PREPARATION OF LACTIC ACIDOLIGOMER
Abstract
The process of obtaining of lactic acid oligomer as by-product for synthesis of biodegradable polylactide was investigated. Synthesis of oligomer was carried out by azeotropic distillation of water. Aromatic hydrocarbons such as toluene, chlorobenzene, bromobenzene and o-dichlorobenzene were used. They form heteroazeotropes. This allowed to control the volume of distilled water. The time of obtaining of oligomer of lactic acid in presence aromatic hydrocarbons and without them was compare in the article. The reaction of obtaining of oligomer was carried out in a rotary vacuum evaporator and in laboratory distillation installation in presence of catalyst (ZnO in the amount of 1.5% by weight) for reaction assessment. It was shown that the using of azeotropic distillation of water from reaction mass allow to reduce the time of oligomer synthesis compared to standard distillation of water from the lactic acid solution. It implements by reducing of viscosity of reaction mass that improves heat and mass transfer in the reactor. These factors contribute to increase rate of distillation of solution water and water which release in the process of polycondensation of lactic acid. The oligomer yield also increases. The actual control of concentrating of the aqueous solution of lactic acid and the oligomer obtaining reaction carried out according to the rate of distillation of the water from the reactor. Also the control was carried out by changing the molecular weight of the oligomer. The molecular weight of the oligomers obtained was determined by gel permeation chromatography. It reached 1600 g/mol. Lactic acid oligomer of a linear structure was obtained under these conditions. IR spectra of the oligomer of lactic acid indicate the simultaneous process of concentration of the lactic acid solution and polycondensation of lactic acid.
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