Soap made from discarded plastics? This is upcycling at its best

To address this issue, the researchers created an oven-like reactor from scratch that could be used to safely burn down plastic.

For this, the bottom of the oven was heated to high degrees to break up the polymer chains, while its top remained at a low temperature to prevent them from breaking down too much. This process is known as temperature-gradient thermolysis.

The resultant was a substance made of short-chain polyethylene, a sort of wax.

The team added a few more steps, including saponification, which allowed them to create the “world's first soap out of plastics.”

This novel process is applicable to both polyethylene and polypropylene, the two most widely used forms of plastic.

They account for over half of all plastic garbage, amounting to nearly 200 million tonnes each year. More than 80 percent of plastic trash is discarded, with less than 10 percent recycled.

"Our research demonstrates a new route for plastic upcycling without using novel catalysts or complex procedures. In this work, we have shown the potential of a tandem strategy for plastic recycling," said Zhen Xu, the lead author of the paper. "This will enlighten people to develop more creative designs of upcycling procedures in the future.”

The study has been published in the journal Science.

Study abstract:

Conversion of plastic wastes to fatty acids is an attractive means to supplement the sourcing of these high-value, high-volume chemicals. We report a method for transforming polyethylene (PE) and polypropylene (PP) at ~80% conversion to fatty acids with number-average molar masses of up to ~700 and 670 daltons, respectively. The process is applicable to municipal PE and PP wastes and their mixtures. Temperature-gradient thermolysis is the key to controllably degrading PE and PP into waxes and inhibiting the production of small molecules. The waxes are upcycled to fatty acids by oxidation over manganese stearate and subsequent processing. PP ꞵ-scission produces more olefin wax and yields higher acid-number fatty acids than does PE ꞵ-scission. We further convert the fatty acids to high-value, large–market-volume surfactants. Industrial-scale technoeconomic analysis suggests economic viability without the need for subsidies.