Exploring the Effect\nof Oligoester Additives on the\nThermal and Mechanical Behavior of Poly-3-hydroxybutyrate Films

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