Polymer scientists from the University of Groningen and NHL Stenden University of Applied Sciences, both in the Netherlands, have developed a polymer membrane from biobased malic acid. It is a superamphiphilic vitrimer epoxy resin membrane that can separate water and oil and is fully recyclable. When the pores are blocked by foulants, it can be depolymerized, cleaned and subsequently pressed into a new membrane.

Superamphiphilic membranes that ‘love’ both oil and water are a promising solution for cleaning up oil spills, but are not yet practical. These membranes are often not robust enough for use outside the laboratory and the membrane pores can clog up due to fouling by algae and sand. As such, Chongnan Ye and Katja Loos from the University of Groningen and Vincent Voet and Rudy Folkersma from NHL Stenden used a new type of polymer to create a membrane that is both strong and easy to recycle.

The new, vitrimer membrane is made by pressing and sintering of polymers from the natural monomer malic acid. This membrane can be recycled by ball milling and subsequent pressing and sintering. Source: Chongnan Ye, University of GroningenThe new, vitrimer membrane is made by pressing and sintering of polymers from the natural monomer malic acid. This membrane can be recycled by ball milling and subsequent pressing and sintering. Source: Chongnan Ye, University of Groningen

Recently, the researchers from both institutes have investigated vitrimer plastics — polymer materials with the mechanical properties and chemical resistance of a thermoset plastic. However, vitrimer plastics can also behave like a thermoplastic, since they can be depolymerized and reused. This means that a vitrimer plastic possess all the qualities to make a membrane appropriate for oil spill remediation.

“Furthermore, it was made from malic acid, a natural monomer,” said Loos.

“The polymers in the vitrimer are crosslinked in a reversible manner,” explained Voet. “They form a dynamic network, which enables recycling of the membrane.” The vitrimer is produced through base-catalyzed ring opening polymerization between pristine and epoxy-modified biobased malic acid. The polymers are ground into a powder by ball milling and turned into a porous membrane through the process of sintering.

Both water and oil will spread out on the resulting superamphiphilic membrane. In an oil spill, much more water is present than oil, which means that the membrane is covered by water that can then pass through the pores.

The membrane is firm enough to filter oil from the water. When sand and algae clog up the pores, the membrane can be depolymerized and recreated from the building blocks after removal of the pollutants.

“We have tested this on a laboratory scale of a few square centimeters,” said Loos. “And we are confident that our methods are scalable, both for the polymer synthesis and for the production and recycling of the membrane.”

The research appears in the journal Advanced Materials.

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