Geoffrey Coates, center, in his lab with James Eagan, a postdoctoral researcher in Coates’ group and researcher Anne LaPointe. Credit: Robert Barker/University Photography
When Geoffrey Coates, Tisch University Professor of Chemistry and Chemical Biology, gives a talk about plastics and recycling, he usually opens with this question: What percentage of the 78 million tons of plastic used annually for packaging – for example, a 2-liter bottle or a take-out food container – actually gets recycled and reused in a similar way? The answer is just 2%. Sadly, nearly a third is leaked into the environment, around 14% is used in incineration and/or energy recovery, and a whopping 40% winds up in landfills.
One of the problems: Polyethylene (PE) and polypropylene (PP), 2/3 of the world’s plastics, have different chemical structures and thus cannot be repurposed together. Or, at least, an efficient technology to meld these two materials into one hasn’t been available in the 60 years they’ve both been on the market. That could change with a discovery out of Coates’ lab. He and his group have collaborated with a group from the University of Minnesota to develop a multiblock polymer that, when added in small measure to a mix of the two otherwise incompatible materials, create a new and mechanically tough polymer.
Scientists for years have tried to develop a polymer that does what Coates, LaPointe and Eagan have achieved. By adding a miniscule amount of their tetrablock (four-block) polymer – with alternating polyethylene and polypropylene segments – the resultant material has strength superior to diblock polymers.
In their test, 2 strips of plastic were welded together using different multi-block polymers as adhesives, then mechanically pulled apart. While the welds made with diblock polymers failed relatively quickly, the weld made of the group’s tetrablock additive held so well that the plastic strips broke instead.
“What’s exciting about this,” he said, “is we can go to as low as 1% of our additive, and you get a plastic alloy that really has super-great properties.” Not only does this tetrablock polymer show promise for improving recycling, Eagan said, it could spawn a whole new class of mechanically tough polymer blends.
“If you could make a milk jug with 30 percent less material because it’s mechanically better, think of the sustainability of that,” he said. “You’re using less plastic, less oil, you have less stuff to recycle, you have a lighter product that uses less fossil fuel to move it.”
Coates is co-founder of Novomer, which uses Cornell-developed catalyst technologies to produce high-performance, cost-effective and environmentally responsible polymers and chemicals.
http://www.news.cornell.edu/stories/2017/02/polymer-additive-could-revolutionize-plastics-recycling
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