A polyurethane, commonly abbreviated PU, is any polymer consisting of a chain of organic units joined by urethane links. A polymer is a large Molecule ( Macromolecule) composed of repeating Structural units typically connected by Covalent Chemical bonds Organic chemistry is a discipline within Chemistry which involves the scientific study of the structure properties composition reactions, and preparation Carbamates, or Urethanes are a group of Organic compounds sharing a common Functional group with the general structure -NH(COO- Polyurethane polymers are formed by reacting a monomer containing at least two isocyanate functional groups with another monomer containing at least two alcohol groups in the presence of a catalyst. A monomer (from Greek mono "one" and meros "part" is a small Molecule that may become chemically bonded to other Isocyanate is the Functional group of atoms &ndashN=C=O (1 Nitrogen, 1 Carbon, 1 Oxygen) not to be confused with the Cyanate In Organic chemistry, functional groups are specific groups of Atoms within Molecules that are responsible for the characteristic Chemical reactions In Chemistry, an alcohol is any Organic compound in which a Hydroxyl group ( - O[[hydrogen H]]) is bound to a Carbon Catalysis is the process in which the rate of a Chemical reaction is increased by means of a Chemical substance known as a catalyst

PU polymer formed by reacting a diisocyanate with a polyol

Polyurethane formulations cover an extremely wide range of stiffness, hardness, and densities. These materials include:

• low density flexible foam used in upholstery and bedding,
• low density rigid foam used for thermal insulation and e. The most general definition of foam is a substance that is formed by trapping many gas Bubbles in a Liquid or Solid. Upholstery is the work of providing Furniture, especially seats with Padding, springs Webbing, and fabric or Leather The term thermal insulation can refer to materials used to reduce the rate of Heat transfer, or the methods and processes used to reduce heat transfer g. automobile dashboards,
• soft solid elastomers used for gel pads and print rollers, and
• hard solid plastics used as electronic instrument bezels and structural parts. A dashboard, dash, and sometimes fascia (chiefly in British English) is a control panel located under the Windshield of an Automobile An elastomer is a Polymer with the property of Elasticity. The term which is derived from elastic polymer, is often used interchangeably with the term

Polyurethanes are widely used in high resiliency flexible foam seating, rigid foam insulation panels, microcellular foam seals and gaskets, durable elastomeric wheels and tires, electrical potting compounds, high performance adhesives and sealants, Spandex fibres, seals, gaskets, carpet underlay, and hard plastic parts. A seal can mean a wax seal bearing an impressed figure or an embossed figure in paper with the purpose of authenticating a document but the term can also mean any device for A gasket is a mechanical seal that fills the space between two objects generally to prevent leakage between the two objects while under compression. Glue or adhesive is a compound that adheres or bonds two items together Spandex or elastane is a Synthetic fiber known for its exceptional elasticity. Synthetic fibers are the result of extensive research by Scientists to improve upon naturally occurring Animal and plant A carpet is any loom-woven felted textile or grass floor covering

Polyurethane products are often called "urethanes". They should not be confused with the specific substance urethane, also known as ethyl carbamate. Ethyl carbamate (also called urethane) is a substance first prepared in the nineteenth century Polyurethanes are not produced from ethyl carbamate, nor do they contain it.

History

The pioneering work on polyurethane polymers was conducted by Otto Bayer and his coworkers in 1937 at the laboratories of I.G. Farben in Leverkusen, Germany. Otto Bayer (1902&ndash1982 was a German industrial Chemist who was head of the research group that discovered the polyaddition for the synthesis of Polyurethanes IG Farben (short for Interessen-Gemeinschaft Farbenindustrie AG, "syndicate of dyestuff corporations" and also called I ^[1] They recognized that using the polyaddition principle to produce polyurethanes from liquid diisocyanates and liquid polyether or polyester diols seemed to point to special opportunities, especially when compared to already existing plastics that were made by polymerizing olefins, or by polycondensation. Ether is a class of Organic compounds which contain an ether group — an Oxygen Atom connected to two (substituted Alkyl Polyester is a category of Polymers which contain the Ester Functional group in their main chain Step-growth polymerization is a Polymerization process that involves a Chemical reaction between multifunctional Monomer molecules The new monomer combination also circumvented existing patents obtained by Wallace Carothers on polyesters. Wallace Hume Carothers ( April 27, 1896 &ndash April 29, 1937) was an American chemist inventor and the leader of Organic chemistry Polyester is a category of Polymers which contain the Ester Functional group in their main chain ^[2] Initially, work focused on the production of fibres and flexible foams. With development constrained by World War II (when PU's were applied on a limited scale as aircraft coating^[2]), it was not until 1952 that polyisocyanates became commercially available. World War II, or the Second World War, (often abbreviated WWII) was a global military conflict which involved a majority of the world's nations, including Commercial production of flexible polyurethane foam began in 1954, based on toluene diisocyanate (TDI) and polyester polyols. Toluene diisocyanate (TDI is an aromatic diisocyanate. It is produced for reaction with Polyols to form Polyurethanes It exists in two The invention of these foams (initially called imitation swiss cheese by the inventors^[2]) was thanks to water accidentally introduced in the reaction mix. This article describes a kind of cheese produced primarily in Canada and the United States. These materials were also used to produce rigid foams, gum rubber, and elastomers. Linear fibres were produced from hexamethylene diisocyanate (HDI) and 1,4-butanediol (BDO). Hexamethylene diisocyanate (HDI is an organic compound in the class known as Isocyanates More specifically it is an aliphatic diisocyanate

The first commercially available polyether polyol, poly(tetramethylene ether) glycol, was introduced by DuPont in 1956 by polymerizing tetrahydrofuran. Poly(tetramethylene ether glycol is a Polyether polyol. It is also known as PTMEG or polytetrahydrofuran and various tradenames such as "Terathane" E I du Pont de Nemours and Company (,) is an American chemical company that was founded in July 1802 as a Gunpowder mill by Eleuthère Irénée "THF" redirects here For other uses see THF (disambiguation. Less expensive polyalkylene glycols were introduced by BASF and Dow Chemical the following year, 1957. BASF SE () is a German chemical company and the largest chemical company in the world The Dow Chemical Company () is an American Multinational corporation headquartered in Midland Michigan. These polyether polyols offered technical and commercial advantages such as low cost, ease of handling, and better hydrolytic stability; and quickly supplanted polyester polyols in the manufacture of polyurethane goods. Another early pioneer in PU's was the Mobay corporation. Mobay Chemical Corporation, based in Pittsburgh Pennsylvania, was a joint venture of Monsanto and Bayer to market Polyurethanes in the ^[2] In 1960 more than 45,000 tons of flexible polyurethane foams were produced. As the decade progressed, the availability of chlorofluoroalkane blowing agents, inexpensive polyether polyols, and methylene diphenyl diisocyanate (MDI) heralded the development and use of polyurethane rigid foams as high performance insulation materials. The haloalkanes (also known as halogenoalkanes or alkyl halides) are a group of Chemical compounds consisting of Alkanes such as Methane Methylene diphenyl diisocyanate, most often abbreviated as MDI, is an aromatic diisocyanate. Rigid foams based on polymeric MDI (PMDI) offered better thermal stability and combustion characteristics than those based on TDI. In 1967, urethane modified polyisocyanurate rigid foams were introduced, offering even better thermal stability and flammability resistance to low density insulation products. Description Polyisocyanurate, also referred to as PIR or ISO, is essentially an improvement on Polyurethane (PUR Flammability is the ease with which a substance will ignite causing Fire or Combustion. Also during the 1960s, automotive interior safety components such as instrument and door panels were produced by back-filling thermoplastic skins with semi-rigid foam. A thermoplastic is a Plastic that Melts to a liquid when heated and freezes to a Brittle, very Glassy state when cooled sufficiently

