Effect of fusion temperature on the crystallization kinetics of poly(butylene terephthalate)

Abstract

A tremendous effect of fusion temperature on the crystallization kinetics of poly(butylene terephthalate) (PBT) was discovered. The crystallization peak shifted by 22 °C towards lower temperatures, and the kinetics changed about ten times. Nonisothermal crystallization experiments revealed that an increase in fusion temperature led to a noticeable shift in the heat flow curve towards lower temperatures, indicating a significant change in the number of nucleation centres. This shift was observed within the temperature range of 232 °C to 246 °C, beyond which the heat flow curve stabilized. The analysis of relative crystallinity showed a decrease in crystallinity with increasing fusion temperature up to 246 °C, accompanied by a shift of the S-curve towards lower temperatures. Detailed analysis revealed that the peak position of the heat flow curve decreased significantly from 232 to 240 °C and then continued to decrease slightly until 246 °C, and then in the range 246–260 °C, it remained constant. The influence of cooling rate on relative crystallinity was also investigated, revealing that faster cooling rates shifted the relative crystallinity curve towards lower temperatures. The Ozawa model was linear and demonstrated the significant effect of the cooling rate (for 15, 20 and 25 °C min⁻¹) on the nonisothermal crystallization kinetics. The Avrami model is perfectly implemented to evaluate the isothermal crystallization kinetics. Isothermal crystallization experiments confirmed the trends observed in the nonisothermal experiments, with the fastest crystallization occurring at lower fusion temperatures. During the isothermal crystallization experiment, the kinetics gradually decreased in the fusion temperature range 232–242 °C, and then in the range 242–250 °C, it remained constant. Overall, the study provides insights into the crystallization behaviour of PBT at different fusion temperatures and cooling rates.