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An effective microwave-assisted process for recycling low-density polyethylene (LDPE) waste into value-added chemicals was developed. To achieve fast and effective oxidative degradation aimed at production of dicarboxylic acids, nitric acid was utilized as an oxidizing agent. Different conditions were evaluated, where recycling time and concentration of oxidizing agent were varied and the end products were characterized by FTIR, NMR, and HPLC. After just 1 h of microwave irradiation at 180 °C in relatively dilute nitric acid solution (0.1 g/mL), LDPE powder was totally degraded. This transformation led to few well-defined water-soluble products, mainly succinic, glutaric, and adipic acids, as well as smaller amounts of longer dicarboxylic acids, acetic acid, and propionic acid. The length of the obtained dicarboxylic acids could to some extent be tuned by adjusting the reaction time, temperature, and amount of oxidizing agent. Finally, the developed process was verified by recycling LDPE freezer bags as model LDPE waste. The freezer bags were converted mainly into dicarboxylic acids with a yield of 71%, and the carbon efficiency of the process was 37%. The developed method can, thus, contribute to a circular economy and offers new possibilities to increase the value of plastic waste.
Bäckström et al. (Mon,) studied this question.