In 1969, Bayer AG exhibited an all plastic car in Dusseldorf, Germany. Parts of this car were manufactured using a new process called RIM, Reaction Injection Molding. Reaction injection molding ( RIM molding) is similar to Injection molding except that a reaction occurs within the mold RIM technology uses high-pressure impingement of liquid components followed by the rapid flow of the reaction mixture into a mold cavity. Large parts, such as automotive fascia and body panels, can be molded in this manner. Fascia (făsh'ē-ə pl fas·ci·ae (făsh'ē-ē adj fascial (făsh'ē-əl (from Latin: a band is the Soft tissue component of Polyurethane RIM evolved into a number of different products and processes. Using diamine chain extenders and trimerization technology gave poly(urethane urea), poly(urethane isocyanurate), and polyurea RIM. A diamine is a type of Polyamine with exactly two Amino groups Examples include The simplest example Hydrazine Diamines In Chemistry a trimer is a reaction product of three identical Molecules Trimers are typically encountered as cyclic trimers The addition of fillers, such as milled glass, mica, and processed mineral fibres gave arise to RRIM, reinforced RIM, which provided improvements in flexural modulus (stiffness) and thermal stability. The word "mica" is thought to be derived from the Latin word la micare, "glitteren" in reference to the brilliant appearance of this mineral (especially Stiffness is the resistance of an elastic body to Deformation by an applied Force. This technology allowed production of the first plastic-body automobile in the United Sates, the Pontiac Fiero, in 1983. The Pontiac Fiero is a mid-engined Sports car that was built by the Pontiac division of General Motors from 1984 to 1988 Further improvements in flexural modulus were obtained by incorporating preplaced glass mats into the RIM mold cavity, also known as SRIM, or structural RIM.

Starting in the early 1980s, water-blown microcellular flexible foam was used to mold gaskets for panel and radial seal air filters in the automotive industry. Since then, increasing energy prices and the desire to eliminate PVC plastisol from automotive applications have greatly increased market share. Costlier raw materials are offset by a significant decrease in part weight and in some cases, the elimination of metal end caps and filter housings. Highly filled polyurethane elastomers, and more recently unfilled polyurethane foams are now used in high-temperature oil filter applications.

Polyurethane foam (including foam rubber) is often made by adding small amounts of volatile materials, so-called blowing agents, to the reaction mixture. A foaming agent is a surfactant which when present in small amounts facilitates the formation of a Foam, or enhances its colloidal stability by inhibiting the coalescence of These simple volatile chemicals yield important performance characteristics, primarily thermal insulation. In the early 1990s, because of their impact on ozone depletion, the Montreal Protocol led to the greatly reduced use of many chlorine-containing blowing agents, such as trichlorofluoromethane (CFC-11). Ozone depletion describes two distinct but related observations a slow steady decline of about 4 percent per decade in the total amount of Ozone in Earth's For other similarly-named agreements see Montreal Convention (disambiguation. Chlorine (ˈklɔriːn from the Greek word 'χλωρóς' ( khlôros, meaning 'pale green' is the Chemical element with Atomic number 17 and Trichlorofluoromethane also called freon-11, CFC-11, or R-11, is a Chlorofluorocarbon. Other haloalkanes, such as the hydrochlorofluorocarbon 1,1-dichloro-1-fluoroethane (HCFC-141b), were used as interim replacements until their phase out under the IPPC directive on greenhouse gases in 1994 and by the Volatile Organic Compounds (VOC) directive of the EU in 1997 (See: Haloalkanes). The haloalkanes (also known as halogenoalkanes or alkyl halides) are a group of Chemical compounds consisting of Alkanes such as Methane Greenhouse gases are gaseous constituents of the atmosphere bothnatural and anthropogenic that absorb and emit radiation at specific wavelengths within the spectrum of thermal infrared The European Union ( EU) is a political and economic union of twenty-seven member states, located primarily in The haloalkanes (also known as halogenoalkanes or alkyl halides) are a group of Chemical compounds consisting of Alkanes such as Methane 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) became more widespread in North America and the EU, although chlorinated blowing agents remained in use in many developing countries. Carbon dioxide ( Chemical formula:) is a Chemical compound composed of two Oxygen Atoms covalently bonded to a single Pentane is any or one of the Organic compounds with the formula C5H12 ^[3]

Building on existing polyurethane spray coating technology and polyetheramine chemistry, extensive development of two-component polyurea spray elastomers took place in the 1990s. Their fast reactivity and relative insensitivity to moisture make them useful coatings for large surface area projects, such as secondary containment, manhole and tunnel coatings, and tank liners. Excellent adhesion to concrete and steel is obtained with the proper primer and surface treatment. Adhesion is the tendency of certain dissimilar molecules to cling together due to Attractive forces. Concrete is a construction material composed of Cement (commonly Portland cement) as well as other cementitious materials such as Fly ash and Slag Steel is an Alloy consisting mostly of Iron, with a Carbon content between 0 During the same period, new two-component polyurethane and hybrid polyurethane-polyurea elastomer technology was used to enter the marketplace of spray-in-place load bed liners. This technique for coating pickup truck beds and other cargo bays creates a durable, abrasion resistant composite with the metal substrate, and eliminates corrosion and brittleness associated with drop-in thermoplastic bed liners.

The use of polyols derived from vegetable oils to make polyurethane products began garnering attention beginning around 2004, partly due to the rising costs of petrochemical feedstocks and partially due to an enhanced public desire for environmentally friendly green products. Petrochemicals are chemical products made from raw materials of Petroleum or other Hydrocarbon origin Environmental friendly, eco-friendly, and nature friendly are synonyms used to refer to Goods and services considered to inflict minimal harm Green chemistry, also called sustainable chemistry is a chemical philosophy encouraging the design of products and processes that reduce or eliminate the use and generation of hazardous ^[4] One of the most vocal supporters of these polyurethanes made using natural oil polyols is the Ford Motor Company. Natural oil polyols, also known as NOPs or biopolyols are polyols derived from Vegetable oils by several different techniques Ford Motor Company is an American Multinational corporation and the world's fourth largest automaker based on Worldwide vehicle sales, following ^[5]

