American scientists have made a breakthrough that could revolutionise the plastic packaging industry, by combining previously incompatible plastics for the first time.

Polyethylene (PE) and isotactic polypropylene (iPP) currently account for two-thirds of the world's plastic waste but, because of their different chemical structures, they cannot be recycled together to make new products, thus creating huge waste management issues.

Both polymers are tough on their own but when simply blended together the resulting material is brittle and cannot be used. Technology to meld the two substances has always proved elusive to scientists, but now researchers at Cornell University and the University of Minnesota may have found the solution.

They have developed a new tetrablock (four-block) polymer - designed with alternating PE and iPP segments - that, when added to a mix of the two plastics, effectively glues them together, creating a new and mechanically tough polymer.

The breakthrough research was published in the journal Science on 23 February in a paper entitled 'Combining polyethylene and polypropylene: Enhanced performance with PE/iPP multiblock polymers'.

The research team welded together two thin film strips of plastic - one PE and one iPP - using miniscule amounts of different multi-block polymers as adhesives, which were then pulled apart.

Welds made with diblock (two-block) polymers failed but their tetrablock polymer formed such a strong weld that the plastic strips themselves broke whilst the weld stayed intact.

The breakthrough could spawn a whole new class of tough polymer blends whilst potentially revolutionising the plastics recycling industry, something that excites Geoffrey Coates, Tisch University Professor of Chemistry and Chemical Biology at Cornell University and a member of the research team.

"The overall goal was to try to find a way to make a better material from the world's number one and number two polymers, and also help recycling of these polymers that are two-thirds of our waste stream," said Coates.

"If you could make the properties better, so that you use less of them, or if could find a way to more efficiently recycle these polymers, we would have a huge impact on sustainability in a way that we don't currently have by making a new polymer.

"The dream is could you take all the world's polyethylene and polypropylene and just throw it together and melt it down and get a material that has good properties, or maybe even better than one of the materials alone.

"The big advantage of that would be, say we could make a milk jug where we use five percent less polymer because the properties are better, think of the world's savings on all that plastic."

Released by Packaging News