Non-isothermal crystallization kinetics of polyethylene terephthalate: a study based on Tobin, Hay and Nakamura models

Appropriate knowledge of non-isothermal crystallization kinetics of polyethylene terephthalate is vital in producing final polymeric parts with a certain degree of crystallization. Hence, PET was synthesized through a two-step esterification and polycondensation method. The structure of prepared PET was examined using FTIR and NMR tests. Due to the practical applications of the crystallization process, non-isothermal crystallization of PET was studied from the melt state under various cooling rates ( Φ ) between 5 and 40 K/min using DSC, demonstrating a wide range of Φ . The experimental results revealed that the crystallization reaches its final value for the cooling rates of 5 and 10 K/min. However, a partial crystallization occurred under higher cooling rates. The recrystallization of these samples during heating was confirmed. Empirical data showed no meaningful change in T g and T m with cooling rate. However, T C and the final degree of crystallization varied linearly with cooling rate. Crystallization kinetic models are classified into two types: nonlinear and those that can be converted to linear. Due to the secondary crystallization of PET, the Avrami model could not make a good prediction. Among the linearizable models, Tobin model fitted the results very well. Among the nonlinear forms, the recently developed Hay model has an excellent ability to describe non-isothermal kinetics. Moreover, the integral type of Nakamura model was fitted instead of the normal differentiation form. A two-step optimization method is presented to achieve a high regression coefficient for nonlinear fitted models. Graphical Abstract