Chemistry

generalized polyurethane reaction

Polyurethanes are in the class of compounds called reaction polymers, which include epoxies, unsaturated polyesters, and phenolics. In Chemistry, epoxy or polyepoxide is a Thermosetting Epoxide Polymer that cures (polymerizes and crosslinks when mixed with a Polyester is a category of Polymers which contain the Ester Functional group in their main chain In Organic chemistry, phenols, sometimes called phenolics, are a class of Chemical compounds consisting of a Hydroxyl group (- ^{[6][7][8][9][10]} A urethane linkage is produced by reacting an isocyanate group, -N=C=O with a hydroxyl (alcohol) group, -OH. Isocyanate is the Functional group of atoms &ndashN=C=O (1 Nitrogen, 1 Carbon, 1 Oxygen) not to be confused with the Cyanate Hydroxyl in Chemistry stands for a molecule consisting of an Oxygen atom and a Hydrogen atom connected by a Covalent bond. In Chemistry, an alcohol is any Organic compound in which a Hydroxyl group ( - O[[hydrogen H]]) is bound to a Carbon Polyurethanes are produced by the polyaddition reaction of a polyisocyanate with a polyalcohol (polyol) in the presence of a catalyst and other additives. In this case, a polyisocyanate is a molecule with two or more isocyanate functional groups, R-(N=C=O)_{n ≥ 2} and a polyol is a molecule with two or more hydroxyl functional groups, R'-(OH)_{n ≥ 2}. The reaction product is a polymer containing the urethane linkage, -RNHCOOR'-. Isocyanates will react with any molecule that contains an active hydrogen. Importantly, isocyanates react with water to form a urea linkage and carbon dioxide gas; they also react with polyetheramines to form polyureas. Urea is an Organic compound with the Chemical formula ( N[[hydrogen H]]22 C[[oxygen O]] Carbon dioxide ( Chemical formula:) is a Chemical compound composed of two Oxygen Atoms covalently bonded to a single Polyurea is a type Elastomer that is derived from the reaction product of an Isocyanate component and a Synthetic resin blend component Commercially, polyurethanes are produced by reacting a liquid isocyanate with a liquid blend of polyols, catalyst, and other additives. Catalysis is the process in which the rate of a Chemical reaction is increased by means of a Chemical substance known as a catalyst These 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. Cross-links are bonds that link one Polymer chain to another They can be Covalent bonds or Ionic bonds "Polymer chains" can refer Surfactants are wetting agents that lower the Surface tension of a liquid allowing easier spreading and lower the Interfacial tension between two liquids Flame retardants are materials that inhibit or resist the spread of Fire. A foaming agent is a surfactant which when present in small amounts facilitates the formation of a Foam, or enhances its colloidal stability by inhibiting the coalescence of For the drug referred to as "pigment" see Black tar heroin.

The first essential component of a polyurethane polymer is the isocyanate. Molecules that contain two isocyanate groups are called diisocyanates. These molecules are also referred to as monomers or monomer units, since they themselves are used to produce polymeric isocyanates that contain three or more isocyanate functional groups. A monomer (from Greek mono "one" and meros "part" is a small Molecule that may become chemically bonded to other Isocyanates can be classed as aromatic, such as diphenylmethane diisocyanate (MDI) or toluene diisocyanate (TDI); or aliphatic, such as hexamethylene diisocyanate (HDI) or isophorone diisocyanate (IPDI). Methylene diphenyl diisocyanate, most often abbreviated as MDI, is an aromatic diisocyanate. Toluene diisocyanate (TDI is an aromatic diisocyanate. It is produced for reaction with Polyols to form Polyurethanes It exists in two In Organic chemistry, compounds composed of Carbon and Hydrogen are divided into two classes Aromatic compounds which contain Benzene rings Hexamethylene diisocyanate (HDI is an organic compound in the class known as Isocyanates More specifically it is an aliphatic diisocyanate Isophorone diisocyanate (IPDI is an organic compound in the class known as Isocyanates More specifically it is an aliphatic diisocyanate An example of a polymeric isocyanate is polymeric diphenylmethane diisocyanate, which is a blend of molecules with two-, three-, and four- or more isocyanate groups, with an average functionality of 2. 7. Isocyanates can be further modified by partially reacting them with a polyol to form a prepolymer. A quasi-prepolymer is formed when the stoichiometric ratio of isocyanate to hydroxyl groups is greater than 2:1. Stoichiometry (sometimes called reaction stoichiometry to distinguish it from composition stoichiometry is the Calculation of Quantitative (measurable A true prepolymer is formed when the stoichiometric ratio is equal to 2:1. Important characteristics of isocyanates are their molecular backbone, % NCO content, functionality, and viscosity. Viscosity is a measure of the resistance of a Fluid which is being deformed by either Shear stress or Extensional stress.

The second essential component of a polyurethane polymer is the polyol. Molecules that contain two hydroxyl groups are called diols, those with three hydroxyl groups are called triols, et cetera. A diol or glycol is a Chemical compound containing two Hydroxyl groups (-OH groups Vicinal diols have hydroxyl groups attached to adjacent atoms In practice, polyols are distinguished from short chain or low-molecular weight glycol chain extenders and cross linkers such as ethylene glycol (EG), 1,4-butanediol (BDO), diethylene glycol (DEG), glycerine, and trimethylol propane (TMP). Ethylene glycol ( monoethylene glycol ( MEG) 12-ethanediol, IUPAC name: ethane-12-diol) is an Alcohol with two -OH Diethylene glycol (DEG is an Organic compound described by the structural formula HO-CH2-CH2-O-CH2-CH2-OH Polyols are polymers in their own right. They are formed by base-catalyzed addition of propylene oxide (PO), ethylene oxide (EO) onto a hydroxyl or amine containing initiator, or by polyesterification of a di-acid, such as adipic acid, with glycols, such as ethylene glycol or dipropylene glycol (DPG). In acid catalysis and base catalysis a Chemical reaction is catalyzed by an Acid or a base. Propylene oxide is a highly toxic flammable Chemical compound. Adipic acid ( IUPAC Systematic name: hexanedioic acid) is a di Carboxylic acid. Polyols extended with PO or EO are polyether polyols. Ether is a class of Organic compounds which contain an ether group — an Oxygen Atom connected to two (substituted Alkyl Polyols formed by polyesterification are polyester polyols. Polyester is a category of Polymers which contain the Ester Functional group in their main chain The choice of initiator, extender, and molecular weight of the polyol greatly affect its physical state, and the physical properties of the polyurethane polymer. Important characteristics of polyols are their molecular backbone, initiator, molecular weight, % primary hydroxyl groups, functionality, and viscosity.

PU reaction mechanism catalyzed by a tertiary amine

carbon dioxide gas formed by reacting water and isocyanate

The polymerization reaction is catalyzed by tertiary amines, such as dimethylcyclohexylamine, and organometallic compounds, such as dibutyltin dilaurate or bismuth octanoate. In Polymer chemistry, polymerization is a process of reacting Monomer Molecules together in a Chemical reaction to form three-dimensional networks Amines are Organic compounds and Functional groups that contain a basic Nitrogen Atom with a Lone pair. Organometallic chemistry is the study of Chemical compounds containing bonds between Carbon and a Metal. Furthermore, catalysts can be chosen based on whether they favor the urethane (gel) reaction, such as 1,4-diazabicyclo[2. 2. 2]octane (also called DABCO or TEDA), or the urea (blow) reaction, such as bis-(2-dimethylaminoethyl)ether, or specifically drive the isocyanate trimerization reaction, such as potassium octoate. DABCO or 14-diazabicyclooctane is a Chemical compound. It is used as a Catalyst, particularly in making Polyurethanes, and complexing Ligand

