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Pyradol
polyols are used in the manufacturing of polyurethanes for Coatings,
Adhesives, Sealants, and Elastomers (CASE).
Basically, Polyurethanes are produced when reacting isocyanates and
polyols. There are many different isocyantes and polyols used, based
on different molecular weights and functionalities to allow for
different polyurethanes to be produced for specific applications.
Pyradol polyols are polyether polyols
based on propylene oxide (PO) containing the repeating ether linkage
–R-O-R- and have two or more hydroxyl groups as terminal functional
groups.
Some
of the Pyradol polyols are capped with ethylene oxide (EO) to yield
terminal primary hydroxyl groups. Since primary hydroxyl groups are
more reactive than secondary hydroxyl groups, these polyols are more
reactive with isocynates.
All Pyradol polyols are either Diols
(initiate with PG), or Triols (initiate with Glycerin).
Diol:
Triol:
Isocyanates are defined by having a
final -N=C=O group on a carbon molecule. This carbon molecule
can be aliphatic (not containing a benzene ring), or aromatic like TDI
and MDI which are very common. Aromatic isocyanates are typically more
reactive than the aliphatic isocyanates.
The basic chemistry of a Urethane
reaction:
R – N = C = O + R’ – OH
-------> R –NH - C – O – R’
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O
Isocyanate
Alcohol
Urethane
By utilizing a diisocyanate (i.e., TDI)
with a polyol (i.e., Diol or Triol) a polyurethane is developed.
An undesirable side reaction with
isocyantes is its’ reaction with water. Isocyanate and water react to
form Carbamic Acid, which is very unstable and reacts further with the
isocyanate to produce Urea and Carbon Dioxide. Polyols should be
stored in dry conditions as to minimize any contamination with water
to prevent undesirable side reactions.
As stated earlier, Pyradol polyols are
used in Coatings, Adhesives, Sealants, and Elastomers (CASE).
Coatings:
Polyols provide the following
benefits:
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Excellent abrasion
resistance
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Good chemical and
solvent resistance
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Very good light
stability and weatherability
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Good flexibility and
high adhesion
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Very good protection
to corrosion
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Often further reacted
to make acrylates
Adhesives:
Polyol characteristics and trends:
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Solvent based, water
based or solvent free
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Available as one or
two component systems
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MDI increasingly
preferred to TDI
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Growing use of
aliphatic isocyanates
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Applications include:
structural adhesives (ie. Transportation, construction), lamination
applications (ie. On textile, plastic films), binder for wood chips
or composite materials, footwear, packaging
Elastomers
Polyol characteristics:
·
Abrasion resistant
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High mechanical
strength
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Good resistance to
many solvents and chemicals except strong acids and a few strongly
polar solvents
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TPU’s, CPU’s, fibers
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Applications include:
ski boots, molded soles for sport shoes, abrasion resistant rollers,
forklift tires and wheels, pump and pipe linings, copier rolls,
conveyer belts, and fibers
Basic principles in formulating a CASE
product.
Feature
Property Benefit
Molecular wt
high flexibility
low stiffness
Functionality
high cross-linking
low elasticity
PO content all
PO hydrophobic, water repellent
EO content
high compatibility with
fillers
EO tip
high reactivity
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