Crystallization and alkaline hydrolysis of poly(3- hydroxybutyrate) films probed by thermal analysis and infrared...

Poly(3-hydroxybutyrate) (PHB) is a microbially synthesized polymer, which is often purified by alkaline treatment. The effect of microstructure on alkaline hydrolysis has been studied by varying concentration of base and the temperature. The morphologies of PHB films before and after degradation were evaluated using DSC and FTIR spectroscopy. The hydrolytic degradation study by weight loss measurement revealed that the crystallinity of PHB greatly decreased the hydrolytic ability of PHB. The crystallization of PHB and the effect of base on hydrolysis was investigated by time dependent FTIR spectroscopy. The normalized absorbance of 3010cm^-1 and 1183cm^-1 were used to characterize the crystalline and the amorphous phases of PHB. FTIR spectroscopy reveal that the extent of hydrolysis decreased with increasing crystallinity. The crotonic acid was detected as a major product after hydrolysis, confirmed by UV/Visible and proton NMR spectroscopy. The normalized absorbance of the crystalline band at 3010cm^-1 band remained constant, suggesting that there is no significant change in crystallinity with degradation. The normalized amorphous band at 1183cm^-1 showed a decrease in absorbance ratio, suggesting degradation of the amorphous phase. Our data suggests that alkaline hydrolysis depends on concentration of base and the crystallinity of PHB.