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.