A different approach for the study of the crystallization kinetics in polymers. Key study: poly(ethylene terephthalate)/ SiO2 nanocomposites

Abstract

Polymer crystallization is complex and difficult to model, especially when it is non-isothermal and even more so when describing cold crystallization. In most cases, two different processes occur, so-called primary and secondary crystallization. In the literature, two assumptions are generally made. Firstly, the validity of the Avrami model is assumed a priori. Secondly, for calculations of the kinetic parameters and activation energy, data from a single differential scanning calorimetry scan at a given heating rate are used. The other popular model, that of Ozawa, is also based on similar assumptions. In the study reported here, a different approach was adopted, which uses multiple scans at various heating rates simultaneously. Here the experimental data of the non-isothermal cold crystallization of an in situ-prepared poly(ethylene terephthalate)/1% SiO2 nanocomposite were used. Data were analysed following both the ordinary procedure and the method proposed in this work. Findings showed that when the Avrami model is a priori supposed to hold and the data of different heating rates are analysed separately, results are not acceptable. The new approach involves calculation of the activation energy through use of the isoconversional methods of Ozawa–Flynn–Wall and Friedman over the whole range of the crystallization conversion. The reaction model f(a) was determined after the evaluation of 16 different models. The best fitting was achieved for the Prout–Tompkins model or for a mechanism involving two steps described by respective Avrami equations with different activation energies. Copyright © 2010 Society of Chemical Industry