Synthesis And Properties Of The Polyester Of LA/DFA/EG Tripolymer

In recent years, with the severity of our environment and economy pressures inwhole world, the new requirements about variety and performance of degradableplastic were proposed. Polylactic acid （PLA） is widely used in agriculture,packaging, medicine and health area because it is a biocompatible, biodegradableand bioresorbable polymer and it has a fine mechanical property. But it is the hardbrittle material and has a poor pliability because it has a high glass transitiontemperature. Thus, it has to be modified to improve the handling characteristics andits application. This was the power of development of degradable plastic polylacticacid.In this paper, the unsaturated polyester resin of DFA-EG and the tripolymerpolyester of LA-DFA-EG were synthesized by using lactic acid, C₃6dimer fatty acid（DFA） and ethylene glycol （EG） as materials. Regularities of synthesis of DFA-EGunsaturated polyester and LA-DFA-EG tripolymer polyester were studied. Propertysof water resistance, oil resistance, mechanics, and thermal of the LA-DFA-EGtripolymer polyester also were studied. The results were as follows:DFA-EG unsaturated polyester was synthesized using dimer fatty acid andethylene glycol as materials by direct melt polycondensation. The optimum reactionconditions were as follows: the molar ratio dimer fatty acid: ethylene glycol is1:2,the catalyst is SnCl2and its preferable amount is0.7%（w/w） of the mass ofmaterials, the reaction temperature is170℃, the reaction time is3h, the reactionneeds vacuum conditions.The tripolymer polyester of LA-DFA-EG was synthesized by two steps. First,the prepolymer of DFA-EG unsaturated polyester was synthesized using dimer fattyacid and ethylene glycol as materials. Then, the tripolymer polyester of LA-DFA-EGwas synthesized using the prepolymer of lactic acid dehydrated and the prepolymerof DFA-EG at170℃under vacuum conditions, the catalyst is SnCl₂and itspreferable amount is0.7%（w/w）, reaction time is14h. The preferable quality ratiolactic acid: DFA-EG is80:20. The tripolymer polyester of LA-DFA-EG obtained hadtensile strength, impact strength, water resistance, oil resistance and so on. The targetproduct was proved by IR spectra and H NMR spectra.The relationship between the inherent viscosity of LA-DFA-EG tripolymer polyester and its average molecular weight was obtained at30℃in tetrahydrofuranby Ubbelohde viscometer. It was as follows:[η]0.01253M^0.6846The thermal analysis showed that the tripolymer polyester of LA-DFA-EGobtained had perfected thermodynamic stability. The decomposition temperature wasat360℃, and the percentage of lost weight was at600℃.