Scalability production and structure-property characterization of medium-chain-length polyhydroxyalkanoate copolymers...

Herein, the scalability of medium-chain-length (mcl) PHA copolymer production was investigated in a 90 L pilot-scale bioreactor using two mutant strains of Cupriavidus necator, MT-68 and mcl-C19. Under mixotrophic carbon sources of molasses and waste palm oil, both strains produced mcl-PHA copolymers containing C4-C10 monomers. The effects of process parameters including inoculums size and oxygen availability via agitation were studied to determine optimal conditions for mcl-PHA production. The scale-up process achieved a maximum PHA titer up to 16.4 ± 1.0 g/L with a PHA content of 76.2 ± 4.9%, demonstrating the feasibility of pilot-scale production. MT-68 and mcl-C19 produced PHA copolymers with 1.3% and 6.6% mcl composition, respectively, resulting in two copolymers with distinct chemical, thermal and mechanical properties. Notably, the incorporation of mcl even at low content led to changes in melting temperature, reduced crystallinity and distinct mechanical behavior at the microscale, contributing to enhanced flexibility and altered thermal properties compared to commercial PHB. These findings highlight the impact of PHA production process scalability, provide the systematic comparison of the two strains, and elucidate the structure-property relationships of the produced mcl-PHA copolymers, which can become platform for their potential industrial applications.