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Getting closer to a circular economy for plastics

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06 Sep, 2024

This post was originally published on Sustainability Matters

A new catalytic process, developed at the University of California, Berkeley, works equally well with the two dominant types of post-consumer plastic waste: polyethylene, the component of most single-use plastic bags; and polypropylene, the component of hard plastics, from microwavable dishes to luggage. It also efficiently degrades a mix of these types of plastics.

Clear plastic water bottles made of polyethylene tetraphthalate (PET), a polyester, were designed in the 1980s to be recycled this way. But the volume of polyester plastics is minuscule compared to that of polyethylene and polypropylene plastics, referred to as polyolefins.

“We have an enormous amount of polyethylene and polypropylene in everyday objects, from lunch bags to laundry soap bottles to milk jugs — so much of what’s around us is made of these polyolefins,” said John Hartwig, a UC Berkeley professor of chemistry who led the research. “What we can now do, in principle, is take those objects and bring them back to the starting monomer by chemical reactions we’ve devised that cleave the typically stable carbon–carbon bonds. By doing so, we’ve come closer than anyone to give the same kind of circularity to polyethylene and polypropylene that you have for polyesters in water bottles.”

Hartwig, together with graduate student Richard J “RJ” Conk, chemical engineer Alexis Bell, who is a UC Berkeley Professor of the Graduate School, and their colleagues, has now published the details of the catalytic process in the journal Science.

Like a string of pearls

One key advantage of the new catalysts is that they avoid the need to remove hydrogen to form a breakable carbon–carbon double bond in the polymer, which was a feature of the researchers’ earlier process to deconstruct polyethylene. Such double bonds are an Achilles heel of a polymer, in the same way that the reactive carbon–oxygen bonds in polyester or PET make the plastic easier to recycle. Polyethylene and polypropylene don’t have this Achilles heel — their long chains of single carbon bonds are very strong.

“Think of the polyolefin polymer like a string of pearls,” Hartwig said. “The locks at the end prevent them from falling out. But if you clip the string in the middle, now you can remove one pearl at a time.”

The two catalysts together turned a nearly equal mixture of polyethylene and polypropylene into propylene and isobutylene — both gases at room temperature — with an efficiency of nearly 90%. For polyethylene or polypropylene alone, the yield was even higher.

Conk added plastic additives and different types of plastics to the reaction chamber to see how the catalytic reactions were affected by contaminants. Small amounts of these impurities barely affected the conversion efficiency, but small amounts of PET and polyvinyl chloride — PVC — significantly reduced the efficiency. This may not be a problem, however, because recycling methods already separate plastics by type.

 Conk adjusts a reaction chamber in which mixed plastics are degraded into the reusable building blocks of new polymers. Image credit: Robert Sanders/UC Berkeley.

Hartwig noted that while many researchers are hoping to redesign plastics from the ground up to be easily reused, today’s hard-to-recycle plastics will be a problem for decades.

“One can argue that we should do away with all polyethylene and polypropylene and use only new circular materials. But the world’s not going to do that for decades and decades. Polyolefins are cheap, and they have good properties, so everybody uses them,” Hartwig said. “People say if we could figure out a way to make them circular, it would be a big deal, and that’s what we’ve done. One can begin to imagine a commercial plant that would do this.”

The researchers believe the process, if scaled up, could help bring about a circular economy for many throwaway plastics, thereby reducing the fossil fuels used to make new plastics.

Top image credit: iStock.com/Andreas Steidlinger

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Australasian Waste Recycling Expo debuts as ReGen at ICC

Australasian Waste Recycling Expo debuts as ReGen at ICC

Australia’s circular resource exhibitors, buyers and thought leaders are set to attend ReGen | Australia’s Circular Resource Expo, taking place on 23–24 July 2025 at ICC Sydney.

The two-day trade event, organised by Diversified Australia, marks the evolution of what was previously known as the Australasian Waste Recycling Expo, a longstanding brand dedicated to resource management and waste reduction for over 15 years.

The rebrand to ReGen reflects the expo’s expanded scope and emphasis on the circular economy, welcoming an array of innovative exhibitors, experts and emerging professionals committed to reducing waste, promoting resource efficiency and fostering sustainable markets.

“At Diversified Australia, we’re proud to produce events that drive positive industry change,” said Ali Lawes, event director for ReGen at Diversified.

“ReGen embodies our commitment to equip and empower industry leaders and practitioners in support of Australia’s ambitious 2035 targets for waste elimination, resource circulation, and pollution reduction.”

ReGen will showcase technical displays, offer vital industry insights and feature keynote addresses, panel discussions and networking opportunities.

The program aims to help attendees — from seasoned experts to newcomers — navigate their roles in creating a circular economy that keeps resources in use, minimises waste and regenerates natural systems.

As part of its evolution, ReGen will incorporate Circularity, Australia’s original circular economy conference, into its 2025 education program.

Since its launch in 2022, Circularity has served as a platform for industry practitioners to discuss Australia’s transition to a circular economy.

Now integrated into ReGen, Circularity will reach a broader audience, offering free sessions on topics such as circular product design and sustainable waste management — ensuring these critical insights remain accessible to all attendees.

For the last three years Circularity has been proudly presented by Planet Ark’s Australian Circular Economy Hub in partnership with Diversified Australia.

Planet Ark CEO Rebecca Gilling said that integrating the country’s leading circular economy event into ReGen would offer even more impactful opportunities to drive Australia’s circular transition.

“The inclusion of Circularity into ReGen is a significant step forward in promoting circular economy principles on a national scale in collaboration with the waste and recycling industry,” Gilling said.

“At Planet Ark, we are thrilled to see Circularity evolve into a broader platform, ensuring critical conversations about sustainable resource management and circular product design reach more professionals and innovators than ever before. This partnership underscores the importance of collaboration in building a circular Australia.”

The expo’s name, ReGen, represents both the regenerative practices it champions and the generational transformation required to meet sustainability goals.

ReGen invites participants to “Rethink, Redesign, Repurpose, and Renew” as they contribute to a circular and sustainable future for Australia.

For more information and to register, visit regenexpo.com.au

Image credit: iStock.com/izusek

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