Thermal and mechanical characterization of solvent-cast poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)

The copolymer poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) [P(HB-co-HHx)], is produced by engineered Ralstonia eutropha strains using lipids and fatty acids as carbon feedstocks. The presence of the 3-hydroxyhexanoate (HHx) monomer disrupts the packing of polymer chains, resulting in less numerous polymer crystals and producing a polymer with favorable thermal and mechanical properties. In this study, copolymers varying in HHx content were recovered from different R. eutropha strains. Tensile constitutive response of solvent-cast samples of PHB and P(HB-co-17 mol% HHx), P(HB-co-23 mol% HHx), and P(HB-co-30 mol% HHx) was investigated using a custom-built micro-tensile tester. Our results show that presence and quantity of HHx monomer has a noticeable impact on P(HB-co-HHx) mechanical properties, such as tensile strength, elongation at break, toughness and thermal properties. It was found that with higher content of HHx in the material, the more flexible and tougher the polymer is, and the greater the reduction of T-m and crystallinity.