The variations of structure and property of poly(p-dioxanone) (PPDO) in the process of photo-oxidative degradation and the mechanism of degradation were investigated in this work. The photo-oxidative degradation of PPDO was performed in air under ultraviolet light with two kinds of wavelength 365.0 nm and 253.7 nm. The extent of photo-oxidative degradation of the polymer was determined by morphological analysis, weight loss ratio, changes of viscosity and scanning electron microscope method (SEM). Infrared spectrometry (IR) and nuclear magnetic resonance (NMR) method were used to infer the mechanism of the photo-oxidative degradation. The changes of glass-transition temperature (Tg) and melting temperature (Tm) were characterized by differential scanning calorimetric (DSC) test. The morphological examination, IR and NMR testing revealed that the extent and mechanism of photo-oxidative degradation for PPDO are not closely correlated with its initial molecular weight. The main influence of initial molecular weight on the degradation is to change the ultimate distribution of the molecular weight. The conclusion is supported by the results of DSC test. All results from the research show the excellent photodegradable property of PPDO.

In this paper, the degradability of thermoplastic starch (TPS) and thermoplastic dialdehyde starch (TPDAS) under controlled composting conditions was investigated and a manual set-up was built according to ISO 14855 for this purpose. Chemical modification of starch can have a major impact on the biodegradation rate and final biodegradation percentage. The TPS degraded faster than TPDAS under controlled composting conditions. For the TPDAS, the degradation rate and final biodegradation percentage were closely related to the degree of oxidation of dialdehyde starch (DAS). The possible reason was also discussed. The biodegradation process of TPS and TPDAS exhibited three phases or stages with different degradation speeds. The biodegradation in the first phase was slow, accelerated in the second phase and leveled off in the third phase. Three kinds of actinomycete were isolated from the compost and identified as micromonospora, nocardia and streptomycete, which were degrading microorganisms of the starch tested. The abilities of these strains to decompose the TPS and TPDAS were also discussed.