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Polymers Project
Polyurethane
Vahidreza Bitarafhaghighi
Advisor: Dr. John Paul
Spring 2013
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Table of Contents
Introduction .................................................................................................................................................. 2
History ........................................................................................................................................................... 3
Chemistry ...................................................................................................................................................... 5
Raw materials................................................................................................................................................ 9
Isocyanates ............................................................................................................................................... 9
Polyols ..................................................................................................................................................... 10
Chain extenders and cross linkers .......................................................................................................... 12
Catalysts .................................................................................................................................................. 15
Surfactants .............................................................................................................................................. 15
Production ................................................................................................................................................... 16
Health and safety ........................................................................................................................................ 16
Fungus ..................................................................................................................................................... 17
Manufacturing ............................................................................................................................................ 17
Dispensing equipment ............................................................................................................................ 17
Tooling .................................................................................................................................................... 21
Applications................................................................................................................................................. 23
Furniture ................................................................................................................................................. 25
Automobile seats .................................................................................................................................... 26
Houses, sculptures, and decorations ...................................................................................................... 28
Water vessels .......................................................................................................................................... 30
Flexible plastics ....................................................................................................................................... 31
Varnish .................................................................................................................................................... 31
Wheels .................................................................................................................................................... 33
Automotive Parts .................................................................................................................................... 33
Electronic components ........................................................................................................................... 35
Adhesives ................................................................................................................................................ 35
Abrasion resistance ................................................................................................................................. 36
Testing ......................................................................................................................................................... 37
Effects of visible light ......................................................................................................................... 37
References .................................................................................................................................................. 38
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Introduction:
Polyurethane
Polyurethane (PUR and PU) is a polymer composed of a chain of organic units joined
by carbamate (urethane) links. While most polyurethanes are thermosetting polymers that do
not melt when heated, thermoplastic polyurethanes are also available.
Polyurethane polymers are formed by reacting an isocyanate with a polyol. Both the
isocyanates and polyols used to make polyurethanes contain on average two or
more functional groups per molecule.
Polyurethane products often are simply called “urethanes”, but should not be confused
with ethyl carbamate, which is also called urethane. Polyurethanes neither contain nor are
produced from ethyl carbamate.
Polyurethanes are used in the manufacture of flexible, high-resilience foam seating; rigid
foam insulation panels; microcellular foam seals and gaskets; durable elastomeric wheels and
tires (such as roller coaster wheels); automotive suspension bushings; electrical potting
compounds; high performance adhesives; surface coatings and surface sealants; synthetic
fibers (e.g., Spandex); carpet underlay; hard-plastic parts (e.g., for electronic instruments);
hoses and skateboard wheels.
Figure 1.Polyurethane synthesis, wherein the urethane groups — NH-(C=O)-O- link the molecular units.
3
History
Otto Bayer and his coworkers at I.G. Farben in Leverkusen, Germany, first made
polyurethanes in 1937.[1] The new polymers had some advantages over existing plastics that
were made by polymerizing olefins, or by polycondensation, and were not covered by
patents obtained by Wallace Carothers on polyesters.[2] Early work focused on the production
of fibres and flexible foams and PUs were applied on a limited scale as aircraft coating
during World War II.[2] Polyisocyanates became commercially available in 1952 and
production of flexible polyurethane foam began in 1954 using toluene diisocyanate (TDI)
and polyester polyols. These materials were also used to produce rigid foams, gum rubber,
andelastomers. Linear fibers were produced from hexamethylene diisocyanate (HDI)
and 1,4-butanediol (BDO).
In 1956 DuPont introduced polyether polyols, specifically poly(tetramethylene ether)
glycol and BASF and Dow Chemical started selling polyalkylene glycols in 1957. Polyether
polyols were cheaper, easier to handle and more water resistant than polyester polyols, and
became more popular. Union Carbide and Mobay, a U.S. Monsanto/Bayer joint venture, also
began making polyurethane chemicals.[2] In 1960 more than 45,000 metric tons of flexible
polyurethane foams were produced. The availability of chlorofluoroalkane blowing agents,
inexpensive polyether polyols, and methylene diphenyl diisocyanate (MDI) allowed
polyurethane rigid foams to be used as high performance insulation materials. In 1967,
urethane modified polyisocyanurate rigid foams were introduced, offering even better
thermal stability and flammability resistance. During the 1960s, automotive interior safety
components such as instrument and door panels were produced by back-
filling thermoplastic skins with semi-rigid foam.
In 1969, Bayer exhibited an all plastic car in Düsseldorf, Germany. Parts of this car, such as
the fascia and body panels were manufactured using a new process called RIM,Reaction
Injection Molding in which the reactants were mixed then injected into a mold. The addition
of fillers, such as milled glass, mica, and processed mineral fibres gave rise to reinforced
RIM (RRIM), which provided improvements in flexural modulus (stiffness), reduction in
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coefficient of thermal expansion and thermal stability. This technology was used to make the
first plastic-body automobile in the United States, the Pontiac Fiero, in 1983. Further
increases in stiffness were obtained by incorporating pre-placed glass mats into the RIM
mold cavity, also known broadly as resin injection molding or structural RIM.
Starting in the early 1980s, water-blown microcellular flexible foams were used to mold
gaskets for automotive panels and air filter seals, replacing PVC plastisol from automotive
applications have greatly increased market share. Polyurethane foams are now used in high
temperature oil filter applications.
Polyurethane foam (including foam rubber) is sometimes made using small amounts
of blowing agents to give less dense foam, better cushioning/energy absorption or thermal
insulation. In the early 1990s, because of their impact on ozone depletion, the Montreal
Protocol restricted the use of many chlorine-containing blowing agents, such
astrichlorofluoromethane (CFC-11). By the late 1990s, the use of blowing agents such
as carbon dioxide, pentane, 1,1,1,2-tetrafluoroethane (HFC-134a) and 1,1,1,3,3-
pentafluoropropane (HFC-245fa) were widely used in North America and the EU, although
chlorinated blowing agents remained in use in many developing countries.[3]
In the 1990s new two-component polyurethane and hybrid polyurethane-polyurea elastomers
were used for spray-in-place load bed liners and military marine applications for the U.S.
