Q&A ABOUT POLYURETHANES

Editor’s note: This new feature from Bayer MaterialScience, an industry leader in polyurethane chemistry, will provide formulating help to readers. Their team of experts can help you improve green strength and heat resistance, or adjust the reactivity of an adhesive, as well as provide solutions to improve the tensile strength, elongation, and UV stability of a sealant. Questions regarding contact bonding and laminating with polychloroprene can be addressed as well. Please see below to find out how to submit a question.

QUESTION: CAN YOU EXPLAIN WHY IT IS RECOMMENDED THAT SOME POLYURETHANE DISPERSION ADHESIVES BE WARMED PRIOR TO USE?

In order to form a lasting bond when adhering to a non-porous substrate such as PVC or other polymer films, it is important that all water be removed from the bond line. This can occur by evaporation of the water at room temperature or by way of a heating operation. Some polyurethane adhesives are non-tacky crystalline solids at room temperature, so they would not be able to wet out the surface to be bonded if the process took place at room temperature. In these cases, it is necessary to heat these adhesive layers above the crystalline melting point of these polymers (~50–65

QUESTION: HOW CAN I ACHIEVE THE PERFORMANCE OF A WATERBORNE TWO-COMPONENT (2K) POLYURETHANE ADHESIVE AND AVOID THE NEED TO HANDLE AND MIX A WATER-DISPERSIBLE POLYISOCYANATE AT MY CUSTOMER'S FACILITY?

You did not mention which aspect of the 2K polyurethane system is most important for your application, but let me address the two most important aspects – heat resistance and chemical resistance. It is possible to achieve an increase in the heat resistance of an adhesive by changing the base polyurethane dispersion in your system. Your polymer supplier would be expected to have a number of products available that differ in molecular weight or changes in polymer building blocks that would influence heat resistance. Another avenue to achieve improved heat and chemical resistance is through the use of encapsulated polyisocyanate crosslinkers. This technology allows the adhesive manufacturer to mix a dispersion of a solid encapsulated isocyanate into the polyurethane dispersion of choice and obtain a stable one-component system that can be supplied to the adhesive end user. Upon briefly exposing this adhesive to low temperatures (65-75

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Jeffrey F. Dormish, Ph.D., holds the position of Research Fellow and is responsible for the development of new polyurethane adhesive applications, with a focus on waterborne raw materials.

Dr. Dormish joined Covestro LLC (then known as Bayer) in 1980. Since that time, he has held various research and application development positions of increasing responsibility, and worked in polyurethane research at Bayer AG in Germany for two years. He has a bachelor’s degree in chemistry from the University of Dayton and a doctorate in chemistry from the Pennsylvania State University. For additional information on the topics addressed or to ask another question, email jeff.dormish@covestro.com with the subject line “Polyurethanes Q&A.”