Most plastic waste is contaminated – our new ‘nano’ recycling tech embraces this messy reality

A plastic drinks bottle is one of the most “recyclable” objects in the modern waste stream. It is lightweight and collected in huge volumes. Yet even for this item, the reality of recycling is messy: labels, inks, caps, food residues, colourants and the occasional wrong plastic all get bundled together. The chemistry may be simple, but the waste is not.

My team is developing a new way to deal with contaminated plastic waste. Instead of assuming perfect sorting, we start from the reality that waste streams are mixed, inconsistent and often dirty – and design chemistry that can tolerate that.

Using nanomaterial-based catalysts, we drive depolymerisation, a process that breaks plastics back into their molecular building blocks. By tuning the reaction, it becomes possible to selectively target specific plastics even in mixed or impure streams. The aim is a process built for real-world waste, not laboratory conditions.

This work matters because the scale of the problem is vast. Globally, only about 9% of plastic waste is recycled after losses and residues are accounted for. Much of the rest is sent to landfill, burned or leaks into the environment.

Recycling can look deceptively successful when you only track what gets collected.

Polyethylene terephthalate (PET) is the single polymer – molecular material – used in many bottles. In Europe, collection for PET drinks bottles has reached around three-quarters in recent years. But collection is only the start. What happens next determines whether plastic truly circulates or quietly exits the system.

Most PET today is recycled mechanically: the plastic is sorted, washed, melted and remoulded. This works well for clean, colourless material, but it is sensitive to contamination and additives. A small amount of the wrong polymer can weaken a batch. Dyes and stabilisers can persist. Each heating cycle can slightly reduce performance. Over time, the material drifts away from the quality required for food-grade packaging and is often downcycled into lower-value products.

That is why chemical recycling attracts attention. Instead of melting plastics into new shapes, the aim is to break the polymer back into small molecules that can be purified and used again, effectively returning it to its chemical building blocks.

Recent reviews of chemical recycling highlight both the promise and the technical challenges, especially when waste streams are mixed. The difficulty is not proving that plastics can be broken down in a laboratory. It is making that chemistry work reliably with real-world waste.

Nanomaterials are engineered at a very small scale – thousands of times thinner than a human hair – which gives them a large reactive surface area. That surface can be tuned to encourage specific chemical reactions while discouraging others, making depolymerisation faster and more controllable. Broader catalytic depolymerisation research highlights how advanced materials may help make these processes more practical at scale.

Embracing imperfections

Contamination tolerance shapes the economics of recycling. Studies in waste management show that mixed or contaminated plastics drive up recycling costs because they require extra separation and cleaning. Water, energy and labour are spent chasing purity. A chemistry that can accept dirtier inputs could shift where value is created.

When plastics cannot be recycled into new products, they are often incinerated or landfilled. A UN roadmap on plastic pollution argues that more circular approaches could significantly reduce waste and emissions. That requires seeing plastic not just as rubbish, but as stored carbon that can be redirected.

Plastics are often treated as rubbish, but chemically they are concentrated carbon and hydrogen. If those molecules can be reorganised rather than discarded, waste plastic becomes a potential feedstock for hydrogen production. Hydrogen is widely discussed as a future fuel and industrial feedstock, yet most hydrogen today is still produced from fossil fuels.

According to the International Energy Agency, global hydrogen production in 2023 emitted about 920 million tonnes of carbon dioxide. If hydrogen demand grows for industry, transport and energy storage, its carbon footprint will matter. Some emerging research explores converting plastic waste into hydrogen-rich gas using catalysts to guide the breakdown of long plastic molecules. By carefully controlling the reaction conditions, the process can favour the production of hydrogen rather than unwanted by-products.

In this way, waste plastic shifts from being purely a recycling challenge to becoming a potential feedstock for lower-carbon energy systems.

The practical test for any of these approaches is straightforward: do they keep working when feedstock changes day to day? A bale that is mostly bottles but includes trays. A batch with too much dye. A stream with traces of paper and glue.

Industrial reality is rarely tidy. If that variability can be dealt with under less than ideal conditions rather than having to eliminate it, plastic waste becomes an imperfect, but still incredibly useful, raw material. In a world where waste is inevitable, designing processes that work with the mess may prove more important than designing ones that only work without it.

Conor Boland receives funding from the Research Ireland - Gas Networks Ireland Innovation Challenge 2025 (25/FIP/GNI/14147)