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

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 phi for the non-isothermal kinetics is expressed using a term of the form (beta(T)/beta(i))(n) with the applied scan rates of cooling beta(i) (i = 1 N) and a function beta(T) dependent only on the temperature T. The reinterpretation involves writing this term as (beta(half)(T)/beta(i))(n)ln(2), where beta(half)(T) is regarded as an inverse function of T-half(beta), i.e., the temperature T-half of phi = 1/2 at a fixed scan rate beta. The temperature-dependent beta(half)(T) is given by the fitting curve of T-half measured at the various scan rates beta(i). The original Ozawa plot shows phi as a function of a finite number of data points beta(i) (i = 1 N) at a certain fixed temperature T. The reinterpreted Ozawa plot is a continuous curve of phi as a function of the T-dependent beta(half)(T) at a fixed scan rate beta, and can be utilized for a more reliable determination of the Ozawa index n. Moreover, beta(half) (T) can be replaced by beta(peak)(T), which is an inverse function of the peak temperature T-peak at a fixed scan rate beta. The applicability of the reinterpreted Ozawa model was examined experimentally for the spherulitic crystallization of poly(vinylidene fluoride) and by numerical calculations.

Automated summary

A reinterpreted analysis method of the Ozawa model is presented for the non-isothermal kinetics of the nucleation and growth processes of polymer spherulites, allowing for a more reliable determination of the Ozawa index n. The reinterpretation involves expressing crystallinity phi as a term dependent on temperature and scan rates, leading to a continuous curve of phi as a function of T-dependent beta(half)(T) in the reinterpreted Ozawa plot. Experimental examination and numerical calculations confirm the applicability of the reinterpreted Ozawa model for the spherulitic crystallization of poly(vinylidene fluoride).