One of the most desirable attributes of polyurethanes is their ability to be turned into foam. Blowing agents such as water, certain halocarbons such as HFC-245fa (1,1,1,3,3-pentafluoropropane) and HFC-134a (1,1,1,2-tetrafluoroethane), and hydrocarbons such as n-pentane, can be incorporated into the poly side or added as an auxiliary stream. Pentane is any or one of the Organic compounds with the formula C5H12 Water reacts with the isocyanate to create carbon dioxide gas, which fills and expands cells created during the mixing process. Carbon dioxide ( Chemical formula:) is a Chemical compound composed of two Oxygen Atoms covalently bonded to a single The reaction is a three step process. A water molecule reacts with an isocyanate group to form a carbamic acid. Carbamic acid is a compound that is unstable under normal circumstances Carbamic acids are unstable, and decompose forming carbon dioxide and an amine. The amine reacts with more isocyanate to give a substituted urea. Water has a very low molecular 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 molecular mass (abbreviated m of a substance, more commonly referred to as molecular weight and abbreviated as MW, is the Mass of one 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. ^[11] Halocarbons and hydrocarbons are chosen such that they have boiling points at or near room temperature. The boiling point of a liquid is the temperature at which the Vapor pressure of the liquid equals the environmental pressure surrounding the liquid Room temperature (also referred to as ambient temperature) is a common term to denote a certain Temperature within enclosed space at which humans are accustomed Since the polymerization reaction is exothermic, these blowing agents volatilize into a gas during the reaction process. In Thermodynamics, the word exothermic "outside heating" describes a process or reaction that releases Energy usually in the form of Heat, but They fill and expand the cellular polymer matrix, creating a foam. It is important to know that the blowing gas does not create the cells of a foam. Rather, foam cells are a result of blowing gas diffusing into bubbles that are nucleated or stirred into the system at the time of mixing. In fact, high density microcellular foams can be formed without the addition of blowing agents by mechanically frothing or nucleating the polyol component prior to use. Microcellular Plastic Foam is plastic that has been specially foamed so as to created micro-pores or cells

Surfactants are used to modify the characteristics of the polymer during the foaming process. They are used to emulsify the liquid components, regulate cell size, and stabilize the cell structure to prevent collapse and surface defects. An emulsion ( IPA: /ɪˈmʌlʃən/ is a mixture of two Immiscible (unblendable liquids 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. The need for surfactant can be affected by choice of isocyanate, polyol, component compatibility, system reactivity, process conditions and equipment, tooling, part shape, and shot weight.

Raw Materials

For the manufacture of polyurethane polymers, two groups of at least bifunctional substances are needed as reactants; compounds with isocyanate groups, and compounds with active hydrogen atoms. The physical and chemical character, structure, and molecular size of these compounds influence the polymerization reaction, as well as ease of processing and final physical properties of the finished polyurethane. In addition, additive such as catalysts, surfactants, blowing agents, cross linkers, flame retardants, light stabilizers, and fillers are used to control and modify the reaction process and performance characteristics of the polymer.

Isocyanates

Isocyanates with two or more functional groups are required for the formation of polyurethane polymers. Isocyanate is the Functional group of atoms &ndashN=C=O (1 Nitrogen, 1 Carbon, 1 Oxygen) not to be confused with the Cyanate Volume wise, aromatic isocyanates account for the vast majority of global diisocyanate production. Aliphatic and cycloaliphatic isocyanates are also important building blocks for polyurethane materials, but in much smaller volumes. There are a number of reasons for this. First, the aromatically linked isocyanate group is much more reactive than the aliphatic one. Second, aromatic isocyanates are more economical to use. Aliphatic isocyanates are used only if special properties are required for the final product. For example, light stable coatings and elastomers can only be obtained with aliphatic isocyanates. Even within the same class of isocyanates, there is a significant difference in reactivity of the functional groups based on steric hindrance. In the case of 2,4-toluene diisocyanate, the isocyanate group in the para position to the methyl group is much more reactive than the isocyanate group in the ortho position.

Phosgenation of corresponding amines is the main technical process for the manufacture of isocyanates. Phosgene is the Chemical compound with the formula COCl2 This colorless gas gained infamy as a Chemical weapon during World War I The amine raw materials are generally manufactured by the hydrogenation of corresponding nitro compounds. For example, toluenediamine (TDA) is manufactured from dinitrotoluene, which then converted to toluene diisocyanate (TDI). Dinitrotoluene ( DNT) or Dinitro is an Explosive with the formula C6H3(CH3(NO22 Diamino diphenylmethane or methylenedianiline (MDA) is manufactured from nitrobenzene via aniline, which is then converted to diphenylmethane diisocyanate (MDI). Nitrobenzene, also known as nitrobenzol or oil of mirbane, is an Organic compound with the Chemical formula C 6 Aniline, phenylamine or aminobenzene is an Organic compound with the formula C6H7N

The two most important aromatic isocyanates are toluene diisocyanate (TDI) and diphenylmethane diisocyanate (MDI). TDI consists of a mixture of the 2,4- and 2,6-diisocyanatotoluene isomers. The most important product is TDI-80 (TD-80), consisting of 80% of the 2,4-isomer and 20% of the 2,6-isomer. This blend is used extensively in the manufacture of polyurethane flexible slabstock and molded foam. ^[12] TDI, and especially crude TDI and TDI/MDI blends can be used in rigid foam applications, but have been supplanted by polymeric MDI. TDI-polyether and TDI-polyester prepolymers are used in high performance coating and elastomer applications. Prepolymers are available that have been vacuum stripped of TDI monomer, which greatly reduces their toxicity. Diphenylmethane diisocyanate (MDI) has three isomers, 4,4'-MDI, 2,4'-MDI, and 2,2'-MDI, and is also polymerized to provide oligomers of functionality three and higher.

Only the 4,4'-MDI monomer is sold commercially as a single isomer. It is provided either as a frozen solid or flake, or in molten form, and is used to manufacture high performance prepolymers. Monomer blends, consisting of approximately 50% of the 4,4'-isomer and 50% of the 2,4'-isomer, are liquid at room temperature and are used to manufacture prepolymers for polyurea spray elastomer applications. 4,4'-MDI blends containing MDI uretonimine, carbodiimide, and allophonate moieties are also liquid at room temperature, and are used in the manufacture of integral skin and microcellular foams. 4,4'-MDI-glycol prepolymers offer increased mechanical properties in the same applications, but are prone to freezing at temperatures below 20°C. Polymeric MDI (PMDI) is used in rigid pour-in-place, spray foam, and molded foam applications. Polymeric MDI that contains a very high portion of high-functionality oligomers is used to manufacture polyurethane and polyisocyanurate rigid insulation boardstock. Modified PMDI, which contains high levels of MDI monomer, is used in the production of polyurethane flexible molded and microcellular foam. The relative percentage of the 4,4'- and 2,4'- isomers is adjusted to change the reactivity and storage stability of the isocyanate blend, as well as the firmness and other physical properties of the finished goods. Other aromatic isocyanate include p-phenylene diisocyante (PPDI), naphthalene diisocyanate (NDI), and o-tolidine diisocyanate (TODI).