Navy. A one-part polyurethane is specified as high durability deck coatings under MIL-PRF-
32171[4] for the US Navy. This technique for coating creates a durable, abrasion resistant
composite with the metal substrate, and eliminates corrosion and brittleness associated with
drop-in thermoplastic bed liners.
Rising costs of petrochemical feedstocks and an enhanced public desire for environmentally
friendly green products raised interest in polyols derived from vegetable oils.[5] One of the
most vocal supporters of these polyurethanes made using natural oil polyols is the Ford
Motor Company.[6]
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Chemistry
Polyurethanes are in the class of compounds called reaction polymers, which
include epoxies, unsaturated polyesters, and phenolics.[7][8][9][10][11] Polyurethanes are
produced by reacting an isociyanate containing two or more isocyanates groups per molecule
(R-(N=C=O)n ≥ 2) with a polyol containing on average two or more hydroxy groups per
molecule (R'-(OH)n ≥ 2), in the presence of a catalyst.
The properties of a polyurethane are greatly influenced by the types of isocyanates and
polyols used to make it. Long, flexible segments, contributed by the polyol, give
soft, elasticpolymer. High amounts of crosslinking give tough or rigid polymers. Long chains
and low crosslinking give a polymer that is very stretchy, short chains with lots of crosslinks
produce a hard polymer while long chains and intermediate crosslinking give a polymer
useful for making foam. The crosslinking present in polyurethanes means that the polymer
consists of a three-dimensional network and molecular weight is very high. In some respects
a piece of polyurethane can be regarded as one giant molecule. One consequence of this is
that typical polyurethanes do not soften or melt when they are heated...they are thermosetting
polymers. The choices available for the isocyanates and polyols, in addition to other
additives and processing conditions allow polyurethanes to have the very wide range of
properties that make them such widely used polymers.
Isocyanates are very reactive materials. This makes them useful in making polymers but also
requires special care in handling and use. The aromatic isocyanates,diphenylmethane
diisocyanate (MDI) or toluene diisocyanate (TDI) are more reactive
than aliphatic isocyanates, such as hexamethylene diisocyanate (HDI) or isophorone
diisocyanate (IPDI). Most of the isocyanates are difunctional, that is they have exactly two
isocyanate groups per molecule. An important exception to this is polymeric
diphenylmethane diisocyanate, which is a mixture of molecules with two-, three-, and four-
or more isocyanate groups. In cases like this the material has an average functionality greater
than two, commonly 2.7. Isocyanates with functionality greater than two act as crosslinking
sites as mentioned in the previous paragraph.
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Polyols are polymers in their own right and have on average two or more hydroxyl groups
per molecule. Polyether polyols are mostly made by polymerizing ethylene
oxide andpropylene oxide. Polyester polyols are made similarly to polyester polymers. The
polyols used to make polyurethanes are not "pure" compounds since they are often mixtures
of similar molecules with different molecular weights and mixtures of molecules that contain
different numbers of hydroxyl groups, which is why the "average functionality" is often
mentioned. Despite them being complex mixtures, industrial grade polyols have their
composition sufficiently well controlled to produce polyurethanes having consistent
properties. As mentioned earlier, it is the length of the polyol chain and the functionality that
contribute much to the properties of the final polymer. Polyols used to make rigid
polyurethanes have molecular weights in the hundreds, while those used to make flexible
polyurethanes have molecular weights up to ten thousand or more.
Table 1. Reactions
PU reaction mechanism catalyzed by a tertiary amine
generalized urethane reaction
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The polymerization reaction makes a polymer containing the urethane linkage, -
RNHCOOR'- and is catalyzed by tertiary amines, such as 1,4-diazabicyclo[2.2.2]octane (also
called DABCO or TEDA), and metallic compounds, such as dibutyltin dilaurate orbismuth
octanoate. This is often referred to as the gellation reaction or simply gelling.
If water is present in the reaction mixture (it is often added intentionally to make foams), the
isocyanate reacts with water to form a urea linkage and carbon dioxide gas and the resulting
polymer contains both urethane and urea linkages. This reaction is referred to as the blowing
reaction and is catalyzed by tertiary amines like bis-(2-dimethylaminoethyl)ether.
A third reaction, particularly important in making insulating rigid foams is the
isocyanatetrimerization reaction, which is catalyzed by potassium octoate, for example.
One of the most desirable attributes of polyurethanes is their ability to be turned into foam.
Making a foam requires the formation of a gas at the same time as the urethane
polymerization (gellation) is occurring. The gas can be carbon dioxide, either generated by
reacting isocyanate with water. or added as a gas or produced by boiling volatile liquids. In
the latter case heat generated by the polymerization causes the liquids to vaporize. The
liquids can be HFC-245fa (1,1,1,3,3-pentafluoropropane) and HFC-134a (1,1,1,2-
tetrafluoroethane), and hydrocarbons such as n-pentane.
Table 2. carbon dioxide gas formation
carbon dioxide gas formed by reacting water and isocyanate
8
When water is used to produce the gas, care must be taken to use the right combination of
catalysts to achieve the proper balance between gellation and blowing. The reaction to
generate carbon dioxide involves water molecule reacting with an isocyanate first forming an
unstable carbamic acid, which then decomposes into carbon dioxide and an amine. The
amine reacts with more isocyanate to give a substituted urea. Water has a very lowmolecular
weight, so even though the weight percent of water may be small, the molar proportion of
water may be high and considerable amounts of urea produced. The urea is not very soluble
in the reaction mixture and tends to form separate "hard segment" phases consisting mostly
of polyurea. The concentration and organization of these polyurea phases can have a
significant impact on the properties of the polyurethane foam.[12]
High-density microcellular foams can be formed without the addition of blowing agents by
mechanically frothing or nucleating the polyol component prior to use.
