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The Lego approach to plastics recycling

A team of researchers at the US Lawrence Berkeley National Laboratory has designed a recyclable plastic in the principles of Lego. A unique characteristic of the material is that it can be easily disassembled into its constituent parts at molecular level and reassembled.

The new recyclable plastic, named polydiketoenamine or PDK by researchers at Berkeley in California, can be repeatedly recreated into a different shape, texture or colour without loss of performance or quality. ‘Most plastics were never made to be recycled,’ says Peter Christensen, a postdoctoral researcher at the Molecular Foundry at the Lawrence Berkeley National Laboratory. ‘But we have discovered a new way to assemble plastics that takes recycling into consideration from a molecular perspective.’

‘Reversible bonds’

Christensen points out that the problem with many plastics is that the chemicals added to make them useful, such as fillers that make a plastic tough, or plasticisers that make a plastic flexible, are bound tightly to the monomers. This means they remain in the plastic even after it’s been processed at a recycling plant.

‘With PDKs, the immutable bonds of conventional plastics are replaced with reversible bonds that allow the plastic to be recycled more effectively,’ explains scientist Brett Helms, who led the project. Unlike conventional plastics, the monomers of PDK plastic can be recovered and freed from any compounded additives by simply exposing it to an acidic solution.

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

Critical point

‘We see an opportunity to make a difference for where there are no recycling options,’ argues Helms. That includes adhesives, phone cases, watch bands, shoes, computer cables, and hard thermosets that are created by moulding hot plastic material.

‘We’re at a critical point where we need to think about the infrastructure needed to modernise recycling facilities for future waste sorting and processing,’ Helms observes. ‘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.’

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