Enzymatic degradation of diol-diacid type polyesters into cyclic oligomers and its application for the selective chemical recycling of PLLA-based polymer blends

The lipase-catalyzed degradation of poly(butylene adipate) (PBA) and poly(butylene succinate) (PBS) into cyclic oligomers and their polymerizability were analyzed. The enzymatic polymerization of a cyclic oligomer was dependent on its ring-size. The highest molecular weight PBA with an Mw of 173000 was produced by the polymerization of the cyclic BA monomer The molecular weight decreased to around M w 60000 by polymerization of the cyclic BA dimer and trimer. Similar results were obtained for PBS. For the efficient chemical recycling of PBA and PBS, the cyclic BA monomer and the cyclic BS dimer had the best oligomer sizes, respectively. As an application of the enzymatic degradation for the chemical recycling of PBS, the selective recycling of the PBS/poly(L-lactic acid)(PLLA) polymer blend was carried out using a lipase and a clay catalyst, montmorillonite K5.