Publication: CO2 as a turning parameter for Bioplastics

How can the properties of bioplastics be specifically tailored without changing the chemical composition of the carbon substrate?

This question represents a key challenge in the design of bioplastics, as the carbon source is often not flexible enough to allow polymers to be customized for specific applications.

Researchers from the IGVP and Fraunhofer IGB have now demonstrated that pressure, a process parameter that is often underestimated, can have a decisive influence on the composition and thus on the material properties of polyhydroxyalkanoates (PHAs). Pressure has a major impact on the solubility of a well-known gas: CO₂. While the influence of this gas on biotechnological processes is generally established, its use as a tuning parameter for bioplastics is novel and enables the production of tailor-made polymers without modifying the carbon source.

Researchers at our institute investigated this relationship in a study published in the Biotechnology Journal. The study reports the production of the bioplastic PHBVV, a type of PHAs, by Cupriavidus necator NCIMB 11599 using levulinic acid as a substrate, at reactor scales ranging from 42 L to 1 m³.

The study shows that increased hydrostatic and headspace pressures enhance the solubility of CO₂ in the fermentation medium, thereby enabling targeted control of polymer composition. As the CO₂ concentration increased, the proportion of the monomer unit 3-hydroxyvalerate in the polymer rose from approximately 48% to as much as 69%. At the same time, the team identified fermenter pressure as a process parameter that has previously been underestimated in the scale-up of PHBVV production.

These findings provide new insights into the relationship between process conditions, CO₂ metabolism, and polymer formation, and establish a basis for the targeted adjustment of material properties in bio-based plastics at industrial scale.