Researchers have developed a multiblock polymer that, when added in small amounts to a mix of the two otherwise incompatible polyolefins, creates a mechanically tough blend.
The researchers added a miniscule amount of their tetrablock (four-block) polymer to alternating segments of polyethylene (PE) and polypropylene (PP)—two incompatible plastics—creating a blend that reportedly has superior strength to the two-block polymers.
The discovery may hold significant benefit to the age-old challenge of recycling plastics, at least PE and PP, which account for two-thirds of the world’s plastics. Because each has a different chemical structure, neither can be repurposed together, until now.
Geoffrey Coates, a professor of chemistry and chemical biology at Cornell University, and his team collaborated with a group from the University of Minnesota to develop the multiblock polymer.
A BOON TO PLASTICS AND RECYCLING?
When Coates discuss plastics and recycling, he often begins with a 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 is recycled and reused in a similar way?
The answer? Just 2%, according to the Ellen MacArthur Foundation, which works with business, government and academia to build a circular economy that is restorative and regenerative by design.
About a third of that nearly 80 million tons of plastic is leaked into the environment, about 14% is used in incineration and/or energy recovery, and a whopping 40% ends up in landfills.
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’s tetrablock additive held so well that the plastic strips broke instead.
“People have done things like this before,” he says. "But they’ll typically put in 10% of a soft material, so you don’t get the nice plastic properties, you get something that’s not quite as good as the original material. What’s exciting about this is we can go to as low as 1% of our additive, and you get a plastic alloy that really has super-great properties.”
A NEW CLASS OF POLYMER BLENDS
The tetrablock polymer hints at more than just improving recycling, says James Eagan, a postdoctoral researcher in Coates’ group and lead author of the paper about the discovery. A whole new class of mechanically tough polymer blends could be in the offing.
"If you could make a milk jug with 30% less material because it’s mechanically better, think of the sustainability of that,” Eagan says. “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.
Study results were published in Science.
BCC Research's Engineering Resins, Polymer Alloys and Blends anticipates the global engineering resin and polymer alloy/blend market to total over 27.9 billion pounds and nearly 36.9 billion pounds in 2017 and 2022, respectively, demonstrating 5.7% CAGR.
