Pilot scale production and evaluation of mechanical and thermal properties of P(3HB) from Bacillus megaterium cultivated on desugarized sugar beet molasses

Abstract

Production of poly[(R)-3-hydroxyalkanoate] (PHA) biopolyesters must become more cost efficient in order to be competitive with conventional plastics as well as other bioplastics. This study introduces a simple and reproducible large-scale production process of poly(3-hydroxybutyrate) P(3HB) with Bacillus megaterium based on desugarized sugar beet molasses and compares its material properties with commercially available types of PHA. A repeated batch cultivation system was evaluated in 1.2 L bioreactors and could be maintained for at least six cycles without a decrease in process stability, yielding a concentration of 20.4 g/L cell dry mass and 12 g/L P(3HB) per average process cycle. Feasibility of P(3HB) production was demonstrated at 500 L pilot scale to provide sufficient amounts of product for the determination of mechanical and thermal polymer properties. A volumetric productivity of 0.2 g L−1 h−1 was achieved. The resulting polymer exhibited a high tensile modulus of 3.73 GPa and tensile strength of 38.5 MPa. Despite a lower ductility and Vicat softening temperature, the properties of the recovered P(3HB) are comparable to commercial grade P(HB)HV polymers.