Study On The Biodegradability And Degradable Mechanism Of The Polyesters Under The Simulative Natural Environment

Aliphatic polyesters such as [poly (lactic acid), PLA], [poly (butylene succinate), PBS] are one of the most promising candidates to replace the traditional plastics. They have good biodegradation, can reduce the environmental pressure that brought by the useless traditional plastics. Therefore, the researche on biodegadation, degradable mechanism and actual application of aliphatic polyesters is a focus point now.In order to popularize and apply biodegradable plastics, considering the soil characteristic of the Northwest, the soil of Shaanxi local land and activated sludge of Xian waste water plant are played the biodegradable medium in this study. During the biodegradable experiment, the films were buried under the soil or dipped in the soil extraction. By the results of experiment, the biodegradation and biodegradable mechanism of alipactic polyesters was investigated.In addition, the mixed films of metallic oxide with PLA and PBS were prepared, the degradable experiments of the mixed films were investigated in the extraction of garden soil.The main contents of the paper are as follows: 1. The study on the biodegradation of the polymers PLA and PBS.The cast films of the purchased polymers of PLA and PBS were prepared. To make the cast films of polymers, the solvent chloroform (CHCl3) was used.The soil of Shaanxi local land and activated sludge of Xian waste water plant played the biodegradable medium in this study. During the process of the biodegradation of the experiment, the films were buried 10cm under the soil. At the same time, the temperature and humidity were controlled steadily. The biodegradation of the polymers have been assessed by the data of the weight loss ratio and the morphology of the filmsurface. The experiment period was four months. By the results of weight loss, the biodegradation speed of PLA is two times than the PBS's. The same conclusion could be supported by the results of light microscopy (LM) and scanning electron microscope (SEM). The remarkable eroded trace of the surface of the films were indicated after degradation.The other medium of the biodegradable experiment was the extraction of garden soil and activated sludge. During the biodegradable experiment, the films were dipped in the soil extraction. At the same time, the temperature and humidity were controlled steadily. The biodegradation of the polymers have been assessed by the data of the weight loss ratio and the morphology of the film surface. The experiment period was 30 days. By the results of weight loss, the biodegradation speed of PLA was higher than that of PBS too. The same conclusion could be supported by the results of LM. We got the same results to that of the buried experiment.Furthermore, the biodegradation mechanism of PLA and PBS has been investigated by the Infrared Spectrometer (IR). The strength ratio of the carbonyl group to methylene in the molecule chain showed that the biodegradable mechanism were different. The PLA's was cut in the chain ends of the polymer molecule, but to the PBS, the random ester bond of molecule chain was cut.2. The study on the biodegradation of the mixed films of metallic oxide with PLA and PBS.The mixed films of the polymers and metallic oxide were prepared. The medium of the biodegradable experiment was the extraction of garden soil. During the biodegradable experiment, the films were dipped in the soil extraction. At the same time, the temperature and humidity were controlled steadily. The biodegradation of the polymers have been assessed by the data of the weight loss ratio and the morphology of the film surface. The experiment period was 30 days. CaO was good for the degradation of PLA and PBS, the latter was better. At the experiment, MgO was also good for the degradation of these two polymers, but the former was better. ZnO had no help to PLA, but to PBS, ZnO had some help.Moreover, we have done some hydrolyzed experiments of the mixed films. Preliminary inference was that, hydrolyzation took the leading role in the degradable experiment of the mixed films.In conclusion, the aliphatic polyesters such as PLA, PBS had good biodegradation in Shaanxi local soil through the researchs on biodegradation and degradable mechanismof PLA and PBS. Adding to a little of metallic oxide could regulate the biodegradation and degradable mechanism of polymers.