No matter how many times you try and recycle plastic, one day it will reach end of life. As a waste stream it is problematic – landfills don’t want it, while environmentalists believe burning it when it is in is residual state, no matter how ‘clean’ the technology, is unacceptable. Those who champion zero waste would rather researchers, and those that produce plastic, work on ways of making it more biodegradable, or give it properties that greatly reduce its end-of-life impact on the environment.
However, turning such a useful product – and it is useful in many ways – into something that is more environmentally friendly is not as easy as it sounds; not without heavy investment and costs that a lot of companies are not willing to spend.
Researchers at RMIT University have claimed to come up with a cleaner, cost-effective way to upcycle used plastic, transforming it into nanomaterials and high-quality fuel.
Lead researcher, associate professor Kalpit Shah from the university’s School of Engineering, said that globally, about 20 per cent of waste plastics are recycled. He said boosting that figure remains a challenge as recycling plastic cleanly can be expensive and usually produces lower-value products, often making it financially unviable.
He said the new method his department is working on produces high-value products from plastic – carbon nanotubes and clean liquid fuel – while simultaneously upcycling agricultural and organic waste.
The team’s two-step process, revealed in the Journal of Environmental Management, converts organic waste into a carbon-rich and high-value form of charcoal, then uses this as a catalyst to upcycle the plastic.
“Our method is clean, cost-effective and readily scalable,” Shah said. “It’s a smart solution for transforming both used plastic and organic waste – whether it’s tonnes of biomass from a farm, or food waste and garden clippings from household green bins. We hope this technology could be used in future by local councils and municipal governments to help turn this waste into genuine revenue streams. It’s vital that we explore sustainable and cost-efficient alternatives beyond recycling. Upcycling plastic with home-grown tech would enable us to draw the greatest possible value out of our limited resources and bring us closer towards a true circular economy.”
The new plastic upcycling approach offers a sustainable alternative for the production of carbon nanotubes (CNTs). These hollow, cylindrical structures have electronic and mechanical properties, with applications across a range of sectors including hydrogen storage, composite materials, electronics, fuel cells and biomedical technologies.
Carbon nanotubes are in growing demand, particularly in aerospace and defence, where they can facilitate the design of lightweight parts. The global market for CNTs has been projected to reach $5.8 billion by 2027.
The new method starts with converting agricultural or organic waste to biochar – a carbon-rich form of charcoal often used for improving soil health. The biochar is used to eliminate toxic contaminants – such as Poly-cyclic Aromatic Hydrocarbons, known as PAHs – as the waste plastic is broken down into its components of gas and oil.
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The process eliminates those contaminants and convert plastics into liquid fuel. At the same time, the carbon in the plastic is converted into carbon nanotubes, which coat the biochar. These nanotubes can be exfoliated for use by various industries, or the nano-enhanced biochar can be used directly for environmental remediation and boosting agricultural soils.
“We focused on polypropylene as this is widely used in the packaging industry,” Shah said. “While we need to do further research to test different plastics, as the quality of the fuel produced will vary, the method we’ve developed is generally suitable for upcycling any polymers – the base ingredients for all plastic.”
The experimental study conducted at lab scale can also be replicated in a new type of hyper-efficient reactor that has been developed and patented by RMIT. The reactor is based on fluidised bed technology and offers improvement in heat and mass transfer, to reduce overall capital and operating costs. The next steps for the upcycling research will involve detailed computer modelling to optimise the methodology, followed by pilot trials in the reactor.
However, some participants on social media disagree with the new technology, with one person posting on Facebook, “There are independent researchers that strongly disagree with this industry perspective. Let’s not forget that pyrolysis technology was created by the coal industry. Biochar is unproven and turning plastic into fuel just exacerbates climate change. This petrochemical industry con is a false solution to the plastic waste crisis. As for nanomaterials, despite the significant health and environmental threat they pose, Australia has no regulatory framework in the industry”.
Shah disagrees on both points.
“Pyrolysis was not created by the coal industry,” he said. “It is a process of decomposing organic waste under oxygen free conditions. If the process is looking at producing only biochar (i.e., charcoal-type material) then it runs at much lower temperatures, unlike combustion, which operates at higher temperatures and has the potential to generate more pollutants. It is reported in the literature that production and consumption of biochar has been known to humans for more than 2,000 years. It was naturally formed, so biochar has a long history. Some people think it came from coal, but that is not correct.
“When you compare pyrolysis to incineration or combustion or gasification-type processes, pyrolysis has much lower environmental emissions. I’m not saying pyrolysis will have no emissions. But you need to understand, what are you going to do with the difficult waste? Ultimately you will have to break it down. If you put that waste in landfill this will cause land, water and air pollution. If you do it the way we are proposing, there may still be some small negative effect in terms of emissions, but the benefits to the environment are significant.”
Shah reiterates, when it comes to residual waste there is no perfect solution. He is looking at the reality of the situation as it stands. Even if a brand new, totally environmentally friendly plastic was to hit the market tomorrow, there would still be billions of tonnes of plastics, including that of the residual kind, needing to be dealt with over the next few decades.
First and foremost, Shah is an environmentalist. He believes in the mantra of ‘first – reduce, reuse and recycle and if that is not possible then go for resource recovery’. To him, there is wishful thinking in only looking sat reduce, reuse and recycle and not dealing with the reality of the situation. The reality being, how can this problematic waste by-product be disposed of with the least amount of impact on the environment if it can’t be reduced, reused or recycled?
“People talk about burning as always a bad thing, but you really need to consider the context. If you put that plastic in landfill, it might end up in the ocean and cause marine life problems. What do you do with all this residual plastic? What I am targeting are plastics that can’t be recycled and need a different approach,” Shah said.
“Overall, there is a great potential that problematic plastics, if processed through our approach, can have much reduced environmental impact. We have to look at what we can do best to damage the environment the least.”