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Polyurethane
Polyurethanes are very versatile thermoset plastics that were originally developed for military use by Otto Bayer in the late 1930's. They are so versatile that they can be made into a compound as soft as bubble-gum, or they can also be formed into compounds that are as hard as a soft metal. Today, polyurethanes are used for many different purposes. Flexible polyurethanes are used to make sofas, cushions, carpet backs, car seats; rigid foams are used for insulation in freezers, refrigerators, and roofs. Many shoe companies also use tough elastomeric polyurethanes for shoe soles. The auto industry also use polyurethanes for dashboards, bumper covers, moldings and fenders. Transparent plastics may be either hard or soft. Some are colored, and others are as clear as glass. These are just a few of the many uses for polyurethanes. The base material used to form polyurethane compounds is actually a by-product of the oil refining process. The end product, polyurethane, is made with two basic ingredients: Isocyanate and Polyol. This is shown in the reaction below: Polyurethane Reaction Isocyanate + Polyol =
Polyurethane
H O R - NCO + R' - OH = R - N - C - O - R' Polyurethanes are produced by reacting an isocyanate and a polyol of various types. Almost all commercial grade polyurethanes available, are based on two different isocyanates; TDI (toluenediisocyanate) and MDI (methylenebisdiphenyl diisocyanate). Both of these isocyanates give different properties to the polyurethane and have varying types of processing systems. The polyol, which is the other reactant in the polyurethane, is available in three different types: PTMEG (polyetetramethylene ether glycol), PPG (polypropylene ether glycol) and polyester. There are other isocyanates and polyols that can be used in the manufacturing of polyurethanes, but these are the most common. This process is also the process that is used in making polyurethane foams. Since polyurethanes can take on many shapes and forms there are many benefits to them. There are however more notable benefits, like the added comfort in your sofa or cushions. Advantages: Abrasion Resistant ~ When severe abrasion is a factor, parts made out of polyurethane will outwear other materials by up to a ratio of 50:1. It's been proven to be vastly superior to rubber plastics and metal in many applications. Load Bearing Capacity ~ Polyurethane has a higher load-bearing capacity than any conventional rubber. Because of this characteristic it is an ideal material for heavy duty couplings, shock pads, and load wheels. Tear Resistant ~ The tear-strengths of polyurethanes range from 500-100 lb./linear inch, which is far superior to rubbers. Because of the high tear-strength, urethane is often used in drive belts, roll covers, and gaskets. Weather Resistant ~ Polyurethane has outstanding resistance to oxygen, ozone, sunlight, and general weather conditions. Electrical Properties ~ Polyurethane has excellent electrical insulating properties and is successfully used in many molded wire and cable harness assemblies. The most notable problem that faces the polyurethane industry is the fact that most of the old processes used CFC's as blowing agents. These emissions are now being strictly controlled and the manufacturers of polyurethane's have to use alternate materials such as HCFC's, which have lower depletion potentials (ODP). The current guidelines show that all CFC production was to have been phased out by 1996 and replaced by HCFC. Another problem the polyurethane foam industry had was the effects they were having on the environment by throwing away their foam scraps. In the past all foam scraps landed in the landfill because there wasn't any other uses for it. But now the foam is ground into small particle size pieces and made into bonded carpet underlay. This process is so successful that there is a demand for polyurethane foam processed scrap. Bonded carpet underlay manufacturers currently use more than 400 million pounds of processed scrap annually. Of that 300 million pounds are purchased from domestic sources and the rest is imported. This is both a way to help save the environment but also for foam manufacturers to turn their scraps into money, which helps reduce the cost of foam material used in end-product manufacturing. Fires also used to be a major problem associated with polyurethanes but now there are more flame retardent in polyurethanes so that fire isn't a major problem anymore.

 



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