Modeling the thermomechanical effects of crystallization in natural rubber: III. Mechanical properties

The model proposed in part I of this series of articles for characterizing the thermomechanical response of natural rubber during crystallization is used in this article to model the mechanical effects of crystallization in natural rubber. Material functions are evaluated such that the model can reproduce existing experimental results on instantaneous rubbery elastic response of fully amorphous natural rubber (22°C), increase in elastic modulus of unconstrained natural rubber as a function of crystallinity (0°C), and stress relaxation associated with crystallization at constant stretch (-26°C). The continuum thermodynamic roots of the modeling process have made it possible to use experimental results at different temperatures to fairly accurately capture, in a single model, the temperature dependence of the mechanical response of natural rubber. Initial comparison to existing data, not used in the development of the model, indicates good agreement between the model and experiment.