# Aqueous Depolymerization of Polyethylene at Ambient Temperature: In Situ Generation of Permanganate Using Ozone

## TL;DR

Scientists developed a new method to break down polyethylene plastic into useful products using water and ozone at room temperature.

## Contribution

A novel ambient-temperature aqueous process for polyethylene depolymerization using in situ permanganate generation.

## Key findings

- LDPE is converted into carboxylic acids and wax using ozone and water at 30°C.
- Diacids with 4-6 carbon units are the main water-soluble products detected by HPLC.
- Oxidation occurs preferentially at branch points, forming linear acids and ketones.

## Abstract

The long sought-after
goal of chemically recycling polyolefins
at ambient temperature and pressure without the use of organic solvents
is realized. Using ozone to regenerate a permanganate oxidant in situ in an aqueous environment, low-density polyethylene
is converted to carboxylic acids and oligomeric wax. LDPE powder (with
average particle sizes between 150 and 250 μm) serves as the
substratereactions are conducted at atmospheric pressure and
30 °C. Water-soluble products are quantified using HPLC, with
diacids having 4, 5, and 6 carbon units as the primary products. The
remaining solid wax was analyzed for crystallinity by calorimetry
(DSC), for acid number by titration, and for molecular functionality
by ATR-IR and NMR spectroscopies. All three measured quantities increase
with increasing reaction time. The acid number of the residual wax
indicates a diacid carbon length of ∼30 (∼450 g/mol).
Polymer oxidation occurs preferentially at side-chain branch points.
Results suggest a two-reaction system in which branch-point tertiary
carbons are selectively oxidized to yield linear carboxylic acids
and ketones, followed by secondary depolymerization to yield water-soluble
diacids. Experimental yields were 10% at 144 h.