One of the largest barriers to plastic recycling is proper separation by type. If you're trying to recycle polyethylene or polypropylene, and you throw some PVC into the mix, it contaminates the batch and makes the whole thing unrecyclable. In countries with disciplined consumers, like South Korea or Japan, you'll see recycling bins asking consumers to separate their recyclables by category; in the standout Japanese town of Kamikatsu, residents sort their garbage into no less than 45 different categories.

Research chemists at Northwestern University are working on a plastic recycling system that does not require sorting. They've discovered "a new, inexpensive nickel-based catalyst that selectively breaks down polyolefin plastics consisting of polyethylenes and polypropylenes — the single-use kind that dominates nearly two-thirds of global plastic consumption. This means industrial users could apply the catalyst to large volumes of unsorted polyolefin waste." Even better, the catalyst is unfazed by PVC, and can break down PVC-contaminated polyolefin.*

"One of the biggest hurdles in plastic recycling has always been the necessity of meticulously sorting plastic waste by type," said Northwestern's Tobin Marks, the study's senior author. "Our new catalyst could bypass this costly and labor-intensive step for common polyolefin plastics, making recycling more efficient, practical and economically viable than current strategies."

"When people think of plastic, they likely are thinking about polyolefins," said Northwestern's Yosi Kratish, a co-corresponding author on the paper. "Basically, almost everything in your refrigerator is polyolefin based — squeeze bottles for condiments and salad dressings, milk jugs, plastic wrap, trash bags, disposable utensils, juice cartons and much more. These plastics have a very short lifetime, so they are mostly single-use. If we don't have an efficient way to recycle them, then they end up in landfills and in the environment, where they linger for decades before degrading into harmful microplastics."

Polyolefin's recycling rates are an abysmal 1% to 10% worldwide, largely because the material is so laborious to separate. If the Northwestern researchers can scale up their process, that could change this equation entirely.

*Explaining PVC contamination: Typically when catalysts are used to break down plastic, and they run into PVC, the PVC starts to decompose and releases hydrogen chloride gas. This gas is corrosive and deactivates the catalyst, halting the recycling process.

In contrast, the catalyst used by the NW researchers actually increases its performance when it runs into PVC.