Plastics have become ubiquitous in our daily lives, but not all plastics are created equal. For example, there’s polyethylene terephthalate, which is used to make soda bottles and clothing fibers, as well as high-density polyethylene, from which shampoo bottles, milk jugs, and cutting boards are derived. Polystyrene is commonly used for packaging, while low-density polyethylene is responsible for cling wrap and grocery bags.
Despite all being considered “plastics,” these materials are chemically and physically incompatible, making them difficult to recycle or re-process into other useful products. As a result, most post-consumer plastics are collected as a mixed stream of waste and end up in landfills. Even when sorted and separated, mechanical recycling often leads to down-cycling and the creation of inferior products.
Fortunately, polymer chemists at Colorado State University have been at the forefront of efforts to address the environmental impact of plastic waste. They have recently developed innovative new chemistry that could provide a solution to the challenge of recycling mixed-use plastics.
A team comprising University Distinguished Professor Eugene Chen from the Department of Chemistry, and Columbia University professors Tomislav Rovis and Sanat Kumar (formerly a faculty member at CSU), have developed an innovative chemical approach. Their technique involves using universal dynamic crosslinkers, which are small molecules specifically designed to be introduced into mixed plastic streams. These crosslinkers have the ability to convert previously unmixable materials into a new set of polymers that can be upcycled into higher-value, re-processable materials. Their findings have been published in the prestigious journal, Nature.
By adding small amounts of dynamic crosslinkers and heating them together, the team has developed a new method of upcycling mixed plastics. The resulting material, called a multiblock copolymer, is produced in-situ and allows previously incompatible plastics to be combined without the need for deconstruction or reconstruction of the original polymers. The process has the potential to recover valuable materials and energy from post-consumer plastics that would typically end up in landfills. The team successfully tested their crosslinkers on various plastics, including mixed polyethylene Ziploc bags and polylactide cups, without any prior purification or removal of additives or dyes. The resulting multiblock copolymers could be reused multiple times, making this a promising solution to the issue of plastic waste. While cost is a key barrier, the team remains optimistic about future potential.
Source: Colorado State University