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Researchers at UC Riverside are making significant developments in sustainability research. In a recent study, Kandis Leslie Abdul-Aziz, a UCR assistant professor of chemical and environmental engineering, and her colleagues detailed a method to convert plastic waste into a highly porous form of charcoal or char. It may be the key to reducing and reusing the hundreds of millions of tons of plastic waste produced every year that pollutes our waterways and oceans. 

The details of this are described in a new Journal of the American Chemical Society paper, “Synergistic and Antagonistic Effects of the Co-Pyrolysis of Plastics and Corn Stover to Produce Char and Activated Carbon,” published in the journal ACS Omega. The lead author is Mark Gale, a former UCR doctoral student who now serves as a lecturer at Harvey Mudd College. UCR undergraduate student Peter Nguyen is a co-author and Abdul-Aziz is the corresponding author.  

The plastic-to-char process was developed at UC Riverside’s Marlan and Rosemary Bourns College of Engineering. A mixture was formed using one of two common plastics and corn waste or corn stover, which includes leftover stalks, leaves, husks and cobs. The plastic material used was polystyrene, the plastic used for Styrofoam packaging, and polyethylene terephthalate, or PET, a material commonly used to make bottles for water and soda. This mixture was then cooked with highly compressed hot water in a process known as hydrothermal carbonization and the result was a highly porous char whose surface area was rather large with a surface area of about 400 square meters per gram of mass.

The charcoal can be repurposed for other uses such as to fertilize soil as it naturally breaks down. It could potentially be added to soil to improve soil water retention and aeration of farmlands due to how the char absorbs and retains carbon. Abdul-Aziz, however, cautioned that more research needs to be conducted before the utility of such char in agriculture can be substantiated.

The ability to make highly porous charcoal by combining plastic and plant biomass waste is an important discovery. “It could be a very useful biochar because it is a very high surface area material,” Abdul-Aziz said. “So, if we just stop at the char and not make it turn into activated carbon, I think there are a lot of useful ways that we can utilize it.” 

The study followed an earlier successful effort to make an activated charcoal made out of corn stover alone to filter pollutants from drinking water. In the follow-up study, Abdul-Aziz and her colleagues pondered if activated charcoal made from a combination of corn stover and plastic also could be an effective water treatment medium but it proved ineffective for water cleanups. She theorized that this was due to the presence of, “Residual plastic on the surface of the materials, which is preventing absorption.”

But the results of the study have been slated to have significant potential in improving sustainability. Plastic has notoriously accumulated in droves across landfills and oceans across the globe where it pollutes environments and harms the wildlife inhabitants. Plastics also break down into micro particles that can get into our bodies and damage cells or induce inflammatory and immune reactions. But alas, it costs more to recycle used plastic than it costs to make new plastic from petroleum. 

Abdul-Aziz’s laboratory has a unique approach to recycling. It is devoted to converting waste products such as plastic back into the economy by upcycling them into valuable commodities.

“I feel like we have more of an agnostic approach to plastic recycling when you can throw it in and use the char to better the soil,” she said. “That’s what we’re thinking.”