Plastic waste can now be turned into soap – thanks to a breakthrough inspired by a scientist staring at a fire.
It has led to a new way of recycling everyday plastic products – from milk cartons and food containers to shopping bags – into soaps and other cleaning products.
A team led by scientists at Virginia Tech College of Science developed a novel method of upcycling plastics into high-value chemicals known as surfactants, which are used to create soap and detergents.
They hope it will prove a cost-effective way of reducing soaring levels of plastic pollution worldwide.
Plastics and soaps tend to have little in common when it comes to texture, appearance, and, most importantly, how they are used.
But the research team explained that there is a surprising connection between the two on a molecular level: the chemical structure of polyethylene – one of the most commonly used plastics in the world – is “strikingly” similar to that of a fatty acid, which is used as a chemical precursor to soap.
Both materials are made of long carbon chains, but fatty acids have an extra group of atoms at the end of the chain.
Professor Guoliang “Greg” Liu believed the similarity implied that it should be possible to convert polyethylene into fatty acids – and with a few additional steps to the process – to produce soap.
He had a “eureka moment” while enjoying a winter evening by a fireplace.
Liu told how he watched the smoke rise from the fire and thought about how the smoke was made up of tiny particles produced during the wood’s combustion.
Although plastics should never be burned in a fireplace for safety and environmental reasons, Liu began to wonder what would happen if polyethylene could be burned in a safe laboratory setting.
He said: “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 polyethylene molecules but stop the process before they break all the way down to small gaseous molecules, then we should obtain short-chain, polyethylene-like molecules.”
Liu built a small, oven-like reactor where the team could heat polyethylene in a process called temperature-gradient thermolysis.
At the bottom, the oven is at a hot enough temperature to break the polymer chains, while at the top, the oven is cooled to a low enough temperature to stop any further breakdown.
After the thermolysis, they gathered the residue – similar to cleaning soot from a chimney – and found that Liu’s hunch had been right: It was composed of “short-chain polyethylene,” or more precisely, waxes.
Liu says it was the first step in developing a method for upcycling plastics into soap.
After adding a few more steps, including saponification, the team made the world’s first soap out of plastics.
To continue the process, the team enlisted the help of experts in computer modeling, economic analysis, and more.
Together, the group documented and refined the upcycling process until it was ready to be shared with the scientific community.
Their work was published in the journal Science.
Study lead author Zhen Xu, a Ph.D. chemistry student in Liu’s lab, 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.”
The team said that although polyethylene was the plastic that inspired the project, the upcycling method can also work on another type of plastic known as polypropylene.
The two materials make up much of the plastic people encounter every day, from product packaging to food containers to fabrics.
Liu’s new upcycling method can be used on both types of plastics at once, meaning that it’s not necessary to separate the two from each other.
The researchers say it is a major advantage over some recycling methods used today, which require careful sorting of plastics to avoid contamination.
They said another benefit of the upcycling technique is that it has “very simple” requirements in plastic and heat.
Although soaps may not initially seem like a particularly expensive commodity, they can actually be worth double or triple the price of plastics when compared by weight.
Liu says the study lays the groundwork for a new way to reduce waste by channeling used plastics into the production of other useful materials,
He hopes that in future recycling facilities around the world will begin to implement the technique.
If so, Liu says people can expect to one day have the chance to buy revolutionary sustainable soap products that also lead to reduced plastic waste in landfills.
He said for that reason, turning plastics into soaps can be demonstrated to be economically viable.
Xu added: “It should be realized that plastic pollution is a global challenge rather than a problem of a few mainstream countries.
“Compared to a sophisticated process and complex catalyst or reagent, a simple process may be more accessible to many other countries worldwide.
“I hope this can be a good start for the war fighting plastic pollution.”
Produced in association with SWNS Talker