HISTORY OF POLYURETHANE
Otto Bayer and his coworkers at I.G. Farben in Leverkusen, Germany, first made polyurethanes in 1937. The new polymers had some advantages over existing plastics that were made by polymerizing olefins, or by polycondensation, and were not covered by patents obtained by Wallace Carothers on polyesters. Early work focused on the production of fibres and flexible foams and PUs were applied on a limited scale as aircraft coating during World War II. Polyisocyanates became commercially available in 1952 and production of flexible polyurethane foam began in 1954 using toluene diisocyanate (TDI) and polyester polyols. These materials were also used to produce rigid foams, gum rubber, and elastomers. Linear fibers were produced from hexamethylene diisocyanate (HDI) and 1,4-butanediol (BDO).
In 1956 DuPont introduced polyether polyols, specifically poly(tetramethylene ether) glycol and BASF and Dow Chemical started selling polyalkylene glycols in 1957. Polyether polyols were cheaper, easier to handle and more water resistant than polyester polyols, and became more popular. Union Carbide and Mobay, a U.S. Monsanto/Bayer joint venture, also began making polyurethane chemicals. In 1960 more than 45,000 metric tons of flexible polyurethane foams were produced. The availability of chlorofluoroalkane blowing agents, inexpensive polyether polyols, and methylene diphenyl diisocyanate (MDI) allowed polyurethane rigid foams to be used as high performance insulation materials. In 1967, urethane modified polyisocyanurate rigid foams were introduced, offering even better thermal stability and flammability resistance. During the 1960s, automotive interior safety components such as instrument and door panels were produced by back-filling thermoplastic skins with semi-rigid foam.
In 1969, Bayer exhibited an all plastic car in D?sseldorf, Germany. Parts of this car, such as the fascia and body panels were manufactured using a new process called RIM, Reaction Injection Molding in which the reactants were mixed then injected into a mold. The addition of fillers, such as milled glass, mica, and processed mineral fibres gave rise to reinforced RIM (RRIM), which provided improvements in flexural modulus (stiffness), reduction in coefficient of thermal expansion and thermal stability. This technology was used to make the first plastic-body automobile in the United States, the Pontiac Fiero, in 1983. Further increases in stiffness were obtained by incorporating pre-placed glass mats into the RIM mold cavity, also known broadly as resin injection molding or structural RIM.
Starting in the early 1980s, water-blown microcellular flexible foams were used to mold gaskets for automotive panels and air filter seals, replacing PVC plastisol from automotive applications have greatly increased market share. Polyurethane foams are now used in high temperature oil filter applications.
Polyurethane foam (including foam rubber) is sometimes made using small amounts of blowing agents to give less dense foam, better cushioning/energy absorption or thermal insulation. In the early 1990s, because of their impact on ozone depletion, the Montreal Protocol restricted the use of many chlorine-containing blowing agents, such as trichlorofluoromethane (CFC-11). By 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) were widely used in North America and the EU, although chlorinated blowing agents remained in use in many developing countries.
In the 1990s new two-component polyurethane and hybrid polyurethane-polyurea elastomers were used for spray-in-place load bed liners and military marine applications for the U.S. Navy. A one-part polyurethane is specified as high durability deck coatings under MIL-PRF-32171 for the US Navy. This technique for coating creates a durable, abrasion resistant composite with the metal substrate, and eliminates corrosion and brittleness associated with drop-in thermoplastic bed liners.
Rising costs of petrochemical feedstocks and an enhanced public desire for environmentally friendly green products raised interest in polyols derived from vegetable oils. One of the most vocal supporters of these polyurethanes made using natural oil polyols is the Ford Motor Company.