Thymine as a Melt-Soluble Nucleating Agent for Poly(3-hydroxybutyrate-co-4-hydroxybutyrate)

Abstract

Poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P(3HB-co-4HB)) is a biopolymer with promising biomedical and sustainable material applications, but its slow crystallization complicates processing. In this study, the potential of thymine as a biocompatible nucleating agent was evaluated using polarized optical microscopy (POM), differential scanning calorimetry (DSC), and tensile testing. Poly(3-hydroxybutyrate) (PHB) and P(3HB-co-4HB) with 6, 7, and 9 mol % 4HB were biosynthesized in-house usingCupriavidus sp. USMAA2-4, ensuring high purity necessary for this study. Thymine was found to dissolve in the polymer melt and recrystallize into needle-like crystals upon cooling, thereby creating effective nucleation sites. The addition of 1 wt % thymine consistently enhanced the crystallization rate under both nonisothermal and isothermal conditions, although it did not exceed the polymers' intrinsic self-nucleation potential. Initial tensile testing on heat-pressed films further revealed improved ductility in thymine-nucleated samples. These findings highlight the potential of thymine as a melt-soluble additive for enhancing the crystallization and mechanical performance of P(3HB-co-4HB).