Degradation of poly(lactic acid) into repolymerizable oligomer using montmorillonite K10 for chemical recycling.

The degradation of poly(L-lactic acid) (PLLA) into a repolymerizable oligomer was carried out using a clay catalyst, montmorillonite K10 (MK10), with the objective of developing a chemical recycling process. PLLA having an Mw of 120,000 was degraded by MK10 in toluene at 100 degrees C for 6 h to produce the corresponding linear-type oligomers having a molecular weight of a few hundreds in a yield of greater than 90%. The oligomer was readily polymerized by a conventional chemical catalyst to give a high-molecular-weight PLLA. No isomerization of L-lactic acid occurred during the degradation process using MK10. The MK10 could be repeatedly used at least five times without any significant decrease in its activity. The degradation of PLLA was accelerated by the addition of a small amount of ethanol in toluene using anhydrous MK10 to produce oligomers with ethyl ester end groups.