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.
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