Plastics recycling is definitely not “new science.” But current processes still don’t make it economically worthwhile because waste plastics get “down-cycled” into lower grade, less useful materials. This represents a continuing obstacle on the path to tackling the growing global pollution crisis caused by single-use plastics.

A multi-institutional team of scientists led by the U.S. Department of Energy’s Ames Laboratory has developed a first-of-its-kind catalyst that is able to process polyolefin plastics such as polyethylene and polypropylene. This type of polymer is widely used in things like plastic grocery bags, milk jugs, shampoo bottles, toys, and food containers.  The process results in uniform, high-quality components that can be used to produce fuels, solvents, and lubricating oils; those products have a high value and could potentially turn these and other used plastics into a valuable untapped resource.

The researchers hypothesized that they could borrow from nature and mimic the processes by which enzymes precisely break apart macromolecules like proteins and cellulose. The unique process relies on nanoparticle technology.

They designed a mesoporous silica nanoparticle consisting of a core of platinum with catalytic “active sites,” surrounded by long silica channels, through which the long polymer chains thread through to the catalyst. With this design, the catalyst is able to hold on to and cleave the longer polymer chains into consistent, uniform shorter pieces that have the most potential to be upcycled into new, more useful end products.

This type of controlled catalysis process has never before been designed based on inorganic materials. And the team was able to show that the catalytic process is capable of performing multiple identical deconstruction steps on the same molecule before releasing it.

Solid-state NMR measurements allowed the team to scrutinize the catalyst’s activity at the atomic scale and confirm that the long polymer chains moved readily through the catalyst channels.

The Department of Energy plans to expand and continue this research.

References
Nature Catalysis, October 12, 2020, “Catalytic upcycling of high-density polyethylene via a processive mechanism,” by Akalanka Tennakoon, et al. © 2020 Springer Nature Limited. All rights reserved.

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