Upcycled food packaging can clean up water

A plant-based solvent that can dissolve waste plastics, that can be converted into membranes, that can be used to clean up industrial wastewater - and create clean water - sounds like a circular economy dream, but it has been made real by scientists in Saudi Arabia.
Polyolefins are a family of thermoplastics that make up almost half of all discarded items in plastic waste streams. They include polyethylene and polypropylene, and are mainly obtained from oil and natural gas, but can also be derived from renewable plant-based resources like sugar cane.
"We successfully made polypropylene membranes using plastic waste from food packaging - transforming single-use plastics into high-performance materials.”
Malinalli Ramírez Martínez, a PhD student who led the research at KAUST - King Abdullah University of Science & Technology, said, “Polyolefins are very popular due to their low cost and high thermal and chemical stability. We find them in food packaging, reusable bags, shampoo bottles, toys and many more products.”
These same properties make these plastics attractive for producing hydrophobic microporous membranes for industrial processes, including oil processing, wastewater treatment and desalination.
“However, the main challenges for processing polyolefins into porous membranes are the high temperatures required to dissolve them — commonly between 140 and 250oC — and the limited range of solvents that can be used, most of them fossil-fuel based,” said Martinez.
In a breakthrough, Martinez's team found that solvents made from organic waste could bring down the temperature, lowering the carbon footprint while reducing dependence on fossil carbon.
“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.”
“We found that terpenes — naturally abundant renewable solvents derived from nonfood biomass — could dissolve polyolefins at just 130oC. Secondly, using these solvents, we successfully made polypropylene membranes using plastic waste from food packaging; transforming single-use plastics into high-performance materials.”
Thanks to their porous structure, plastic membranes are used to treat wastewater and seawater, reducing the environmental footprint of industrial processes and making more fresh water available for other uses.
“Traditional membrane fabrication approaches mostly use pristine fossil-based non-renewable materials, which have a negative environmental impact and contradict the sustainability benefits,” Martínez says. “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.
“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.”
The research is published in Green Chemistry journal.