Effect of Nucleating Agent on Crystallization of Poly[(R)‑3-hydroxybutyrate-co-(R)‑3-hydroxyhexanoate]

The effect of pentaerythritol (PERT) as a nucleating agent on the crystallization behavior of poly-[(R)-3-hydroxybutyrate-co-(R)-3-hydroxy-hexannoate] (P-(3HB-co-3HH)) was examined. Isothermal crystallizations with and without PERT at various temperatures were monitored in real time using simultaneous synchrotron radiation wide-angle X-ray diffraction and small-angle X-ray scattering techniques. Heterogeneous nucleation was observed at significantly higher temperatures, where the crystallization of pure P-(3HB-co-3HH) scarcely occurs. The crystal form and morphological parameters of P-(3HB) remained unchanged in the presence of the nucleating agent. However, the induction period for crystallization with PERT was significantly reduced. Structural analysis confirmed that the nucleating agent enhances overall crystallinity due to a higher density of nucleation sites. In addition, the interaction between the molecular chain and the substrate surface was investigated through molecular dynamics (MD) simulations. The MD simulations indicated that the molecular chain tends to interact attractively with the substrate surface, with the carbonyl groups of P-(3HB) oriented toward the hydroxy groups of PERT. These results suggested that the formation of hydrogen bonds, rather than crystalline lattice matching, plays a crucial role in the heterogeneous nucleation of P-(3HB) on PERT.