Recovery of lactide from polylactic acid/polyethylene blend with extruder

Abstract

To achieve the chemical recycling of poly (L-lactic acid) (PLLA) from polymer mixtures, a blend of PLLA with linear-type low-density polyethylene (LLDPE) was prepared and depolymerized to recover a cyclic monomer: a lactide with a twin-screw extruder. Magnesium oxide (MgO) was used as a depolymerization catalyst. The selective depolymerization of PLLA from PLLA/LLDPE/MgO [20/80/5 (wt/wt/wt)] was performed under selected conditions: resin temperature of 250°C, a short retention time of less than 5 min in a melted resin, and a pressure at the vent-port of lower than 4.4 kPa, this process gave lactide in a 74.5% yield. However, the racemization of the lactide also proceeded in a remarkable way to give a mixture Of L,L-, D,D-, and meso-lactides, in which the desired L,L-lactide was recovered in a maximal purity of 55.%. This is the first report of chemical recycling of PLLA from a polymer blend with an extruder.