Thermodynamic Description of Strain-Induced Crystallization of Natural Rubber by a Combination of the Tube Model and a Scaling Argument

Abstract

The addition of nanoparticles remarkably improves the mechanical properties and strain-induced crystallizability of natural rubber. To reveal the underlying mechanism for the enhancement of these physical properties, we analyzed the microstructural changes of rubber due to the inclusion of clay and carbon black by using the tube model. The rubber filled with clay exhibited a stronger confinement effect of entanglements on the chain conformation compared with the pure rubber and that filled with carbon black. As a result, we propose a new thermodynamic approach to the entropic elasticity of entangled rubber by a combination of the blob scaling argument and the tube model. The thermodynamic analysis demonstrated that the restriction effects of both entanglements and the filler network led to a reduction of the conformational entropy in clay-filled rubber, resulting in the decrease of the onset strain of crystallization. These results revealed the mechanism of the strain-induced crystallization and filler reinforcement from the viewpoint of thermodynamics.