Greener' Stain-Resistant Coatings Developed
When it comes to fighting stains, "greener" is better. Chemists at the University of North Carolina at Chapel Hill (UNC) announced on Aug. 29 they have developed an alternative material for making stain-resistant coatings that does not lead to the contamination of the environment with perfluorooctanoic acid (PFOA), a pervasive chemical that has been termed a "likely carcinogen" by an EPA advisory board.
PFOA is used directly in the manufacture of the coatings used in nonstick cookware and is also produced by the gradual breakdown in the environment of stain-resistant coatings on clothing and paper goods. Both materials, which have similar properties, are manufactured under a variety of brand names. A growing number of researchers believe that fabric-based, stain-resistant coatings, which are ubiquitous, may be the largest environmental source of the controversial chemical.
The new materials use a novel type of short-chain fluorocarbon that does not degrade into PFOA and is less likely to cause health effects, the UNC scientists say. The greener compounds are primarily intended to replace conventional stain-resistant coatings that are now used in clothing and packaging that eventually degrade into PFOA, they say. The compounds are not designed to replace the coatings used in nonstick cookware that are manufactured using PFOA, the researchers point out. Their finding was described on Aug. 29 at the 230th national meeting of the American Chemical Society.
"These new compounds can go a long way toward reducing PFOA in the environment while still providing the convenience of stain-repellant coatings," says study leader Joseph M. DeSimone, PhD, a chemistry professor at UNC and director of the National Science Foundation (NSF) Science and Technology Center for Environmentally Responsible Solvents and Processes. "That's good news, because once PFOA gets in the environment and in the body, it tends to stay there."
An estimated 95 percent of people in the United States have the chemical in their blood, according to the Centers for Disease Control and Prevention (CDC). But scientists are not sure how the chemical is getting into the body and have limited information on its long-term health effects.
PFOA, also known as C8, is a human-made chemical that has been used for almost 40 years in a variety of commercial applications. The compound is used in the manufacture of fluoropolymers, which are used to make nonstick materials that are used in some cookware, according to the researchers. The compounds are not present in the nonstick coating itself, they add.
PFOA also is produced indirectly through the gradual breakdown of fluorotelomers, compounds that are used to provide water, stain and grease resistance to many fabric and paper goods, such as clothing and food packaging. Because stain-resistant coatings are so widely used, many researchers believe that these coatings may be a larger source of PFOAs than the manufacture of nonstick materials, DeSimone said.
Fluorotelomers are long-chain (eight carbon) compounds that tend to form a protective layer on fabrics and paper goods that are coated with the compounds. Over time, oxidation can cause the fluorotelomers to degrade to PFOA, which is difficult to break down due to its durability and bond strength. PFOA also has a tendency to accumulate in cells due to its polarized structure, which has both hydrophobic (water-repelling) and hydrophilic (water-loving) parts, similar to the cell membrane, the researchers said.
DeSimone and his associates, Paul Resnick, PhD, and graduate student Ji Guo, designed a group of shorter, four-carbon fluorotelomers, called "C4 plus" that are less bulky than the longer chain fluorotelomers. The newer compounds do not produce PFOA and do not appear to be capable of accumulating in the body upon oxidation. In early laboratory tests, coatings made with the new C4 plus compounds performed as well as or better than the conventional coatings, the researchers said.
The researchers have filed a patent for these new materials, which they say have the same beneficial properties as conventional coatings and can easily be scaled up to industrial standards. Several textile companies have expressed an interest, DeSimone said. His study is funded by NSF.
Several years ago, DeSimone and researchers found a way to manufacture many different fluoropolymers in supercritical carbon dioxide that avoids the use of PFOA. DeSimone received a Presidential Green Chemistry Challenge Award in 1997 for developing this process. Like C4 plus, this process also shows great potential for reducing PFOA in the environment, particularly in the manufacture of nonstick coatings used in cookware, the researcher said.
"The high quality of Joe DeSimone's science is well-established as a Presidential Green Chemistry Challenge Award winner," says Paul Anastas, Ph.D., director of the ACS Green Chemistry Institute. "It takes that high-quality science to address one of the great chemistry challenges of our time: designing our molecules so that they do not persist and bioaccumulate in humans and in the environment."
Additional information on Joseph M. DeSimone and his research can be found at http://www.chem.unc.edu/people/faculty/desimonejm/jmdindex.html
Additional information about green chemistry can be found at EPA's Web site: http://www.epa.gov/greenchemistry.
This article originally appeared in the 09/01/2005 issue of Environmental Protection.