Case Study

Reducing VOC: New polymer coating process combines high degree of flexibility with improved environmental properties

Published: November 9, 1999

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A new coating material that emits virtually no volatile organic compounds (VOC) during application could replace conventional solvent-based paints and anti-corrosion coatings in a wide range of uses. Based on a durable polyester material, the new coating can be tailored to provide the specific properties required by different applications.

Developed by a research team at the Georgia Institute of Technology, the patented ultra-low VOC coating would meet new environmental regulations expected to severely limit VOC emission from paints and other coatings.

"The potential applications are enormous," says Dr. Robert E. Schwerzel, a principal research scientist at the Georgia Tech Research Institute (GTRI). "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."

In addition to the coating's environmental attractiveness, the novel process used to produce it also offers formulators a high degree of flexibility in selecting the resulting properties of the coating. The work was described at a meeting of the American Chemical Society earlier this year. 

"We have developed a system for applying coatings that can be tuned for a whole group of different properties," says Dr. Charles Eckert, a professor in Georgia Tech's School of Chemical Engineering and director of the Specialty Separations Center. "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. But the new Georgia Tech process removes and captures that small molecule during the manufacturing process — and does not require a solvent.

"Our coating molecules are applied to a surface, and with light or heat and a suitable catalyst, rearranged to form a strong, durable coating without any need for solvents or any need for removal of the small molecules," Eckert explains. "This leaves us with a virtually zero VOC paint."

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 adds. "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 Air Lines 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, Eckert notes. This could produce 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 notes.

Early test results on aluminum and iron alloy substrates show the coating has the desired hardness and durability, though additional research must be done 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, says team member Dr. Charles Liotta, a professor in the School of Chemistry and Biochemistry and Georgia Tech's Vice-Provost for Research.

"The fundamental science, the construction of the cyclic oligomers, their physical and chemical properties, and the polymers that are produced on surfaces are all fairly well characterized," he says. "But for this to be commercially viable, we need to be able to produce thousands of tons per year. We are still exploring how to do that."

Research will also be needed to provide ideal viscosity, adhesion and other properties needed for smooth application of the coatings, Schwerzel says. The researchers also must explore other catalysts used to trigger the curing process.

"These are solvable issues," Schwerzel adds, "but they will take some time and effort in both basic chemical research and chemical engineering process design."

Regardless of the research outcome, this project by three different Georgia Tech departments has already provided benefits to the chemists and chemical engineers of tomorrow.

"This project combines expertise on the practical applications of new materials, chemical engineering and the fundamental aspects of chemistry," Liotta says. "That is a great teaching tool for our students, because it gives them an opportunity to collaborate with all the different disciplines involved."

Beyond the researchers already mentioned, the research team has included Dr. Henry Paris, former GTRI research scientist; Zhenguo Liu, graduate student in the School of Chemistry and Biochemistry, and Dr. David Bush and graduate student Kevin West from the School of Chemical Engineering. Research sponsors included Delta Air Lines, the U.S. Air Force and Scientific Applications International Corp.