Master of Science (MS)
Biological and Agricultural Engineering
Anaerobic biodegradation in sewage sludge and aerobic biodegradation in compost of polyhydroxybutyrate (PHB) were investigated to determine degradation kinetics and identify changes in polymer properties. To determine the impact of a natural plasticizer on biodegradation, tributyl citrate (TBC) was blended with some test specimens. For comparison to another bioplastic, polylactic acid (PLA) was biodegraded in the anaerobic study. Evolved gaseous carbon was measured to assess biodegradability according to ASTM standards D5210 and D5338. Mass loss experiments were performed to facilitate determination of degradation kinetics. Melt-pressed plates of the bioplastic with five different initial mass-to-surface-area ratios (plate thicknesses of 0.24, 0.5, 1.2, 3.5 and 5.0 mm) were biodegraded to investigate the relationship between this parameter and decay rate coefficients for first order decay kinetics. Results showed that degradation rate coefficients were influenced by initial mass-to-surface-area ratio of the bioplastic seemingly according to saturation kinetics. In the first anaerobic mass loss experiment, degradation rate coefficients with respect to initial surface area of the 0.5-mm, 1.2-mm, and 3.5-mm PHB plates were 0.58, 1.29, and 2.07 mg cm-2 d-1, respectively. In the second anaerobic mass loss experiment, coefficients for the 0.24-mm, 1.2-mm, and 5-mm PHB plates were 0.32, 0.73, and 0.95 mg cm-2 d-1, respectively. Coefficients for the 1.2-mm PHB/15% TBC blend and PLA were 0.38 and 0.00 mg cm-2 d-1, respectively. In the first aerobic mass loss experiment, coefficients for the 0.5-mm, 1.2-mm, and 3.5-mm PHB plates were 0.33, 0.62, and 1.57 mg cm-2 d-1, respectively. In the second aerobic mass loss experiment, coefficients for the 0.24-mm, 1.2-mm, and 5-mm PHB plates were 0.16, 1.05, and 1.11 mg cm-2 d-1, respectively, and 0.04 mg cm-2 d-1 for the PHB/15% TBC blend. In both degrading environments, the TBC additive hindered the degradation rate of the PHB. Thermal properties, molecular bonding, and molecular weight as measured by DSC, FT-IR, and Size Exclusion Chromatography, respectively, seemed only slightly affected by biodegradation. Decreasing Izod pendulum impact strength of the PHB was the obvious result of polymer loss. Furthermore, scanning electron micrographs of degraded specimens were recorded for visual illustration of the degradation process.
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Stevens, Benjamin Edward, "Biodegradation and Characterization of a Bio-based Polyester" (2007). LSU Master's Theses. 2061.
Chandra S. Theegala