Biocatalytic oxidation of polyethylene by Agrocybe aegerita mycelium

Polyethylene resistance to biochemical attack is a well-known limit, preventing the development of green strategies, based on enzymatic catalysis, for the bioconversion of waste polyethylene into smaller molecules and subsequently second-life products. This inertness derives from the chemical structure of the polymer, consisting of repeating methylene groups, without any hydrolysable moiety. Oxidation of polyethylene is therefore the first goal to be pursued. Differently from the attempts disclosed in literature, consisting of harsh physical treatments requiring high energy consumption, we developed an innovative two-step process for the biocatalytic oxidation of polyethylene. Polyethylene was first melt-blended with fatty acids to loosen the dense packing among its polymeric chains and to allow its colonization by fungal mycelia. Subsequently, incubation with Agrocybe aegerita mycelium highlighted an impressive ability of its secretome to oxidize the polyethylene chains, detected by the formation of a carbonyl peak in the ATR-FTIR spectra and quantified by means of the calculation of the Carbonyl Index. Samples incubated with Agrocybe aegerita showed a four-time higher formation of carbonyl groups compared to the best results reported in literature so far. This work demonstrates how the synergistic effect of the designed pretreatment with the employment of an oxidizing fungal mycelium strain, like Agrocybe aegerita, results in efficient polyethylene biooxidation, laying the bases for the development of biocatalytic recycling processes.