A dry cleaner in Wake Forest and a Teflon® plant in Bladen County would appear to have little in common, but they are linked by a technology developed through a joint program at NC State and the University of North Carolina at Chapel Hill. The Center for Environmentally Responsible Solvents and Processes, founded in 1999 through a 10-year, $40 million National Science Foundation grant, has found numerous ways to replace water and toxic chemicals with high-pressure carbon dioxide as a solvent.
When CO2 is pressurized to about 1,000 pounds per square inch at slightly more than room temperature, its density approaches that of a liquid, allowing it to dissolve many small molecules. Dr. Joseph DeSimone, who holds a joint position as chemistry professor at UNC and chemical engineering professor at NC State, has discovered a number of polymers that are soluble in such “supercritical CO2.” Scientists on both campuses have since found applications for the high-pressure gas in fields as diverse as dry cleaning, microelectronics, and pharmaceuticals. “One of our successes has been our flexibility,” says Dr. Ruben Carbonell, chemical engineering professor and co-director of the center. “We’ve changed directions several times and moved into new applications.”
Many industries use toxic chemicals like benzene and trichloroethylene as cleaning solvents. The chemicals then evaporate or are washed off, but Carbonell says they pollute the environment either way. Supercritical CO2 not only eliminates chemicals from some manufacturing processes, he says, but also conserves water and energy because products no longer need to be rinsed and dried after a chemical bath. “Companies are not going to change their processes just for environmental reasons,” he says. “The CO2 has to create an advantage that results in more efficient processes or better products.”
The first advantage was to the dry cleaning industry, when MiCell Technologies, Inc., a joint NC State and UNC spin-off, founded the Hangers chain of dry cleaners to use CO2 instead of perchlorethylene to eliminate stains. DuPont then licensed the technology to manufacture Teflon® and other similar coatings. Center researchers are now cleaning and etching circuit patterns on semiconductors with the supercritical fluid. Because the CO2 can penetrate much smaller spaces than liquid solvents, designers can pack more circuits on a chip.
Another joint spin-off, Liquidia Technologies, Inc., uses a process developed by DeSimone to create polymer nanoparticles for drug delivery, sensors, and other applications. Such new avenues for research are important for the center to continue after the NSF grant runs out. “I see this evolving into a way that NC State and UNC students can seamlessly move between engineering, the sciences, and medicine,” DeSimone says. “There are so many applications for this technology, including improving the health and well-being of people, that it goes well beyond preserving the environment.”