PROCESS AND APPARATUS FOR PREPARATION OF A CRYSTALLIZABLE POLYLACTIC ACID MIXTURE, AND POLYLACTIC ACID MIXTURE

摘要

The present invention relates to a process which can be carried out continuously or batchwise for the preparation of crystallizable polylactic acid mixtures proceeding from lactic acid. This includes polycondensation of lactic acid to obtain an oligomer, depolymerization of the oligomer to obtain crude lactide, and purification of crude lactide to obtain pure lactide, wherein the purification includes L- and D-lactide-rich fractions And fractional distillation into a meso-lactide-rich fraction, and a separate ring-opening polymerization of the subsequently obtained lactide fraction is performed. Subsequently, the individual batches or streams of polylactic acid produced by ring-opening polymerization are mixed. The process according to the invention achieves excellent yields based on the lactic acid used. The invention also relates to an apparatus for carrying out the method outlined above, and to a polylactic acid mixture.