Used Rubber Gloves Converted into Carbon Capture Material

The nitrile glove sits in a pressure vessel in Aarhus, shredded into small pieces, bathed in solvent under 30 bars of hydrogen. Twenty-four hours later, something chemically improbable has happened. The nitrogen-rich polymer chains — designed to resist bodily fluids and keep nurses’ hands clean — have been rearranged into something altogether more useful. Amine groups now stud the surface of the rubber. The glove, which until recently faced incineration, has become a carbon trap.

Over 100 billion nitrile gloves are produced every year. Nearly all are worn once, stripped off, and disposed of. Unlike PET drinks bottles, which slot neatly into deposit-return schemes, the thermoset rubber that makes gloves impermeable and durable is also what makes them essentially impossible to recycle by conventional means. Vulcanisation — the process that gives rubber its strength — cross-links polymer chains in a way that resists the heat and chemicals usually needed to break materials down. So they burn. That incineration releases CO₂ and other noxious gases, which is roughly the worst possible end for a material derived from crude oil.

Simon Kildahl, a postdoc at Aarhus University’s Department of Chemistry, has been working on a different exit route. His group, part of the Novo Nordisk Foundation CO₂ Research Center, has already managed to recycle materials widely considered unrecyclable — polyurethane foam from mattresses, epoxy and glass fibres from wind turbine blades. Rubber gloves seemed like a natural next target. “A plastic bottle can be recycled relatively easily, as we know from deposit-return systems,” he says. “But other plastic materials are problematic because they cannot be reused in the same way. Therefore, they often end up being burned, which is currently the case for rubber gloves.”

What makes nitrile rubber chemically interesting is the acrylonitrile content — typically 33 to 40 per cent by weight — that gives the material its name. Those nitrile groups, each containing a carbon triple-bonded to a nitrogen, can be hydrogenated: treated with hydrogen under pressure in the presence of a catalyst, converting them into amine groups. Amines are what make carbon capture materials work. They bind CO₂ through a reversible chemical reaction, holding it until heated — at which point they release it, refreshed and ready to capture again. Kildahl’s insight was that gloves already contain the chemical architecture needed; it just needs coaxing into the right form.

The catalyst of choice turned out to be a ruthenium complex called RuMACHO, a commercially available pincer compound that had previously proved effective for small-molecule nitrile reduction. Applying it to bulk polymer was, the paper notes, a more demanding proposition. Vulcanised gloves can’t dissolve in the reaction medium — they swell instead, making catalyst access harder and requiring higher loadings. The team shredded gloves from Ansell, a major manufacturer, tested both rough-cut particles and finer powders from cryogenic milling (freezing the rubber in liquid nitrogen before grinding, to stop it deforming rather than fracturing), and found, somewhat to their relief, that particle size barely mattered. The nitrile conversion proceeded with high efficiency regardless.

The resulting material, a pale powder of hydrogenated nitrile rubber, then went into a thermogravimetric analyser — an instrument that measures mass changes as a gas flows over a sample. The results were unexpected. “In our experiments, we converted the glove so that it can capture CO₂ instead of becoming a waste product that releases CO₂ and other harmful gases during incineration,” says Kildahl. More intriguingly, the adsorbent performed better at 90°C than at room temperature. For a non-porous material — one with essentially no internal surface area for gas to permeate — this is counterintuitive. Porous materials like metal-organic frameworks work through surface contact; the greater the surface, the more CO₂ can be grabbed. Rubber has a surface area of less than 1 square metre per gram. It should, by rights, be terrible at this. But the flexible polymer chains, which have glass transition temperatures well below zero, become increasingly mobile at higher temperatures, improving gas permeability — CO₂ hopping from amine to amine through the rubber matrix in a process resembling facilitated transport membranes. At 90°C with a realistic 10 per cent CO₂ concentration (mimicking industrial flue gas), the material captures 1.68 millimoles per gram over five hours, and around 0.5 to 1.25 mmol/g in a more industrial-relevant 15-minute window.

That 90°C sweet spot turns out to be serendipitous. In China, where coal-fired power plants account for nearly two-thirds of electricity generation, flue gas is routinely cooled to exactly that temperature before exhaust treatment — partly to avoid acid dewpoint corrosion in pipework. The leading solid adsorbent on the market, Calgary Framework 20 (a metal-organic framework commercialised by Svante and BASF), performs very well at room temperature but captures only around 0.5 mmol/g at 90°C. The rubber materials don’t match CALF-20 under its optimal conditions, but at the temperatures relevant to actual power plant operation, they are complementary — and in some cases superior. The team put their four best adsorbents through 40 successive capture-and-release cycles and found capacity losses of between two and seven per cent. Acceptable for a material whose feedstock would otherwise go up in smoke.

The scope extends beyond gloves. Styrene-butadiene-styrene rubber — produced at 1.8 million tonnes a year, used in shoe soles and as an asphalt additive — lacks the nitrogen-containing groups of nitrile rubber. The Aarhus team added them using a two-step hydrocyanation-hydrogenation sequence, first inserting nitrile groups using a nickel catalyst and carefully controlled hydrogen cyanide gas (generated in situ in a sealed two-chamber reactor, away from the main reaction), then reducing them to amines. A shoe sole from the brand Monki was among the substrates tested. It worked.

“That is why it is smart to utilise a waste material available in such large quantities, rather than extracting more oil from the ground,” Kildahl says. “With the rubber glove, we can create a CO₂ capture material where almost every atom in the product comes from waste, except for a small amount of hydrogen, which can ideally be obtained from water via Power-to-X.” The logic is circular in the best sense. Waste rubber, which would otherwise release carbon on incineration, becomes a tool for removing carbon from power plant emissions. The CO₂ it captures can go into underground storage or feed Power-to-X processes producing green fuels.

Kildahl is candid about where things stand. The work is at technology readiness level 3 or 4 on a scale of 9 — proof of concept in the laboratory, grams rather than kilograms. The ruthenium catalyst is expensive, which matters considerably when you’re imagining million-tonne production scales. “We are working on a gram scale right now, and reactions can look and behave differently when we scale up to kilograms,” he says. “But our results look very promising.” The IPCC estimates that meeting Paris Agreement targets will require removing 5 to 16 billion tonnes of CO₂ from the atmosphere annually by 2050. Current direct air capture facilities remove a few tens of thousands of tonnes per year. The gap between those numbers is where materials chemists are working. Discarded gloves, it seems, might be part of the answer.

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