What Is Polyurethane Made Of?
Polyurethane is a linear polymer material that consists of carbamate groups, also known as urethane, which is formed by a chemical reaction between a polyol and a diisocyanate. Developed during late 1930s, polyurethane is considered to be one of the most flexible polymers and is used for diverse applications such as in building insulation, adhesives, surface coatings, solid plastics and apparel for athletes.
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Structure
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Polyurethane, also referred to as polycarbamate, is a synthetic polymer that belongs to the class of compounds known as polymers and is distinguished with a molecular backbone of -NHCO2 (carbamate groups). Polymers are basically macromolecules that are formed of monomers (smaller and identical units). The polyurethanes that have significant commercial applications characteristically contain other active groups in the molecule like ethers, esters, urea or amides.
History
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In 1937, Friedrich Bayer, a German chemist, first studied polyurethane chemistry and produced early samples through the chemical reaction of toluene diisocyanate with dihydric alcohols. This work eventually resulted in the development of the pioneering crystalline polyurethane fibers called "Perlon U."
The production of the first versatile polyurethane foam started in the United States in 1953. Several enhanced prototypes of polyurethane polymers have been developed over the ensuing years, comprising Spandex fibers, thermoplastic elastomers and polyurethane coatings. -
Raw Materials
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Polyurethane is produced using numerous raw materials, such as monomers and prepolymers that help protect the original chemical composition of the polymer and the colorants. One of the primary material used for producing polyurethane are diisocyanates. These are characterized by a group of highly potent alcohols (i.e. NCO). The most commonly used isocyanates include PMDI (polymeric isocyanate) and TDI (toluene diisocyanate).
The second most important group of reactive material that is required for fabricating polyurethane are polyols, which are compounds of multiple alcohol groups (i.e. OH). The material that is normally used for this application is a polymer formed from cyclic ethers (i.e. polyether polyols).
Additives
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Some types of polyurethane are susceptible to damage from light, heat, chlorine and atmospheric contaminants. Due to this factor, several stabilizers are added to protect the integrity of the polymer. One variety of stabilizers that helps provide protection against damage from light is hydroxybenzotriazole, which is a UV screener. Numerous antioxidants like polymeric and monomeric hindered phenols are used to offer protection from oxidation reactions.
The polymers, when first produced, have a natural white color. To add to their aesthetic appeal, colorants are added to the polymers, common ones being dispersed and acid dyes.
Design
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Polyurethane is produced in four forms: elastomers, flexible foams, coatings and cross-linked foams. Elastomers are primarily stretchable materials that ultimately return to their original shape after being stretched. Coatings have a resistance quality to solvent degradation and have considerable resistance to impact as well.
Polyurethanes in the form of flexible foams are the most widely used in commercial applications, as they have the quality of high impact strength. They have applications such as making cushions for furniture and soles for athletic shoes. Cross-linked, or rigid polyurethane foams used for manufacturing laminates and boards with insulation properties are common in the construction industry.
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Resources
- Photo Credit gmilburn.ca