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). Isophorone diisocyanate (IPDI is an organic compound in the class known as Isocyanates More specifically it is an aliphatic diisocyanate They are used to produce light stable, non-yellowing polyurethane coatings and elastomers. Because of their toxicity, aliphatic isocyanate monomers are converted into prepolymers, biurets, dimers, and trimers for commercial use. HDI adducts are used extensively for weather and abrasion resistant coatings and lacquers. IPDI is used in the manufacture of coatings, elastomeric adhesives and sealants. H₁₂MDI prepolymers are used to produce high performance coatings and elastomers with optical clarity and hydrolysis resistance. Other aliphatic isocyanates include cyclohexane diisocyanate (CHDI), tetramethylxylene diisocyanate (TMXDI), and 1,3-bis(isocyanatomethyl)cyclohexane (H₆XDI).

Polyols

Polyols are higher molecular weight materials manufactured from an initiator and monomeric building blocks. The name polyols refers to Alcohols containing multiple Hydroxyl groups They are most easily classified as polyether polyols, which are made by the reaction of epoxides (oxiranes) with an active hydrogen containing starter compounds, or polyester polyols, which are made by the polycondensation of multifunctional carboxylic acids and hydroxyl compounds. An epoxide is a cyclic Ether with only three ring atoms This ring approximately is an Equilateral triangle, i Carboxylic acids are Organic acids characterized by the presence of a Carboxyl group, which has the formula -C(=OOH usually written -COOH or -CO2H They can be further classified according to their end use as flexible or rigid polyols, depending on the functionality of the initiator and their molecular weight. Taking into account functionality, flexible polyols have molecular weights from 2,000 to 10,000 (OH# from 18 to 56). Rigid polyols have molecular weights from 250 to 700 (OH# from 300 to 700). Polyols with molecular weights from 700 to 2,000 (OH# 60 to 280) are used to add stiffness or flexibility to base systems, as well as increase solubility of low molecular weight glycols in high molecular weight polyols.

Polyether polyols come in a wide variety of grades based on their end use, but are all constructed in a similar manner. Polyols for flexible applications use low functionality initiators such as dipropylene glycol (f=2) or glycerine (f=3). Polyols for rigid applications use high functionality initiators such sucrose (f=8), sorbitol (f=6), toluenediamine (f=4), and Mannich bases (f=4). Solubility of Pure SucroseTemperature(Cg Sorbitol, also known as glucitol, is a Sugar alcohol that the body metabolises slowly A mannich base is an amine which is formed in the reaction of electrophilic Imine salt and enol of a Carbonyl compound (usually Ketone or Aldehyde Propylene oxide is then added to the initiators until the desired molecular weight is achieved. Propylene oxide is a highly toxic flammable Chemical compound. Polyols extended with propylene oxide are terminated with secondary hydroxyl groups. In order to change the compatibility, rheological properties, and reactivity of a polyol, ethylene oxide is used as a co-reactant to create random or mixed block heteropolymers. A heteropolymer or copolymer is a Polymer derived from two (or more Monomeric species as opposed to a Homopolymer where only one monomer is Polyols capped with ethylene oxide contain a high percentage of primary hydroxyl groups, which are more reactive than secondary hydroxyl groups. Because of their high viscosity (470 OH# sucrose polyol, 33,000 cps at 25°C), carbohydrate initiated polyols often use glycerine or diethylene glycol as a co-initiate in order to lower the viscosity to ease handling and processing (490 OH# sucrose-glycerine polyol, 5,500 cps at 25°C). Diethylene glycol (DEG is an Organic compound described by the structural formula HO-CH2-CH2-O-CH2-CH2-OH 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. A heteropolymer or copolymer is a Polymer derived from two (or more Monomeric species as opposed to a Homopolymer where only one monomer is Acrylonitrile is the Chemical compound with the formula CH2CHCN 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. PHD polyols are also used to modify the combustion properties of HR flexible foam. Solids content ranges from 14% to 50%, with 22% and 43% being typical. 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. Ethylenediamine (abbreviated as en when a Ligand) is the Organic compound with the formula C2H4(NH22 Triethanolamine, often abbreviated as TEA, is an Organic chemical compound which is both a tertiary Amine and a tri- Alcohol. They are used to increase system reactivity and physical property build, and to reduce the friability of rigid foam molded parts. A special class of polyether polyols, poly(tetramethylene ether) glycols are made by polymerizing tetrahydrofuran. Poly(tetramethylene ether glycol is a Polyether polyol. It is also known as PTMEG or polytetrahydrofuran and various tradenames such as "Terathane" "THF" redirects here For other uses see THF (disambiguation. They are used in high performance coating and elastomer applications.

Polyester polyols fall into two distinct categories according to composition and application. 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. They are distinguished by the choice of monomers, molecular weight, and degree of branching. While costly and difficult to handle because of their high viscosity, they offer physical properties not obtainable with polyether polyols, including superior 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) or dimethylterephthalate (DMT) distillation bottoms with glycols such as diethylene glycol. See also Gluconeogenesis, which carries out a process wherein glucose is synthesized rather than catabolized Uses PET can be semi-rigid to rigid depending on its thickness and is very lightweight These low molecular weight, aromatic polyester polyols are used in the manufacture of rigid foam, and bring low cost and excellent flammability characteristics to polyisocyanurate (PIR) boardstock and polyurethane spray foam insulation. Description Polyisocyanurate, also referred to as PIR or ISO, is essentially an improvement on Polyurethane (PUR

Specialty polyols include polycarbonate polyols, polycaprolactone polyols, polybutadiene polyols, and polysulfide polyols. Polycaprolactone ( PCL) is a Biodegradable Polyester with a low Melting point of around 60°C and a Glass transition temperature of Polybutadiene is a Synthetic rubber that is a Polymer formed from the Polymerization of the Monomer 13-butadiene. Polysulfides are a class of Chemical compounds containing chains of Sulfur atoms 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 oils are used to make elastomers, flexible bunstock, and flexible molded foam. Natural oil polyols, also known as NOPs or biopolyols are polyols derived from Vegetable oils by several different techniques Castor oil is a Vegetable oil obtained from the Castor bean (technically castor seed as the castor plant Ricinus communis, is not a member of

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. Cross-links are bonds that link one Polymer chain to another They can be Covalent bonds or Ionic bonds "Polymer chains" can refer 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. ^{[13][14][15][16][17]} 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). 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 the its derived bis-phenyl urethane undergoes unfavorable degradation at high hard segment levels. ^[18] 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.

