Engineering Professors Developing Technology to Help Upcycle Waste Plastic

Polyethylene, or PE, is one of the most commonly produced plastics in the world. It is used primarily for making grocery bags, trash bags and packaging films and wraps as well as food containers, water bottles, housewares and toys. Currently, more than 100 million tons of PE are produced every year worldwide, accounting for about 34% of the $600 billion-plus global plastics market.

However, most PE products are discarded in landfills after a single use. They also end up in the environment, polluting oceans and endangering marine ecosystems. 

Two chemical engineering faculty researchers, Assoc. Profs. Dongming Xie and Hsi-Wu Wong, are trying to change that. Supported by a three-year, $463,000 grant from the National Science Foundation, they are developing technology that would help reduce waste PE through upcycling, a process in which discarded materials are converted into products of higher value than the original.

“Waste PE accounts for more than 50% of the world’s plastics waste stream,” says Xie, who is the project’s principal investigator. “PE’s projected annual manufacturing growth rate of 12%, combined with the lack of effective recycling options, makes PE a major environmental concern.”

According to Xie, current recycling and upcycling methods used for waste PE, such as mechanical shredding, thermochemical treatment and biochemical conversion, all result in low product qualities, inefficient conversion rates to value-added products and high processing costs.

“None of the existing PE recycling or upcycling methods alone will likely contribute to a circular economy for plastics,” notes Wong.

Circular economy is a relatively new concept in sustainability and innovation. Rather than the usual practice of plastics being used once and discarded, plastic materials in a circular economy constantly flow around a “closed loop” system, retaining their value and prolonging their useful life through repeated reuse, repair and recycling. The materials are discarded only as a last resort.

Wong estimates that nearly 100 million tons of Earth-warming greenhouse gases are emitted into the atmosphere annually from waste PE. 

“If 10% of this waste can be upcycled using our proposed technology, this would save our planet 10 million tons of greenhouse gases each year,” he says.

According to Xie, the goal is to develop a new, two-step hybrid approach to upcycling waste PE. 

First, the researchers will use a thermochemical process, called oxidative catalytic pyrolysis, to decompose waste PE under high temperatures into intermediate molecules, such as alkanes, alkenes, aldehydes and alcohols. Second, they will use a safe, genetically engineered yeast strain in a biomanufacturing process to convert these molecules into value-added products used in industry. These include long-chain diacids for producing new nylon polymers as well as platform chemicals used in making polymer plasticizers, adhesives, emulsifiers, fungicides and biopharmaceuticals.

“The success of this research would help pave the way for the future manufacturing of a wide range of platform chemicals from waste PE and other waste plastics,” notes Xie. 

He says these new chemicals would have significant competitive advantages over similar products manufactured in other countries that use petroleum-based raw materials and potentially hazardous pathogen strains in biomanufacturing.

Two Ph.D. students, Umer Abid from Xie’s lab and Doga Tekbas from Wong’s lab, are working on the project. 

“We expect to recruit at least one more Ph.D. student and one or two part-time undergraduate students to join our team during the project period,” says Xie.