ADVANCED MATERIALS & PROCESSES | SEPTEMBER 2024 72 3D PRINTSHOP REVERSIBLE PRINTING VIA SALTING-OUT EFFECT Researchers at the University of California San Diego are using the salting-out effect, where salt ions draw water molecules out of a polymer solution, to print solid structures. The process uses a liquid polymer solution known as poly(N-isopropylacrylamide), or PNIPAM for short. When this PNIPAM ink is extruded through a needle into a calcium chloride salt solution, it instantly solidifies as it makes contact with the salt water. The removal of water causes the hydrophobic polymer chains in the PNIPAM ink to densely aggregate, creating a solid form. The process is also reversible. The solid structures produced can be easily dissolved in fresh water, reverting to their liquid form. This allows the PNIPAM ink to be reused for further printing. “This is all done under ambient conditions, with no need for additional steps, specialized equipment, toxic chemicals, heat, or pressure,” says professor and senior author of the study, Jinhye Bae. To demonstrate the versatility of their method, the researchers printed structures out of PNIPAM inks containing other materials. For example, they printed an electrical circuit using an ink made of PNIPAM mixed with carbon nanotubes, which successfully powered a light bulb. This printed circuit could also be dissolved in fresh water, showcasing the potential for creating water-soluble and recyclable electronic components. Bae and her team envision that this simple and reversible 3D-printing technique could contribute to the development of environmentally friendly polymer manufacturing technologies. ucsd.edu. PRINTED OBJECTS REMOVE CHEMICALS FROM WATER Ceramic-infused monolith devices developed at the University of Bath will bond with so-called “forever chemicals” in water, removing up to 75% of the chemicals. Perfluorooctanoic acid (PFOA) is one of the most common perfluoroalkyl and polyfluoroalkyl substances (PFAS) that are often referred to as “forever chemicals” due to the long time they take to break down. Made of ink infused with the ceramic indium oxide, the 4-cm monoliths are created by extruding the ink from a 3D printer and forming it into a lattice shape. Because indium oxide bonds with PFAS, the chemicals immediately stick to the monoliths and can be removed from the water in under three hours. “Using 3D printing to create the monoliths is relatively simple, and it also means the process should be scalable,” says Liana Zoumpouli, a research associate in Bath’s Department of Chemical Engineering and a member of the Center for Digital, Manufacturing, and Design. “3D printing allows us to create objects with a high surface area, which is key to the process. Once the monoliths are ready, you drop them into the water and let them do their work.” Testing of the monoliths has surprisingly shown they have become more effective under repeated use—they undergo high-temperature thermal “regeneration” treatment after each use. This is something the researchers are keen to understand more fully with further experimentation. www.bath.ac.uk. Additive manufacturing data captured by the Department of Energy’s Oak Ridge National Laboratory is now available for free through an online platform. The breadth of the datasets can significantly boost efforts to verify the quality of additively manufactured parts using only information gathered during printing, without requiring expensive and time-consuming post-production analysis. doi.org/10.13139/ORNLNCCS/2001425. BRIEF Donghwan Ji demonstrates the sustainable 3D printing method. Courtesy of Liezel Labios/UC San Diego Jacobs School of Engineering. 3D-printed ceramic lattices have been proven to remove harmful “forever chemicals” from water. Courtesy of University of Bath.
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