Virginia Tech chemist and chemical engineer Guoliang "Greg" Liu and his lab have developed a process that converts the plastic polyvinyl chloride (PVC) into polyalphaolefin, a key component in lubricants such as engine oil.
Published Aug. 5 in the journal Nature, the research could help address two environmental challenges: recycling one of the world's most difficult plastics and producing a valuable industrial material.
Because of its chlorine content and the variety of additives used by different manufacturers, PVC is among the hardest plastics to recycle. As a result, much of it ends up in landfills.
At the same time, lubricants such as engine oil are environmentally costly to produce and are in growing demand. By converting discarded PVC into a key lubricant ingredient, the Liu lab's process offers a potential way to reduce plastic waste while creating a high-value product.
Lubricants may go unnoticed, but they keep the world running smoothly. Engine oil is used in everything from lawn mowers and passenger vehicles to jet engines, making a reliable supply of lubricant components essential across industries.
The Liu lab has developed an effective process to possibly reverse an already alarming plastics pollution problem.
The team takes the PVC you'd find around your home in plumbing, window structures, and even your credit cards, and puts it into a solvent. Aluminum trichloride and alpha-olefins are added and the whole mixture is heated to 158 degrees Fahrenheit for three hours. The product extracted from the solvent is a relatively thick oil — 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 idea for the process started with the team's earlier publications, featured in Science and Nature Sustainability, about converting other types of plastic waste into surfactants such as soap and detergents. When that proved successful, researchers turned their attention to PVC.
"We want to help improve the recycling and upcycling of PVC," Liu said.
To move the project forward, Liu assembled a team of graduate researchers. He tapped Eric Munyaneza Nuwayo, a doctoral student in the final year of his doctoral program, to lead the effort. Connor S. Thompson, a graduate student in the chemistry department, was initially focused on a different research project. When Liu proposed a new direction, Thompson embraced the challenge.
The team also included Abby Civiello, a first-year graduate student whose contributions quickly made a substantial impact in the lab.
"I often called them the three musketeers," Liu said.
Team members started by attempting to transform the PVC molecules into something different and playing around with the 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.
Despite the efforts, the material they produced was never something functional. It was always soft — a little gooey — and not as high-performing as they wanted.
"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.
But as team members advanced the process, converting PVC into new molecules and testing the performance of the resulting product, Liu realized they had uncovered something far more promising than a recycling method.
He turned to colleagues in the field to help clarify exactly what they had created. Liu sent samples of the oil to Ali Erdemir at Texas A&M University, and researchers there tested the final materials. Liu also worked with William Goddard from Caltech on chemical computations. Virginia Tech colleague Xi Chen then aided in the economics and production perspective, working out models for how this oil could be produced on a large scale.
The next step, said Liu, is making the lubricant even more sustainable and more accessible.
"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.
