Study On The Degradation Of PLA For Biological Recycling

Polylactic acid (PLA) is a synthetic polymer, due to its synthetic raw materiallactic acid fermented by substances such as starch, sugars from biodegradable, PLA isdegraded into H2O and CO2in the natural environment, doesn’t pollution theenvironment, is the most development prospects for a class of biodegradable plastic.However, it is very slow that PLA was degraded in the natural environment, thuslimiting the controlled degradation and the biological cycles of the PLA, the study onthe degradation of the biological cycle of PLA has not many reports.This paper was studied through laboratory strains A.orientalis ssp.orientalis. Theorientalis were studied that can degrade PLA, this experiment were divided into twoparts: First, using strains degraded PLA, explore the culture conditions that the highyield of lactic acid monomer; second, using PLA depolymerases degraded PLA,explore the optimal conditions for enzyme production and the optimum conditions ofenzyme reaction, using the crude enzyme solution obtained under optimal conditionsdegraded the PLA particles, which characterize the enzyme activity.The main results are as follows:1. Degradation by A.orientalis ssp.orientalisThe preserved strains A.orientalis ssp.orientalis have been confirmed to degradePLA, experiments take a different single factor in order to explore the impact of theproduction of lactic acid monomer, the results show that the different culture time,gelatin content, carbon content, the inoculation, the initial pH is more important to theyield of lactic acid. Orthogonal experimental design of five factors and four levels oflactic acid monomer yield: the inoculation is5ml/100ml, pH is8, the carbon contentof2.0g/100ml, gelatin content of0.2g/100ml, the cultivation time is6d.The yield rate of lactic acid using strain degrade PLA particles is2.1%.2. Degradation by PLA depolymerase(1) The optimal conditions for enzyme productionFermentation time, gelatin content, carbon content, inoculation, initial pH wereimportant to the yield of PLA depolymerase by single factor experiment; five factorsand four levels orthogonal experiment was designed to determine the more importantfactors on the yield of PLA depolymerase; fermentation time, the carbon content, thegelatin content were used as the main factors for the response surface analysis, to determine the optimum conditions for enzyme production: cultivation time is2.81days, the carbon content is0.39g/100ml, gelatine content is0.34g/100ml, andfermentation in this condition, enzymatic activity was up to154.2U/l.(2) The optimum reaction conditions of PLA depolymerase and the influencingfactors of enzyme.The optimum reaction conditions of PLA depolymerase is: reaction temperatureis60°C, between40°C-60°C for6h the enzyme is stable, optimal pH is10.6, whenpH between6.0-10.6the enzyme is still stable. The experiments show that metal ionsand chemical reagents: Co2+can improve the activity of PLA depolymerase, and othermetal ions inhibite the activity of the PLA depolymerase; Tween80can moderatelyimprove the activity of PLA depolymerase, TritonX-100can moderately inhibite theactivity of PLA depolymerase, PMSF and EDTA can significantly inhibit the activityof PLA depolymerase.(3) Using the PLA depolymerase degrade the PLA particles200mg of PLA particles into150ml flask containing50ml crude enzyme solutiondegraded8h, the yield of lactic acid was up to750mg/l; after degraded five days, theweightlessness rate of PLA particles is100%.(4) The yield of lactic acid when using the PLA depolymerase degrade PLAUsing the PLA depolymerase degrade emulsifiable PLA, the yield rate of lacticacid is84%; using the PLA depolymerase degrade the PLA particles, the yield rate oflactic acid is19%.