Scientists turn plastic wastes into soap

This new technique could one day enlist plastic trash as part of a war on grime

Pieces of soap made from plastic waste are displayed against a blue background. The soap has the color and reflectiveness of beeswax and is cut in various shapes, including a star, a moon and playing card suits.

Researchers developed a process to turn plastic waste into surfactants, the key ingredients in dozens of products, including these cute bars of soap. 

Zhen Xu

The time may be coming to wash our hands of plastic trash. Literally. And we may use that plastic trash to do it. 

Surfactants are chemicals with a cool trait. They can stick together materials that typically would not mix — such as oil and water. It’s what makes these ingredients key to dozens of products found around the home. Among them are detergents, soaps and lubricants. And now there’s a way to turn old plastic into surfactants.  

This could be great news for recyclers. 

Almost two-thirds of all the plastics ever made now sit in landfills or litter the environment. Even now, only about a tenth of plastic waste gets recycled. Much of what is recycled ends up being low-quality material. It tends to be reused only in things such as park benches. So chemists have been searching for ways to “upcycle” plastic, turning it into more valuable raw materials. 

“To me, plastic waste basically [is] aboveground crude oil,” says Guoliang Liu. He’s a chemist at Virginia Tech in Blacksburg. To make valuable chemicals, he says, we don’t always need to “go deep into the ocean or underground to mine [them] anymore.” In fact, this upcycling could offer a truly greener and cleaner way to deal with discarded plastic. 

The two most used plastics — polyethylene and polypropylene — are both made of very long chains of thousands and thousands of bound carbon atoms. Surfactants are also made of bound carbon chains. But their chains are far shorter. The surfactant chains also are capped with groups of water-attracting atoms. 

To turn plastics into surfactants, Liu and his team developed a special reactor. It carefully heats and condenses plastic into a wax that has short carbon chains. Then they capped the wax molecules with groups of oxygen atoms. They also treated them with an alkaline solution. This processing turned the wax into a surfactant.  

To make tiny bars of soap, all it took was adding a bit of dye and fragrance. Researchers shared their finding in the Aug. 10 Science.  

Alas, upcycled plastic probably won’t be washing away messes tomorrow. Right now, the Virginia Tech team can make only about a half gram of surfactant at a time. That mass is equal to about one pumpkin seed or one and a half green peas.  

But Liu’s team is working to scale up the process. If they succeed, they hope to partner with industry to make plastic waste a bit cleaner — or, should we say, into a cleaner.

Watch this short video to learn what surfactants are and why they play a critical role in soaps and detergents.

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