Reversible Plastic Developed That Can Be Repeatedly Recycled

Researchers at the US Department of Energy’s Lawrence Berkeley National Laboratory have developed a new kind of plastic that they say will allow for endless recycling of plastic that often ends up in a landfill or worse.

Endlessly Recyclable Plastic

Plastic is a remarkable material whose versatility and durability is its greatest strength, but also the environment’s worst nightmare. Billions of tons of plastic are produced each year, and much of it ends up in landfills.

As it turns out, plastics that should be recycled can’t be because of certain chemical qualities that the material has taken on because of additives, reducing the effectiveness of global recycling efforts. The most recyclable form of plastic, polyethylene terephthalate, is only recycled at a rate between 20 to 30 percent, with the rest going into landfills or incinerators.

Depolymerized Plastics
Source: Peter Christensen | Brett Evans | Angelique Scheuermann | Kathryn Loeffler/ Berkeley Lab

Now, scientists at the Lawrence Berkeley National Laboratory (Berkeley Lab) have developed a form of plastic that can be molecularly disassembled and reassembled to eliminate the chemically bonded additives that prevent these materials from being recycled, all without the loss of quality or performance that makes plastic such an in-demand material.

“Most plastics were never made to be recycled,” said Peter Christensen, a postdoctoral researcher at Berkeley Lab’s Molecular Foundry and lead author of the study. “But we have discovered a new way to assemble plastics that takes recycling into consideration from a molecular perspective.”

Christensen was joined by Berkeley Lab staff scientist Brett Helms, who led the research effort, and undergraduate researchers Angelique Scheuermann and Kathryn Loeffler (no relation) in publishing the new study last month in the journal Nature Chemistry.

All plastics are made up of different monomers that bond with different chemicals to take on unique properties, such as additives that strengthen the plastic to make it tough and sturdy or others that make the plastic more pliable and stretchy. The problem is when these additives bond with the monomers, they become all but inseparable so that when the plastic is shredded into pieces and mixed with other types of plastic and then melted, there is no way to know which characteristic the recycled plastic will inherit from the component materials. While plastics could be sorted by the different type of plastic used, this is impractical given the enormous amount of plastic produced every year.

“Circular plastics and plastics upcycling are grand challenges,” said Helms. “We’ve already seen the impact of plastic waste leaking into our aquatic ecosystems, and this trend is likely to be exacerbated by the increasing amounts of plastics being manufactured and the downstream pressure it places on our municipal recycling infrastructure.”

Closed Loop Plastics
Source: Peter Christensen | Brett Evans | Angelique Scheuermann | Kathryn Loeffler/ Berkeley Lab

What the Berkeley Lab researchers did was create a new kind of plastic called polydiketoenamine (PDK) that takes the bonds that monomers make with additives and makes them reversible. This means that when it comes time to recycle the plastic, the monomers and the additives are chemically separated using an acidic solution, leaving the monomers free to bond with different additives to make different kinds of plastics.

“We’re interested in the chemistry that redirects plastic lifecycles from linear to circular,” said Helms. “We see an opportunity to make a difference for where there are no recycling options.”

Source: Interesting Engineering