Synthesis, Structure, and Properties of Polyhydroxybutyrate Derived from Azotobacter Vinelandii N-15

Biodegradable polymers are of great interest in addressing the current pollution problem caused by synthetic petroleum-based polymers. It is well known that various microorganisms synthesize and store high-molecular-weight polyhydroxyalkanoates in their cytoplasm as water-insoluble inclusions. In this study, the bacterium Azotobacter vinelandii N-15 strain is used for bioplastic production. The optimal polyhydroxybutyrate (PHB) yield (62% of biomass, 23.6 g L^-1 dry cells) is achieved by cultivating the bacteria in Burke's medium with molasses as a carbon source (5 wt.%) at 30 °C, 220 rpm, for 50 h. The resulting polymer was characterized using thin-layer chromatography, UV-Vis, fourier transform infrared, nuclear magnetic resonance spectroscopy, gas chromatography, and X-ray diffraction. The results confirmed that the polymer is PHB with a purity of 98.9%, a molecular weight of 1.2 MDa, a crystallinity of 73%, a melting point of 179 °C, a decomposition temperature of 275 °C, a density of 1.22 g cm^{- 3}, a melt flow index of 10 g 10 min^-1, a Shore hardness of 82, a tensile strength of 30 MPa, and a relative elongation at break of 4.5%. Thus, a bioplastic with properties suitable for practical applications is successfully obtained using molasses-a byproduct of sugar production.