Synthesis And Characterization Of The Polyester Of PLA-(DFA-EG)_m Tripolymer

In recent years, with the severity of our environment and economy pressures in wholeworld, the new requirements about variety and performance of degradable plastic wereproposed. Polylactic acid (PLA) is widely used in agriculture, packaging, medicine and healtharea because it is a biocompatible, biodegradable and bioresorbable polymer and it has a finemechanical property. But it is the hard brittle material and has a poor pliability because it hasa high glass transition temperature. Thus, it has to be modified to improve the handlingcharacteristics and its application. This was the power of development of degradable plasticpolylactic acid.In this paper, the unsaturated polyester resin of DFA-EG, PLA and the tripolymerpolyester of PLA-(DFA-EG)mwere synthesized by using lactic acid, C36dimer fatty acid(DFA) and ethylene glycol (EG) as the main raw materials. The reaction conditions and theirimpacts on these copolymers of reaction time, reaction temperature, the amount of catalystand the molar ratio were studied. The results were as follows:DFA-EG unsaturated polyester was synthesized using dimer fatty acid and ethyleneglycol as materials by direct melt polycondensation. The optimum reaction conditions wereas follows: the molar ratio ethylene glycol: dimer fatty acid is2:1, the catalyst is SnCl2andits preferable amount is0.7%(w/w) of the mass of materials, the reaction temperature is170℃, the reaction time is3h, the reaction needs vacuum condition. The unsaturated polyesterobtained under this condition had a higher reaction degree.PLA was synthesized using lactic acid as material by direct melt polycondensation. Theimpact of the amount of catalyst, reaction temperature and reaction time on acid value andreaction degree of the copolymer PLA was studied. The results were as follows: the catalystis SnCl2and its preferable amount is0.7%, the reaction temperature is170℃, the reactiontime is7h. The reaction degree under this condition was reach to95%.The tripolymer polyester of PLA-(DFA-EG)mwas synthesized using the PLA and theunsaturated polyester resin of DFA-EG by direct melt polycondensation. The reaction conditions were as follow: the preferable quality ratio polylactic acid: DFA-EG is80:20, thereaction temperature is170℃, the catalyst is SnCl2and its preferable amount is0.7%,reaction time is10h. The reaction degree under this condition was reach to95%. The targetproduct of purification of the copolymer was verified by infrared spectroscopy.