Unsorted Plastic Waste Can Become Hydrogen Fuel, and Most of Its Carbon Stays Locked Away

Worldwide, about 9% of discarded plastic gets recycled. Another 79% goes to landfill and 12% is burned, according to figures in the UCLA release that ScienceDaily carried on July 31, 2026. A study in Proceedings of the National Academy of Sciences (PNAS) describes a laboratory process that takes mixed, unsorted plastic from that pile and turns it into hydrogen gas of more than 90% purity, while holding most of the plastic's carbon out of the air.

The work was co-led by the UCLA Samueli School of Engineering and Ewha Womans University in South Korea. Its co-corresponding authors are Ah-Hyung "Alissa" Park, the Samueli school's dean, and Woo-Jae Kim, a professor of chemical engineering and materials science at Ewha. Co-authors came from Ewha, Korea Aerospace University, Kangwon National University and Sogang University, and the National Research Foundation of Korea provided funding. The paper is titled "Selective and direct hydrogen generation from mixed plastic waste via alkaline thermal treatment with inherent carbon storage."

What Alkaline Thermal Treatment Does

The method is called alkaline thermal treatment. Sodium hydroxide reacts with organic material under heat, and the reaction releases hydrogen. Park and Kim first developed the approach to turn seaweed into hydrogen. The new study applies it to the three most common consumer plastics, polyethylene terephthalate (PET), polyethylene (PE) and polypropylene (PP), fed together into a single reactor with no sorting step.

Sodium hydroxide also captures carbon. The study reports that more than 75% of the plastic's carbon ends up in stable carbonate compounds or liquid organic residues, and no more than 13% enters the gas phase. The UCLA release adds that the resulting sodium carbonate can be converted to calcium carbonate for permanent mineral storage.

Why Mixed Plastic Was the Hard Part

Earlier low-temperature routes to hydrogen worked only on oxygen-containing plastics such as PET, which left polyethylene and polypropylene out of reach. Conventional steam gasification handles a wider mix, but it runs at high temperatures and releases substantial carbon dioxide. The alkaline process runs 300 to 400°C cooler than steam gasification, according to the UCLA release.

Sorting is the other barrier. Conventional recycling needs each plastic type separated first, which Ewha's announcement names as a limit for mixed waste streams. A reactor that accepts the mix as it arrives removes that step from the equation.

One detail complicates the clean version of this story. ScienceAlert reports that the PE and PP samples received a pre-treatment of heating and oxidation to raise their reactivity, so the plastics are not fed in raw. The same coverage says only tiny laboratory samples were tested, and the UCLA release states that further work is needed to optimize the process and evaluate its economic viability before deployment at scale.

What This Does and Does Not Mean

The established part is a peer-reviewed laboratory result: mixed PET, PE and PP produced hydrogen above 90% purity in one reactor at temperatures 300 to 400°C below steam gasification, with more than 75% of the carbon retained as carbonate or liquid residue. The UCLA release and Interesting Engineering's coverage do not give the hydrogen yield per gram of plastic, and none of the coverage reviewed for this article gives a cost figure.

The next steps are the ones the authors named: optimizing yields, emissions and temperature, then testing whether the economics hold beyond tiny samples. For a plastic stream that mostly ends in landfills and incinerators, a hydrogen route that keeps its carbon locked away now has a published, testable baseline.