Researchers at the U.S. Department of Energy’s (DOE) Lawrence Berkeley National Laboratory (Berkeley Lab) have designed a recyclable plastic that can be disassembled into its constituent parts at the molecular level. The plastic can then be reassembled into a different shape, texture and color without loss of performance or quality.

The new material is called poly(diketoenamine), or PDK, and was reported in the journal Nature Chemistry.

Left to right: Peter Christensen, Kathryn Loeffler, and Brett Helms. Credit: Marilyn Chung/Berkeley LabThe researchers said that because plastics contain various additives, like dyes, fillers, or flame retardants, few can be recycled without loss in performance or aesthetics. Even the most recyclable plastic, PET – or poly(ethylene terephthalate) – is recycled at a rate of 20-30%, with the rest typically going to incinerators or landfills.

Furthermore, chemicals added to make plastics useful are tightly bound to the monomers and stay in the plastic even after it has been processed at a recycling plant.

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

Change in composition

The researchers first discovered the exciting circular property of PDK-based plastics when they applied 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, the sample’s molecular structure was analyzed with an NMR (nuclear magnetic resonance) spectroscopy instrument. The researchers found the structures retained the original monomers.

The team demonstrated that not only does acid break down PDK polymers into monomers, the process also allows the monomers to be separated from entwined additives.

PDK plastics are 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. Credit: Peter Christensen et al./Berkeley LabNext, 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.

The researchers next 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.