Exploring the Effect of Oligoester Additives on the Thermal and Mechanical Behavior of Poly-3-hydroxybutyrate Films

Poly-3-hydroxybutyrate (PHB) is a promising biopolymer that has the potential to replace fossil-based plastics yet is currently limited by its poor mechanical properties. A library of oligomeric polyesters containing adipates, furanoates, phathalates, and pyridinecarboxylates were enzymatically synthesized and evaluated as PHB additives. Across the series of additives, the pyradinecarboxylate oligoesters served as the most efficient plasticizers, whereas the phthalate was found to influence the rate of crystallization to the greatest extent. Due to the differences in additive miscibility, plasticization, and extent of crystallization, the compounds showed significantly different mechanical properties. Several additives promoted efficient crystallization at high cooling rates, such as phthalate oligomer P5, which resulted in a material that crystallized four times faster than pure PHB, and produced a material with smaller spherulites. This difference in morphology was to some extent reflected in the mechanical properties, as addition of PHB–P5 resulted in a 42% decrease in the Young’s modulus. Overall, the combined effects of the degree and rate of crystallization, as well as the nature of the amorphous phase, prevented obvious trends from emerging.