A new process for making plastics might help break down one of the barriers to recycling, researchers at a Colorado university say.
Plastics are formed by stringing together hydrocarbon molecules into chains with the help of a chemical catalyst. But most of them can be recycled only once or twice before the material degrades, requiring new raw materials — largely derived from petroleum. Chemicals used to make different types of plastics don’t always mix well, and ones that can be easily broken down to their component parts tend to lack the strength needed for everyday use.
But chemists at Colorado State University say they have found a way to make a plastic that can be recycled multiple times by starting from a different material.
Instead of using a common plastic precursor like ethylene, they say they’ve found a way to use a chemical called gamma-butyrolactone, or GBL. GBL is most often used as a solvent for cleaning circuit boards or stripping paint. It’s not normally used to make plastics — but by altering the structure of the molecule using a chemical catalyst, they can produce a sturdy polymer that “can be repeatedly and quantitatively recycled” back to its source material, or monomer.
“The results showed that, with judiciously designed monomer and polymer structures, it is possible to create chemically recyclable polymers that exhibit quantitative recyclability and useful materials properties,” the researchers wrote in a paper reporting the results. About 85 percent of the GBL used to produce the plastic could be recovered, they found.
The results were published April 26 in the research journal Science. In an accompanying piece, European researchers say similar studies may point the way toward “a world in which plastics at the end of their life are not considered as waste but as raw materials to generate high-value products and virgin plastics.”
“This will both incentivize recycling and encourage sustainability by reducing the requirement for new monomer feedstocks,” chemists Haritz Sardon of Spain’s University of the Basque Country and Andrew P. Dove of Britain’s University of Birmingham wrote. “Current chemical recycling processes are expensive and energetically unfavorable, and further advances in monomer and polymer development and catalyst design are required to facilitate the implementation of economically viable sustainable polymers.”
Lightweight, durable plastic is a valuable product that has revolutionized many industries. But much of it goes to make disposable packaging that ends up in landfills. A study published in 2017 found less than 10 percent of the polymers produced since 1950 have been recycled — and while that rate has improved in recent years as recycling has become more widely available, it’s still about 15 percent.
Roland Geyer, the University of California, Santa Barbara industrial ecologist who co-authored that study, told Seeker that breaking down polymers to their constituent parts is already done on a small scale, with the resulting material either used to make other plastics or to generate a liquid fuel. Current processes cost more and have a bigger environmental footprint than other processes, but may be useful for recycling textiles like polyester that can be broken down more easily chemically than mechanically.
But he said using less plastic, buying more recycled goods and making recycling easier may make a bigger impact.
“I fear that the real challenge of the plastic waste problem is behavioral rather than technical,” Geyer said. “There are plenty of great technologies already.”