Plastics account for the lion’s share of marine waste, and we only recycle a fraction of it in Australia. But a new recycling technique could transform how households dispose of “scrunchable” plastics.
We’re in the midst of a plastic pollution crisis, with plastics expected to outnumber fish in the ocean in just over a quarter of a century.
Australians consume a sizable amount of plastic, including 70 billion pieces of soft or “scrunchable” plastic, such as food wrappers, each year, with only 13 per cent of plastics actually recycled.
As our oceans choke on plastic, use is increasing – and is expected to double by 2040.
But a team of researchers from the University of New South Wales led by Dr Vipul Agarwal and Professor Per Zetterlund are on the way to cracking the plastic recycling problem.
Outdated processes
Mechanical recycling of plastics such as polyethylene terephthalate (PET) is a multi-step process that entails sorting and cleaning of waste, followed by grinding and extrusion.
But “cleaning” plastics is a mission in and of itself, including removal of:
- Food or product waste remaining in the packaging, such as oil or shampoo
- Additives added during the processing of plastics to get the desired properties, such as durability
- Contamination from different plastics
“There are also underlying polymers in layering,” Agarwal said. “For example, a PET product might have a polyethylene lining, which will need to be removed so the PET can be recycled properly.”
Next, plastics are subjected to high temperatures to melt the polymers so they can be reused – a highly energy-intensive process.
“Then there are other methods applied to degrade or change the polymer into a monomer, then make it a polymer again,” he said.
Mechanical recycling is also restrictive, with a “pure source” required at the outset.
“For example, you can only mechanically recycle PET, not a mixture of PET, recycling polypropylene, polyethylene or PVC,” Agarwal explained.
Aqueous dispersion for the win
Through a patented polymer-to-polymer process, Agarwal and Zetterlund have converted waste plastic into an aqueous dispersion of plastic polymer nanoparticles.
“They are not “microplastics” or “nanoplastics”, they are nanoparticles dispersed in water,” Agarwal said. “That material can either be used directly or dry powder can be made … which can then be used to make new products.”
There is no need for extensive cleaning either, including removing contaminants for other plastics.
“For example, if you want to recycle PET, it can have some level of contamination from polyethylene or polypropylene,” he said.
“Our process is intrinsically able to sort that out in situ, during the recycling step. Dyes can be removed using this recycling technology.”
As the process doesn’t require polymers to be transformed, their intrinsic nature should remain intact during the recycling process – which can’t be achieved with existing recycling methods.
“We can cater to a mixed source and still recover almost entirely one polymer type at a time,” Agarwal added.
Closing the loop
Once extracted, pellets or powder can be produced from the aqueous dispersion of nanoparticles to make new plastic materials, including coatings.
When transformed into a powder, the nanoparticles can be extruded to make films and materials such as bottles or panels.
One application currently being explored is increasing the strength of concrete and asphalt through incorporating recycled plastic nanoparticles.
While waste plastics are currently used as partial aggregate replacements or mixture modifiers, the high temperature required to melt the plastic generates toxic gases.
This is a step not required through the team’s aqueous dispersion process. Nor does it produce any additional waste, generating 99 per cent yield to date, Agarwal said.
“If we put one g through the process, we get almost one g at the end,” he said. “So no intrinsic waste is being generated from the source material, meaning we can virtually recycle all of it.”
But, rather than upcycling, the ultimate goal for the team is to close the loop. Currently, there’s a limit to the number of times plastics can be recycled, which is something the team is trying to remedy.
“Every time you extrude a plastic, the polymer chains typically become shorter and shorter to the point that the plastic doesn’t retain its intrinsic properties,” Agarwal said. “We’re aiming to retain the properties of these polymer chains, so we can recycle plastics a number of times.”
By both eliminating waste generation and increasing the number of times the same plastic can be recycled, the environmental benefits are expected to be enormous.
“Through our process, we are not generating any carbon dioxide, and we are also reducing the need for crude oil-based virgin plastic,” he said.
With the CSIRO estimating Australia is missing out on an estimated $419 million of economic value each year by not recovering all PET and high-density polyethylene (HDPE) materials, creating “almost virgin-like” material should prove to be particularly lucrative.
A commercial winner
So far, the prospects for the technology are looking healthy, with the initial patent for the PET-aspect of the research licensed to FP Paradigm’s commercial arm, Paco Industries.
“In collaboration with PACO Industries, we are leading a research contract to commercialise PET recycling in Australia,” Agarwal said.
Two companies have successfully been brought on board – biscuit giant Arnott’s and coffee roaster Pablo & Rusty’s – which have both made sustainability a focus.
In collaboration with FP Paradigm and Paco Industries, the UNSW team made PET sheets from extruded recycled material in combination with virgin PET.
“Now, we are trying to come up with a way to make products out of it that can be used by our industry partners,” Agarwal said.
They also have their sights set on conquering polyethylene, which they have been able to recycle through the process.
“In plastic recycling, soft plastic is the holy grail – because it doesn’t get recycled,” he said. “We’re trying to prove we can recycle it at a larger scale in house before we look for partners and consider commercialising the technology,” he said.
From there, the team hopes to move soft plastics from the red to the yellow bin indefinitely.
“Eventually, we’d like to convince the government to change the legislation so soft plastics can go in the yellow bin and we can recycle them using our technology.”