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Polyurethanes get greener.

The demand for high performance coatings that are not only easier to use but also contain lower levels of volatile organic compounds (VOC) and other potentially harmful ingredients continues to grow as regulations become stricter and the awareness of consumers and other end users increases. It is not surprising, then, that much effort has been directed at developing more environmentally friendly versions of polyurethane coatings, which are recognized as offering high levels of protection in numerous applications, including those in the automotive, industrial, marine, and flooring industries. Tremendous strides have been made in water-based polyurethane dispersions (PUDs) for coating applications. Most recently, researchers at Battelle have developed a completely solvent-free PUD derived from soy-based polyols that, based on initial test results, shows promising performance characteristics.

The polyol used in the preparation of the new polyurethane was also developed at Battelle, and licensed in 2011 to Emery OleoChemicals LLC, which has been commercially manufacturing the product for about a year. That project began in 2005-2006 with the goal of generating functional-ized polyols useful for the synthesis of a wide variety of materials, particularly polyurethanes. The process, ultimately licensed by Emery, involves ozonolysis of unmodified soybean oil or other natural and renewable oils, a reaction that is challenging and which requires special operating conditions. Fortunately, it is one that Emery has extensive experience using on a commercial scale.

Ozonolysis was selected as the key methodology in part because it is a relatively benign process that uses a reagent found in the air, produces only oxygen as a byproduct, and is a solvent-less reaction, according to Rick Heggs, senior marketing manager at Battelle. Most importantly, ozonolysis is a very effective method for functionalizing the olefinic groups in soybean oil. "The polyols that are obtained using this technology are ester-based, and have a high oxygen content, which gives the unique reactivity. In addition, they have high hydrophilicity and good water compatibility," he adds.

While there are several types of biobased polyols on the market, the Battelle process generates products that have several advantages, according to Heggs. Most commercially available soybean oil-based polyols maintain the triglyceride structure found in the soybean oil raw material, which limits the types of polyols that can be generated. The Battelle process, on the other hand, is much more flexible, and a wide range of polyols with different hydroxyl values and viscosities can be obtained. Thus, the properties can be tailored to meet the needs of specific applications. In addition, Heggs notes that, because excess glycerin is used in the process, the cost of producing these renewable polyols is competitive with the cost of manufacturing conventional petroleum-based materials.

Certain characteristics of the polyols now made by Emery were important contributors to the development of the new PUDs. "With their lower viscosity and high oxygen content, solvent compatibilization is not required. That means that the solvents used for this purpose can be eliminated from PU formulations based on these unique polyols," explains Heggs.

Another important advance of this PUD technology is the fact that N-methylpyrrolidone (NMP) is not required during the synthesis of the resins. Typically, according to Heggs, the neutralization of certain acidic ingredients is necessary during the synthesis of polyurethane dispersions. NMP has come under scrutiny due to its reproductive toxicity. It is currently under evaluation in the European Union as a substance of very high concern (SVHC), and many coating formulators around the world are looking for NMP-free solutions. Battelle has tackled this problem in its new PUD by developing a unique neutralization method that avoids NMP, and thus reduces costs, handling, reporting requirements, and waste. The PUD also has lower odor compared to petroleum-based PUDs. The specifics of the process remain proprietary at this time, however, because Battelle is currently writing and filing patents on the technology.

It also should be noted that the PUD is prepared from typical isocyanates and does not require the use of any specialized equipment. In addition, the Battelle researchers designed the process with commercial scale-up in mind.

While the formulation has not yet been optimized, the scientists have demonstrated that a fairly high solids content of 50-60% is possible. Preliminary testing of coatings prepared with the PUD shows very promising results, including high hardness and good clarity. Not surprisingly, since wood coatings are the largest end-use for PUDs, Battelle is targeting this market, but other potential applications include inks, seal coatings, adhesives, composites, and even textiles. Coatings formulated with the PUD also meet Chemical Agent Resistant Coatings (CARC) standards, which means it can be used in military applications. Talks are currently underway with major coating manufacturers, many of which have requested samples. At this point, the researchers can produce the PUD on a large laboratory scale in approximately five-gallon quantities.

"We are excited about the prospects for this new technology, because it is environmentally friendly and does the same job at a comparable price as older polyurethanes without using volatile organic solvents such as NMP," Heggs notes.

Battelle has been working on the development of a wide range of renewable raw materials from soy beans for many years. In addition to products derived from soybean oil, they have engineered hydrogels from the soy plant that can also be in coatings, as well as printer ink/toners, plastics, deicers, and other materials. Much of this effort has been supported by the Ohio Soybean Council and the United Soybean Board, which are farmer-based organizations seeking to grow various markets for soybeans. "The development of the soybean oil-based polyols and the new PUD fits perfectly with Battelle's mission to be good stewards of the environment while helping our customers achieve economic viability, and we look forward to the licensing and commercialization of the PUD technology," Heggs concludes.
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Publication:JCT CoatingsTech
Date:Mar 1, 2013
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