PVC is one of those plastics that tends to stick around for all the wrong reasons. Now, Virginia Tech researchers say they have found a way to turn it into a key ingredient used in high-performance lubricants, including engine oil.
The team, led by Virginia Tech chemist and chemical engineer Guoliang “Greg” Liu, developed a method for transforming polyvinyl chloride, or PVC, into polyalphaolefin. Their study was published August 5 in Nature.
The work aims at two problems at once: PVC is notoriously hard to recycle, and industrial lubricants can carry a significant environmental cost to produce.
PVC is especially difficult to recycle because it contains chlorine and can include a wide range of additives depending on how it was manufactured. As a result, large quantities of PVC end up in landfills.
At the same time, demand is growing for lubricants such as engine oil, which industries use in equipment ranging from lawn mowers and passenger cars to jet engines.
Liu’s lab developed a process that starts with PVC similar to material used in household plumbing, window structures, and credit cards. Researchers place the PVC in a solvent, then add aluminum trichloride and alpha olefins. They heat the mixture to 158 degrees Fahrenheit for three hours, then extract a relatively thick oil from the solvent that functions as a lubricant.
“Number one, we have proved that it is feasible to use plastic waste to make high-performance lubricants. Number two, these lubricants are green, and they can meet the emerging needs for sustainability by the market,” Liu said.
The project built on the team’s earlier work, published in Science and Nature Sustainability, converting other types of plastic waste into surfactants used in products such as soaps and detergents.
“We want to help improve the recycling and upcycling of PVC,” Liu said.
Liu put together a graduate research team to take on the project. Eric Munyaneza Nuwayo, a doctoral student in the final year of his program, led the effort. Connor S. Thompson, a graduate student in the chemistry department, shifted from another research project to join the work. Abby Civiello, a first-year graduate student, also contributed to the research.
“I often called them the three musketeers,” Liu said.
At first, the researchers tried to chemically transform PVC molecules into different materials.
“The idea was simple. PVC, as one of the most activated forms of polyethylene, ought to be easily converted into some other molecules by replacing the chlorine atoms with other groups,” Liu said.
Those early results did not produce the performance the researchers wanted. The materials stayed soft and somewhat gooey.
“One day I realized — if this polymer is so gooey and so soft, why don’t I just keep breaking the polymer chains down to smaller segments?” said Liu.
The team then kept breaking down PVC, producing new molecules and evaluating the resulting material. To test the oil, Liu sent samples to Ali Erdemir at Texas A and M University, where researchers tested the final materials.
Liu also worked with William Goddard at Caltech on chemical computations. Virginia Tech colleague Xi Chen contributed an economic and production analysis, including models for how the oil might eventually be manufactured on a much larger scale.
The researchers now want to make the lubricant production process more sustainable and the product more widely available.
“Lubricants are the silent hero out there. We often don’t recognize they exist, but they are out there working quietly. We want to be able to produce the oil on a larger scale to reach more people in the world,” Liu said.
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