Modified avrami equation for the bulk crystallization kinetics of spherulitic polymers

Abstract An explanation of the anomalous fractional values of the Avrami exponent found for the crystallization of a number of polymers is presented. The interpretation is based on a model which postulates the constant radial growth of spherulites, followed by an increase in crystallinity within them by a first order process. The model is supported by direct microscopic observations of other workers. Crystallization isotherms for polymethylene, poly(ethylene oxide), and poly(decamethylene terephthalate) are fitted to this model. Apart from the removal of the fractional values of the Avrami exponent, which have no physical meaning, this model gives a considerably better fit than the Avrami equation to most isotherms analyzed. The temperature dependence of the rate constants found for the two rate processes of this model is also discussed. An interpretation of the results of seeded experiments is presented in terms of this model.