Chemistry, Materials & Packaging
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Breakthrough Innovations Forging Next-Gen Plastic Recycling Solutions

Unilever pioneers solution that enables recycling of black plastic

Image credit: The Drum

Unilever UK has pioneered the use of a new, detectable black pigment for its High Density Polyethelyne (HDPE) bottles for its TRESemmé and Lynx brands, so they can be detected by recycling plant scanners and sorted for recycling. This means that roughly 2,500 more tonnes of plastic bottles can now potentially be sorted and sent for recycling each year — equivalent to the weight of 200 London buses, or 1,250 family-sized cars.

To date, standard black plastic — commonly used as trays for microwaveable, prepared meals; as well as bottles and other containers — goes undetected by the automatic, optical sorting machines in recycling plants because they use near infra-red light, which is absorbed by the ‘carbon black’ pigment traditionally used to color them. This effectively makes them invisible to the sorter and leads to them being rejected and sent for waste.

Through extensive trials — in partnership with RECOUP and waste management partners Veolia, SUEZ, Viridor and TOMRA — Unilever has proven that this new pigment can be technically detected within their material recycling facilities in the UK. The company says it will share the knowledge and expertise from developing this technical solution for detectable black bottles with others in the industry, as well as to other markets globally, to enable wide use of this technology and approach.

“We have deployed an innovative solution within the software and invested in our sorting technology at our flagship recycling facility in Southwark, and this — together with Unilever modifying the pigment in the black dye for their HDPE packaging — enables it to be successfully detected. If all recyclers and manufacturers follow this, black plastic becomes detectable black,” explains Richard Kirkman, Chief Technology and Innovation Officer at Veolia UK & Ireland. “Adjusting the detection mechanism in this way — with both technology and packaging modified — was the key. It’s the first time a hi-tech solution like this has been applied to black plastics and can be rolled out at scale — a eureka moment for recycling and a rallying call for similar partnerships to take shape. This is exactly the kind of thing the [UK] Plastics Pact was set up for, and it’s inspiring a generation of engineers.

“Recycling is a chain of events from manufacturer, consumer to recycler and we need each part of the chain to make changes to have successful, scalable results."

Unilever’s solution will enable TRESemmé and Lynx bottles to be detected by recycling scanners, with minor adjustments at the material recycling facilities, so they can be technically separated, sorted and sent for recycling, becoming a useful resource rather than ending up as waste.

The new detectable bottles will be phased in this year and will allow Unilever to further ‘close the loop’ and include the recycled black plastic in new packaging. In 2019, TRESemmé and Lynx will both introduce a minimum of 30 percent recycled material into their packs — one step closer to Unilever’s goal of ensuring all of its plastic packaging is reusable, recyclable or compostable by 2025, as well as increasing use of recycled plastic content in its packaging.

This move to using the new detectable black plastic is part of Unilever UK’s commitment to the UK Plastics Pact and its new #GetPlasticWise campaign, a Five-Point Plastic Plan that aims to tackle plastic waste in the UK; and move towards a closed loop — where plastic stays within the plastic economy, not the environment.

“Tackling plastic waste is complex and involves collaboration across the supply chain,” said Helen Bird, Strategic Engagement Manager at WRAP, which manages The UK Plastics Pact. “We welcome this move by Unilever and steps taken by waste management companies to trial the sorting of the packaging. We now call for wide scale adoption of detectable black pigments by brands and retailers, and the sorting and reprocessing of that packaging by the recycling sector.”

In addition to helping to achieve its 2025 goals around packaging, Unilever’s Five-Point Plan sees the company collaborating with partners on solutions, while supporting and educating consumers on how they can reduce plastic consumption.

Sebastian Munden, General Manager of Unilever UKI, said: “We’ve been working on a solution for black plastic for some time, and this move to using detectable black plastic in our TRESemmé and Lynx bottles means we will potentially be removing around 2,500 tonnes of plastic from the waste stream. We’re proud our innovation will help us towards achieving our [2025 goal], as well as making a significant contribution towards the UK Plastics Pact targets. We’d like to thank our industry partners for their part in working with us to make this possible.”

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Berkeley Lab breakthrough recycles plastic from the inside out

Image credit: Berkeley Lab

Meanwhile, even the most recyclable plastic, PET, is only recycled at a rate of 20-30 percent, with the rest typically going to incinerators or landfills, where the carbon-rich material takes centuries to decompose.

But a team of researchers at the US Department of Energy’s (DOE) Lawrence Berkeley National Laboratory (Berkeley Lab) has just designed a recyclable plastic that, like a Lego playset, can be disassembled into its constituent parts at the molecular level, and then reassembled into different shapes, textures and colors, again and again, without loss of performance or quality. The new material, called poly(diketoenamine), or PDK, was discussed in the journal Nature Chemistry.

