable to expect that the chemical changes would be affected by sufficiently large deformations, an interaction referred to as ‘mechanochemistry’. A kinetic theory of the breakdown of solids by Zhurkov [Kinetic concept of strength of solids, Int. J. Fract. Mech. 1 (1965) 311–323. [15]] attributes this interaction to the lowering of activation energy by mechanical work.In a recent constitutive theory, an expression was developed that relates the chemical kinetics of scission of the original elastomeric network to time, temperature and activation energy. The kinetic theory of Zhurkov suggests a method for modifying this expression to account for the influence of deformation. This is explored in the case of simple shear deformations, such as those occurring during torsion of elastomeric cylinders held at fixed length. Using the approach of Penn and Kearsley [The scaling law for finite torsion of elastic cylinders, Trans. Soc. Rheology 20 (1976) 227–238. [16]], it is shown that experiments in torsion can be used to determine the influence of shear deformations on the chemical kinetics of scission.