Cutting the range of additives permitted in plastics could boost recycling and cut pollution, according to Imperial researchers.

A new briefing paper, published by the Institute for Molecular Science and Engineering (IMSE), surveyed the impacts of the 10,000 chemicals which can be added to plastics to boost their performance. The huge range of permitted chemicals makes recycling difficult. Many of these chemicals are also toxic to humans and the environment. As the quantity of plastics produced every year continues to increase (reaching 391 million tonnes in 2021), so does the impact of these chemicals.

Download the briefing paper here

“The global rate of recycling is currently 8.7%, while the theoretical maximum is 85%” said Professor Jason Hallett, of the Department of Chemical Engineering. “So we're a 10th of the way there. It's very hard to design a holistic recycling system when you might have 1000s of different components. ”

IMSE held a public panel discussion on 2 November to launch the briefing paper and kick off the debate. Authors Professor Jason Hallett of the Department of Chemical Engineering and Dr Agi Brandt-Talbot of the Department of Chemistry were joined by Victor Dewulf of Imperial spinout Recycleye, which uses AI to sort waste for recycling. The audience members included policy experts, anti-plastic campaigners, plastic industry representatives and researchers in sustainable plastics.

It's very hard to design a holistic recycling system when you might have 1000s of different components. Jason Hallett Professor of Sustainable Chemical Technology

The briefing paper proposed radically restricting the range of additives permitted for use the commonest plastics in the UK. This reduction in variability should simplify and boost recycling, and well as reducing exposure to toxic additives.

“Today, coloured plastic has a close to 100% chance that it will not get recycled,” said Victor Dewulf. “Although the plastic is technically recyclable, it’s not economic. The price today of mixed coloured plastics is less than half that of clear plastic. So it’s downcycled into flower pots. Restricting dyes would make an enormous difference to recycling rates.”

Watch the panel discussion here

Panellists Agi Brandt-Talbot, Victor Dewulf and Jason Hallett responding to audience questions. Image credit: Imperial College London

No one wants soggy crisps

Multi-layered crisp and confectionery packets are an example of a type of plastic that is hard to recycle. This kind of packaging consists of 7-10 layers of different materials to keep out light, oxygen and water. The packaging is also strongly coloured to convey brand identity. The colourants in the branding, and aluminium layer which acts as a barrier to oxygen, are particularly hard to separate from the polymers.

“These contain usually five different polymers including the polyurethane glues that hold them together. It's not the polymers that are the problem,“ said Jason Hallett.

The briefing paper recommends investment into new technologies to tackle hard-to-recycle plastics like crisp packets.

Additives in plastic

More than 10,000 chemicals are added to plastics to improve their properties, such as colour, flame resistance, or stiffness. Many of these chemicals have known toxicity. In the UK, these chemicals are regulated by the Health and Safety Executive via UK REACH. Regulating each of these chemicals individually is very expensive and laborious. It has also resulted in the substitution of one hazardous molecule by another with similar toxic behaviour, e.g. bisphenols, or per- and perfluoroalkyl substances. Restricting additives should also reduce exposure to toxic additives.

“In addition we’ve got to think about biodegradable plastics differently,” said Agi Brandt-Talbot. “If you have biodegradable plastic you need to definitely make sure that the additives are also biodegradable and environmentally benign. Otherwise, you're basically making a release system. So it's really important that it's taken into account when designing these new plastics.”

Institute for Molecular Science and Engineering

The Institute for Molecular Science and Engineering was founded in 2015. The Institute transcends disciplinary boundaries, bringing together Imperial's world class engineers, scientists, clinicians and business researchers. The Institute focuses on research questions where this kind of interdisciplinary working using both a molecular and an engineering lens is essential. These include plastic pollution, alternative fuels and technologies to tackle antimicrobial resistance. The next briefing paper will be on microplastics pollution, to launch in February 2024.