Q&A About Polyurethanes

By Dr. Jeffrey F. Dormish

This feature from Bayer MaterialScience, an industry leader in polyurethane chemistry, will provide formulating help to readers.

We want to develop a cost-effective, high-performance sealant. What are the benefits of polyurethane-based products compared to a different polymer type?

Polyurethane sealants have a long history of use in commercial and DIY markets, and are widely used in construction and transportation markets. They are known for producing sealants with excellent adhesion to a variety of substrates, such as wood, concrete and primed metal. In addition, polyurethanes demonstrate excellent elongation, recovery and weather resistance. Polyurethane sealants typically meet the ASTM C 920 standard for elastomeric sealants - a demanding standard that other sealant types may not meet. In addition, they have a history of excellent durability and are commonly expected to have a service life of 20-30 years.

Typical formulations contain an isocyanate prepolymer that is compounded with inorganic fillers, plasticizers and antioxidants. Cure rates for one-component polyurethane sealants depend on ambient moisture and are comparable to other systems, such as silicones and silylated polyurethanes. Sealants can be produced in self-leveling or sag-resistant formulations. Sealants made with aromatic isocyanates may discolor over time. Compared to silicone sealants, polyurethanes are paintable and typically less costly. Other polymer types, such as waterborne acrylics, are used in less-demanding applications in the DIY market. Sealants can also be produced from polyurethane dispersions to yield products with high elongation and low hardness values.

As we develop new products for our company, we are evaluating them from a sustainability standpoint. How would polyurethane chemistry help us to achieve our sustainability goals?

Polyurethane chemistry is based on synthetic raw materials; however, the adhesives and sealants developed from them demonstrate many valuable traits in sustainability evaluations. High-performance polyurethane adhesives can be produced in 100%-solids or waterborne formulations, thus eliminating VOC concerns. Waterborne polyurethane adhesives are widely used in flexible packaging, furniture, automotive and shoe adhesives with virtually no loss in performance. One- and two-component 100%-solids adhesives are used as structural adhesives in composites bonding for the automotive and truck market. They are also used in the construction of windmill blades in the alternative energy market. In addition, there are many applications in the construction market for wood bonding. These polyurethane adhesives can displace existing products based on less desirable formaldehyde chemistry.

In general, these structural adhesives also exhibit long-term durability, which decreases the carbon footprint of the adhesive and the overall structure since they do not need to be replaced as often. It is also possible to prepare polyurethane adhesives from polyols based on natural products (e.g., soybean and castor oil) and without the need for heavy metal catalysts or phthalate plasticizers, which increases the green aspect of these systems.

For additional information on the topics addressed, or to ask another question, send e-mail to jeff.dormish@bayermaterialscience.com with the subject line “Polyurethane Q&A."

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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.”