Structure analysis and thermal stability of PHB recovered from sugar industry waste

The current article emphasized on cultural conditions for Alcaligenes sp. NCIM 5085 to synthesize Polyhydroxybutyrate (PHB) from sugar industry waste during batch fermentation. Alcaligenes sp. NCIM 5085 was found to grow best in conditions that included 40 g l^-1 of cane molasses, 1 g l^-1 of ammonium sulphate, 10% inoculum with neutral pH and 48 h of incubation time. Sudan Black B staining was employed to verify the PHB synthesis initially, and further TEM analysis was performed to confirm it. The structural analysis of recovered PHB was carried out by using GC-MS, FTIR, ¹H NMR and ¹³C NMR analysis. The absorption peak at 1724.56 cm^-1 revealed the presence of C=O (carbonyl) group by FTIR, which is an indicator of PHB presence. Furthermore, results of NMR and GC-MS analysis confirmed the recovered polymer was PHB. The thermal properties of recovered polymer were analyzed by TGA, DTG and DSC and showed thermal stability of PHB. The observed glass transient temperature (T_g) -2.8°C was within the normal PHB range of T_g. However, melting temperature of recovered PHB was 161.7°C, where the degree of crystallinity was lower than standard PHB that widens the application possibilities.