Researchers say that a newly developed additive containing a “linker” molecule will allow otherwise unrelated plastics to be recycled together.
Plastics do not break down naturally, so until now, there has been no way to dispose of these materials in an eco-friendly way. While advances in the development of recycling streams have improved plastic waste disposal, finding uses for recycled material is easier said than done.
The existing recycling infrastructure relies on separate recycling streams for different materials. This careful sorting is required because differences in the chemical structures of polymers make them incompatible. For instance, two of the world’s most common plastics won’t mix even in their liquid phase. But recently, researchers have developed an additive that enables these polymers to be recycled together.
Materials produced from a mix of these polymers—polyethylene (PE) and isotactic polypropylene (iPP)—exhibit distinct phases; where these phases interface, the polymers adhere poorly to one another, which results in materials that are mechanically weak when compared to their individual components. Municipal waste generally has a 70/30 ratio of PE/iPP, making for a significant amount of material to separate.
The interdisciplinary team of researchers developed an additive that is comprised of a material called a block copolymer, which is connected blocks of PE and iPP. Essentially, this single polymer chain has side branches that may contain a variable number of either of the polymers. Even if the two main polymers remained separate, the block copolymer will link them together, since its side branches are compatible with both PE and iPP.
If this approach were to be added today to recycling streams, we could reuse significantly more plastic, with enhanced efficiency. Additional studies that evaluate the use of simpler random copolymers may potentially lead to developing additives that are both easier to produce and less expensive.