The Study On Synthesis And Biodegradation Of The Aliphatic Polyesters

The aliphatic polyesters such as poly(butylenes succinate) (PBS), poly(lactide acid) (PLA) and poly(caprolactone) (PCL), have been paid much attention in recent years as the polymers have accepted mechanical properties and biodegradation. It is considered that the polymers PE and PPE will be replaced by the PBS in the near future because of its applied characteristics. It has been found that molecular weight and crystallinity of the PBS are the key factors which determine the biodegradation of it. It has ever been well thought that it is too difficult to synthesize the high molecular weight aliphatic polyesters.Using the compound titanium tetraisopropoxide (TTP) as the catalyst and the inorganic compounds as assistant catalyst, we successfully synthesized the high molecular weight polymers PBS and its copolymers by polycondensation. The biodegradation speed of polymers can be changed by adding different ratio components. In this paper, the polyesters PBS, Poly(BS-co-CL), Poly(BS-co-LA) and Poly(BS-co-CL-co-LA) were prepared. The characteristics such as molecular weight, structures and crystallinity of polymers were characterized by (nuclear magnetic resonance, NMR) (gel permeation chromatography, GPC), (x-ray diffraction, XRD).We investigated the biodegradation of PBS, PLA, PCL and copolymers in the extracts of activated sludge and garden soil, as study the relationship between biodegradation and structures and crystallinity of polymers. We also discussed the biodegadation mechanism of PBS, PLA and PCL. The main contents of the paper are as follows:1. The synthesis of the PBS.Without solvent, under 230 °C, using the TTP as catalyst, we synthesized the high molecular weight the polyester (Mn=10.6xl04) PBS and copolymers Poly(BS-co-CL), Poly(BS-co-LA)and (Mn=10.82xl04)?o\y(BS-co-CL-co-LA) by polycondensation process in two hours. The results indicated that the synthesis time was decrease 60% than before. The data of GPC showed that the copolymers molecular weight distributions were less than 2.0. The copolyesters had applied thermal stability supported by the results of TG2. The study on the biodegradation of the polymers PBS, PCL and PLA.The cast film and annealed film of the purchased polymers of PBS, PCL, PLA were prepared. To make the cast film of the polymers, the solvent CHCI3 was used. The medium of the biodegradation experiment was the extracts of activated sludge and garden soil (garden soil was taken from the garden of the university). The pH of the solutions were 6.9 and the film were (2cmx2cm). The conclusion that the degradation speed of PCL is higher than that the PLA and PBS was supported by the results of loss weight ratio and the photo of SEM. The experiment of all the films had the same results than in the extracts of garden soil.The biodegadable mechanism of PBS and PCL is considered that the microorganism erode any ester group in polymer chain, but to the PLA the microrgannism erode the end group of chain. The hypothesis is supported by the data of FT-IR.3. The study on the biodegradation of the copolymers of PBS.The copolymers films were used for biodegradation experiments. The loss weight rates indicated that the biodegradability of Poly(BS-co-CL) enhanced obviously, as the CL ratio increased of the polymers. The biodegradable speed can be controlled by changing CL ratio. The loss weight ratio showed that as the ratio LA increased, the biodegradability of Poly(BS-co-LA) decreased. But the biodegradabilify of Poly(BS-co-LA) was better than PBS. The photo of SEM showed that there were obvious scar by the microorganism eroded on the surface of film. After the degradation, polymers' mechanical property decreased. The results show that these films have perfect biodegradability. It effect the process of biodegradation which we choose themode of manufacture the film,. This research concluded that we may control the CL or LA rate of copolymers for the purpose of adjusting the biodegradable speed of polymers.In conclusion, by using the catalyst and assistant catalyst, we successfully synthesized high molecular polyesters. The connection of CL or LA content on the crystallinity, thermal stabilities and mechanical properties of copolymers was investigated. The research of biodegradeation showed that aliphatic polyesters have well biodegradability in the soil of Xi'an. We may conclude that the biodegradable speed of polymer can be changed by the CL or LA ratio of copolymers.