A Resistance To A Liquid In Flowing Is Called Polyurethanes History

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Polyurethanes History

The pioneering work on polyurethane polymers was done by Otto Bayer and his colleagues in 1937 in the laboratory of IG Farben in Leverkusen, Germany. They recognized that using the polyaddition principle to produce polyurethanes from liquid diisocyanates and liquid polyethers or polyester dials represented a special opportunity, especially when compared to existing plastics that were made by polymerizing olefins or polycondensation. The new monomer combination also circumvented an existing patent obtained by Wallace Carothers on polyesters. Initially, the focus was on the production of fiber and flexible foams. Polyisocyanates did not become commercially available until 1952, with development due to World War II (when PU was used in limited quantities as an aircraft coating). Commercial production of flexible polyurethane foam began in 1954, based on toluene diisocyanate (TDI) and polyester polyols. The discovery of these foams (initially called imitation Swiss cheese by inventors) was attributed to the accidental introduction of water into the reaction mixture.

This material was also used to make rigid foams, gum rubber, and elastomers. Linear fibers were prepared from hexamethylene diisocyanate (HDI) and 1,4-butanediol (BDO). The first commercially available polyether polyol, poly(tetramethylene ether) glycol), was introduced by DuPont in 1956 by polymerizing tetrahydrofuran. The following year, in 1957, BASF and Dow Chemical introduced the less expensive polyalkylene glycol. These polyether polyols offered technical and commercial advantages such as low cost, ease of handling, and better hydrolytic stability; and quickly replaced polyester polyols in the manufacture of polyurethane products. Another early pioneer in PU was Mobe Corporation. More than 45,000 tons of flexible polyurethane foam were produced in 1960. As the decade progressed, the availability of chlorofluoroalkane blowing agents, inexpensive polyether polyols, and methylene diphenyl diisocyanate (MDI) led to the development and use of polyurethane rigid foams as high performance insulation materials. Rigid foams (PMDI based on polymeric MDI) are good. stability and combustion characteristics than those based on TDI. In 1967, urethane modified polyisocyanurate rigid foams were introduced, offering even better thermal stability and flammability resistance to low density insulation products.

Also in the 1960s, automotive interior safety components such as instrument and door panels were manufactured by back-filling thermoplastic skins with semi-rigid foam. In 1969, Bayer AG exhibited an all-plastic car in Dusseldorf, Germany. The car parts were manufactured using a new process called RIM, Reaction Injection Molding. RIM technology utilizes high-pressure impingement of liquid components followed by rapid flow of the reaction mixture into the mold cavity. Large parts, such as automotive fascia and body panels, can be molded in this manner. Polyurethane RIM evolved into a variety of products and processes. Using diamine chain extender and trimerization technologies gave poly(urethane urea), poly(urethane isocyanurate), and polyurea RIMs. The addition of fillers, such as milled glass, mica, and processed mineral fibers, improved the RRIM, reinforced RIM, which improved the flexural modulus (stiffness) and thermal stability. This technology allowed the production of the first plastic-bodied automobile in the United States, the Pontiac Fiero, in 1983. Further improvements in flexural modulus were achieved by incorporating glass mats into the RIM mold cavity, also known as SRIM or structural RIM. In the early 1980s, water-blown microcellular flexible foam was used in the automotive industry to mold gaskets for panels and radial seal air filters. Since then, rising energy costs and the desire to phase out PVC plastisol from automotive applications have increased market share. Expensive raw materials are offset by a significant reduction in part weight and, in some cases, the elimination of metal end caps and filter housings.

Overfilled polyurethane elastomers and more recently unfilled polyurethane foams are now used in high-temperature oil filter applications. Polyurethane foam (including foam rubber) is often made by adding small amounts of volatile substances, so-called blowing agents, to the reaction mixture. These simple volatile chemicals provide important performance characteristics, primarily thermal insulation. In the early 1990s, the Montreal Protocol greatly reduced the use of many chlorine-containing blowing agents, such as trichlorofluoromethane (CFC-11), due to their impact on ozone depletion. Other haloalkanes such as the hydrochlorofluorocarbon 1,1-dichloro-1-fluoroethane (HCFC-141b) were used in 1994 under the IPPC Directive on Greenhouse Gases and as an interim replacement under the Volatile Organic Compounds (VOC) Directive. EU in 1997 (see: Haloalkanes). In the late 1990s, the use of blowing agents such as carbon dioxide, pentane, 1,1,1,2-tetrafluoroethane (HFC-134a) and 1,1,1,3,3-pentafluoropropane (HFC-245fa) increased. Widespread in North America and the EU, although chlorinated blowing agents are still in use in many developing countries.

Extensive development of two-component polyurea spray elastomers took place in the 1990s, based on existing polyurethane spray coating technology and polyetheramine chemistry. Their rapid reaction and relative insensitivity to moisture make them useful coatings for large surface projects such as secondary containment, manhole and tunnel coatings, and tank liners. Excellent adhesion to concrete and steel is achieved with proper primer and surface treatment. During the same period, new two-component polyurethane and hybrid polyurethane-polyurea elastomer technologies were used to enter the spray-in-place load bed liner market. This technique creates a durable, abrasion resistant composite with the metal substrate for coating pickup truck beds and other cargo bays and eliminates corrosion and brittleness associated with drop-in thermoplastic bed liners. The use of polyols derived from vegetable oils to make polyurethane products began to gain attention around 2004, partly due to the rising cost of petrochemical feedstocks and partly due to increased public desire for environmentally friendly green products. One of the most vocal proponents of this polyurethane, made from natural oil polyols, is the Ford Motor Company.

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