“Most plastics were never made to be recycled,” said lead author Peter Christensen, a postdoctoral researcher at Berkeley Lab’s Molecular Foundry. “But we have discovered a new way to assemble plastics that takes recycling into consideration from a molecular perspective.”

Christensen was part of a multidisciplinary team led by Brett Helms, a staff scientist at the Molecular Foundry; along with Angelique Scheuermann (then of UC Berkeley) and Kathryn Loeffler (then of the University of Texas at Austin), who were undergraduate researchers at the time of the study.

All plastics, from water bottles to automobile parts, are made up of large molecules called polymers, which are composed of repeating units of shorter carbon-containing compounds called monomers According to the researchers, the problem with many plastics is that additives — such as fillers that make a plastic tough, or plasticizers that make a plastic flexible — are tightly bound to the monomers and stay in the plastic even after it’s been processed at a recycling plant.

During processing at such plants, plastics with different chemical compositions — such as hard, stretchy, clear or candy-colored plastics — are mixed together and ground into bits. When that hodgepodge of plastic bits is melted to make a new material, it’s hard to predict which properties it will inherit from the original plastics.

This unpredictability has prevented plastic from becoming what many consider the Holy Grail of recycling: a “circular” material, whose original monomers can be recovered for reuse for as long as possible, or “upcycled” to make a new, higher-quality product.

So, for example — when a reusable shopping bag made from recycled plastic gets threadbare with wear and tear, it can’t be upcycled or even recycled to make a new product. And once the bag has reached its end of life, it’s either incinerated to make heat, electricity or fuel, or ends up in a landfill, Helms said.

“Circular plastics and plastics upcycling are grand challenges,” he said. “We’ve already seen the impact of plastic waste leaking into our aquatic ecosystems, and this trend is likely to be exacerbated by the increasing amounts of plastics being manufactured and the downstream pressure it places on our municipal recycling infrastructure.”

Recycling plastic one monomer at a time

The researchers want to divert plastics from landfills and the oceans by incentivizing the recovery and reuse of plastics, which could be possible with polymers formed from PDKs.

“With PDKs, the immutable bonds of conventional plastics are replaced with reversible bonds that allow the plastic to be recycled more effectively,” Helms said.

Unlike conventional plastics, the monomers of PDK plastic could be recovered and freed from any compounded additives simply by dunking the material in a highly acidic solution. The acid helps to break the bonds between the monomers and separate them from any chemical additives.

“We’re interested in the chemistry that redirects plastic lifecycles from linear to circular,” Helms said. “We see an opportunity to make a difference for where there are no recycling options.” That includes adhesives, phone cases, watch bands, shoes, computer cables, and hard thermosets that are created by molding hot plastic material.

The researchers first discovered the exciting circular property of PDK-based plastics when Christensen was applying various acids to glassware used to make PDK adhesives, and noticed that the adhesive’s composition had changed. Curious as to how the adhesive might have been transformed, Christensen analyzed the sample’s molecular structure with an NMR (nuclear magnetic resonance) spectroscopy instrument. “To our surprise, they were the original monomers,” Helms said.

After testing various formulations at the Molecular Foundry, they demonstrated that not only does acid break down PDK polymers into monomers, but the process also allows the monomers to be separated from entwined additives. Next, they proved that the recovered PDK monomers can be remade into polymers, and those recycled polymers can form new plastic materials without inheriting the color or other features of the original material — so if that broken black watchband is made with PDK plastic, it could find new life as a computer keyboard; or it could be upcycled by adding additional features, such as flexibility.

Moving toward a circular plastic future

The researchers believe that their new recyclable plastic could be a good alternative to many nonrecyclable plastics in use today.

“We’re at a critical point, where we need to think about the infrastructure needed to modernize recycling facilities for future waste sorting and processing,” Helms said. “If these facilities were designed to recycle or upcycle PDK and related plastics, then we would be able to more effectively divert plastic from landfills and the oceans. This is an exciting time to start thinking about how to design both materials and recycling facilities to enable circular plastics."

The researchers say they plan to develop PDK plastics with a wide range of thermal and mechanical properties for applications as diverse as textiles, 3D printing and foams. In addition, they are looking to expand the formulations by incorporating plant-based materials and other sustainable sources.

The Molecular Foundry is a DOE Office of Science User Facility that specializes in nanoscale science. This work was supported by the DOE’s Laboratory Directed Research and Development (LDRD) program.