Oxidative Depolymerization and Bioconversion of Polyethylene to Oxidized Waxes and Polyhydroxyalkanoates (PHAs) in Thermus thermophilus HB8

Aqueous oxidative depolymerization of low-density polyethylene (LDPE) can convert highly recalcitrant, water-insoluble, and biologically persistent polyethylenes to value-added products. In this study, aqueous oxidation reaction conditions including temperature, time, KMnO4 loading, and initial O2 pressure were screened for their impact on the yields of water-soluble and water-insoluble products, water-soluble product distributions, and water-insoluble product properties. Additionally, the potential for biological utilization of the water-soluble fraction was demonstrated. It was shown that increasing oxygen consumption during the oxidation reaction is correlated to increased water-soluble product yields and that the primary water-soluble products are C4 to C9 saturated linear diacids and hydroxy- and oxo-substituted diacids as determined by LC-QTOF. Water-insoluble products are expected to comprise >C10 oxidized waxes that can be recovered by ethanol solubilization. Characterization of physical properties of the water-insoluble products shows the trends that increasing oxygen, carbonyl, and/or carboxylate contents correlate to decreasing thermal transition temperatures (melting and crystallization temperatures as determined by DSC), decreasing crystallinity, and increasing ethanol solubility. Finally, it was demonstrated that Thermus thermophilus HB8 could grow on water-soluble products of LDPE oxidation as the sole carbon source and accumulate polyhydroxyalkanoates (PHAs) from growth on these substrates.

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