Plastics are a fundamental part of modern life but managing them after use has long been a global headache – especially when it comes to mixed plastic waste.
Recycling plastics made from a single type of polymer is relatively straightforward. Collection, sorting, washing, shredding, and reprocessing can return them to usable granules.
It becomes far more complicated recycling mixed plastic waste, where different polymers are combined.
What is mixed plastic waste?
Mixed plastic waste consists of a wide range of plastic products – such as bottles, packaging, and textiles – collected from multiple waste streams. These plastics vary in colour, polymer type, and composition.
One of the largest sources is end-of-life vehicles, which generate 9.2 million tonnes of mixed plastic waste globally each year, not including waste from households, industry, or agriculture.
The complexity of mixed plastic waste makes it extremely difficult to recycle. Most facilities lack the capability to efficiently separate the various materials, and additives or fillers further complicate the process.
Plastics melt at different temperatures, and when reprocessed together, the resulting materials often have poor physical properties due to incompatibility between polymers.
Current strategies – and their limits
Several strategies have emerged to manage mixed plastic waste, each with trade-offs in terms of environmental impact, economic value, and scalability.
- Landfill and incineration remain the most common solutions but pose environmental and public health risks, including microplastics, toxic emissions, and carbon dioxide pollution.
- Physical recycling: CRDC Global has developed RESIN8, a synthetic lightweight aggregate made from mixed plastic waste, used in concrete and asphalt. While promising, the final product is still a low-value material.
- Chemical recycling: Pyrolysis can convert plastics into oil and chemicals, but the process is energy-intensive and generates large volumes of harmful gases.
More recently, researchers at Oak Ridge National Laboratory in the U.S. developed an organo-catalyst that can convert various plastic types into valuable chemicals in the lab. Its effectiveness in real-world waste streams, where plastics contain fillers and contaminants, is still uncertain.
Despite ongoing innovation, a scalable and sustainable solution to mixed plastic waste has remained elusive.
A breakthrough from Queensland
Researchers at the University of Southern Queensland (UniSQ) are working with Australia Sunlight Group (ASG), one of Queensland's largest plastic recycling companies, to develop advanced upcycling technology that transforms mixed plastic waste into graphene and green hydrogen.
Supported by the AU-UK Hydrogen Energy Partnership program, the team has successfully produced gram-scale quantities of graphene and separated pilot-scale green hydrogen in the lab.
Building on ASG's proprietary metal-based catalyst technology, UniSQ researchers Professor Pingan Song and Professor Xuesen Zeng have further enhanced the catalyst's performance.
This improved system can now convert waste plastics not just into multi-walled carbon nanotubes (MWCNT), but also into single-walled carbon nanotubes (SWNT) – a highly valuable nanomaterial often referred to as "Black Gold."
Why is SWNT so valuable?
Single-walled carbon nanotubes are among the strongest materials known, with a theoretical tensile strength of 100–200 GPa – nearly 100 times stronger than steel and about six times lighter. They also offer exceptional thermal and electrical conductivity.
High-purity SWNT sells for between $50 and $1,000 per gram, depending on quality—making it far more valuable than gold.
These properties make SWNT ideal for high-end industrial applications such as:
- Transparent heaters and antennas
- Electromagnetic interference shielding
- Advanced batteries
- Red frequency shielding
UniSQ's team can currently produce gram-scale SWNT in the lab and plans to begin pilot production within two years.
Green hydrogen is also produced during the process and can be isolated using advanced gas separation technology developed by Dr Aaron Li of the University of Melbourne, another AU-UK program partner.
The case for bold investment
While this upcycling solution has proven effective in the lab, scaling it to commercial production is costly. Pilot-scale equipment for the catalyst and SWNT production may cost several million dollars per unit.
Government support is vital to help bridge the gap between proof of concept and commercialisation. Traditional recycling methods often produce low-value plastics with limited financial return, leaving little incentive for recyclers.
If policymakers want to realise a low or zero-waste future, they must prioritise investment in next-generation recycling technologies that deliver both environmental and economic benefits.
This groundbreaking technology requires bold, sustained policy and financial support to enable Australia to lead the world in converting plastic waste into high-value resources.