Surfactants are used in polyurethane foams to emulsify the liquid components, regulate cell
size, and stabilize the cell structure to prevent collapse and surface defects. Rigid foam
surfactants are designed to produce very fine cells and a very high closed cell content.
Flexible foam surfactants are designed to stabilize the reaction mass while at the same time
maximizing open cell content to prevent the foam from shrinking.
An even more rigid foam can be made with the use of specialty trimerization catalysts which
create cyclic structures within the foam matrix, giving a harder, more thermally stable
structure, designated as polyisocyanurate foams. Such properties are desired in rigid foam
products used in the construction sector.
Careful control of viscoelastic properties — by modifying the catalysts and polyols used —
can lead to memory foam, which is much softer at skin temperature than at room
temperature.
Foams can be either "closed cell", where most of the original bubbles or cells remain intact,
or "open cell", where the bubbles have broken but the edges of the bubbles are stiff enough
to retain their shape. Open cell foams feel soft and allow air to flow through so they are
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comfortable when used in seat cushions or mattresses. Closed cell rigid foams are used
as thermal insulation, for example in refrigerators.
Microcellular foams are tough elastomeric materials used in coverings of car steering
wheels or shoe soles.
Raw materials
The main ingredients to make polyurethane are isocyanates and polyols. Other materials are
added to help processing the polymer or to change the properties of the polymer.
Isocyanates
Isocyanates used to make polyurethane must have two or more isocyanate groups on each
molecule. The most commonly used isocyanates are the aromatic diisocyantes,toluene
diisocyanate (TDI) and methylene diphenyl diisocyanate, MDI.
TDI and MDI are generally less expensive and more reactive than other isocyanates.
Industrial grade TDI and MDI are mixtures of isomers and MDI often contains polymeric
materials. They are used to make flexible foam (for example slabstock foam for mattresses or
molded foams for car seats),[13] rigid foam (for example insulating foam in refrigerators)
elastomers (shoe soles, for example), and so on. The isocyanates may be modified by
partially reacting them with polyols or introducing some other materials to reduce volatility
(and hence toxicity) of the isocyanates, decrease their freezing points to make handling easier
or to improve the properties of the final polymers.
10
Figure 2. the aromatic methylene diphenyl diisocyanate, MDI
Aliphatic and cycloaliphatic isocyanates are used in smaller volumes, most often in coatings
and other applications where color and transparency are important since polyurethanes made
with aromatic isocyanates tend to darken on exposure to light.[14] The most important
aliphatic and cycloaliphatic isocyanates are 1,6-hexamethylene diisocyanate (HDI), 1-
isocyanato-3-isocyanatomethyl-3,5,5-trimethyl-cyclohexane (isophorone diisocyanate,
IPDI), and 4,4'-diisocyanato dicyclohexylmethane, (H12MDI or hydrogenated MDI).
Polyols
Polyols can be polyether polyols, which are made by the reaction of epoxides with an active
hydrogen containing starter compounds, or polyester polyols, which are made by the
polycondensation of multifunctional carboxylic acids and hydroxyl compounds. They can be
further classified according to their end use. Higher molecular weight polyols (molecular
weights from 2,000 to 10,000) are used to make more flexible polyurethanes while lower
molecular weight polyols make more rigid products.
Polyols for flexible applications use low functionality initiators such as dipropylene
glycol (f=2), glycerine (f=3) or a sorbitol/water solution (f=2.75).[15] Polyols for rigid
applications use high functionality initiators
such sucrose (f=8), sorbitol (f=6), toluenediamine (f=4), and Mannich bases (f=4). Propylene
oxide and/or ethylene oxide is added to the initiators until the desired molecular weight is
11
achieved. The order of addition and the amounts of each oxide affect many polyol properties,
such as compatibility, water-solubility, and reactivity. Polyols made with only propylene
oxide are terminated with secondary hydroxyl groups and are less reactive than polyols
capped with ethylene oxide, which contain a higher percentage of primary hydroxyl
groups. Graft polyols (also called filled polyols or polymer polyols) contain finely
dispersed styrene-acrylonitrile, acrylonitrile, or polyurea (PHD) polymer solids chemically
grafted to a high molecular weight polyether backbone. They are used to increase the load-
bearing properties of low-density high-resiliency (HR) foam, as well as add toughness to
microcellular foams and cast elastomers. Initiators such
as ethylenediamine and triethanolamine are used to make low molecular weight rigid foam
polyols that have built-in catalytic activity due to the presence of nitrogen atoms in the
backbone. A special class of polyether polyols, poly(tetramethylene ether) glycols, which are
made by polymerizing tetrahydrofuran, are used in high performance coating, wetting and
elastomer applications.
Conventional polyester polyols are based on virgin raw materials and are manufactured by
the direct polyesterification of high-purity diacids and glycols, such as adipic acid and 1,4-
butanediol. Polyester polyols are usually more expensive and more viscous than polyether
polyols, but they make polyurethanes with better solvent, abrasion, and cut resistance. Other
polyester polyols are based on reclaimed raw materials. They are manufactured by
transesterification (glycolysis) of recycled poly(ethyleneterephthalate) (PET)
ordimethylterephthalate (DMT) distillation bottoms with glycols such as diethylene glycol.
These low molecular weight, aromatic polyester polyols are used in rigid foam, and bring
low cost and excellent flammability characteristics to polyisocyanurate (PIR) boardstock and
polyurethane spray foam insulation. Specialty polyols
include polycarbonate polyols, polycaprolactone polyols, polybutadiene polyols,
and polysulfide polyols. The materials are used in elastomer, sealant, and adhesive
applications that require superior weatherability, and resistance to chemical and
environmental attack. Natural oil polyols derived from castor oil and other vegetable oilsare
used to make elastomers, flexible bunstock, and flexible molded foam.
