Originally two German chemists named Wurtz, in 1848, and Hentschel, in 1884 made the first Isocyanates, one of the building blocks of Polyurethane. Originally polyurethane was developed for military use by Otto Bayer, in the late 1930s, and was the first to make polyurethane commercially available.
Polyurethane is a polymer that consists of repeating units [__ROOCNH__R’__]n. ‘R’ can represent a different alkyl group, which is obtained by removing a hydrogen atom from a hydrocarbon. Polyurethane’s are mostly thermoset plastics meaning the resins cross-link and cannot be melted and remoulded. Some polyurethane’s are Linear Aliphatic Polyurethane which is thermoplastics. This means the resins are linear and do not cross-link, subsequently they can be reprocessed. Thermoplastic polyurethane is not only linear but has highly crystalline structures. It is because of this that it forms an abrasion-resistant material. The diagram above shows the molecular structure of complex polyurethane. Complex polyurethane is considered this because it is made from an isocyanate base. This type of urethane is created through the reaction between an isocyanate and a polyol (Alcohol).
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There are many different types of polyurethane’s to include the following: rigid foams, flexible foams, adhesives, sealants, coatings, cast elastomers, and spandex fibres. All polyurethane’s have one thing in common: they contain urethane linkages formed by the chemical reaction between the isocyanate and the polyol. These various forms make polyurethane a very versatile plastic in liquid and solid form.
Rigid foams or hard foams are used as insulation for buildings, water heaters, refrigeration, and floatation devices. Flexible foams or soft, open-celled polyurethane foams are used as cushion padding under carpets, furniture cushioning, mattresses, and packaging material. Adhesives and sealants are used where high strength, moisture resistance and durability is needed such as in construction, automotive and marine applications. Mainly in the automotive field, you will see polyurethane as the paint or clear coat on your car, and the glue used to assemble items in your vehicle, and the soft cushions that make up your seat backs and bottoms you sit on. Some foams are also used as the soft cushioning on your dashboard, headliner, steering wheel, and gearshift handles.
Most urethanes used in the automotive field are paints and coatings, as well as, foam rubbers. Thermoplastic elastomers include cast elastomers and Reaction Injection Molded (RIM) products like athletic footwear, skate wheels, machinery housings, and electronic media (computer disks), to name a few.
Mechanical recycling, energy recovery, and chemical recycling are all ways to recycle polyurethane. Mechanical recycling is done by regrinding polyurethane foams into powders allowing them to be reused in the production of new foam as filler. The methods of reuse are flexible foam bonding, adhesive pressing, and compression moulding.
Flexible foam bonding utilizes foam pieces and adheres them together to make padding type products. Adhesive pressing is where the polyurethane granules are coated with a binder (glue) then cured under heat and pressure to make parts like floor mats for your car or tire covers. Compression moulding is where the polyurethane granules are moulded under high heat and pressure to create rigid or hard parts such as pump and motor housing.
Energy recovery is a method in which polyurethane can be burned efficiently resulting in total consumption of the material. Chemical recycling has several different methods such as Glycolysis, Hydrolysis, Pyrolysis, and Hydrogenation. Glycolysis is where polyurethane is chemically mixed and heated to 200° C and will produce polyol, which can be used to make more polyurethane or it, can be used as a fuel. Hydrolysis is like Glycolysis however it produces polyol and amine intermediates and can be used for fuel and producing more polyurethane. Pyrolysis creates gas and oil under heated, oxygen-free conditions. Hydrogenation, like Pyrolysis it creates gas and oils but under heat and pressure and the hydrogen produced is purer.
Nylon is the material used in Parachutes, Paragliders, Powered parachutes and Glider wings. As the material is exposed to the UV rays of the sun, normal use and weathering it becomes more porous and dangerous, for this particular use. Polyurethane is used to make nylon material less porous or perhaps non-porous. Even old nylon, if not ripped or torn, can perhaps be refurbished by a coating of polyurethane. Not only does it help eliminate the porosity, temporarily, but will reduce weathering and UV exposure. This will keep the material from being permanently damaged and the polyurethane barrier will wear instead.
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