Influence of biodegradation in thermophilic anaerobic aqueous conditions on crystallization of poly(butylene succinate)

Abstract

This work investigates the biodegradation of poly(butylene succinate) (PBS) in an environment of thermophilic (55 °C) and mesophilic (37 °C) anaerobic sludge. The thermophilic anaerobic sludge was prepared in a laboratory from mesophilic sludge sourced from a municipal waste water treatment plant and placed under thermophilic conditions. It was confirmed that PBS failed to decompose under mesophilic anaerobic conditions (2 wt. %), while the degree of biodegradation achieved under thermophilic conditions reached 24.8 wt. %. Abiotic hydrolysis of PBS in an environment of phosphate buffer (pH = 7) at 55 °C reached 17.8%, leading to the conclusion that hydrolytic enzymes present in thermophilic anaerobic sludge are involved in the biodegradation process as well as abiotic hydrolysis. Nonisothermal crystallization kinetics of PBS before and after biodegradation was investigated by differential scanning calorimetry (DSC). After biodegradation, a large shift in melting temperature Tm was observed, while shift of crystallization temperature Tc was even more pronounced. Lower Tm means smaller crystals. Crystallization kinetics was approximately 50% slower, which could be explained by lower nucleation density. Scanning electron microscopy (SEM) revealed a beautiful spherulitic structure after biodegradation at elevated temperature. During biodegradation, microorganisms assimilated mostly in the amorphous part of the polymer, and elevated temperature helped healing of crystal imperfections. By X-ray diffraction (XRD), it was found that biodegradation does not have a large effect on crystal form of PBS.