Copolymerizing chlorotrifluoroethylene or tetrafluoroethylene with vinyl ethers containing
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hydroxyalkyl vinyl ether produces fluorinated (FEVE) polyols. Two component fluorinated
polyurethane prepared by reacting FEVE fluorinated polyols with polyisocyanate have been
applied for make ambient cure paint/coating. Since fluorinated polyurethanes contain high
percentage of fluorine-carbon bond which is the strongest bond among all chemical bonds.
Fluorinated polyurethanes have excellent resistance to UV, acids, alkali, salts, chemicals,
solvents, weathering, corrosion, fungi and microbial attack. These have become the first
choice for high performance coating/paints.
Chain extenders and cross linkers
Chain extenders (f=2) and cross linkers (f=3 or greater) are low molecular weight hydroxyl
and amine terminated compounds that play an important role in the polymer morphology of
polyurethane fibers, elastomers, adhesives, and certain integral skin and microcellular foams.
The elastomeric properties of these materials are derived from the phase separation of the
hard and soft copolymer segments of the polymer, such that the urethane hard segment
domains serve as cross-links between the amorphous polyether (or polyester) soft segment
domains. This phase separation occurs because the mainly non-polar, low melting soft
segments are incompatible with the polar, high melting hard segments. The soft segments,
which are formed from high molecular weight polyols, are mobile and are normally present
in coiled formation, while the hard segments, which are formed from the isocyanate and
chain extenders, are stiff and immobile. Because the hard segments are covalently coupled to
the soft segments, they inhibit plastic flow of the polymer chains, thus creating elastomeric
resiliency. Upon mechanical deformation, a portion of the soft segments are stressed by
uncoiling, and the hard segments become aligned in the stress direction. This reorientation of
the hard segments and consequent powerful hydrogen bonding contributes to high tensile
strength, elongation, and tear resistance values.[9][16][17][18][19] The choice of chain extender
also determines flexural, heat, and chemical resistance properties. The most important chain
extenders are ethylene glycol, 1,4-butanediol (1,4-BDO or BDO), 1,6-
hexanediol, cyclohexane dimethanol and hydroquinone bis(2-hydroxyethyl) ether (HQEE).
13
All of these glycols form polyurethanes that phase separate well and form well defined hard
segment domains, and are melt processable. They are all suitable for thermoplastic
polyurethanes with the exception of ethylene glycol, since its derived bis-phenyl urethane
undergoes unfavorable degradation at high hard segment levels.[7] Diethanolamine and
triethanolamine are used in flex molded foams to build firmness and add catalytic activity.
Diethyltoluenediamine is used extensively in RIM, and in polyurethane and polyurea
elastomer formulations.
Table 3. table of chain extenders and cross linkers [20]
hydroxyl compounds – difunctional molecules MW s.g. m.p. °C b.p. °C
ethylene glycol 62.1 1.110 -13.4 197.4
diethylene glycol 106.1 1.111 -8.7 245.5
ztriethylene glycol 150.2 1.120 -7.2 287.8
tetraethylene glycol 194.2 1.123 -9.4 325.6
propylene glycol 76.1 1.032 supercools 187.4
dipropylene glycol 134.2 1.022 supercools 232.2
tripropylene glycol 192.3 1.110 supercools 265.1
14
1,3-propanediol 76.1 1.060 -28 210
1,4-butanediol 92.1 1.017 20.1 235
1,6-hexanediol 118.2 1.017 43 250
ethanolamine 61.1 1.018 10.3 170
diethanolamine 105.1 1.097 28 271
methyldiethanolamine 119.1 1.043 -21 242
hydroxyl compounds – trifunctional molecules MW s.g. f.p. °C b.p. °C
glycerol 92.1 1.261 18.0 290
triethanolamine 149.2 1.124 21 -
amine compounds – difunctional molecules MW s.g. m.p. °C b.p. °C
diethyltoluenediamine 178.3 1.022 - 308
dimethylthiotoluenediamine 214.0 1.208 - -
15
Catalysts
Polyurethane catalysts can be classified into two broad categories, amine compounds and
metal complexes. Traditional amine catalysts have been tertiary amines such
astriethylenediamine ( TEDA, 1,4-diazabicyclo[2.2.2]octane
or DABCO), dimethylcyclohexylamine (DMCHA), and dimethylethanolamine (DMEA).
Tertiary amine catalysts are selected based on whether they drive the urethane
(polyol+isocyanate, or gel) reaction, the urea (water+isocyanate, or blow) reaction, or the
isocyanate trimerization reaction (e.g., using potassium acetate, to form isocyanurate ring
structure). Catalysts that contain a hydroxyl group or secondary amine, which react into the
polymer matrix, can replace traditional catalysts thereby reducing the amount of amine that
can come out of the polymer.[21][22]
Metallic compounds based on mercury, lead, tin, bismuth, and zinc are used as polyurethane
catalysts. Mercury carboxylates, are particularly effective catalysts for polyurethane
elastomer, coating and sealant applications, since they are very highly selective towards the
polyol+isocyanate reaction, but they are toxic. Bismuth and zinc carboxylates have been
used as alternatives. Alkyl tin carboxylates, oxides and mercaptides oxides are used in all
types of polyurethane applications. Tin mercaptides are used in formulations that contain
water, as tin carboxylates are susceptible to hydrolysis.[23][24]
Surfactants
Surfactants are used to modify the characteristics of both foam and non-foam polyurethane
polymers. They take the form of polydimethylsiloxane-polyoxyalkylene block
copolymers, silicone oils, nonylphenol ethoxylates, and other organic compounds. In foams,
they are used to emulsify the liquid components, regulate cell size, and stabilize the cell
structure to prevent collapse and sub-surface voids. In non-foam applications they are used as
air release and anti-foaming agents, as wetting agents, and are used to eliminate surface
defects such as pin holes, orange peel, and sink marks.
