Polyurethanes (PU)

Properties and Applications

Polyurethanes (PUR) are one of the largest classes of polymers with properties that can be tailored over a wide range for a large number of application. They can be thermosetting or thermoplastic, rigid and hard or flexible and soft. They are formed from the reaction of an organic diisocyanate with a diol compound. Foamed structures are produced by deliberately adding water. During molding, the isocyanate groups react with the water to urea, which releases carbon dioxide that acts as a blowing agent. Two major drawbacks of PURs are their susceptibilty to microbial attack and the tendency of aromatic urethanes to discolor (yellow) when exposed to UV light.
The versatile urethane chemistry allows for the production of a wide range of products including flexible and rigid foams, solid elastomers, extrusion parts, coatings, and adhesives. Flexible, high-resilient foamed products include mattresses, upholstered furniture, carpet underlays and auto parts like cushions, backs, and armrests. Rigid foamed products with a closed cell morphology are used as insulations for commercial and residential buildings. Elastomeric urethanes find many uses in the automotive industry. Some examples are bumpers, fenders, steering wheels, instrument and door panels, and gaskets for trunks, windows and windshields. Polyurethanes are also used as electrical potting compounds, adhesives, coatings, sealants, and for the fabrication of synthetic fibers (Spandex).

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