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Powder Coatings Clinic Marek W. Urban, Ph.D. Clemson University Ying Yang, Ph.D. Clemson University A new breakthrough in self-healing acrylic polymers Self-healing polymers represent a new and upcoming technology that will improve a coating's performance, sus- tainability, and customer satisfaction. Scratches and fractures of coatings will heal like skin without external inter- vention, resulting in a longer life span of coatings. Researchers have been working on developing self-healing materials for almost two decades, but none of these studies have provided feasible, practical, and affordable solu- tions. e primary inhibiting factors have been the scale-up production as well as the cost of producing the self-healing coatings. Recently, how- ever, a new series of self-healing mate- rials based on acrylic copolymers were reported, which are very close to in- dustrial scale production. 1 In the powder coating industry, acrylic resins are typically used as high-performance clear topcoats in automotive sectors, which provide outstanding clarity, smoothness, and resistance to chemicals, scratches, and weathering. The newly reported self-healing polymers are simply based on methyl methacrylate (MMA)/n- butyl acrylate (nBA) or their deriva- tives, but the copolymer compositions must be in a narrow compositional range. e side groups interlock with each other, joining adjacent chains, thus making them difficult to be sepa- rated when external mechanical force is applied. When scratched, damage can close without external interven- tion within about 14 hours at room temperature. Even when the material is completely severed, self-healing be- gins within a few minutes after being physically reattached and recovers about 90 percent of its mechanical properties after approximately 80 hours under ambient conditions. ese self-healing acrylic copolymers may soon find applications in the coating industry, as their mass pro- duction does not require new facili- ties. e existing acrylic powders in- clude glycidyl methacrylate (GMA), acrylic urethanes, and hybrids systems containing polyester or epoxy. Among them, GMA acrylic is the most popu- lar. It contains glycidyl methacrylate (GMA) monomer copolymerized with other acrylate or methacrylate monomers formulated to the desired glass transition temperature (Tg). GMA acrylics are cured by polycar- boxylic acid crosslinking agents via ring opening reactions of epoxides. methyl methacrylate (MMA) n-butyl acrylate (nBA) glycidyl methacrylate (GMA) To develop self-healable acrylic pow- der products, the powder needs to be stable enough to be stored while the resulting coating, upon curing, should exhibit self-healing properties. It is also worth pointing out that creating favorable heterogeneities may also fa- cilitate damage closure and the subse- quent self-healing of polymers. 2 PC References 1. Urban, Marek W., Dmitriy Davydovich, Ying Yang, Tugba Demir, Yunzhi Zhang, and Leah Casabianca. "Key-and-lock commodity self-healing copolymers." Science 362, no. 6411 (2018): 220-225. 2. Yang, Ying, Dmitriy Davydovich, Chris C. Hornat, Xiaolin Liu, and Marek W. Urban. "Leaf-inspired Self-healing polymers." Chem 4, no. 8 (2018): 1928-1936. Editor's note For further reading, visit Powder Coat- ing magazine's website at www.pcoat ing.com and search the Article Archive by keyword, subject, organization, author, or issue date. All articles listed in the archive are available for free download to registered users. Marek W. Urban is J . E . S i r r i n e Foundation endowed chair and professor in the Department of Materials Science and Engineering at Clemson University, 299 A Sirrine Hall, Clemson, SC 29634; 864/656-1155; mareku@clem- son.edu. Until 2012, he was a professor of polymer science and engineering in the School of Polymers and High P e r f o r m a n c e M a t e r i a l s a t t h e University of Southern Mississippi- Hattiesburg (USM). After 13 years at North Dakota State University, he joined USM where he established and d i r e c t e d t h e N a t i o n a l S c i e n c e Foundation Materials Research Science Engineering Center (MRSEC) on Stimuli-Responsive Polymeric Films and Coatings. He is co-director of the formally National Science Foundation Cooperative Research Center in Coatings and recently renamed O O O O O O O 22 POWDER COATING, November 2018