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Production
Polyurethanes are produced by mixing two or more liquid streams. The isocyanate is usually
added by itself and the polyol stream is usually more complex, containing catalysts,
surfactants, blowing agents and so on. The two components are referred to as a polyurethane
system, or simply a system. The isocyanate is commonly referred to in North America as the
'A-side' or just the 'iso'. The blend of polyols and other additives is commonly referred to as
the 'B-side' or as the 'poly'. This mixture might also be called a 'resin' or 'resin blend'. In
Europe the meanings for 'A-side' and 'B-side' are reversed. Resin blend additives may include
chain extenders, cross linkers, surfactants, flame retardants, blowing agents, pigments,
and fillers. Polyurethane can be made in a variety of densities and hardnesses by varying the
isocyanate, polyol or additives.
Health and safety
Fully reacted polyurethane polymer is chemically inert.[25] No exposure limits have been
established by OSHA (Occupational Safety and Health Administration) or ACGIH
(American Conference of Governmental Industrial Hygienists). It is not regulated by OSHA
for carcinogenicity. Polyurethane polymer is a combustible solid and can be ignited if
exposed to an open flame.[26] Decomposition from fire can produce mainly carbon monoxide,
and trace nitrogen oxides and hydrogen cyanide. Firefighters should wear self-contained
breathing apparatus in enclosed areas.
Liquid resin blends and isocyanates may contain hazardous or regulated components. They
should be handled in accordance with manufacturer recommendations found on product
labels, and in MSDS (Material Safety Data Sheet) and product technical literature.
Isocyanates are known skin and respiratory sensitizers, and proper engineering controls
should be in place to prevent exposure to isocyanate liquid and vapor. Additionally, amines,
glycols, and phosphate present in spray polyurethane foams present unknown risks to the
individuals exposed to them.[27] Proper hygiene controls and personal protective
17
equipment (PPE), such as gloves, respirators, and protective clothing and eye wear should be
used.
In the United States, additional health and safety information can be found through
organizations such as the Polyurethane Manufacturers Association (PMA) and the Center for
the Polyurethanes Industry (CPI), as well as from polyurethane system and raw material
manufacturers. In Europe, health and safety information is available from ISOPA,[28] the
European Diisocyanate and Polyol Producers Association. Regulatory information can be
found in the Code of Federal Regulations Title 21 (Food and Drugs) and Title 40 (Protection
of the Environment).
Fungus
Students at Yale University have noticed a fungus that eats polyurethane.[29] This fact was
reported from a trip to the Ecuadorian Amazon and the fungus is called Pestalotiopsis
microspora.[29]
Manufacturing
The methods of manufacturing polyurethane finished goods range from small, hand pour
piece-part operations to large, high-volume bunstock and boardstock production lines.
Regardless of the end-product, the manufacturing principle is the same: to meter the liquid
isocyanate and resin blend at a specified stoichiometric ratio, mix them together until a
homogeneous blend is obtained, dispense the reacting liquid into a mold or on to a surface,
wait until it cures, then demold the finished part.
Dispensing equipment
Although the capital outlay can be high, it is desirable to use a meter-mix or dispense unit for
even low-volume production operations that require a steady output of finished parts.
Dispense equipment consists of material holding (day) tanks, metering pumps, a mix head,
18
and a control unit. Often, a conditioning or heater-chiller unit is added to control material
temperature in order to improve mix efficiency, cure rate, and to reduce process variability.
Choice of dispense equipment components depends on shot size, throughput, material
characteristics such as viscosity and filler content, and process control. Material day tanks
may be single to hundreds of gallons in size, and may be supplied directly from drums, IBCs
(intermediate bulk containers, such as totes), or bulk storage tanks. They may incorporate
level sensors, conditioning jackets, and mixers. Pumps can be sized to meter in single grams
per second up to hundreds of pounds per minute. They can be rotary, gear, or piston pumps,
or can be specially hardened lance pumps to meter liquids containing highly abrasive fillers
such as wollastonite, chopped or hammer milled glass fibres.
Figure 3. A high pressure polyurethane dispense unit, showing control panel, high pressure pump, integral day tanks, and hydraulic drive unit.
19
Figure 4. A high pressure mix head, showing simple controls. Front view.
Figure 5. A high pressure mix head, showing material supply and hydraulic actuator lines. Rear view
20
The pumps can drive low-pressure (10 to 30 bar, ~1 to 3 MPa) or high-pressure (125 to 250
bar, ~12.5 to 25.0 MPa) dispense systems. Mix heads can be simple static mix tubes, rotary
element mixers, low-pressure dynamic mixers, or high-pressure hydraulically actuated direct
impingement mixers. Control units may have basic on/off – dispense/stop switches, and
analogue pressure and temperature gauges, or may be computer controlled with flow meters
to electronically calibrate mix ratio, digital temperature and level sensors, and a full suite of
statistical process control software. Add-ons to dispense equipment include nucleation or gas
injection units, and third or fourth stream capability for adding pigments or metering in
supplemental additive packages.
.
Figure 6. A low pressure mix head with calibration chamber installed, showing material supply and air actuator lines.
17
Figure 7. Low pressure mix head components, including mix chambers, conical mixers, and mounting plates
Figure 8. 5-gallon (20-liter) material day tanks for supplying a low pressure dispense unit.
22
Tooling
Distinct from pour-in-place, bun and boardstock, and coating applications, the production of
piece parts requires some type of tooling to contain and form the reacting liquid. The choice
of mold-making material is dependent on the expected number of uses to end-of-life (EOL),
molding pressure, flexibility, and heat transfer characteristics.
RTV silicone is used for tooling that has an EOL in the thousands of parts. It is typically
used for molding rigid foam parts, where the ability to stretch and peel the mold around
undercuts is needed. The heat transfer characteristic of RTV silicone tooling is poor. High-
performance, flexible polyurethane elastomers are also used in this way.
Epoxy, metal-filled epoxy, and metal-coated epoxy is used for tooling that has an EOL in the
tens-of-thousands of parts. It is typically used for molding flexible foam cushions and
seating, integral skin and microcellular foam padding, and shallow-draft RIM bezels and
fascia. The heat transfer characteristic of epoxy tooling is fair; the heat transfer characteristic
of metal-filled and metal-coated epoxy is good. Copper tubing can be incorporated into the
body of the tool, allowing hot water to circulate and heat the mold surface.
