When , the 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 鈥 for example, a 2-liter bottle or a take-out food container 鈥 actually gets recycled and reused in a similar way?
The answer, according to the Ellen MacArthur Foundation, is just 2 percent. Sadly, nearly a third is leaked into the environment, around 14 percent is used in incineration and/or energy recovery, and a whopping 40 percent winds up in landfills.
One of the problems: Polyethylene (PE) and polypropylene (PP), which account for two-thirds of the world鈥檚 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鈥檛 been available in the 60 years they鈥檝e both been on the market.
That could change with a discovery out of Coates鈥 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.
Their work is detailed in a paper, 鈥淐ombining polyethylene and polypropylene: Enhanced performance with PE/iPP multiblock polymers,鈥 published online Feb. 23 in Science.
James Eagan, a postdoctoral researcher in Coates鈥 group, is lead author of the paper. Other collaborators included researcher Anne LaPointe and former visiting scientist Rocco DiGirolamo.
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 鈥 with alternating polyethylene and polypropylene segments 鈥 the resultant material has strength superior to diblock (two-block) polymers they tested.
In their test, two 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鈥檚 tetrablock additive held so well that the plastic strips broke instead.
鈥淧eople have done things like this before,鈥 Coates said, 鈥渂ut they鈥檒l typically put 10 percent of a soft material, so you don鈥檛 get the nice plastic properties, you get something that鈥檚 not quite as good as the original material.鈥
鈥淲hat鈥檚 exciting about this,鈥 he said, 鈥渋s we can go to as low as 1 percent of our additive, and you get a plastic alloy that really has super-great properties.鈥
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.
鈥淚f you could make a milk jug with 30 percent less material because it鈥檚 mechanically better, think of the sustainability of that,鈥 he said. 鈥淵ou鈥檙e using less plastic, less oil, you have less stuff to recycle, you have a lighter product that uses less fossil fuel to move it.鈥
Coates is co-founder of Novomer, which uses Cornell-developed catalyst technologies to produce high-performance, cost-effective and environmentally responsible polymers and chemicals.
Financial support for the collaboration between Coates鈥 group and the group led by Frank Bates, University of Minnesota professor of chemical engineering and materials science, came from the Center for Sustainable Polymers, a National Science Foundation (NSF) Center for Chemical Innovation.
鈥淣SF believed in our idea of bringing together these pieces to be able to do science as a whole that we can鈥檛 do individually,鈥 Coates said.
This article also appears in the .
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