Recycling by-design of plastic through formulation with thermally protected enzymes in layered double hydroxide structures

Abstract

The use of polymer-degrading enzymes in polymer formulation is a very attractive strategy for the life-cycle of plastics. The design of a material able to degrade on-demand could help reach the ambitious targets pursued by recent European policies. Only 32% of the resulting waste from the 50 million tonnes of plastics consumed each year in Europe is actually recycled. Since packaging accounts for more than 40% of all plastics produced every year, the improvement of its circularity from origin to subsequent life cycles is now a priority. The present research suggests a solution to improve the recyclability of plastics via a life cycle approach employing thermally stable enzymes as innovative materials providing a new potential for plastic and its end life. More specifically, cutinase, selected as a highly degrading polyester hydrolytic enzyme, was thermally protected by immobilization in Mg/Al layered double hydroxide structures. The cutinase immobilization efficiency was found to be high, as well as its release ability in an appropriate medium. The thermal stability of cutinase was strongly improved after immobilization, as highlighted by a 6-times increase of its half-life at 90 °C, compared to the free enzyme, and by a high activity retention (>60%) after short exposure to temperatures up to 200 °C. Moreover, it was demonstrated that a film of poly (butylene succinate-co-adipate) formulated with 5 wt% of immobilized cutinase, completely degraded within 24 h.