What exactly are PHA?

Polyhydroxyalkanoates (PHA) are among the most promising biopolymers as substitute of oil-based plastics because of some unique features, which include: full biodegradability under both aerobic and anaerobic conditions; not a single polymer but a family of copolymers with largely tunable properties; the possibility to be microbially synthesized with mild process conditions, as well as the possibility to be obtained from a large range of available waste feedstock. Indeed, PHA are synthesized by over 300 species of microorganisms (including both gram-negative and gram positive bacteria, aerobic and anaerobic phPHA structureotosynthetic bacteria, and certain Archea) and function as carbon and energy storage compounds, which accumulate in the cell cytoplasm as insoluble granules. In particular, the PHA storage occurs when microorganisms are unable (for the lack of essential nutrients in the growth medium and/or for limitations in anabolic enzyme levels and activity) to grow at the same rate as they are able to take up the substrate. Even though these properties make PHA suitable for a large market, some drawbacks need to be faced, such as: the high production cost and the development of strategies able to improve PHA properties according to their final applications. The high cost of production is due to the fact that industrial biotechnological processes are based on pure culture fermentations which require well-defined substrate and aseptic conditions resulting in high substrate costs, expensive equipments, and high energy consumption. As for PHA properties, these are strictly correlated to polymer composition. As an example, polyhydroxybutyrate (PHB), which is the simplest polymer among the PHA family, is highly crystalline, stiff, and brittle whereas the copolymer poly(3-hydroxybutyrate/3-hydroxyvalerate) (P(HB/HV)) has better physical and thermal properties which, however, depend on the content of the hydroxyvalerate (HV) units. Moreover, HV units in polymer chain also increase elasticity and flexibility. Overall, the enormous possible variations in the length and composition of the side chains make the PHA polymer family suitable for an array of potential applications.

Besides PHA production, the RES URBIS Project will also focus on the production of biosolvents (to be reused in the PHA extraction process) and fibers (to be reused for the generation of PHA biocomposites).