Definitions of Resins - Polyurethanes

Introduced commercially in 1954, the urethanes have made an impact on a broad spectrum of U.S. industry. They are extremely versatile plastics in terms of the forms in which they are available: flexible or rigid foams, solid elastomers (or rubbers), coatings, adhesives and sealants. Their versatility also extends to chemical structure in that, although the urethanes are generally considered to be thermosets, there are grades of urethane elastomers that are thermoplastic in nature and are supplied in pellet form for molding, calendering and extrusion. Polyurethane’s major and best known form, however, is a foamed or “cellular” material. Like all urethanes, the foams are prepared by first reacting two liquid components--polyols and isocyanates--together. In the presence of a blowing agent, this reaction will produce a foamed material having excellent thermal insulating properties, and, in fact, polyurethane foam is widely used in building insulation. The foams can either be soft and flexible or tough, and rigid, with all the possible variations in-between. Flexible foams have oustanding cushioning characteristics, excellent energy-absorbing properties and long life. They are used in furniture, cushioning, carpet underlay, bedding, packaging, textiles and automotive seating and safety padding. Rigid foams offer outstanding insulating values, excellent compressive strength, good dimensional stability and bouyancy. Besides building insulation, they are also found in refrigerators, trucks, boats (for flotation), and in the construction of furniture components. As coatings, polyurethanes impart excellent protective and decorative effects to wood, metals, rubber, textiles, concrete, paper, leather, other plastics and many other materials. In the form of elastomers, polyurethanes offer superior abrasion resistance and toughness, and are used in applications in which good performance and long service life are important: printing rolls, gaskets and seals, cable insulation, drive and conveyor belts, solid tires and automotive applications. Elastomers can also be processed by reaction injection molding, an important technique for producing automotive panels, front ends and bumpers. The commonly used isocyanates for manufacturing polyurethanes are toluene diisocyanate (TDI) [CH3C6H3(NCO)2], methylene diphenyl isocyanate (MDI) [OCNC6H4CH2C6H4NCO], and polymeric isocyanates (PMDI), obtained by the phosgenation of polyamines derived from the condensation of aniline [C6H5NH2] with formaldehyde (HCHO]. Polyols (with hydroxyl groups) are macroglycols which are either polyester or polyether based. Polyurethane elastomers and resins take the form of liquid castings systems thermoplastic elastomers and resins, microcellular products, and millible gums.

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