Читать книгу Poly(lactic acid) - Группа авторов - Страница 80

In this method, a four‐step process is applied. After polycondensation and depolymerization, the depolymerization product is led by a carrier gas, which preferably is nitrogen, through a cooling zone (−78–10°C) into a cold cyclone for separation of unreacted PLA from the mixture of lactide and depolymerization impurities. In the last step, the mixture of lactide and impurities are mixed with water (v/v ratio of 1/0.5–5) to separate lactide in a separation vessel to remove a liquid containing water and impurities formed at the top and to recover only lactide crystals from the bottom. The mixing may be performed at a temperature between 5 and 30°C. The unreacted LA separated can be recycled, and the process may be a continuous cyclic process. The method is advantageous in that the lactide can be obtained at a high yield by a simple method, compared to the above‐mentioned conventional production methods [108].