Study On The Synthesis Of Polylactic Acid Byammonium Lactate Generated From Fermination Of Kitchen Garbage

Poly(lactic acid) (PLA) bears wonderful biologic compatibility andbiodegradable properties, which is harmless and non-toxic to the human body andenvironment as it can finally biodegrade into CO2and H2O. At the same time, withphysical mechanical properties similar to popular plastics, PLA can substitute forthem. PLA will become an industrial material with considerable perspective. In thepaper,theammonium lactatefermented from kitchengarbagewas extractedfrom thefermentation broth as butyl lactate by esterification. Thus PLA was polymerized bythebutyl lactatethrough melt polycondensation-solidstatepolymerization. Synthesisof PLA from kitchen garbage can not only provide low-cast raw material forproducingPLA,butalsosolvethepollutionofkitchengarbage.The preparation of the modified resin catalyst was studied and the preparedproducts were characterized. The optimum reaction condition was determined asreaction temperature 78℃,reaction time 6h, the practical dosage of FeCl3·6H2O is 3times as much as the theoretical dosage. Under the condition, the actualcomplexation rate of Fe in the resin is 11.8%, which is 90.1% of the theoreticalcomplexation rate. The esterification reactions of ammonium lactate and butanol toprepare butyl lactate using the prepared catalyst were studied. Under the optimumreaction condition as molar ratio of butanol to ammonium lactate 3:1, catalyst 1.5%(w/w), reaction time 6h, the highest esterification rate is 96.1%. Comparing theexperiments usingdifferent catalysts, it canbeconcludedthat the catalytic efficiencyof the modified resin is obviously better than those of resin and FeCl3·6H2O. Theexperiments showed that the solid acid catalyst, prepared fromFeCl3·6H2O modifiedmacroporous styrene series strongly acidic cation-exchanger, has the better catalyticperformance. The replacement of the traditional sulphuric acid catalyst by the solidacid catalyst can effectively resolve the catalyst-caused erosion of the equipment.The reactions ofmelt polycondensation-solid state polymerization of PLAwerediscussed. The results showed that the optimum reaction condition of the meltpolycondensation is: SnCl2 of 0.5wt% as catalyst, TSA of 0.5wt% as acid catalyst,prior period of prepolymerizationreaction temperature 160℃, reaction time 6h; laterperiod of polymerization reaction temperature 160℃, reaction time 4h, gradually lower reaction system pressure to 5000Pa.Under the condition, the molecular weightof the LA low(-grade) polymer is around 5800. In the stage of solid statepolymerization, the best reaction condition is: reaction system pressure 10000Pa,reaction temperature 140℃, reaction time 25h. Under the condition, the molecularweight of the PLAis up to around 22000, which is 4 times more than that of the LAlow(-grade)polymer.