초록
<P>Biodegradable polymer polyhydroxyalkanoates are one of the promising alternatives for conventional plastics. The present article focuses on a modified and novel method for the synthesis of poly (3‐hydroxybutyrate) (PHB) by two microorganisms, viz. <I>Bacillus megaterium</I> and <I>Cupriavidus necator</I>. These microbial cells were grown over fructose as a carbon source, and the produced PHB was recovered using ultrasound as well as solvent assisted extraction. The extracted PHB was characterized using FTIR, <SUP>1</SUP>H, and <SUP>13</SUP>C NMR to observe the functional groups in the PHB molecule. The XRD characterization confirmed the partial crystalline nature of PHB, and the results of TGA, DTG, and DSC analysis attributed to the thermal stability of PHB. The major step of weight loss of PHB derived by <I>B. megaterium</I> and <I>C. necator</I> in TGA analysis was found to be 415°C and 289°C, respectively. These values were comparatively higher than standard PHB, for which it is 260°C. Similarly, the maximum degradation temperature for standard PHB is 236°C, whereas the maximum degradation temperature of PHB synthesized by <I>B. megaterium</I> and <I>C. necator</I> are 248°C and 277°C, respectively. This ascertains that the produced PHB has greater resistance to thermal degradation as compared with PHB standard. The melting point of synthesized PHBs were found to be 175°C to 176°C, which is similar to standard PHB. The glass transition temperature of the synthesized PHBs varies from –8°C to 6°C. The plausible reason behind the variances could be due to difference in crystallinity and molecular weight of polymer matrix. Nevertheless, thermal properties of PHB produced by <I>B. megaterium</I> and <I>C. necator</I> are found to be similar or much better than commercial PHB. The degree of crystallinity of synthesized PHBs are lower than previously reported literatures, which extends its range of applications.</P>