Collaboration between Cornell University and the University of Minnesota could change the way that the world approaches plastics recycling by creating a new additive that allows for the blending of typically incompatible materials, polyethylene (PE) and polypropylene (PP).
Geoffrey Coates, center, in his lab with James Eagan, a postdoctoral researcher in Coates’ group
and researcher Anne LaPointe. (Robert Barker/University Photography)
The two materials make up two-thirds of the world’s plastics but because of their chemical structures were not able to be repurposed together efficiently, which was a stumbling block to recycling efforts.
At Cornell, researchers added a tiny amount of tetrablock (four-block) polymer between alternating PE and PP segments to create a material that was stronger than two-block polymers that were tested in the lab.
According to an article on the Cornell website, “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.”
While there have been previous efforts to combine the two plastics, larger amounts of the polymer substance were necessary, which changed the properties of the resultant mixture. Now, with just one percent of the additive, the researchers have created a plastic alloy that boasts similar properties as the original plastic.
As an article from Ars Technica pointed out, “One weakness of the current recycling infrastructure is the reliance on separate recycling streams for different materials. This careful sorting of materials is necessary due to differences in chemical structures of polymers that make them poorly compatible.”
It concluded, “If we added this approach to the recycling streams today, we could be able to reuse significantly more plastic with enhanced efficiency.”
The research was recently published in Science. The abstract stated:
“Polyethylene (PE) and isotactic polypropylene (iPP) constitute nearly two-thirds of the world’s plastic. Despite their similar hydrocarbon makeup, the polymers are immiscible with one another. Thus, common grades of PE and iPP do not adhere or blend, creating challenges for recycling these materials.
“We synthesized PE/iPP multiblock copolymers using an isoselective alkene polymerization initiator. These polymers can weld common grades of commercial PE and iPP together, depending on the molecular weights and architecture of the block copolymers.
“Interfacial compatibilization of phase-separated PE and iPP with tetrablock copolymers enables morphological control, transforming brittle materials into mechanically tough blends.”
Learn more about this new additive in the video below: