Compatibilisers | additives


Returning recovered post-consumer waste plastics back into high value applications


requires technologies capable of handling immiscible resin mixtures. Peter Mapleston takes a look at the latest additive introductions


Compatibilisers recycle the mix


Plastics recycling has long been a marginal business where, even at the best of times, the profit associated with reintegrating post-industrial and, especially, post-consumer plastics back into production processes has been slim. The decline in the price of virgin polymers, particularly commodities, over the past two years or so has made this situation worse. As a consequence, cost-efficient ways of upgrading recycled plastics to put them back on a par with virgin materials are in strong demand. Fortunately, developers of additive products that compatibilise normally immisci- ble polymers, as well as producers of other perfor- mance-enhancing additives, are making significant progress. This article takes a look at some of the most recent innovations. Two of the most common polymers used in packag-


ing—polyethylene (PE) and polypropylene (PP)—are, despite their very similar chemical natures, incompat- ible with each other and cannot be easily repurposed together. Matters are made worse by the fact that mixed streams—both post-industrial and post-consumer— containing PP and PE are often difficult to separate due to the similarities in densities. But, according to Geoffrey Coates, Tisch University Professor of Chemis- try and Chemical Biology at Cornell University in the


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US, that could change very soon. He says that a group of researchers that he leads has collaborated with another group at the University of Minnesota in the US to develop a tetrablock polymer that, when added in small measure to a mix of these two otherwise incompatible polymers, creates a new and mechanically tough product. This new polymer has alternating polyethylene and polypropylene segments. The work is detailed in a paper, “Combining


polyethylene and polypropylene: Enhanced performance with PE/iPP multiblock polymers,” that was published in February in Science magazine. “We can go to as low as one percent of our additive, and you get a plastic alloy that really has super-great properties,” says Coates. Fellow researcher James Eagan adds that, not only does this tetrablock polymer show promise for improving recycling, but it could spawn a whole new class of mechanically tough polymer blends. The researchers experimented with a heterogene-


ous- grade polyolefin blend containing 70 wt% polyeth- ylene and 30 wt% PP, and assessed the consequences of adding 5 wt% tetrablock PP60


PE80 PP75 PE90 to the


mixture. Interfacial activity of the block copolymer was evidenced by a reduction in the average droplet size from 2.2 to 0.55 microns with the addition of the


June 2017 | PLASTICS RECYCLING WORLD 43


Main image: Compatibilisers are designed to enable


up-cycling of mixed post- consumer waste into high value


applications


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