Polyurethane

Polyurethanes are a family of resilient, versatile plastic materials that have a wide variety of practical and industrial applications. Classified as polymers, which are substances whose molecules are composed of numerous repeating units called monomers, polyurethanes are created when two different monomers are combined. The chemical reaction that results from this combination ultimately yields polyurethane. Depending on which monomers are used in the production process, manufacturers can create many different forms of polyurethane, including foams, solid fibers, liquid coatings, and rubber-like materials known as elastomers. Because of the unique variability of their properties, polyurethanes have a broad range of potential uses. When it was originally developed in the 1930s, polyurethane was intended to serve as a replacement for rubber. Since that time, polyurethanes have come to be used in the manufacture of everything from insulation to mattresses, varnishes, couches, paints, foam toys, adhesives, and elastic fibers.

History

The study and development of polyurethane began during the preliminary stages of World War II in the late 1930s. At the time, scientists were hard at work trying to find a suitable replacement for rubber that could be used to fulfill a variety of purposes during the war. In 1937, German chemist Otto Bayer made a critical breakthrough in this effort when he successfully developed Perlon U, one of the first crystalline polyurethane fibers ever created. For his accomplishment, Bayer was dubbed the "father" of the polyurethane industry. Soon after Bayer's discovery, manufacturers began making polyurethane coatings used to produce mustard gas–resistant clothing, high-gloss airplane finishes, and corrosion-resistant substances designed to help protect metals and other sensitive construction materials. Manufacturers also used polyurethane to make impregnated paper, which is paper treated with polyurethane to the extent that the polyurethane permeates the paper itself to make it stronger and more resistant to moisture and grease. By the time World War II ended in 1945, manufacturers were producing a wide variety of polyurethane coatings tailor-made for a broad range of applications on an industrial scale. In the 1950s, many of these manufacturers also began producing polyurethane foams, adhesives, and elastomers. Over the years that followed, numerous other polyurethane formulations and processing techniques were developed, all of which allowed manufacturers to find a wide array of uses for polyurethanes in the production of a seemingly endless list of everyday consumer products.

How It Is Made

Although the process of making polyurethane is quite complex, the underlying fundamentals of that process are relatively easy to understand. At the most basic level, polyurethane is the product of the chemical reaction that occurs when isocyanates are combined with polyols. Isocyanates are reactive materials that contain a series of highly reactive alcohols. Most often, the isocyanates used to make polyurethane are toluene diisocyanate (TDI) and polymeric isocyanate (PMDI). Polyols, on the other hand, are compounds that contain multiple alcohol groups. Some of the more commonly used polyols in the polyurethane production process include polyethylene glycol, polypropylene glycol, and polytetramethylene glycol. When a selected isocyanate and polyol are combined, a number of special additives are also thrown into the mix. Generally, these additives help to ensure that newly created polyurethane materials are not damaged during the reaction or afterward by heat, light, or other possible contaminants. Once an isocyanate and a polyol have been combined and allowed to react with each other, polyurethane is formed.

Types of Polyurethane

There are a number of unique types of polyurethane that can be produced for different purposes, including flexible polyurethane foam, rigid polyurethane foam, thermoplastic polyurethane, binders, waterborne polyurethane dispersions, and a wide variety of coatings, adhesives, sealants, and elastomers. Flexible polyurethane foam is used most often as a form of cushioning for a range of consumer and commercial products. Rigid polyurethane foam serves as one of the most versatile and energy-efficient types of insulation available and is used in homes across the United States. Thermoplastic polyurethane is a flexible, highly elastic material that is resistant to impact, abrasion, and weather and can be melted for use in many different applications. Polyurethane binders are used to bind certain particles and fibers together in the manufacture of various building materials. Waterborne polyurethane dispersions are special coatings and adhesive materials that utilize water as their primary solvent. Polyurethanes are also used in a variety of coatings, adhesives, sealants, and elastomers to provide binding advantages and extend the life and appearance of products.

Applications

Polyurethanes have an incredible range of potential applications that encompasses everything from apparel to electronics. In the garment industry, polyurethane threads are often combined with nylon to create especially lightweight and stretchable clothing. Car manufacturers use polyurethanes to make a variety of car parts, including bumpers, seat foam, and spoilers. Polyurethanes and materials containing polyurethanes are also used for numerous purposes, including as insulation in homes and other buildings. Many home appliances include components made from polyurethanes, such as the thermal insulation systems used in refrigerators and freezers. Polyurethanes are also often used to improve the appearance and durability of flooring, either in the form of a foam underlay or a coating. In the manufacture of composite wood, polyurethane-based binders are used to permanently bind organic materials to particleboard, fiberboard, straw board, and other forms of lumber. Many couches and other pieces of furniture are stuffed with polyurethane foam. Polyurethane packing foam is widely used to protect goods when they are prepared for shipping. Boat manufacturers use polyurethane resins and foams to protect the appearance and improve the performance of the marine vessels they produce. In the medical industry, polyurethanes are used frequently in the manufacture of hospital bedding, tubing, and surgical dressings. Electronics manufacturers often use non-foam polyurethanes called potting compounds to seal and insulate microelectronic components, printed circuit boards, and underwater cables that are fragile and sensitive to pressure.

Bibliography

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"Introduction to Polyurethanes." American Chemistry Council. American Chemistry Council, Inc. Web. 25 Feb. 2016. polyurethane.americanchemistry.com/Introduction-to-Polyurethanes. Accessed 21 Nov. 2024.

"Polyurethanes." The Essential Chemical Industry Online. CIEC Promoting Science at the University of York, York, UK. Web. 25 Feb. 2016. www.essentialchemicalindustry.org/polymers/polyurethane.html. Accessed 21 Nov. 2024.

Sonnenschein, Mark F. Polyurethanes: Science, Technology, Markets, and Trends. Hoboken: John Wiley & Sons, 2014. Print.