Development and characterization of polyhydroxybutyrate biocomposites and their application in the removal of heavy metals

Polyhydroxybutyrate (PHB) is the well-known polyhydroxyalkanoate (PHA) accumulated by many bacterial species under conditions of nutrient limitation. General applications of PHB and its composites include food packaging, agriculture, medicine, drug delivery, tissue engineering, etc. Herein, we report biosynthesis of PHB from Bacillus cereus using both chemical and physical extraction methods. As a result, the physical method (0.451 g/L) was found to be advantageous when compared to chemical method (0.345 g/L). In order to improve the properties of PHB, it was blended with polyethylene glycol (PEG) and starch to obtain biocomposites viz., PHB-PEG 4000, PHB-PEG 6000 and PHB-Starch. The obtained PHB and its biocomposites were characterized by FTIR, TGA/ DSC, SEM and XRD techniques. FTIR spectroscopy results showed the vibrational frequencies for all the expected functional groups. The thermal studies revealed that the composites are thermally stable than pure PHB. The SEM images showed highly porous structure of PHB-Starch composite when compared to PHB-PEG composites. The crystalline nature of PHB and its composites were confirmed from powder XRD patterns. The application of these biocomposites in the removal of heavy metals was demonstrated by successful adsorption of Pb2+ ion from aqueous solution in a batch process mode.