New polymer coating process reduces VOCs
A new coating material that emits virtually no volatile organic compounds (VOCs) during application could replace conventional solvent-based paints and anti-corrosion coatings in a wide range of uses.
"The potential applications are enormous," said Dr. Robert E. Schwerzel, a principal research scientist at the Georgia Tech Research Institute. "These coatings could, in principle, replace many of the solvent-based paints, enamels and varnishes that are currently used to coat everything from stoves and refrigerators to aircraft."
The process used to produce the coating also offers formulators flexibility in selecting the resulting properties of the coating.
"We have developed a system for applying coatings that can be tuned for a whole group of different properties," said Dr. Charles Eckert, professor at Georgia Tech's School of Chemical Engineering. "We believe we will be able to adapt this to a variety of applications, each with different needs and different constraints."
Conventional polyester coatings are cross-linked and cured in a process that involves removing a small volatile molecule and evaporating an organic solvent. The small molecule and solvent usually evaporate into the atmosphere, becoming pollutants. However, the Georgia Tech process removes and captures that small molecule during the manufacturing process, and does not require a solvent.
Using novel chemical processes, the researchers produce cyclic polyester oligomer molecules that are polymerized using an organo-tin or organo-titanate catalyst to form a material that can be either a powder or liquid at room temperature. Once applied to a surface, the coating is cured using heat or ultraviolet light to rearrange the cyclic polymer to a linear and cross-linked structure.
"The properties of these molecules can be changed by altering not only the backbone of the polymer, but also the side groups of the polymer," Eckert said. "We have been able to make structural changes and get virtually any melting point we would like."
The research team has worked with the U.S. Air Force and Atlanta-based Delta Airlines on potential aerospace applications. By altering the surface properties, the researchers believe they could produce a coating that would make aircraft less susceptible to icing. In addition to improving flight safety, such a coating could also reduce the amount of environmentally undesirable ethylene glycol used for aircraft de-icing.
Eliminating the hazardous solvent from the coatings could also make them easier to use and reduce the amount of equipment and ventilation now required to protect workers. This could produce large cost savings for aircraft operators and others using large quantities of coatings.
A solvent-less coating also provides an important logistical benefit: a reduction in the volume of product that must be handled. In existing paints and coatings, solvents significantly increase the volume of product. Containers of the new coating would include only the polyester material, an issue important to military users and others who would be able to reduce transportation and storage costs, Schwerzel noted.
Early test results on aluminum and iron alloy substrates show the coating has the desired hardness and durability, though additional research is needed to show long-term properties on larger surfaces.
So far, researchers have produced only small quantities of their new coating. Scaling up the process to provide commercial quantities at a competitive cost poses the next challenge, said team member Dr. Charles Liotta.
Research will also be needed to provide ideal viscosity, adhesion and other properties needed for smooth application of the coatings, said Schwerzel. The researchers also must explore other catalysts used to trigger the curing process.
For more information, contact Georgia Tech's John Toon at 404-894-6986 or via e-mail at email@example.com, or check out www.gtri.gatech.edu/rco.html.
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This article originally appeared in the 09/01/1999 issue of Environmental Protection.
Gerald F. Connell, ChE is a consultant, retired after 30 years with Capital Controls Group, Severn Trent Service Inc., Colmar, Pa. Mr. Connell is author of "The Chlorination/Chloramination Handbook," published by the American Water Works, and a forthcoming "Chlorination/Dechlorination Handbook" to be published by WEF.