Catalysts

Polyurethane catalysts can be classified into two broad categories, amine compounds and organometallic complexes. Catalysis is the process in which the rate of a Chemical reaction is increased by means of a Chemical substance known as a catalyst Amines are Organic compounds and Functional groups that contain a basic Nitrogen Atom with a Lone pair. Organometallic chemistry is the study of Chemical compounds containing bonds between Carbon and a Metal. They can be further classified as to their specificity, balance, and relative power or efficiency. Traditional amine catalysts have been tertiary amines such as triethylenediamine (TEDA, also known as 1,4-diazabicyclo[2. DABCO or 14-diazabicyclooctane is a Chemical compound. It is used as a Catalyst, particularly in making Polyurethanes, and complexing Ligand 2. 2]octane or DABCO), dimethylcyclohexylamine (DMCHA), and dimethylethanolamine (DMEA). DABCO or 14-diazabicyclooctane is a Chemical compound. It is used as a Catalyst, particularly in making Polyurethanes, and complexing Ligand Dimethylaminoethanol, also known as DMAE or dimethylethanolamine, is an Organic compound. 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. Since most tertiary amine catalysts will drive all three reactions to some extent, they are also selected based on how much they favor one reaction over another. For example, tetramethylbutanediamine (TMBDA) preferentially drives the gel reaction over the blow reaction. On the other hand, both pentamethyldipropylenetriamine and N-(3-dimethylaminopropyl)-N,N-diisopropanolamine balance the blow and gel reactions, although the former is more potent than the later on a weight basis. 1,3,5-(tris(3-dimethylamino)propyl)-hexahydro-s-triazine is a trimerization catalyst that also strongly drives the blow reaction. Molecular structure gives some clue to the strength and selectivity of the catalyst. Blow catalysts generally have an ether linkage two carbons away from a tertiary nitrogen. Examples include bis-(2-dimethylaminoethyl)ether and N-ethylmorpholine. Strong gel catalysts contain alkyl-substituted nitrogens, such as triethylamine (TEA), 1,8-diazabicyclo[5. Triethylamine is the Chemical compound with the formula N(CH2CH33 commonly abbreviated Et 3N 4. 0]undecene-7 (DBU), and pentamethyldiethylenetriamine (PMDETA). PMDTA, formally NNN'N'N"-pentamethyldiethylenetriamine is an organic compound with the formula 2NMe (Me is CH3 Weaker gel catalysts contain ring-substituted nitrogens, such as benzyldimethylamine (BDMA). Dimethylbenzylamine is the Organic compound with the formula C6H5CH2N(CH32 Trimerization catalysts contain the triazine structure, or are quaternary ammonium salts. A triazine is one of three Organic chemicals Isomeric with each other whose Empirical formula is 333 Quaternary ammonium cations, also known as quats, are positively charged Polyatomic ions of the structure NR4+ with R being Two trends have emerged since the late 1980s. The requirement to fill large, complex tooling with increasing production rates has led to the use of blocked catalysts to delay front end reactivity while maintaining back end cure. In the United States, acid- and quaternary ammonium salt-blocked TEDA and bis-(2-dimethylaminoethyl)ether are common blocked catalysts used in molded flexible foam and microcellular integral skin foam applications. Increasing aesthetic and environmental awareness has led to the use of non-fugitive catalysts for vehicle interior and furnishing applications in order to reduce odor, fogging, and the staining of vinyl coverings. Catalysts that contain a hydroxyl group or an active amino hydrogen, such as N,N,N'-trimethyl-N'-hydroxyethyl-bis(aminoethyl)ether and N'-(3-dimethylamino)propyl)-N,N-dimethyl-1,3-propanediamine that react into the polymer matrix can replace traditional catalysts in these applications. ^[20][21]

Organometallic compounds based on mercury, lead, tin (dibutyltin dilaurate), bismuth (bismuth octanoate), and zinc are used as polyurethane catalysts. Mercury (ˈmɜrkjʊri also called quicksilver or hydrargyrum, is a Chemical element with the symbol Hg ( Latinized hydrargyrum Characteristics Lead has a dull luster and is a dense, Ductile, very soft highly Tin is a Chemical element with the symbol Sn (stannum and Atomic number 50 Bismuth (ˈbɪzməθ is a Chemical element that has the symbol Bi and Atomic number 83 Zinc (ˈzɪŋk from Zink is a Metallic Chemical element with the symbol Zn and Atomic number 30 Mercury carboxylates, such as phenylmercuric neodeconate, are particularly effective catalysts for polyurethane elastomer, coating and sealant applications, since they are very highly selective towards the polyol+isocyanate reaction. A carboxylate anion is an Ion with Negative charge that contains the group -COO&minus Mercury catalysts can be used at low levels to give systems a long pot life while still giving excellent back-end cure. Lead catalysts are used in highly reactive rigid spray foam insulation applications, since they maintain their potency in low-temperature and high-humidity conditions. Due to their toxicity and the necessity to dispose of mercury and lead catalysts and catalyzed material as hazardous waste in the United States, formulators have been searching for suitable replacements. Since the 1990s, bismuth and zinc carboxylates have been used as alternatives but have short comings of their own. In elastomer applications, long pot life systems do not build green strength as fast as mercury catalyzed systems. In spray foam applications, bismuth and zinc do not drive the front end fast enough in cold weather conditions and must be otherwise augmented to replace lead. Alkyl tin carboxylates, oxides and mercaptides oxides are used in all types of polyurethane applications. For example, dibutyltin dilaurate is a standard catalyst for polyurethane adhesives and sealants, dioctyltin mercaptide is used in microcellular elastomer applications, and dibutyltin oxide is used in polyurethane paint and coating applications. Tin mercaptides are used in formulations that contain water, as tin carboxylates are susceptible to degradation from hydrolysis. ^[22][23]

Surfactants

Surfactants are used to modify the characteristics of both foam and non-foam polyurethane polymers. Surfactants are wetting agents that lower the Surface tension of a liquid allowing easier spreading and lower the Interfacial tension between two liquids They take the form of polydimethylsiloxane-polyoxyalkylene block copolymers, silicone oils, nonylphenol ethoxylates, and other organic compounds. Silicones are largely inert compounds with a wide variety of forms and uses Nonylphenol is an organic compound of the wider family of Alkylphenols It is a product of industrial synthesis formed during the Alkylation process of Phenols 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.

Production

The main polyurethane producing reaction is between a diisocyanate (aromatic and aliphatic types are available) and a polyol, typically a polypropylene glycol or polyester polyol, in the presence of catalysts and materials for controlling the cell structure, (surfactants) in the case of foams. Isocyanate is the Functional group of atoms &ndashN=C=O (1 Nitrogen, 1 Carbon, 1 Oxygen) not to be confused with the Cyanate In Organic chemistry, compounds composed of Carbon and Hydrogen are divided into two classes Aromatic compounds which contain Benzene rings The name polyols refers to Alcohols containing multiple Hydroxyl groups Polypropylene glycol or polypropylene oxide is the Polymer of Propylene glycol. Catalysis is the process in which the rate of a Chemical reaction is increased by means of a Chemical substance known as a catalyst Surfactants are wetting agents that lower the Surface tension of a liquid allowing easier spreading and lower the Interfacial tension between two liquids Polyurethane can be made in a variety of densities and hardnesses by varying the type of monomer(s) used and adding other substances to modify their characteristics, notably density, or enhance their performance. A monomer (from Greek mono "one" and meros "part" is a small Molecule that may become chemically bonded to other The density of a material is defined as its Mass per unit Volume: \rho = \frac{m}{V} Different materials usually have different Other additives can be used to improve the fire performance, stability in difficult chemical environments and other properties of the polyurethane products.

Though the properties of the polyurethane are determined mainly by the choice of polyol, the diisocyanate exerts some influence, and must be suited to the application. The cure rate is influenced by the functional group reactivity and the number of functional isocyanate groups. The mechanical properties are influenced by the functionality and the molecular shape. The choice of diisocyanate also affects the stability of the polyurethane upon exposure to light. Polyurethanes made with aromatic diisocyanates yellow with exposure to light, whereas those made with aliphatic diisocyanates are stable. ^[24]

Softer, elastic, and more flexible polyurethanes result when linear difunctional polyethylene glycol segments, commonly called polyether polyols, are used to create the urethane links. A material is said to be elastic if it deforms under stress (e Carbamates, or Urethanes are a group of Organic compounds sharing a common Functional group with the general structure -NH(COO- This strategy is used to make spandex elastomeric fibers and soft rubber parts, as well as foam rubber. Spandex or elastane is a Synthetic fiber known for its exceptional elasticity. More rigid products result if polyfunctional polyols are used, as these create a three-dimensional cross-linked structure which, again, can be in the form of a low-density foam.

