PolyUrethanes are Linear Polymers that have a molecular backbone containing
carbamate groups (-NHCO2). These groups, called Urethane, are produced through
a Chemical reaction between a diIsocyanates and a polyol.
Polymers are macromolecules:
PolyUrethanes, also known as polycarbamates, belong to a larger class of compounds
called Polymers. Polymers are macromolecules made up of smaller, repeating units
known as monomers. They consist of a primary long-ch ain backbone molecule with
attached side groups. PolyUrethanes are characterized by carbamate
groups (-NHCO 2 ) in their molecular backbone.
Reacting Monomers in a Reaction vessel:
Like PolyUrethane, produced by reacting monomers in a reaction vessel. A step
also known as condensation reaction is performed. In Chemical reaction,
the monomers that are present contain reacting end groups.
Monomers to form a Larger Molecule:
A diIsocyanates (OCN-R-NCO) is reacted with a diol (HO-R-OH). First step of reaction
results in the Chemical linking of the two molecules leaving a reactive alcohol
(OH) on one side and a reactive Isocyanates (NCO) on the other. These groups
react further with other monomers to form a larger, longer molecule.
High Molecular Weight Materials:
This is a process which yields high molecular weight materials at room temperature.
PolyUrethanes have important commercial uses typically contain other functional
groups in the molecule including esters, ethers, amides, or urea groups.
A variety of raw materials are used to produce PolyUrethanes. These include monomers,
prePolymers, stabilizers which protect the integrity of the Polymer, and colorants.
Isocyanatess: Key reactive materials required
to produce PolyUrethanes are diIsocyanatess. These compounds are characterized by
a (NCO) group, which are reactive alcohols. Widely used Isocyanatess employed
in PolyUrethane production are toluene diIsocyanates (TDI) and Polymeric
Isocyanates (PMDI). TDI is produced by Chemically adding nitrogen groups
on toluene, reacting these with hydrogen to produce a diamine, and
separating the undesired isomers.
PMDI is derived by a phosgenation reaction of aniLine-formaldehyde polyamines.
In addition to these Isocyanatess, higher end materials are also available. These
include materials like 1,5-naphthalene diIsocyanates and bitolylene diIsocyanates.
These more expensive materials can provide higher melting, harder segments
in PolyUrethane elastomers.
Polyols: The other reacting species required
to produce PolyUrethanes are compounds that contain multiple alcohol groups (OH),
called Polyols. Materials often used for this purpose are Polyether Polyols,
which are Polymers formed from cyclic ethers. They are typically produced through
an Alkylene oxide Polymerization process. They are high molecular weight Polymers
that have a wide range of viscosity. Various Polyether Polyols that are used
include polyethylene Glycol, polypropylene Glycol, and polytetramethylene Glycol.
These materials are generally utilized when the desired PolyUrethane is going
to be used to make flexible foams or thermoset elastomers.
Additives: Some PolyUrethane materials can be
vulnerable to damage from heat, light, atmospheric contaminants, and chlorine.
For this reason, stabilizers are added to protect the Polymer. One type of
stabilizer that protects against light degradation is a UV screener called
hydroxybenzotriazole. To protect against oxidation reactions, antioxidants are
used. Various antioxidants are available such as monomeric and Polymeric hindered
phenols. Compounds which inhibit discoloration caused by atmospheric pollutants
may also be added.
The Manufacturing Process:
While PolyUrethane Polymers are used for a vast array of applications, their production
method can be broken into three distinct phases. The bulk Polymer product is made.
Polymer is exposed to various processing steps. Polymer is transformed into its final
product and shipped. This production process can be illustrated by looking at
the continuous production of PolyUrethane foams.
At the start of PolyUrethane foam production, the reacting raw materials are held
as liquids in large, stainless steel tanks. These tanks are equipped with agitators
to keep the materials fluid. A metering device is attached to the tanks so that
the appropriate amount of reactive material can be pumped out.
Ratio of polyol to diIsocyanates is 1:2
Ratio of polyol to diIsocyanates is 1:2. Since the ratio of the component materials
produces Polymers with varying characteristics, it is strictly controlled.
The exchanger adjusts the temperature to the reactive level
Inside the pipes, the Polymerization reaction occurs. By the time the Polymerizing
liquid gets to the end of the pipe, the PolyUrethane is already formed. End of the
pipe is a dispensing head for the Polymer.
The dispensing head is hooked up to the processing Line. For the production of rigid
PolyUrethane foam insulation, a roll of baking paper is spooled at the start of
the processing Line. This paper is moved along a conveyor and brought under
the dispensing head.
As the paper passes under, PolyUrethane is blown onto it. As the Polymer is dispensed,
it is mixed with carbon Dioxide causes it to expand. It continues to rise as it moves
along the conveyor.
After the expansion reaction begins:
A second top layer of paper is rolled on. Additionally, side papers may also be
rolled into the process. Each layer of paper contains the PolyUrethane foam
giving it shape. The rigid foam is passed through a series of panels that control
the width and height of the foam bun. As they travel through this section of
the production Line, they are typically dried.
At the end of the production Line:
The foam insulation is cut with an automatic saw to the desired length. The foam
bun is then conveyored to the final processing steps that include packaging,
stacking, and shipping.
Ensure the quality of the PolyUrethane material, producers monitor the product during
phases of production. These inspections begin with an evaluation of the incoming raw
materials by quality control chemists. Test various Chemical and physical
characteristics using established methods. Some of characteristics that are
tested include the pH, specific gravity, and viscosity or thickness. Appearance,
color, and odor may also be examined. Manufacturers have found that by strictly
controlling the quality at the start of production can ensure that a consistent
finished product will be achieved.
After production the PolyUrethane product is tested:
PolyUrethane coating products are evaluated in the same way the initial raw materials
are checked. Characteristics like dry time, film thickness, and hardness are tested.
PolyUrethane fibers are tested for things such as absorbency,elasticity and resilience.
PolyUrethane foams are checked to ensure the proper resistance, density and flexibility.
Wishing you all the best,