From bowling balls to hip joints: Chemists create recyclable alternative to durable plastics

Known as thermosets, this type of plastic boasts a "crosslinked polymer" chemical structure that guarantees longevity but has also made these petrochemical-based materials -- which comprise 15%-20% of all polymers produced -- impossible to recycle.

"Currently, zero percent of the world's thermoset materials are recycled -- they're either incinerated or thrown in landfills," said Brett Fors, professor of chemistry and chemical biology at Cornell.

The Fors lab has addressed that environmental challenge by creating an alternative made from a bio-sourced material that has crosslinked thermosets' durability and malleability but can be easily recycled and degraded.

"The whole process, from creating to reusing, is more environmentally friendly than current materials," said Reagan Dreiling, a doctoral student in the field of chemistry and first author of the paper, which published in Nature.

The Fors group studies dihydrofuran (DHF), a monomer -- or chemical building block -- that can be made from biological materials and has the potential to eventually compete with petroleum-based feedstocks.

Dreiling used DHF, a circular monomer with a double bond, as a building block for two successive polymerizations, the second of which results in a crosslinked polymer that can be recycled through heating and will degrade naturally in the environment.

DHF thermosets show comparable properties to commercial thermosets, including high-density polyurethane (used in electronics instruments, packaging and footwear, for example) and ethylene propylene rubber (used in garden hoses and automotive weatherstripping).

In contrast to current petrochemical thermosets, the DHF-based materials offer a circular economy of use, Fors said. Chemically recyclable, the material can be made back into its building block monomer and used again from scratch. And when some of the material inevitably leaks into the environment, these materials will degrade over time into benign components.

The researchers are working toward applications, including making the DHF-based material useful for 3D printing. They are also experimenting to expand the properties with additional monomers.

"We've spent 100 years trying to make polymers that last forever, and we've realized that's not actually a good thing," Fors said. "Now we're making polymers that don't last forever, that can environmentally degrade."