Modeling the thermomechanical effects of crystallization in natural rubber: I. The theoretical structure

Using the theoretical framework introduced in a previous work (Negahban, M., 1997. Thermodynamic modeling of the thermomechanical e€ects of polymer crystalliation: A general theoretical structure. International Journal of Engineering Science 35, 277±298), a model is proposed for capturing the thermomechanical response of natural rubber during and after crystallization. The model is given in a form which will allow the incorporation of both the known mechanical response and the known thermal response observed before, during, and after crystallization in natural rubber. In particular, one can include in this model known experimental results characterizing the stress relaxation due to crystallization, increase in rigidity with crystallization, heat capacity, heat of crystallization, and the melting temperature. In this ®rst article, a basic overview is presented of the model, and the thermal expansion of the amorphous and crystalline phases of natural rubber are incorporated into the model. The speci®c form of the free energy used to characterize the response of natural rubber is presented in the following article