Polyethylene happens to be one of the most commonly used plastics in today’s world. It also shares a strikingly similar chemical structure with the primary fatty acid in soap.
At Virginia Tech, a breakthrough has emerged, revealing a long-sought method to transform polyethylene into this soap-like compound, opening the door to innovative upcycling possibilities.
This transformative compound, referred to as a surfactant, is now recognized as a potent means to repurpose polyethene plastics into valuable products, such as soap and detergents.
The brain behind this ingenious concept happens to be Guoliang Liu, a researcher at Virginia Tech. He believed that there was probably a way to divide the long polyethylene chains into shorter, but not too short, fatty acid chains that could possibly be used to make soap.
He also felt that there was potential for a new upcycling approach that could elevate plastic waste into high-value, practical commodities.
After thinking about this for quite some time, Liu experienced a moment of inspiration during a rather cold and wintery night sitting by the fireplace. While watching the smoke rise from the burning wood, he also thought about how the smoke was made up of tiny particles generated during the wood’s combustion.
While plastics should never be burned in a fireplace, for both environmental and safety reasons, he also began to wonder what would happen if polyethene was burned in a safe laboratory setting. Would it also yield a form of “smoke” that was the same as that produced when burning wood? And if someone managed to capture that smoke, what exactly would it be made of?
Liu explained, “Firewood is mostly made of polymers such as cellulose. The combustion of firewood breaks these polymers into short chains, and then into small gaseous molecules before full oxidation to carbon dioxide.”
“If we similarly break down the synthetic polyethene molecules but stop the process before they break all the way down to small gaseous molecules, then we should obtain short-chain, polyethene-like molecules,” he added.
With the help of two other Ph.D. chemistry students from his lab, Liu built a laboratory oven specifically designed for this experiment. Inside the oven, a process known as temperature-gradient thermolysis was used. The oven’s lower region maintained a sufficiently high temperature to break down the polymer chains of polyethylene, while the upper portion of the oven remained cool to prevent further breakdown.
Following the thermolysis process, they gathered the residue, which was very similar to cleaning soot from a chimney, and found that Liu’s inkling was right from the beginning. It consisted of “short-chain polyethylene,” which more precisely, happens to be waxes. This marked the initial step toward developing a method for upcycling plastics into soap, said Liu.
Building upon this breakthrough, the team introduced additional steps, including saponification, ultimately achieving the remarkable feat of creating the world’s first soap derived from plastics. To continue this process, the team even enlisted those with expertise in computational modeling, economic analysis, and other specialists.
Lead author of the paper published in Science and one of the Ph.D. students, Zhen Xu, said, “Our research demonstrates a new route for plastic upcycling without using novel catalysts or complex procedures. In this work, we have shown the potential of a tandem strategy for plastic recycling. This will enlighten people to develop more creative designs of upcycling procedures in the future.”
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