Molecular stitches for enhanced recycling of packaging

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Science  24 Feb 2017:
Vol. 355, Issue 6327, pp. 797-798
DOI: 10.1126/science.aam5803

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Polymers made of even slightly different repeat units are usually immiscible and form materials with two separate phases, like oil and water. Not only do different polymers not mix, but the interfaces between them are very sharp and mechanically weak. This lack of interfacial strength poses a very serious challenge to the recycling of blends of different polymers and, notably, polyethylene (PE) and isotactic polypropylene (iPP), the two polymers most commonly found in the industrial and domestic waste that come from packaging. If these two tough polymers are simply blended together, the resulting material is brittle and cannot be used. On page 814 of this issue, Eagan et al. (1) report that adding just 1% of a suitable block copolymer—a chain of PE connected to a chain of iPP—can create molecular stitches between the two phases and make the resulting blend as tough as iPP and PE themselves.