A reinterpretation of the Ozawa model for non-isothermal crystallization at fixed scan rates

Abstract

Listen

Translate article

A reinterpreted analysis method of the Ozawa model is presented for the non-isothermal kinetics of the nucleation and growth processes of polymer spherulites. The Ozawa model is based on the Avrami model which is valid for an isotropic crystallization with randomly dispersed nuclei and with growth rate dependent only on temperature. The crystallinity ϕ for the non-isothermal kinetics is expressed using a term of the form (β(T)/βi)n with the applied scan rates of cooling βi (i=1−N) and a function β(T) dependent only on the temperature T. The reinterpretation involves writing this term as (βhalf(T)/βi)nln(2), where βhalf(T) is regarded as an inverse function of Thalf(β), i.e., the temperature Thalf of ϕ=1/2 at a fixed scan rate β. The temperature-dependent βhalf(T) is given by the fitting curve of Thalf measured at the various scan rates βi. The original Ozawa plot shows ϕ as a function of a finite number of data points βi (i=1−N) at a certain fixed temperature T. The reinterpreted Ozawa plot is a continuous curve of ϕ as a function of the T-dependent βhalf(T) at a fixed scan rate β, and can be utilized for a more reliable determination of the Ozawa index n. Moreover, βhalf(T) can be replaced by βpeak(T), which is an inverse function of the peak temperature Tpeak at a fixed scan rate β. The applicability of the reinterpreted Ozawa model was examined experimentally for the spherulitic crystallization of poly(vinylidene fluoride) and by numerical calculations.