Aluminum is used for tooling that has an EOL in the hundreds-of-thousands of parts. It is
typically used for molding microcellular foam gasketing and cast elastomer parts, and is
milled or extruded into shape.
Mirror-finish stainless steel is used for tooling that imparts a glossy appearance to the
finished part. The heat transfer characteristic of metal tooling is excellent.
Finally, molded or milled polypropylene is used to create low-volume tooling for molded
gasket applications. Instead of many expensive metal molds, low-cost plastic tooling can be
formed from a single metal master, which also allows greater design flexibility. The heat
transfer characteristic of polypropylene tooling is poor, which must be taken into
consideration during the formulation process.
23
Applications
Polyurethane products have many uses. Over three quarters of the global consumption of
polyurethane products is in the form of foams, with flexible and rigid types being roughly
equal in market size. In both cases, the foam is usually behind other materials: flexible
foams are behind upholstery fabrics in commercial and domestic furniture; rigid foams
are inside the metal and plastic walls of most refrigerators and freezers, or behind paper,
metals and other surface materials in the case of thermal insulation panels in the
construction sector. Its use in garments is growing: for example, in lining the cups of
brassieres. Polyurethane is also used for moldings which include door frames, columns,
balusters, window headers, pediments, medallions and rosettes.
Figure 9. Polyurethane foam made with an aromatic isocyanate, which has been exposed to UV light. Readily apparent is the discoloration that occurs over time. This particular foam piece is approximately four inches wide and 1½ inches thick.
24
Polyurethane formulations cover an extremely wide range of stiffness, hardness, and
densities. These materials include:
Low-density flexible foam used in upholstery, bedding, and automotive and truck seating
Low-density rigid foam used for thermal insulation and RTM cores
Soft solid elastomers used for gel pads and print rollers
Low density elastomers used in footwear
Hard solid plastics used as electronic instrument bezels and structural parts
Flexible plastics used as straps and bands
Polyurethane foam is widely used in high resiliency flexible foam seating, rigid foam
insulation panels, microcellular foam seals and gaskets, durable elastomeric wheels and
tires, automotive suspension bushings, electrical potting compounds, seals, gaskets,
carpet underlay, and hard plastic parts (such as for electronic instruments).
Figure 10. characteristics of polyurethane materials
25
Usage per application
Table 4. The following table shows how polyurethanes are used (US data from 2004):[35]
Application Usage (millions of pounds) Percentage of total
Building & Construction 1,459 26.8%
Transportation 1,298 23.8%
Furniture & Bedding 1,127 20.7%
Appliances 278 5.1%
Packaging 251 4.6%
Textiles, Fibers & Apparel 181 3.3%
Machinery & Foundry 178 3.3%
Electronics 75 1.4%
Footwear 39 0.7%
Other uses 558 10.2%
Total 5,444 100.0%
Furniture
Open cell flexible polyurethane foam (FPF) is made by mixing polyols, diisocyanates,
catalysts, auxiliary blowing agents and other additives and allowing the resulting foam to
rise freely. Most FPF is manufactured using continuous processing technology and also
can be produced in batches where relatively small blocks of foam are made in open-
topped molds, boxes, or other suitable enclosurers. The foam is then cut to the desired
shape and size for use in a variety of furniture and furnishings applications.
Applications for flexible polyurethane foam include upholstered furniture cushions,
automotive seat cushions and interior trim, carpet cushion, and mattress padding and
solid-core mattress cores.
Flexible polyurethane foam is a recyclable product. [36]
26
Automobile seats
Flexible and semi-flexible polyurethane foams are used extensively for interior
components of automobiles, in seats, headrests, armrests, roof liners, dashboards and
instrument panels.
Figure 11. Polyurethane foam in the lower half of the mold in which it was made. When assembled into a car seat, this foam makes up the seat back. The forward-facing part of the seat back is the surface of the foam which is face-down in the mold.
27
Polyurethanes are used to make automobile seats in a remarkable manner. The seat
manufacturer has a mold for each seat model. The mold is a closeable "clamshell" sort of
structure that will allow quick casting of the seat cushion, so-called molded flexible
foam, which is then upholstered after removal from the mold.
It is possible to combine these two steps, so-called in-situ, foam-in-fabric or direct
moulding. A complete, fully assembled seat cover is placed in the mold and held in place
by vacuum drawn through small holes in the mold. Sometimes a thin pliable plastic film
backing on the fabric is used to help the vacuum work more effectively. The metal seat
frame is placed into the mold and the mold closed. At this point the mold contains what
could be visualized as a "hollow seat", a seat fabric held in the correct position by the
vacuum and containing a space with the metal frame in place.
Polyurethane chemicals are injected by a mixing head into the mold cavity. Then the
mold is held at a preset reaction temperature until the chemical mixture has foamed, filled
the mold, and formed stable soft foam. The time required is two to three minutes,
Figure 12. Foam after removal from the mold.
28
depending on the size of the seat and the precise formulation and operating conditions.
Then the mold is usually opened slightly for a minute or two for an additional cure time,
before the fully upholstered seat is removed.
Houses, sculptures, and decorations
The walls and ceiling (not just the insulation) of the futuristic Xanadu House were built
out of polyurethane foam. Domed ceilings and other odd shapes are easier to make with
foam than with wood. Foam was used to build oddly shaped buildings, statues, and
decorations in the Seuss Landing section of the Islands of Adventure theme park.
Speciality rigid foam manufactures sell foam that replace wood in carved sign and 3D-
topography industries. PU foam is also used as a thermal insulator in many houses.
Polyurethane resin is used as an aesthetic flooring material. Being seamless and water
resistant, it is gaining interest for use in (modern) interiors, especially in Western Europe.
Figure 13. Polyurethane being used as an insulator in house construction
29
Filling of spaces and cavities
Two Binary liquids, one of which is a polyurethane (either T6 or 16), when mixed and
aerated, expand into a hard, space-filling aerosolid.
