Enzymatic transformation of aliphatic polyesters into cyclic oligomers using enzyme packed column under continuous flow of supercritical carbon dioxide with toluene

The enzymatic degradation of chemically synthesized typical biodegradable plastics, such as poly(R,S-3-hydroxybutanoate), poly(ε-caprolactone) and poly(butylene adipate), into reactive cyclic oligomers under the continuous flow of supercritical or subcritical carbon dioxide (scCO2) with toluene through an enzyme column was studied with reference to chemical recycling. It was confirmed that all the tested polymers were quantitatively transformed into the corresponding cyclic oligomers by passage through the column packed with immobilized lipase from Candida antarctica (Novozym 435) at 40 °C under the continuous flow of scCO2 with some organic solvent. Compared to the pure organic solvents, by the addition of scCO2 as a mobile phase degradation of the polymer was significantly promoted with respect to the reaction time, temperature and polymer concentration for complete transformation of the polyesters into oligomers through the enzyme column. This phenomenon is ascribed to the high diffusivity, low viscosity and better mass-transfer properties of scCO2 as the reaction media. The degradation activity of the enzyme column was maintained for at least 6 months at 40 °C.