New plastic that could be fully recycled created

Scientists say they have created a next-generation plastic that can be fully recycled into new materials of any colour, shape, or form, without loss of performance or quality.

As plastics contain various additives, like dyes, fillers, or flame retardants, very few plastics can be recycled without loss in performance or aesthetics, said researchers at the US Department of Energy's (DOE) Lawrence Berkeley National Laboratory (Berkeley Lab).

Even the most recyclable plastic, PET -- or polyethylene terephthalate -- is only recycled at a rate of 20-30 per cent, with the rest typically going to incinerators or landfills, where the carbon-rich material takes centuries to decompose.

 

Now, a team of researchers at Berkeley Lab has designed a recyclable plastic that, like a Lego playset, can be disassembled into its constituent parts at the molecular level.

Described in the journal Nature Chemistry, the plastic, called poly diketoenamine, or PDK, can be reassembled into a different shape, texture, and colour again and again without loss of performance or quality.

"Most plastics were never made to be recycled," said Peter Christensen, a postdoctoral researcher at Berkeley Lab.

"But we have discovered a new way to assemble plastics that takes recycling into consideration from a molecular perspective," Christensen said.

All plastics, from water bottles to automobile parts, are made up of large molecules called polymers, which are composed of repeating units of shorter carbon-containing compounds called monomers.

According to the researchers, 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 tightly bound to the monomers and stay in the plastic even after it is been processed at a recycling plant.

During processing at such plants, plastics with different chemical compositions -- hard plastics, stretchy plastics, clear plastics, candy-coloured plastics -- are mixed together and ground into bits.

When that hodgepodge of chopped-up plastics is melted to make a new material, it is hard to predict which properties it will inherit from the original plastics.

"With PDKs, the immutable bonds of conventional plastics are replaced with reversible bonds that allow the plastic to be recycled more effectively," said Brett Helms, from Berkeley Lab, who led the study.

Unlike conventional plastics, the monomers of PDK plastic could be recovered and freed from any compounded additives simply 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.

After testing various formulations, the researchers demonstrated that not only does acid break down PDK polymers into monomers, but the process also allows the monomers to be separated from entwined additives.