Construction sealants and firestopping
Figure 14. Polyurethane used as a flooring material
Figure 15. Being poured as a liquid after which it hardens, polyurethane is a floor material that can be applied seamlessly.
30
Polyurethane sealants are available in one, two and three part systems, and in cartridges,
buckets or drums. Polyurethane sealants are used to fill gaps thereby preventing air and
water leakage. They are also used in conjunction with inorganic insulation, such as
rockwool or ceramic fibres, for firestopping. Firestops can thwart smoke and hose-stream
passage.
Water vessels
Inflatable boats
Some raft manufacturers use urethane for the construction of inflatable boats. AIRE uses
urethane membrane material as an air-retentive bladder inside a PVC shell, whereas
SOTAR uses urethane membrane materials as a coating on some boats. Maravia uses a
liquid urethane material which is spray-coated over PVC to enhance air retention and
increase abrasion resistance.
Surfboards
Some surfboards are made with a rigid polyurethane core. A rigid foam blank is molded,
shaped to specification, then covered with fiberglass cloth and polyester resin.
Rigid-hulled boats
Some boat hulls have a rigid polyurethane foam core sandwiched between fiberglass
skins. The foam provides strength, buoyancy, and sound deadening.
Boat decks and outdoor marine surface areas
Some boat decks including U.S Navy vessels use specialized polyurethane sealants to
protect from constant moisture and harsh oceanic elements. As an example, Durabak-
M26 uses a custom single-part polyurethane to prevent water seepage to unwanted areas.
31
Flexible plastics
Tennis grips
Polyurethane has been used to make several Tennis Overgrips such as Yonex Super Grap,
Wilson Pro Overgrip and many other grips. These grips are highly stretchable to ensure
the grip wraps neatly around the racquet's handle.
Watch-band wrapping
Polyurethane is used as a black wrapping for timepiece bracelets over the main material
which is generally stainless steel. It is used for comfort, style, and durability.
Textiles
A thin film of polyurethane finish is added to a polyester weave to create polyurethane
laminate (PUL), which is used for its waterproof and windproof properties in outerwear,
diapers, shower curtains, and so forth. PU is used in some cutting-edge swimsuits to
provide buoyancy for competitive swimmers. There are restrictions as the buoyancy
enhances swimming performance.[citation needed]
A still more popular use of polyurethane in textiles is in the form of spandex, also known
as elastane or by DuPont's brand name Lycra. Polyurethane fibers in the form of spandex
can stretch up to 600% and still return to their original shape. Spandex is spun with other
fibers, such as cotton, nylon, or polyester, to create stretchable fibers essential for
clothing for both sports and fashion.[37]
Varnish
Polyurethane materials are commonly formulated as paints and varnishes for finishing
coats to protect or seal wood. This use results in a hard, abrasion-resistant, and durable
32
coating that is popular for hardwood floors, but considered by some to be difficult or
unsuitable for finishing furniture or other detailed pieces. Relative to oil or shellac
varnishes, polyurethane varnish forms a harder film which tends to de-laminate if
subjected to heat or shock, fracturing the film and leaving white patches. This tendency
increases when it is applied over softer woods like pine. This is also in part due to
polyurethane's lesser penetration into the wood. Various priming techniques are
employed to overcome this problem, including the use of certain oil varnishes, specified
"dewaxed" shellac, clear penetrating epoxy, or "oil-modified" polyurethane designed for
the purpose. Polyurethane varnish may also lack the "hand-rubbed" lustre of drying oils
such as linseed or tung oil; in contrast, however, it is capable of a much faster and higher
"build" of film, accomplishing in two coats what may require many applications of oil.
Polyurethane may also be applied over a straight oil finish, but because of the relatively
slow curing time of oils, the presence of volatile byproducts of curing, and the need for
extended exposure of the oil to oxygen, care must be taken that the oils are sufficiently
cured to accept the polyurethane.
Unlike drying oils and alkyds which cure, after evaporation of the solvent, upon reaction
with oxygen from the air, polyurethane coatings cure after evaporation of the solvent by a
variety of reactions of chemicals within the original mix, or by reaction with moisture
from the air. Certain products are "hybrids" and combine different aspects of their parent
components. "Oil-modified" polyurethanes, whether water-borne or solvent-borne, are
currently the most widely used wood floor finishes.
Exterior use of polyurethane varnish may be problematic due to its susceptibility to
deterioration through ultra-violet (UV) light exposure. All clear or translucent varnishes,
and indeed all film-polymer coatings (i.e., paint, stain, epoxy, synthetic plastic, etc.) are
susceptible to this damage in varying degrees. Pigments in paints and stains protect
against UV damage, while UV-absorbers are added to polyurethane and other varnishes
(in particular "spar" varnish) to work against UV damage. Polyurethanes are typically the
33
most resistant to water exposure, high humidity, temperature extremes, and fungus or
mildew, which also adversely affect varnish and paint performance.
Wheels
Polyurethane is also used in making solid tires. Industrial applications include forklift
drive and load wheels, grocery cart and, rollercoaster wheels. Modern roller blading and
skateboarding became economical only with the introduction of tough, abrasion-resistant
polyurethane parts, helping to usher in the permanent popularity of what had once been
an obscure 1960s craze. The durability of polyurethane wheels allowed the range of tricks
and stunts performed on skateboards to expand considerably. Polyurethane is also used to
make small equipment tires in the lawn and garden industry for wheelbarrows, hand
trucks, lawn mowers, carts, etc. They provide the bounce and feel of an air-filled tire with
the benefit of no flats. They weigh about the same as air-filled tires as well, even though
they are solid polyurethane all the way through. Other constructions have been developed
for pneumatic tires, and microcellular foam variants are widely used in tires on
wheelchairs, bicycles and other such uses. These latter foam types are also widely
encountered in car steering wheels and other interior and exterior automotive parts,
including bumpers and fenders.
