NJIT Chemist Leads Effort to Help Create the Circular Plastic Economy of the Future

Less than 13% of our plastic waste is truly recycled today, with most consumer plastics either downcycled into lower-quality products or joining the billions of tons discarded in landfills and oceans each year. But what if our plastics could be endlessly recycled, like aluminum?

As Director of NJIT's Polymer Laboratory for the Advancement of Sustainable Technology and Innovative Chemical Synthesis (PLASTICS), Trevor Del Castillo aims to do just that.

His lab is developing new plastics with potential to be chemically recycled back into virgin plastic at the end of their life. The prospect, he says, could transform the industry's environmental impact and economics of plastic recycling. Of the 400 megatons of plastic produced globally, only about .1% is chemically recycled.

"We use plastic a lot and we aren't great at dealing with it once we're done, mainly because we've made it too good. The same chemistry that makes plastic so durable and useful to us also makes it persist in the environment for centuries," explained Del Castillo, an assistant professor of chemistry. "We want to make plastics that can be converted back into their molecular building blocks, or monomers, like turning stale bread back into flour.

"I envision plastics of the future that are so recyclable that plants will pay you for them."

To do this, Del Castillo's lab is turning to a chemical process called ring-opening polymerization (ROP).

He says that unlike traditional processes for making consumer plastics, which involve extracting small carbon-based molecules from crude oil or natural gas and chemically linking them together in a long chain under heat (a process called polymerization), the ROP process also allows plastics to be broken back down into pristine monomers (or depolymerization) to make virgin plastic.

"Most plastics are made from very reactive monomers like ethylene that can be polymerized to form a long chain of polyethylene with much more stable chemical bonds. The problem is it's like rolling a boulder downhill - easy to do, but it requires an incredible amount of energy to roll back up so it's often not feasible to reverse these bonds," explained Del Castillo.

"Ring-opening polymerization is different. It's like making a paper clip chain - you break rings to form a chain, and you can also break the chain back into rings. The same amount of energy is used either way, so we may be able to use this process and get back to the starting material."

The method has already been used to create bioplastics such as polylactic acid and polycaprolactone, used in food packaging and biomedical applications like stents or dentures. However, Del Castillo's lab has a more challenging target - polyurethanes, a durable class of plastics used in everything from mattresses to car seats and insulation.

"One of the nice things about polyurethanes is that they have carbonate linkages that engage in hydrogen bonding, giving them strength and flexibility. … It would be great to be able to recycle worn-out mattresses or car seats into brand new polyurethane products," Del Castillo explains. "We're leveraging recent innovations in forming carbamate bonds to produce suitable monomers, and exploring the development of catalysts and chemical modifications to increase the carbamate bond's reactivity.

"If we can find ways to break and reform these bonds with our approach, we could make polyurethanes that are not only useful but also infinitely recyclable."

Del Castillo's lab also sees potential for future collaborations with government agencies like the New Jersey Department of Environmental Protection to accelerate the development of chemically recyclable plastics.

"Such collaborations would be key to understanding the scalability and environmental safety of these new plastics. However, these materials could have great value," Del Castillo says. "It would be cheaper to make new plastics from old plastic rather than from petroleum feedstocks. That economic incentive could finally make plastic recycling worthwhile, helping us shift towards a circular economy where plastic is endlessly cycled back into new products."