The Research Of Influence Factors And The Process Of PLA Enzymatic Degradation

Polylactic acid(PLA) was a kind of synthetic non-natural polymer, it was considered to be an alternative to the traditional plastic material, because of its excellent physical and chemical properties and biodegradability. As a typical example of non natural compounds could be degraded by natural enzymes, the research of PLA biodegradation received much concern. However, the current studies mostly focused on degrading microbial and enzymes of PLA, while less attention was focused on the impact of substrate on enzymatic degradation.The films made by polylactic acid(PLA) 4032 D from Natue Works with various specifications and blending films with P(3HB-co-4HB)、Si O2 and Ca CO3 were test the degradation by proteinase K under different conditions. At the same time, the process study of the enzymatic hydrolysis of the PLA film has been made to research the change of surface morphology, crystallinity and molecular weight under degradation.The results showed that the enzymatic degradation of PLA was significantly influenced by the factors of enzymatic degradation conditions, the physical properties of material, film-forming methods,crystallization methods and the addition of modifier.In enzymatic degradation conditions, the enzyme concentration, reaction temperature, p H and the replacing time of enzyme had a certain impact on the degradation of the specimens, the optimum conditions were 0.2mg/m L,50℃,p H10.0 Tris- HCl buffer solution and 12 h.In physical properties of material, the thinner, lower molecular weight and crystallinity, the faster degradation rate.In research of the influence of film-forming methods to enzymatic degradation, compare to hot press crystallization methods, the sample of solvent evaporation-phase seperation had higher crystallinity.In case of same crystallinity, the degradation rate of the samples with different film-forming methods were as follows:chloroform > dichloromethane > hot press film-forming method. The crystallization methods also had great effect on the degradation of PLA. In case of same crystallinity, the sample of hot press cold crystallization method had a faster degradation rate than hot press thermal crystallization method.Meanwhile, on the current situation of a growing number of PLAmodified products, we selected the modifier of P(3HB-co-4HB)、Si O2 and Ca CO3,which had a commonly used in laboratory and in previous work had been proved with improved mechanical strength and other characteristics of materials, in order to research the influence of blending modification on degradation. The results showed that the small amounts addition of P(3HB-co-4HB) in PLA could contribute to the degradation of PLA, however, a large number of P(3HB-co-4HB) added in PLA would inhibit the degradation of PLA.The addition of Si O2 and Ca CO3 also could accelerate the degradation of PLA.In addition, we also measured and analyzed the surface morphology, crystallinity, and molecular weight change of PLA film before and after degradation, after that we discussed the processes and mechanisms of enzymatic degradation of PLA films. The results showed that the process of enzymatic degradation, the amorphous regions were degraded in preference to the crystalline regions. In the early degradation of PLA films, the preferentially degradation of amorphous regions sparked a more regular structure, so the crystallinity of entire film increased, and as the deepening degradation, the structure of crystal was damaged, resulting in the decrease of regularity, and then decreased the crystallinity. During degradation, there was almost no change in the molecular weight, but the molecular weight distribution index decreased, indicating that proteinase K cut from the end of the chain of PLA, the segment of small molecular weight was first degraded, and released into the solution.This research focused on the impact of substrate characteristics of PLA on enzymatic degradation and the change of the substrate during degradation, the results improved the mechanism of biological enzyme of PLA and provided a theoretical and experimental information for the controllable biodegradation and the different products modification.