Study on synthesis of D,L-lactide at low vacuum condition

With D,L-lactic acid as monomer,D,L-lactide has been synthesized by polymerization and depolymerization in low vacuum level condition.The effects of dehydration temperature,ratio of dehydration,catalyst dosage,polymerization and depolymerization temperature on the yield of D,L-lactide were studied.It is showed that the optimal conditions were as follows:amount of catalyst zinc oxide(ZnO) was 1.2%;dehydration temperature was 120~160 ℃,depolymerization temperature was 220~250 ℃,the purification method from coarse product was improved by using absolute ethyl alcohol and ethyl acetate as solvents.Under this optimal conditions,the yield of D,L-lactide reached 40.2%.Melting point of product was measured by capillary tube method and the ring lactide with high purity was identified by IR,DSC and XRD.