New additive allows two most common plastics to be recycled together

Don't cross the streams! Two streams run through the facility in parallel, created simply by dropping the stream onto a prism-shaped divider. (credit: John Timmer)

Plastics do not readily break down naturally, so there has been no great way to dispose these materials in an environmentally friendly manner. Advances such as the development of recycling streams have improved plastic waste management, but it's not always easy to find uses for the recycled material.

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. For example, if we were to combine two of the most ubiquitous plastics in the world, they wouldn't even mix when in a liquid phase. Recently, however, an interdisciplinary team of researchers has developed an additive that enables these two polymers to be recycled together.

The plastics in question are polyethylene (PE) and isotactic polypropylene (iPP). Materials produced from a mix of these polymers exhibit two distinct phases; at the interface of the phases, the polymers adhere poorly to one another, resulting in materials that are mechanically weak compared to the individual components. General municipal waste typically has a 70/30 ratio of PE to iPP, so there's a significant amount of material to separate out.

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