Apr 26, 2018

Scientists grapple with the world's plastic problem

Illustration of plastic bubble wrap with one bubble including the Earth.

Illustration: Rebecca Zisser/Axios

A new plastic was created that can be recycled repeatedly — the latest advance in the lab as scientists try to address the world's growing plastics problem.

The problem: Roughly 4.9 billion tons of plastic waste produced since the 1950s hasn't been recycled or burned. And, plastic production is expected to double over the next two decades.

The challenge: Plastic needs to be durable to be useful. Today, plastic bottles made of polyethylene terephthalate (PET) are largely broken down through mechanical recycling — it's separated, shredded, washed and melted. The process is labor intensive and the product is degraded plastics that are often made into lower-value secondary products that are not recycled again.

  • Via chemical recycling, PET can be "cracked" at temperatures of 500 degrees Celsius or higher to recover gases, hydrocarbon fuels and waxes that can be used elsewhere.
  • However, that process currently requires too much energy and isn't selective enough to recover the valuable monomer, chemist Jeannette Garcia from IBM Research tells Axios.
  • In Science today, Haritz Sardon and Andrew Dove write:
"This is the central paradox of the plastic problem: Although we desire our plastics to be readily recyclable or not to persist in the environment, they must also be sufficiently robust to function in their desired application."

What's new: Researchers from Colorado State University today report designing a plastic that can be recycled repeatedly without degrading the polymer and retaining its most useful properties — strength and stability.

  • They used a small amount of catalyst to convert a monomer into a polymer that has properties of common plastics. They could then convert it back to its monomer and polymerize it again. "This process can be done repeatedly to establish a circular monomer-polymer-monomer cycle," says study author Eugene Chen, a professor of chemistry at Colorado State University.  
  • It's "a great example" of where the field is headed, Garcia says. "We build plastics through the use of catalysts and chemical techniques, so it makes sense to me on a rationale level that that might be the way we take them apart."
  • The advantage of Chen's process is that it addresses the problems associated with "cracking" PET — the monomer is changed into a polymer at room temperature and the starting material can be recovered.
  • The hitch: The monomer starting product is currently too expensive to be used on an industrial scale. Chen says they need to develop new routes to make the monomer so it could be more economically competitive. "But since we can get the monomer back completely from recycling of the polymer, the economics is different from the conventional linear economy model."

Meanwhile, another team of scientists announced last week that they'd engineered an enzyme that can break PET down into its component parts that can then be used to make more plastic. It's still slow —it can digest only a few milligrams of plastic per day, The Economist points out.

The big picture: The reach and impact of plastic pollution is still being determined. In a study published earlier this week, researchers report finding 2–3 times more microplastics — pieces less than 5mm long — in ice cores from the Arctic Ocean than they had previously measured.

  • The bits of plastic are from largely from packaging materials, cigarette filters, nylon and paints.
  • They suspect the microplastics in the ice cores they studied originated in water from the Great Pacific Garbage Patch as well as from local fishing and shipping.
  • The concern is that microplastics are ingested by marine animals and eventually make their way to humans.
  • Yes, but: The Economist points out that little is known about whether plastic travels the food chain and how it affects human health.
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