Polyhydroxyalkanoates (phas) Degradation Mechanism

The biodegrability of Polyhydroxyalkanoates (PHAs) was studied and discussed in this paper. The result indicates that PHAs show significantly biodegrability in all kinds of environments (soil, water, sewage sludge). In addition to the influence of the environmental factors (temperature, pH value, O2), PHAs structure (crystal degree, first class structure, polymeric degree, thickness etc.) and extraction methods also affect the degradability of the polymers. The factors correlate and coact on the degradation of PHAs until it was decomposed into small molecular. HB and HV monomer can be detected in degradation products by using GC analyzer. The end products of PHAs are CO2 and H2O. At the same time, the change of PHAs surface was observed by Scanning Electronic Microscope (SEM), at the first stage of degradation, there formed a lot of pits on the surface, the number and dimension of the pits increased with the degradation carrying on. Finally the pits connect each other and penetrate the PHAs film. The degradation rate reach 50% in Xingqing lake for 12 days, 50% in soil for 22 days. For comparison, degradation rate are less than 3% in PBS buffer or in sterile water for the same period of time.Furthermore, a stain of Bacillus sphaericus was isolated from the sewage sludge to degrade PHAs. The optimum condition is 30, 150rpm, and load ratio is 0.2. No HB and HV monomer is detected in by using GC analyzer. The bacteria secrete esterase to decompose PHAs into HB and HV dimer.