Shelby Thames, the noted University of Southern Mississippi coatings and polymer scientist and driving force behind the highly regarded annual International Waterborne, High-Solids and Powder Coatings Symposium, has long chased an elusive dream: the emergence of VOC-free waterborne coatings on a large scale.
But for Thames, who holds the title of distinguished university professor at USM, an ordinary VOC-free paint isn't the object of this dream. His has been a pursuit of a no-VOC coating with top-notch performance and application properties and ambient-cure capabilities - a technology that would allow uses such as interior and exterior architectural paints and other coatings.
"What I wanted to do was get the VOCs out of waterbased paints," Thames said during a recent conversation, as he recalled the original impetus for the launch of the Waterborne Symposium nearly 30 years ago. "At that time, we believed we would see the removal of organic solvents from waterborne paints in the not-too-distant future."
Waterborne coatings minus the organic solvents have made their appearance in the architectural-coatings marketplace - but perhaps not on the scale envisioned by Thames and other pioneers of low-VOC coatings technology. To date, the no-VOC architectural-paint products on the market have largely been restricted to interior applications, and in niche markets such as hospitals, schools, and other settings where emissions and odor are important considerations.
But Thames and his research collaborators at USM believe they have achieved a breakthrough in the quest to develop no-VOC coatings systems that offer an impressive blend of performance, application and environmental attributes. Through a recently launched company named Southern Diversified Products, Thames and his team are positioned to manufacture commercial quantities of architectural paint based on a recently developed resin technology given the name Castor Acrylated Monomer, or CAM.
The monomer technology, the result of an R&D project initiated five years ago, delivers coating-film coalescing capabilities and cured-film performance properties without the use of cosolvents, Thames said. In producing latex polymers based on the technology, the monomer is attached to the backbone of a conventional latex polymer. The monomer acts as a plasticizer, providing good flow properties and a smooth finish, he said.
Performance properties such as durability and scrub resistance are enhanced by the system's crosslinking mechanism, Thames said. In addition, the monomer can be given various functionalities to allow combinations with different resin chemistries, including acrylics, esters, epoxies, and others. Formulation of coatings with various gloss levels is also said to be feasible.
The initial paint products to be derived from the CAM technology are architectural coatings, but Thames said CAM-based polymers offer potential for use in industrial coatings, adhesives and other products.
"It's a room-temperature crosslinking paint, and that is hard to come by," Thames said. He believes the monomer and the resulting polymer combinations represent one of the most significant coatings-technology breakthroughs in years.
"We're taking a renewable commodity" - the oil of the castor bean - "and making an environmentally friendly product, and I think that has a lot of appeal," he said. "It has essentially no VOCs and little or no odor." And although castor oil has been used to make the monomer, other plant-derived oils - lesquerella and soy - can be used.
Plasticizing, Crosslinking Called Keys to Performance
A paper presented earlier this year at the Waterborne Symposium in New Orleans described the process used to incorporate the CAM technology in ambient-cure architectural coatings, and also discussed test data indicating that the resulting coating formulations deliver an impressive combination of application and performance properties. The paper's authors are Corey L. King of CREANOVA Inc., Thames and Oliver W. Smith, also of USM.The monomer is derived from ricinoleic acid, which comprises 90% of the fatty acids of castor oil, according to the paper, titled "One-Component, Low-VOC, Ambient-Cure Architectural Coatings Formulated Using CAM Acrylic Latexes." Synthesis takes place by the transesterification of castor oil with methanol, followed by acrylation with acrylic acid or acryloyl chloride. Latex polymers used in the coating formulations discussed in the paper were produced using methyl methacrylate, butyl acrylate, methacrylic acid, and CAM as co-monomers.
The paper discusses evaluation of film formation of latex coatings formulated with the CAM-modified polymers, employing atomic force microscopy. The evaluation indicated that higher concentrations of CAM enhance film formation due to a reduction in glass-transition temperature (Tg). But film formation is followed by rapid cure to higher-Tg films that provide the needed coating properties.
The paper reviews testing of block resistance in the applied coating films of semigloss interior paint formulations incorporating the CAM. The testing indicated that the coatings delivered performance that exceeded commercial latexes containing coalescent solvents, providing evidence of ambient-cure capabilities of the CAM latexes, the authors state. The block resistance can be accelerated further with a higher level of cobalt catalyst, they say. Results were also found to be dependent on the use of certain CAM concentrations.
Testing of dirt-pickup resistance, an indicator of coating Tg, crosslinking and hydrophobicity, also demonstrated performance comparable to commercial control latex formulations for the exterior CAM formulations, even though the CAM coatings initially possessed a lower Tg that facilitated film formation at sub-ambient temperatures.
The paper concludes that CAM is a "flexibilizing co-monomer that facilitates coalescence of high-molecular-weight latex polymers by depressing the polymer Tg. The polymer Tg then increases as the CAM polymers undergo crosslinking in the presence of oxygen when applied to a substrate." The increase in Tg is "significant...and rapid" and results in coating films that provide strong block resistance in interior acrylics and dirt-pickup resistance in exterior acrylics. Thus, the CAM-modified polymers allow formulation of waterborne coatings that meet performance demands with no or very low VOCs and odor, the paper concludes.
The paper describing the CAM acrylic latexes received the Elias Singer Award as the best paper presented at the 2001 Waterborne symposium.
Going to Market
The ultimate test of any new technology, of course, resides in that rigorous competitive forum known as the marketplace. Thames said he and his team of researchers-manufacturers are ready to enter the arena, beginning with an initial order from the U.S. Defense Department. Southern Diversified Products will manufacture 20,000 gallons of interior flat latex paint for application at the Pentagon building in Washington.Southern Diversified, located in Jackson, MS, is headed by president Jim Watts, a 30-year veteran of the coatings industry. The ownership group also includes USM's Thames, Oliver Smith and Jim Evans. The company was formed under a Mississippi state program called the Mississippi University Research Act, which allows university researchers to market the results of their work. USM holds the CAM patents and will receive royalties from product sales.
Thames said the CAM technology will be available to the general coatings industry, with monomer and polymer products to be offered for sale to manufacturers. He added that the products will be priced competitively compared to existing materials.
Watts, the production-company president, said the CAM technology has the potential to significantly alter the waterborne-coatings landscape. "Within three years, I think this product will be in a major portion of the latex paint produced in this country," he said.