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.

There are then two main foam variants: one in which most of the foam bubbles (cells) remain closed, and the gas(es) remains trapped, the other being systems which have mostly open cells, resulting after a critical stage in the foam-making process (if cells did not form, or became open too soon, foam would not be created). This is a vitally important process: if the flexible foams have closed cells, their softness is severely compromised, they become pneumatic in feel, rather than soft; so, generally speaking, flexible foams are required to be open-celled.

The opposite is the case with most rigid foams. Here, retention of the cell gas is desired since this gas (especially the fluorocarbons referred to above) gives the foams their key characteristic: high thermal insulation performance.

A third foam variant, called microcellular foam, yields the tough elastomeric materials typically experienced in the coverings of car steering wheels and other interior automotive components.

Health and safety

Fully reacted polyurethane polymer, CAS # 9009-54-5 (CAS registry number), is chemically inert. CAS registry numbers are unique numerical identifiers for Chemical compounds Polymers biological sequences mixtures and Alloys They are also referred to In the United States, no exposure limits have been established by OSHA (Occupational Safety and Health Administration) or ACGIH (American Conference of Governmental Industrial Hygienists). The United States Occupational Safety and Health Administration (OSHA is an agency of the United States Department of Labor. The American Conference of Governmental Industrial Hygienists (ACGIH is a professional association of industrial hygienists and practitioners of related professions It is not regulated by OSHA for carcinogenicity. Polyurethane polymer is a combustible solid and will ignite if exposed to an open flame for a sufficient period of time. Decomposition products include carbon monoxide, oxides of nitrogen, and hydrogen cyanide. Hydrogen cyanide is a Chemical compound with Chemical formula HCN Firefighters should wear self-contained breathing apparatus in enclosed areas. When heated above about 200°C the PU polymer will thermally degrade and emit not only the isocyanates it was made from but also a number of mono isocyanates like methyl isocyanate (MIC) and isocyanic acid (ICA), depending on the type of PU being heated. Methyl isocyanate (MIC is an organic compound with the molecular formula C2H3NO arranged as H3C-N=C=O Heating of any PU material (e. g. soft foam, paint dust after sanding, textiles, PU painted flooring etc. ) should be avoided at any cost. Polyurethane polymer dust can cause mechanical irritation to the eyes and lungs. Proper hygiene controls and personal protective equipment (PPE), such as gloves, dust masks, respirators, mechanical ventilation, and protective clothing and eye wear should be used. Personal protective equipment (PPE refers to protective Clothing, Helmets, Goggles, or other garment designed to protect the wearer's body or Clothes should be changed and hands, hair and face should be cleaned before smoking.

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. A material safety data sheet ( MSDS) is a form containing data regarding the properties of a particular substance Isocyanates are known skin and respiratory sensitizers, and proper engineering controls should be in place to prevent exposure to isocyanate liquid and vapor.

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^[25], 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). The Code of Federal Regulations (CFR is the codification of the general and permanent rules and regulations (sometimes called administrative law) published in the

Uses

characteristics of polyurethane materials

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. A refrigerator (often called a " fridge " for short is a cooling appliance comprising a thermally insulated compartment and a Heat pump - The term thermal insulation can refer to materials used to reduce the rate of Heat transfer, or the methods and processes used to reduce heat transfer 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.

The precursors of expanding polyurethane foam are available in many forms, for use in insulation, sound deadening, flotation, industrial coatings, packing material, and even cast-in-place upholstery padding. Since they adhere to most surfaces and automatically fill voids, they have become quite popular in these applications.

The following table shows how polyurethanes are used (US data from 2004):^[26].

Varnish

Polyurethane materials are commonly formulated as paints and varnishes for finishing coats to protect or seal wood. Paint is any Liquid, liquifiable or mastic composition which after application to a substrate in a thin layer is converted to an opaque Solid Varnish is a transparent, hard protective finish or film primarily used in Wood finishing but also for other materials Wood finishing refers to the process of embellishing and/or protecting the surface This use results in a hard, abrasion-resistant, and durable coating that is popular for hardwood floors, but considered by some to be difficult or unsuitable for finishing furniture or other detailed pieces. The term hardwood is used to describe Wood from broad-leaved angiosperm Trees mostly Deciduous, but not necessarily in the case of tropical 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 article is about the tree For other uses of the term "pine" see Pine (disambiguation. 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. Shellac is the commercial resin marketed in the form of amber flakes made from Lac, the secretion of the family of lac-producing insects though most commonly from the In Chemistry, epoxy or polyepoxide is a Thermosetting Epoxide Polymer that cures (polymerizes and crosslinks when mixed with a 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 multiple applications of oil. A drying oil is an Oil which hardens to a tough solid film after a period of exposure to air Flax (also known as common flax or linseed) (binomial name Linum usitatissimum) is a member of the genus Linum Tung oil is used as a Wood finishing product It has two distinct meanings pure tung oil and tung oil finishes, which are often confused 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. A drying oil is an Oil which hardens to a tough solid film after a period of exposure to air Alkyd coatings are a class of Polyester coatings derived from the reaction of an Alcohol (alkohol and an acid or acid Anhydride hence the term alk-yd from Curing is a term in Polymer chemistry and Process engineering that refers to the toughening or hardening of a Polymer material by Cross-linking Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the Evaporation is the process by which Molecules in a Liquid state (e A solvent is a liquid or gas that dissolves a solid liquid or gaseous Solute, resulting in a Solution. A chemical substance is a Material with a definite chemical composition. 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 light exposure. Ultraviolet ( UV) light is Electromagnetic radiation with a Wavelength shorter than that of Visible light, but longer than X-rays It must be noted, however, that all clear or transluscent varnishes, and indeed all film-polymer coatings (i. A polymer is a large Molecule ( Macromolecule) composed of repeating Structural units typically connected by Covalent Chemical bonds e. paint, stain, epoxy, synthetic plastic, etc. Paint is any Liquid, liquifiable or mastic composition which after application to a substrate in a thin layer is converted to an opaque Solid A stain is a discoloration that can be clearly distinguished from the sufrace In Chemistry, epoxy or polyepoxide is a Thermosetting Epoxide Polymer that cures (polymerizes and crosslinks when mixed with a Plastic is the general common term for a wide range of synthetic or semisynthetic organic solid materials suitable for the manufacture of industrial products ) 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. For the drug referred to as "pigment" see Black tar heroin. Paint is any Liquid, liquifiable or mastic composition which after application to a substrate in a thin layer is converted to an opaque Solid A stain is a discoloration that can be clearly distinguished from the sufrace Ultraviolet ( UV) light is Electromagnetic radiation with a Wavelength shorter than that of Visible light, but longer than X-rays In Sailing, a spar is also know as a round pole of wood or Metal used on a Sailing ship. Varnish is a transparent, hard protective finish or film primarily used in Wood finishing but also for other materials Ultraviolet ( UV) light is Electromagnetic radiation with a Wavelength shorter than that of Visible light, but longer than X-rays Polyurethanes are typically the 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. This article is about tires used on road Vehicles including pneumatic tires and solid tires. 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 60s craze. Roller skating is the Traveling on smooth terrain with roller skates Skateboard wheels had previously been made of clay, and broke constantly. {Can somebody check this? I believe they were made of a phenolic material, and never knew of one breaking. The problem was that they were sensitive to debris, and every tiny stick or pebble would stop the board dead, while you went flying. } The durability of Polyurethane wheel allowed the range of tricks and stunts performed on skateboards to expand considerably. 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.

