An event hosted by the NSW Smart Sensing Network this week in Sydney delivered a full debrief on a $1.5 million smart sensing project that will enable recycling companies to produce 100% recycled HDPE by eliminating the label adhesive contaminant that currently remains on the plastic flakes when HDPE milk bottles are recycled.
Labelmakers Group, Bega, Lactalis and Saputo are industry players involved in a collaboration with researchers from three leading universities in NSW, to bring to fruition a project that will ultimately enable recycling companies to produce 100% recycled HDPE.
Coordinated by the NSW Smart Sensing Network (NSSN) and led by PEGRAS Asia Pacific, these Australian companies will work with researchers to develop novel solutions for sensing and treating residual contaminants on recycled HDPE plastic chips.
The collaboration draws upon the research strengths of three NSSN member universities, including UNSW, the University of Sydney, and University of Technology Sydney (UTS).
What is the problem being solved?
When HDPE milk bottles are recycled, the labels (which have been hot-melt glued to the bottle) are hard to remove in the washing process and contaminate the recyclate.
As explained by Associate Prof Brian Hawkett of the University of Sydney, the key problem is to remove the labels and the glue without contaminating the whole batch with the glue. Current practice tries to dissolve the glue and wash it and the labels free. This causes the adhesive to permeate the system and have a drastic impact on the recyclability of HDPE and prevents a fully circular reuse of the material.
The current global best practice for food grade HDPE recycling enables resource reuse of about 25% of recycled content, combined with virgin HDPE that has zero glue contamination, to form a new milk bottle. Any higher and the residual glue contamination from the recycled component impacts the bottle production quality.
Figures cited for Australia put the current recycling rate for the rigid HDPE stream at about 25% and the average recycled content was estimated to be only about 2%.
The message reinforced by all speakers at the event was that improved recycling of HDPE could have a significant impact in meeting the 2025 National Packaging Targets and supporting the local recycling industry in response to the Waste Export Ban.
A complex, world-first solution
The University of Sydney University has developed a world-first (patent pending) sensing method for testing residual glue levels on recycled HDPE batches. Also under development is a mechanical separation technology – applying the physics of impact delamination – to remove the labels and glue from the HDPE surface.
As Prof Hawkett explained, "Glue content in HDPE flake after impact delamination and removal of the label is approximately 0.08% without washing."
He continued: "Presently, a washing process is still needed if we want to produce a very high quality recycled product. A washing process has been devised that forms a stable emulsion of glue at room temperature but phase separates at high temperature, allowing the glue to be skimmed off and removed, and the washing solution to be reused."
Both the impact delamination and the washing solution are the subject of a patent application.
UNSW has also made a significant contribution to the project, as explained by Associate Professor Yansong Shen. UNSW has used a supercomputer to monitor and understand the forces governing the washing process and design the laboratory tests that will be fundamental to scaling up the process.
"The washing process is the key step in separating the labels from the bottles – it should be optimised for efficient and low-cost operation," Prof Shen says, noting though that it is both expensive and risky to run real plant tests.
UNSW has applied the Digital Twin concept to model the washing reactor and run virtual laboratory experiments.
According to Prof Shen, this will enable the testing of new designs and different operational scenarios, and the development of a laboratory test rig for concept proof and model validation. This will lead to the optimal design and process parameters for the washing reactor, moving from laboratory scale concept proof to viable industry scale technology implementation, which will be tested by Labelmakers in a facility that is currently under construction.
UTS is also involved in the project. Working with industry partners, UTS will provide a very accurate and high-resolution material flow analysis for the HDPE milk bottle supply chain.
“Our approach will enable us to understand the impact of the innovation and also identify corresponding system changes that can support a closed-loop recycling solution, including technology and policy interventions,” said Dr Melita Jazbec.
Panel weighs in
Labelmakers Group technical manager Graeme Lang, who has been involved at the heart of the project, said he was delighted with the progress that had thus far been four years in the making.
He said making any serious inroads towards a truly circular economy requires improving the detection of the individual component parts and their separation.
“We need to design materials that lend themselves to separation within the existing infrastructure,” said Lang.
“It’s really advanced technology that’s going to allow us to separate materials, verify their integrity, and then allow them to be recycled. We can’t rely on humans to do this [task] with the accuracy level and at the volume that is needed.”
Lang's colleague and head of sales and marketing at Labelmakers, Jessica Walters said, "As a label manufacturer, we certainly recognise that while the label represents about 1% of the mass of the total pack, it's actually impacting 99% [of the material recovery].
"So we need to take responsibility for the waste that we've created, while also recognising that the label plays an incredibly important role for the brand, but also in communicating nutritional information to the consumer," she said.
"What Labelmakers really hopes to gain from this project is to take the technical insights that are being learned and shared and translate these into a label solution that we know is aligned to the recycling supply chain in Australia."
Bega Cheese packaging & technology director Ad van Dijk weighed in on the virtues of HDPE as a material ideal for milk bottles, and noted that the industry had already come a long way in the 'reduce' side of material consumption, by lightweighting the bottles significantly. He agreed developing a truly circular model for HDPE would be welcomed by all the dairy players involved in the project and the wider industry.
Commenting on recycling and arguing for a change in legislation that would support recyclate being classified as virgin materials where appropriate, Prof Thomas Maschmeyer of Sydney University and Gelion Technologies said, "Worldwide, not just in Australia, regulation is lagging innovation. And we hit problems in terms of having recycled materials treated as waste, [versus] recycled materials treated as virgin input into products. And there, I think the collaboration between the research sector and between industry and government is very, very important to give directions to the regulators... we want to have a well regulated society. But well regulated means also regulation that takes into account the very fast improving and evolving technology."
Where to from here?
In summary, in this industry-led project, NSSN member university researchers are tasked with developing scalable technologies that accurately sense and remove contaminants such as label adhesives from HDPE plastic chips, and to investigate the complete life cycle of such plastics.
PEGRAS Asia Pacific managing director and CEO Dr Stephanus Peters said the technology has the potential to reduce the number of milk bottles going to landfill significantly.
“When completed the technology could have applications for recycling other plastics such as coloured HDPE and PET,” Dr Peters said.
NSSN development manager Dr Don McCallum said there is a big market for recycled HDPE, but currently the product struggles on cost.
“We aim to improve the process efficiencies of HDPE recycling facilities to reduce the cost of recycled HDPE to comparable or cheaper than virgin HDPE,” said Dr McCallum.
“The sensing science will work closely with removal chemistry to get the technology out of the lab and into the industry sites.
“The outcome of this project is critically important for Australian recycling and Australian innovation."