Automotive Parts
Polyurethane usage has increased over the past twenty years in the automotive industry. It
is being used to replace traditional rubber bushings which are known to fail or wear out
on road surfaces prone to large amounts of salt and chemical debris.
Using polyurethane bushings can have many benefits like maintaining the right alignment
of caster, camber and toe and thereby increasing the overall control and handling. It also
increases the lifespan, provides more resistance to wear out and is less pervious to oil and
similar road contaminants.[38]
34
Polyurethane (PU) is popularized in the manufacturing of some of the highest quality
aerodynamic components /body kits (kits) for varying automobiles (car, truck, and SUV)
on the market. These components include bumpers [1], side skirts, roll pans, and wiper
cowls. Polyurethane allows production of durable components unlike the conventional
fiberglass (FRP) that can easily break upon impact. Polyurethane is highly flexible
therefore more resistant to damage. Including durability, these body kits when produced
by a reputable manufacturer, exhibits less imperfections, are easy to install and maintain,
and are affordable.[39]
Super-Polyurethane (SPU) is a much stronger- weather proof
polyurethane material researched and developed and used exclusively by JP Tokyo and
JP USA, Co.
When fiberglass body kits begin to show cracks, chips from usual wear and tear, a well
manufactured polyurethane components have similar durability to a factory installed
bumper. As mentioned above, when produced by a reputable manufacturer, tend to have
less pinholes and casting imperfections. Flexibility of polyurethane makes them easy to
work with. Installation can be completed individually as a "do-it-yourself" project.
Maintenance is extremely simple. Concerning pricing, it may vary depending on the
manufacturer but are kept between an affordable range. As good as it sounds,
polyurethane body kits too have its downfalls. Fiberglass or carbon fiber components are
lighter in weight than most polyurethane kits. Polyurethane, again is flexible but more
material and thickness is most often needed to keep adequate stiffness for road use. For
drivers seeking speed for their higher performance vehicle, this can become a problem.
Also, unlike fiberglass, polyurethane cannot be patched or repaired. Though it is much
harder to damage, if damage did occur, the entire component must be removed and
replaced.[39]
There are varying options when purchasing polyurethane kits. The following
list includes reputable polyurethane components manufacturer: Xenon, JP USA Co,
Kaminari. All consumers must be aware of lower quality replicas on the market.
35
Electronic components
Often electronic components are protected from environmental influence and mechanical
shock by enclosing them in polyurethane. Typically polyurethanes are selected for the
excellent abrasion resistances, good electrical properties, excellent adhesion, impact
strength, and low-temperature flexibility. The disadvantage of polyurethanes is the
limited upper service temperature (typically 250 °F (121 °C)). In production the
electronic manufacture would purchase a two-part urethane (resin and catalyst) that
would be mixed and poured onto the circuit assembly (see Resin dispensing). In most
cases, the final circuit board assembly would be unrepairable after the urethane has cured.
Because of its physical properties and low cost, polyurethane encapsulation (potting) is a
popular option in the automotive manufacturing sector for automotive circuits and
sensors.
Adhesives
Polyurethane can be used as an adhesive, especially as a woodworking glue. Its main
advantage over more traditional wood glues is its water resistance. It was introduced to
the general North American market in the 1990s as Gorilla Glue and Excel, but had been
available in Europe much earlier.
On the way to a new and better glue for bookbinders, a new adhesive system was
introduced for the first time in 1985. The base for this system is polyether or polyester,
whereas polyurethane (PUR) is used as prepolymer. Its special features are coagulation at
room temperature and resistance to moisture.
First generation (1988)
Low starting solidity
High viscosity
Cure time >3 days
36
Second generation (1996)
Low starting solidity
High viscosity
Cure time <3 days
Third generation (2000)
Good starting solidity
Low viscosity
Cure time between 6 and 16 hours
Fourth generation (present)
Good starting solidity
Very low viscosity
Cure reached within a few seconds due to dual-core systems
Advantages of polyurethane glue in the bookbinding industry:
PUR is significantly better than hotmelt or cold glue. Because of the lack of moisture in
the glue, papers with contrary grain direction can be processed without problems. Even
printed and supercalandered paper can be bound without problems. It is the most
economical glue, with a theoretical application thickness of 0.01 mm. However, in actual
use, it is not practical to apply less than 0.03 mm.
PUR glue is extremely weather-proof, and stable at temperatures from −40 °C to 100 °C.
Abrasion resistance
Thermoset polyurethanes are also used as a protective coating against abrasion. Cast
polyurethane over materials such as steel will absorb particle impact more efficiently.
Polyurethanes have been proven to last in excess of 25 years in abrasive environments
where non-coated steel would erode in less than 8 years. Polyurethanes are used in
industries such as:
Mining and mineral processing
37
Aggregate
Transportation
Concrete
Paper processing
Power
Inflatable boat manufacture
Polyurethane is also used in the concrete construction industry to create formliners.
Polyurethane formliners serves as a mold for concrete, creating a variety of textures and
art.
In 2007, the global consumption of polyurethane raw materials was above 12 million metric
tons, the average annual growth rate is about 5%.[30]
Testing
Effects of visible light
Polyurethanes, especially those made using aromatic isocyanates,
contain chromophores which interact with light. This is of particular interest in the area of
polyurethane coatings, where light stability is a critical factor and is the main reason
that aliphatic isocyanates are used in making polyurethane coatings. When PU foam, which
is made using aromatic isocyanates, is exposed to visible light it discolors, turning from off-
white to yellow to reddish brown. It has been generally accepted that apart from yellowing,
visible light has little effect on foam properties.[31][32] This is especially the case if the
yellowing happens on the outer portions of a large foam, as the deterioration of properties in
the outer portion has little effect on the overall bulk properties of the foam itself.
It has been reported that exposure to visible light can affect the variability of some physical
property test results.[33] Consequently, it was recommended that foam samples should be
protected from exposure to light prior to testing.
Higher-energy UV radiation promotes chemical reactions in foam, some of which are
detrimental to the foam structure.[34]
38
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28. ^ http://www.isopa.org ISOPA
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