Scientists have designed a new material system to overcome one of the biggest challenges in recycling consumer products: mixed-plastic recycling.

The achievement will help enable a much broader range of fully recyclable plastic products and brings into reach an efficient circular economy for durable goods like automobiles.

A team of scientists from Lawrence Berkeley National Laboratory are tackling the mixed-plastic challenge using 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.

Brett Helms, of the Molecular Foundry, headed up the multidisciplinary team, which also included researchers from the Joint BioEnergy Institute (JBEI) and Berkeley Lab’s Advanced Light Source, among others.

Two different PDK plastics in acidic solution, demonstrating how each polymer easily breaks down into individual monomers in different steps conducted at different temperatures, which allows for complete recycling of both plastics.

The team showed that they can create customized PDKs specifically tailored for mixed-plastic recycling and that they can fully recover the constituent plastics from a blended product composed of multiple PDKs and other common manufacturing materials.

“An example might be a shoe, where a textile is bonded to a rubber by an adhesive,” told Brett Helms. “Conventional materials used in such products can’t be recycled for reuse, since they can’t be deconstructed independently. Yet, if they were made from different, specially designed PDK polymers, then they could be for the first time.”

For this work, the researchers started by making a variety of PDKs with slightly different chemical structures and showed that each could be “depolymerized” or broken down to its respective monomers with high yields of recovery. This is essentially the process of plastic recycling, as those recovered monomers can then be used to create a new batch of PDK.

The team found that each PDK depolymerized at a different temperature and rate. To better understand those properties, they used theoretical calculations and computational models (density functional theory) to simulate the different polymers and explore how they form and depolymerize.

Using those theoretical insights, the team identified the best PDK molecules for the job and further optimized their design.

With those optimized molecules, 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 colors, 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 – PP and 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.

In a final demonstration of their approach, the researchers constructed an object from a mix of different PDKs along with glass and stainless steel, to simulate the challenges of automobile recycling, 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 people approach the manufacture of durable goods, enabling a circular economy in which products are designed to be fully recovered and reused.

Scientists have designed a new material system to overcome one of the biggest challenges in recycling consumer products: mixed-plastic recycling.

The achievement will help enable a much broader range of fully recyclable plastic products and brings into reach an efficient circular economy for durable goods like automobiles.

A team of scientists from Lawrence Berkeley National Laboratory are tackling the mixed-plastic challenge using 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.

Brett Helms, of the Molecular Foundry, headed up the multidisciplinary team, which also included researchers from the Joint BioEnergy Institute (JBEI) and Berkeley Lab’s Advanced Light Source, among others.

Two different PDK plastics in acidic solution, demonstrating how each polymer easily breaks down into individual monomers in different steps conducted at different temperatures, which allows for complete recycling of both plastics.

The team showed that they can create customized PDKs specifically tailored for mixed-plastic recycling and that they can fully recover the constituent plastics from a blended product composed of multiple PDKs and other common manufacturing materials.

“An example might be a shoe, where a textile is bonded to a rubber by an adhesive,” told Brett Helms. “Conventional materials used in such products can’t be recycled for reuse, since they can’t be deconstructed independently. Yet, if they were made from different, specially designed PDK polymers, then they could be for the first time.”

For this work, the researchers started by making a variety of PDKs with slightly different chemical structures and showed that each could be “depolymerized” or broken down to its respective monomers with high yields of recovery. This is essentially the process of plastic recycling, as those recovered monomers can then be used to create a new batch of PDK.

The team found that each PDK depolymerized at a different temperature and rate. To better understand those properties, they used theoretical calculations and computational models (density functional theory) to simulate the different polymers and explore how they form and depolymerize.

Using those theoretical insights, the team identified the best PDK molecules for the job and further optimized their design.

With those optimized molecules, 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 colors, 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 – PP and 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.

In a final demonstration of their approach, the researchers constructed an object from a mix of different PDKs along with glass and stainless steel, to simulate the challenges of automobile recycling, 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 people approach the manufacture of durable goods, enabling a circular economy in which products are designed to be fully recovered and reused.