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No chemistry required (it would not hurt to know some)
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Some chemistry or physics required
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| Applications |
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Polyurethane foams
are used in applications such as
cushioning or insulation. For most cushioning applications polyurethane
foams are soft and elastic. Most foams used in insulation are hard and rigid
foams. Often foams are prepared with additional properties, such as flame
retardancy.
A typical polyurethane is prepared by blending of a polyol
component with a diisocyanate. The polyol component contains also the a
volatile blowing agent, a surfactant foam stabilizer and a catalysts. Most
foam preparation is done on automatic mixing equipment which can mix
precisely different streams of all the components. Foams for insulation can
be cast in place or cast in large equipment and later sliced in
sheets.
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Flexible foams are prepared from linear predominately di-functional
polyol and diisocyanates. The polyols are of higher molecular weight and the
Tg of the polyurethane is low. On the other hand the rigid foams are
prepared from highly functional polyols and from di or polyisocyanates.
These polyols are highly crosslinked and high in urethane content. Rigid
foams can also be prepared with large levels of polyisocyanate and with the
use of special catalysts which trimerize the isocyanate to an isocyanurate
group. This isocyanate group can improve the flame retardancy of the foam.
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Elastomers
are linear polyurethane polymers with
a low degree or no crosslinking. To achieve the high MW required the exact
ration of hydroxyl and isocyanate has to be used. The preparation of
isocyanate terminated prepolymers and extending this prepolymer with a diol
is one of the methods used to obtain a good control of the molecular weight.
Phase separation is used to achieve elastomeric properties in an elastomer.
The diol or diamine used in chain extension of an isocyanate terminated
prepolymer has a significant effect on phase separation. Depending on the
size and the refractive index of the second phase the elastomer can be clear
or hazy in appearance.
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Diamines; 3,5-Diethyl-2,4-diaminotoluene 3,5-Dimethylthio-2,4-toluenediamine
4,4'-Methylenebis(2-chloraniline) (MOCA)
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Diols;
1,4-Butanediol, 1,3-Propanediol,
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Coatings
utilize polyurethanes in solvent and
waterborne coatings. Applications are in abrasion resistant coatings,
primers and in topcoats. For most coating applications the high reactivity
of the isocyanate and the potential for low temperature crosslinking is
important. The information on coatings will be expanded in the future.
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Most coatings use as polymers polyester or acrylic backbones
which are either crosslinked or chain extended with di or polyisocyanates.
Coatings represents a large market for aliphatic light stable
isocyanates.
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Adhesives
are very similar in composition to
elastomers. The only difference with an adhesive might be the application
methods and how the adhesive is formulated.
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Last edited on:
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November 20, 2006
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Copyright®, Design, Layout and Technical Content by:
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