Science & Technology (Commonwealth Union) – The need to effectively dispose plastic has been a pressing issue for many decades. In more recent years an increase in possible viable options has emerged.
As plastic is deeply embedded in everyday life and found in items ranging from beverage bottles and grocery bags to vehicle interiors the need to dispose them eventually becomes a factor. However, after being thrown away, it remains one of the most challenging materials to recycle. Traditional recycling methods often depend on separating plastics according to their chemical types before processing, a time-consuming and expensive requirement. As a result, only about 9% of discarded plastic is recycled, while roughly 79% ends up in landfills and another 12% is burned, a process that releases carbon dioxide into the atmosphere.
A study led by researchers from the University of California, Los Angels (UCLA) Samueli School of Engineering and Ewha Womans University has now developed a chemical technique that can transform a combination of the three most widely used plastics into high-quality hydrogen fuel. The method operates at much lower temperatures than conventional gasification technologies and captures carbon dioxide by converting it into a stable solid mineral, preventing its release as a greenhouse gas.
Published in Proceedings of the National Academy of Sciences, the study highlights the potential of alkaline thermal treatment (ATT), a process where sodium hydroxide reacts with organic materials under heat to generate hydrogen. The researchers found that ATT can process mixed waste containing polyethylene terephthalate (PET), polyethylene (PE), and polypropylene (PP) together in a single reactor. The approach produces hydrogen with purity levels above 90% while eliminating the need to sort plastics before treatment.
“We are solving two urgent global problems at the same time,” explained the co-corresponding author Ah-Hyung “Alissa” Park, the Ronald and Valerie Sugar Dean of UCLA Samueli and a professor of chemical and biomolecular engineering. “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 ATT process was based on a technique originally created by Park and co-corresponding author Woo-Jae Kim as a carbon-neutral approach for transforming biomass, including seaweed, into hydrogen gas. In laboratory trials, the researchers adapted the ATT method to break down PET, PE and PP plastics and successfully generate high-purity hydrogen. The process produced considerably higher hydrogen yields from PET while requiring temperatures that were 300–400 degrees Celsius lower than conventional steam gasification methods.
Compared with PET, polyethylene and polypropylene initially showed poorer hydrogen production because their structures are made entirely of carbon-hydrogen bonds, making them chemically resistant under alkaline conditions. To overcome this challenge, the researchers introduced a thermal oxidation pre-treatment step, briefly heating the plastics in air before the main reaction. This process adds oxygen-based functional groups to the polymer chains, forming reactive points that allow the alkaline treatment to effectively break them down.
After activation, all three plastics were efficiently decomposed. The carbon released from the plastics during the reaction was absorbed by the sodium hydroxide reagent and turned into solid sodium carbonate, rather than being released into the atmosphere as carbon dioxide. Post-process analysis revealed that more than 75 % of the original carbon in plastics was conserved in stable carbonate compounds or liquid organic products. Less than 13% was turned into gases, with almost no direct emissions of carbon to the atmosphere, only a tiny fraction of that.
The recovered sodium carbonate can be further converted to calcium carbonate by a simple recovery process, permanently sequestering the carbon in a mineral form widely used in industries that have traditionally been associated with high carbon emissions.
