A team of scientists from Lawrence Berkeley National Laboratory (Berkeley Lab), USA,  are tackling the mixed-plastic challenge using a custom-designed material called polydiketoenamine (PDK), a new type of plastic they developed to be recycled efficiently and indefinitely, providing a low-carbon manufacturing solution for plastic products that never have to end up in a landfill.

The researchers demonstrated the success of their material system by creating blended plastics, each made from two different PDKs, and then completely depolymerizing and recovering the constituent materials. They repeated the demonstration with PDKs of different colours, addressing a particular industry challenge, and showed that with a slightly more complex process they could once again recover the PDK monomers with high yields.

The team also showed how PDK can be used to make recyclable, flexible plastic packaging out of conventional plastics. They formed a multilayer film from common plastics – polypropylene (PP) and polyethylene terephthalate (PET) – using a “tie layer” of PDK to bond them together. Normally the PP and PET couldn’t be extracted from a multilayer material, but here the researchers leveraged their control over the PDK layer to separate and recover the PP and PET films as well.

They also constructed an object from a mix of different PDKs along with glass and stainless steel, to simulate the challenges of recycling in the vehicle industry, and went through the recycling process again, demonstrating high-yield recovery of the PDK monomers as well as the glass and metal.

These results could lead to a meaningful shift in how we approach the manufacture of durable goods, enabling a circular economy in which products are designed to be fully recovered and reused.

Brett Helms, of Berkeley Lab’s Molecular Foundry, explained:

“Complex consumer products are simply not recycled today; they are either incinerated, landfilled, or downcycled.

“Here we’ve laid the groundwork for how to recycle such products back to their original monomer building blocks, in stride facilitating the recovery of materials bound to them for reuse, including valuable metals or glass. In this way, PDK materials bring more circularity to manufacturing with intrinsically low carbon intensity.”

Click on this link to access the research paper: Circularity in mixed-plastic chemical recycling enabled by variable rates of polydiketoenamine hydrolysis

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