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

In recent years, the development of biodegradable macromolecule materials is one of the important ways to resolve the environment pollution. In these biodegradable macromolecule materials, the aliphatic polyesters such as poly butylenes succinate (PBS) and poly lactic acid (PLA) is considered as the substitutes for the traditional plastics such as polyethylene (PE) and polypropylene (PP) because of accepted mechanical properties and biodegradation.Therefore, the research on biodegradation, degradable mechanism and actual application of aliphatic polyesters is a focus point now around the world. But in our country, the study on the degradation and degradable mechanism of the polyesters on the spot is few. Especially the area of our country is great and the environment, weather and condition of soil are different. All of these are the great difficulties to the research and actual application of the polyesters.This paper studied the biodegradability of PLA and PBS in the soil of Shaanxi local land through the experiment of PLA and PBS in the soil supernatant. By the results of experiment, the relationship between biodegradation and structures of the polymers was studied. And the biodegradable mechanism of aliphatic polyesters was investigated.In addition, the biodegradation of PLA and PBS in the soil supernatant with metal ion was researched. By the results of experiment, the influence of metal ion in the soil on the biodegradability of the polyesters was studied.The main contents of the paper are as follows:1. The study on the biodegradation of the polymers PLA and the relation with metal ionThe cast films of the purchased polymers of PLA and were prepared. To make the cast films of polymers, the solvent chloroform (CHCl₃) was used.The soil supernatant with metal ion played the biodegradable medium in this study. 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, PLA has excellent biodegradability in the soil supernatant. The metal ion of Mg²⁺, Zn²⁺ and Ca²⁺ can accelerate the biodegradation of PLA. The biodegradable speed of PLA in the soil supernatant with Ca²⁺ is the best. The following is Mg²⁺ and Zn²⁺ and the last is the soil supernatant without metal ion. So it can be concluded that in the area with Mg²⁺, Zn²⁺ and Ca²⁺ we can popularize the material of PLA.By the results of the experiment, it was found that the metal ion also can accelerate the hydrolyzation of PLA. The speed of hydrolyzation is Ca²⁺ > Zn²⁺ > Mg²⁺ > distilled water.Furthermore, the biodegradation mechanism of PLA has been investigated by the Infrared Spectrometer (IR). The strength ratio of the carbonyl group to methylene in the molecule chain showed that in the soil supernatant and that with Mg²⁺ and Zn²⁺ respectively PLA was cut in the chain ends of the polymer molecule, but in the soil supernatant with Ca²⁺ the random ester bond of the molecule chain of PLA was cut.Thermal properties were measured by Differential Scanning Calorimetry. The results of DSC showed that after degradation thermal property of PLA reduced.2. The study on the biodegradation of the polymers PBS and the relation with metal ionThe loss weight rates indicated that the biodegradability of PBS was restrained by the metal ion of Mg²⁺, Zn²⁺ and Ca²⁺. The biodegradable speed of PBS in the soil supernatant without metal ion is the best. The following is Zn²⁺ and Mg²⁺, the last is the soil supernatant with Ca²⁺.By the results of the experiment, it was found that the metal ion also can accelerate the hydrolyzation of PBS. The speed of hydrolyzation is Mg²⁺ > Zn²⁺ > Ca²⁺ > distilled water.The results of FT-IR showed that in the soil supernatant and that with Mg²⁺ and Ca²⁺ respectively the random ester bond of the molecule chain of PBS was cut, but in the soil supernatant with Zn²⁺ PBS was cut in the chain ends of the polymer molecule.In conclusion, the aliphatic polyesters such as PLA, PBS had good biodegradation in Shaanxi local soil through the research on biodegradation and degradable mechanism of PLA and PBS. The metal ions in the environment have different influence on the biodegradability of PLA and PBS.