Technological watch

Northwestern University researchers have used simple chemistry to address long- standing barriers associated with recycling about a quarter of today’s plastics — materials that Northwestern’s John Torkelson say hold a tremendous amount of embedded energy.
Two-step Chemistry for Sustainability
Torkelson, a professor of chemical and biological engineering and of materials science and engineering in the McCormick School of Engineering at Northwestern, will present on seven novel techniques to transform tires and other similar thermoset polymers into recyclable materials at the American Physical Society (APS) on March 14. Torkelson’s breakthrough research builds on excitement in the sustainability field and will help mitigate fires, pollution and the lost economic value associated with synthetic polymer waste.
“This is our case of looking at a class of materials that were considered hopeless in terms of recycling,” Torkelson said. “And using one- or two-step chemistry to transform them into recyclable material with full recovery of properties to see how that can really help address some major issues with regard to sustainability.”

Making Crosslinks Robust
The Torkelson research group has found several ways to create a new type of crosslink called dynamic covalent crosslinks. Such crosslinks create robust crosslinking at conditions they’re used for yet allow materials to melt at high temperatures (ie., at 280 degrees F, much hotter than a temperature a normal car tire faces). Then, when the recycled polymer is cooled again, Torkelson says crosslinks come back together just as strong, with the same properties as before.
“We’ve been able to effectively transform the thermosets into thermoplastics for recycling,” Torkelson said. “We can make crosslinks that are just as robust as regular crosslinks at use temperatures, but at high temperatures, they come apart temporarily.”

Reducing R&D Efforts
Researchers face an uphill battle when trying to address problems with entirely new materials, including trying to convince manufacturers to reinvent their literal and figurative wheel by adopting practices that may balance out years later. Torkelson’s solutions involve chemical reactions to existing materials, taking many steps — and years of development and implementation — out of the equation.
Torkelson’s presentation will highlight success in synthesizing addition-type polymers, which are used to make car tires; step-growth-type polymers, with applications including foam mattresses and insulation; and sister crosslinked polymers, made without toxic compounds so a highly viable material for recycling. Torkelson also will present a potential solution to an “Achilles’ heel” associated with reprocessible polymer networks.
Source: Northwestern University