Only about 9% of discarded plastic is recycled; 79% ends up in landfills and 12% is incinerated, in large part because recycling usually requires plastics to be sorted by type first. Now researchers at UCLA and Ewha Womans University in South Korea have demonstrated a chemical approach that skips sorting entirely.

The process, published in the Proceedings of the National Academy of Sciences, uses alkaline thermal treatment (ATT) — sodium hydroxide reacting with organic material under heat — to convert a mixture of the three most common plastics — PET, polyethylene and polypropylene — into hydrogen gas with purity above 90% in a single reactor. It operates at temperatures 300–400°C lower than conventional steam gasification.

The key innovation is locking carbon away: more than 75% of the plastic's carbon ends up as solid sodium carbonate or liquid organic residues rather than escaping as atmospheric CO2. The carbonate can then be converted to calcium carbonate, permanently fixing the carbon in a mineral used by carbon-intensive industries. Earlier low-temperature methods could only handle oxygen-containing plastics like PET; high-temperature gasification handles mixed plastics but releases large amounts of CO2.

'We are solving two urgent global problems at the same time,' said Alissa Park, dean of UCLA Samueli and co-corresponding author. 'Plastic waste is accumulating at alarming rates, and clean hydrogen is essential for decarbonizing energy. This technology tackles both of these challenges in a creative and scalable way.' The team says further work is needed to optimize the process and evaluate its economics.

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