New Polymer Additive May Improve Plastic Recycling, Lead to New Materials

Thursday, May 25, 2017

Source: Design News

With the growing awareness that discarded plastic and the need to recycle it are becoming an overwhelming ecological problem, researchers are trying to find ways to reuse the plastic that already exists and limit the use of the material or find more eco-friendly alternatives.

To the former end, a researcher at Cornell University has led a team that’s developed a new material that solves a significant problem that’s been hindering plastic recycling.

Geoffrey Coates, a professor of chemistry and chemical biology at Cornell University, often begins discussions about plastic recycling by pointing out that a mere 2 percent of plastic is currently recycled, he said. That means nearly a third of it goes into the environment, 14 percent is used in incineration and/or energy recovery, and a significant 40 percent ends up in landfills.

These disheartening numbers about plastic recycling inspired Coates to seek better ways to recycle plastic. One of those has been through a collaboration with the University of Minnesota in which researchers developed a multiblock polymer that, when added to a mix of two of the world’s top plastics, creates a new and mechanically tough polymer that solves an existing problem.

That issue—which has plagued recycling for years--is that Polyethylene (PE) and polypropylene (PP), which account for two-thirds of the world’s plastics, have different chemical structures and historically could not be repurposed together because the technology to meld them together wasn’t available.

That could change thanks to what the Cornell-University of Minnesota team has achieved. When a small amount of the tetrablock, or fourblock, polymer created by the team was added to alternating polyethylene and polypropylene segments, the resultant material has strength superior to diblock, or two-block, polymers they tested. The results are something that many researchers have been trying for years but haven’t managed yet, they said.

To test the material, the team welded together two strips of plastic using different multi-block polymers as adhesives, then pulled them apart mechanically. The welds made with diblock polymers failed relatively quickly, but the weld made of the group’s tetrablock additive held so well that the plastic strips broke instead.

While researchers have achieved similar results before, typically they will use 10 percent of a soft material, so the result doesn’t have typical plastic properties and normally is not quite as good as the original, Coates said.

“What’s exciting about this is we can go to as low as 1 percent of our additive, and you get a plastic alloy that really has super-great properties,” he said. 
In addition to holding promise for a new type of recycled plastic from existing plastics, the new polymer also could allow for the development of a brand new class of mechanically tough polymer blends, according to the team. This will allow typical objects and containers made with plastic to be fabricated with less material, creating a more sustainable solution, researchers said.



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