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Реферат: Poluurethane Essay Research Paper PolyurethanePolyurethanes are very

Название: Poluurethane Essay Research Paper PolyurethanePolyurethanes are very
Раздел: Топики по английскому языку
Тип: реферат Добавлен 21:50:23 13 ноября 2010 Похожие работы
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Poluurethane Essay, Research Paper

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. This is why they are so common in our everyday life’s. Today a wide variety of polyurethanes are used for many different applications, such as; 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 a variety of reasons, including dashboards, bumper covers, moldings and fenders. And these are just a few of the many use 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: a 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. The structural formula of a polyurathane monomer is:

On the following page there is a chart with some examples of common polyurethane products, their general descriptions and their applications.

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 retardant’s in polyurethanes so that fire isn’t a major problem anymore.

I believe that the benefits of polyurethanes by far outweigh the problems associated with their use. I believe this because polyurethanes are such a versatile product that there are polyurethanes everywhere in our daily lives. The average family owns between 25-100 lb. of polyurethane, and probably don’t even realize it. This can be recycled when they are finished with it, so there isn’t much damage to the environment. There is however the problem of CFC’s in polyurethanes, but this issue is being dealt with and CFC’s are being replaced with a less harmful substance, HCFC. Even HCFC’s are expected to be phased out in 30 years, each year being phased out a little bit more. So I feel that polyurethane is a good product with a lot of good uses with only a few negative effects, but what product doesn’t have negative effects?

Bibliography

1) Polyurethane Intermediates

http://www.apci.com/chemicals/polyint.html

2) Extract from “Intouch” Magazine

http://www.tsmfoam.com/extract.html

3) San Diego Plastics – Polyurethanes

http://www.sdplastics.com/polyuret.html

4) Thermoplastic Polyurethanes

http://eetsg22.bd.psu.edu/research/projects/pu/pu.html

5) 100% Solids Polyurethanes

http://www.corrosion.com:80/madison/polyurethane.html

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