Plastic waste could be upcycled to clean up waste

Plastic waste could be upcycled as a raw material for making high performance porous membranes, which could be used by the chemical industry for the separation of chemical mixtures or to clean up waste streams.

According to Malinalli Ramirez Martinez, a PhD student who led the research in Suzana Nunes’ group at King Abdullah University of Science and Technology (KAUST), polymeric membranes could address many sustainability challenges. They have a selectively permeable porous structure, which can reduce the environmental footprint of industrial separations, help in the treatment of waste effluent and create access to fresh water.

Ramirez Martinez said traditional membrane fabrication approaches use fossil-based non-renewable materials, which negatively impact the environment.

“We wanted to take polymeric membrane sustainability one step further by replacing some of the conventional materials used for their fabrication with bio-based solvents and waste plastics, following the principles of circular economy and green chemistry.”

Polyolefin plastics make up almost half of all discarded items in plastic waste streams.

“Polyolefins are very popular due to their low cost and high thermal and chemical stability,” Ramírez Martínez said. “We find them in food packaging, reusable bags, shampoo bottles, toys and many more products.”

These properties make polyolefins suitable for producing hydrophobic microporous membranes for oil purification and other industrial purification processes. The main challenge for processing them is the limited range of solvents that can be used and the high temperatures required to dissolve them, usually between 140 and 250°C.

While the main solvents that can be used are usually fossil fuel-based, two bio-based solvents can be used to significantly improve the sustainability of the process.

“We found that terpenes — naturally abundant renewable solvents derived from nonfood biomass — could dissolve polyolefins at just 130°C,” Ramirez Martinez said. “Secondly, using these solvents we successfully made polypropylene membranes using plastic waste from food packaging, transforming single-use plastics into high-performance materials.”

These membranes were successful in separating the water-in-oil emulsions that certain industrial processes generate.

“The rejection values and oil purity we recorded were comparable to state-of-the-art membranes reported in the literature,” Ramirez Martinez said. “We consider it a great achievement to have proved that membranes prepared from plastic waste can have a competitive performance compared to those made from pristine materials.”

Image credit: 2023 KAUST; Morgan Bennett Smith.