Isothermal and nonisothermal crystallization kinetics of modified hydroxyapatite-enhanced poly(3-hydroxybutyrate-co-4-hydroxybutyrate)

Poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P34HB) is a biodegradable material, and efforts have been devoted to enhancing its mechanical properties and biocompatibility for biomedical applications. However, there is a lack of research confirming the influence of nucleating agents on its crystallization behavior. In this study, the isothermal crystallization process was described using the Avrami model. The non-isothermal crystallization process was investigated using the Avrami-Jeziorny and Mo models. The effects of different calcium hydroxyapatite (CA-HA) contents on the nucleation activity, crystallization activation energy, and equilibrium melting point of P34HB/CA-HA composites were compared. The impact of CA-HA on the crystallization rate, nucleation rate, and crystal growth rate of the polymer matrix was discussed. The results indicate that with an increase in CA-HA content, the crystallization rate initially decreases and then increases. The minimum crystallization rate is observed at a CA-HA content of 9 wt%. Moreover, as the CA-HA content increases, nucleation activity is enhanced, suggesting that CA-HA acts as a nucleating agent, facilitating the nucleation process. When the CA-HA content exceeds 9 wt%, the increase in crystallization rate may be attributed to the further enlargement of molecular clusters formed by CA-HA, leading to a reduced dispersion of CA-HA in the polymer matrix. Furthermore, when the CA-HA content surpasses 9%, a significant decrease in crystallization activation energy is observed, indicating a reduction in the mobility of polymer chain segments.