Biodegradation and Characterization of Polyhydroxybutyrate Exposed to Anaerobic Municipal Sludge

Abstract

The anaerobic biodegradability of Polyhydroxybutyrate (PHB) was investigated to determine degradation kinetics and the effects of degradation on characteristics of the plastic. PHB was melt-pressed into plates of thicknesses 0.24, 0.5, 1.2, 3.5 and 5.0 mm. Three experiments, which assessed biodegradability based on evolved gaseous carbon, were performed according to ASTM D 5210. In addition, two mass loss studies were performed to facilitate the determination of degradation kinetics. Melt-pressed plates of the PHB were extracted from the degrading medium and weighed at appropriate time intervals for determining the degradation kinetics. In the mass-loss experiments, melt-pressed plates of the bioplastic with five different initial mass-to-surface-area ratios were investigated for the purpose of establishing a relationship between this parameter and decay rate coefficients for first order decay kinetics. It was found that the degradation rate coefficient of the PHB is dependent upon the initial mass-to-surface-area ratio of the bioplastic seemingly according to saturation kinetics. In the first anaerobic mass loss experiment, the degradation rate coefficients with respect to initial surface area of the 0.5-mm, 1.2-mm, and 3.5-mm PHA plates were 0.5846, 1.2920, and 2.0656 mg cm-2 d-1, respectively; in the second anaerobic mass loss experiment, the degradation rate coefficients with respect to initial surface area of the 0.24-mm, 1.2-mm, and 3.5-mm PHA plates were 0.3191, 0.7308, and 0.9484 mg cm-2 d-1, respectively. This data also demonstrated that the particular sewage sludge medium used to degrade the PHB has a significant impact on the degradation kinetics. Furthermore, the effects of biodegradation on certain characteristics of the bioplastic as determined by analyses such as DSC, FT-IR, and Size Exclusion Chromatography were tested.