Study on synthesis of polylac-tide from kitchen garbage

Abstract

Polylactide is regarded as the most promising biodegradable plastics because of its high quality in physical properties as well as chemical recyclability and compostability. Furthermore, lactic acid (LA) as a raw material of this polymer can be produced from organic wastes. In this study, recovery LA from fermentation broth of kitchen garbage was carried out by esterification of ammonium lactate in fermentation broth with the butanol to produce butyl lactate, purification of butyl lactate and subsequent hydrolysis of the purified butyl lactate. The purity of recovered LA was 90%. Then the recovered LA was used to produce lactide as an intermediate of polylactide. Through an orthogonal-design experiment, the optimum condition of synthesizing lactide was determined and under this condition the yield of synthesizing lactide was 75%. And moreover, polylactide was conventionally obtained by a ring-opening polymerazation from the above lactide, and the viscosity average molecular weight was up to 9.2 × 104, which could meet requirement to produce biodegradable plastics. In the present process, the neutral ammonium lactate in the fermentation broth was employed as a starting material, thereby eliminating the need to use a reactor with acid resistance properties. In addition, the liberated butanol in hydrolysis process and unreacted butanol in esterification process can be recycled to the above esterification. Therefore, the present process is economic.