Furniture

Polyurethane is also used in furniture manufacture for casting soft edges around table tops and panel that are stylish, very durable and prevent injury. These are used in school tables, hospital and bank furniture as well as shop counters and displays. It is used on the bottom of some mouse pads. A mousepad (sometimes mouse pad, mousemat, or mouse mat) is a surface for enhancing the Usability of a Computer mouse.

Much of the foam used in chairs (including beanbag chairs), couches, mattresses is polyurethane foam. A chair is a kind of Furniture for Sitting, consisting of a back and sometimes arm rests commonly for use by one person A bean bag (also beanbag) is a sealed bag containing dried Beans or PVC pellets with various applications A couch is an upholstered item of Furniture for the comfortable seating of more than one person and typically has an armrest on either side A mattress is a mat or pad usually placed atop a Bed, upon which to sleep or lie This type of foam is made by mixing polyols, diisocyanates, catalysts, blowing agents and other additives and allowing the resulting foam to rise freely. The name polyols refers to Alcohols containing multiple Hydroxyl groups Isocyanate is the Functional group of atoms &ndashN=C=O (1 Nitrogen, 1 Carbon, 1 Oxygen) not to be confused with the Cyanate This can be done in a batch process where relatively small blocks of foam are made in an open-topped mold, or continuously where the components are poured onto an inclined moving belt. The foam is then cut to the desired shape and size for use in making furniture. Safety concerns about the flammability of polyurethane foam, particularly in upholstered furniture, sometimes requires the addition of flame retardants to this foam. Flammability is the ease with which a substance will ignite causing Fire or Combustion. Flame retardants are materials that inhibit or resist the spread of Fire.

Polyurethane is used for flooring in houses, offices and public areas. A floor is the walking surface of a room or vehicle Floors vary from simple dirt in a cave to many-layered surfaces using modern technology

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. A dashboard, dash, and sometimes fascia (chiefly in British English) is a control panel located under the Windshield of an Automobile

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 face-down in the mold. The two holes in the foam at the top of the picture are for the headrest posts.

Foam after removal from the mold.

Polyurethanes are used to make automobile seats in a remarkable manner. The seat manufacturer has a mold for each seat model. Molding is the process of Manufacturing by shaping pliable raw material using a rigid frame or model called a pattern. 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 a stable soft foam. The time required is two to three minutes, 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. Universal's Islands of Adventure is a Theme park located in Orlando, Florida. Speciality rigid foam manufactures sell foam that replace wood in carved sign and 3D topography industries .

Watercraft

Some surfboards are made with a solid polyurethane core. Surfboards are elongated platforms used in the sport of Surfing. A rigid foam blank is molded, shaped to specification, then covered with fiberglass cloth and polyester resin.

The hull of the Boston Whaler motorboat is polyurethane foam sandwiched in a fiberglass skin. Boston Whaler, or just "Whaler" is a brand of Motorboat manufactured in the United States. A motorboat is a vessel propelled by an Internal combustion engine driving a jet pump or a Propeller. The foam provides strength, buoyancy, and sound deadening.

Construction sealants and firestopping

Head-of-Wall Firestop Joint: the presence of penetrants demonstrates the need to have both operational and fire-tested compatibility between the joint sealant and mechanical/electrical through-penetrations. A firestop is a Passive fire protection System of various components used to seal openings and joints in fire-resistance rated wall A building joint is a junction where Building elements meet without applying a static load from one element to another In other words, it is easier to insist on the use of joint firestops that can also be used for penetration seals, as otherwise penetrants may be run by mechanical and electrical subtrades that unintentionally void the fire-resistance rating of the wall, which jeopardises the entire fire safety plan in place for a building.

Head-of-Wall Firestop Joint penetrated by both electrical and mechanical services, demonstrating the need for operational and fire-tested compatibility between the joint firestop system and penetrants, be they electrical, mechanical or structural. A firestop is a Passive fire protection System of various components used to seal openings and joints in fire-resistance rated wall A fire test is a means of determining whether or not Fire protection products meet minimum performance criteria as set out in a Building code or other applicable legislation A building joint is a junction where Building elements meet without applying a static load from one element to another

Polyurethane sealants are available in 1, 2 and even 3 part systems, either in cartridge, bucket or drum format. Polyurethane sealants are also sold for firestopping applications. A firestop is a Passive fire protection System of various components used to seal openings and joints in fire-resistance rated wall Obviously, the sealant by itself provides no serious hindrance to fire, as its hydrocarbon bonds readily support combustion. Fire is the heat and light energy released during a Chemical reaction, in particular a combustion reaction. In Organic chemistry, a hydrocarbon is an Organic compound consisting entirely of Hydrogen and Carbon. However, when backed by inorganic insulation, such as rockwool or ceramic fibres, it can act as an effective seal to thwart smoke and hose-stream passage, particularly in inorganic joints. The term thermal insulation can refer to materials used to reduce the rate of Heat transfer, or the methods and processes used to reduce heat transfer Mineral wool, also known as mineral fibers or man-made mineral fibers are Fibers made from natural or synthetic Minerals or Metal Smoke is the collection of airborne solid and liquid Particulates and Gases ref> ''Smoke Production and Properties'' - SFPE Handbook of Fire Protection Engineering A fire test is a means of determining whether or not Fire protection products meet minimum performance criteria as set out in a Building code or other applicable legislation It is, however, advisable to avoid direct contact with metallic penetrants and through-penetrating cables, as the heat carried by the penetrants may jeopardise the sealant. In Physics, heat, symbolized by Q, is Energy transferred from one body or system to another due to a difference in Temperature This, however, requires a lot of vigilance. In concrete to concrete, or concrete to masonry joints, however, that are free of mechanical or electrical penetrants, it works well and dependably. Concrete is a construction material composed of Cement (commonly Portland cement) as well as other cementitious materials such as Fly ash and Slag

Tennis Grips

Polyurethane has been used to make several Tennis Overgrips such as Yonex Supergrap, Wilson Pro Overgrip and many other grips. These grips are highly stretchable to ensure the grip wraps neatly around the racquet's handle.

Electronic Components

Often electronic components are protected from environmental influence and mechanical shock by enclosing them in polyurethane. A resin casting system is a technical installation to process Casting resin for the purpose of filling sealing covering or soaking technical parts especially in the field 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 casting). A resin casting system is a technical installation to process Casting resin for the purpose of filling sealing covering or soaking technical parts especially in the field 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 is used as an adhesive, especially as a woodworking glue. Glue or adhesive is a compound that adheres or bonds two items together Wood glues are Adhesives used to tightly bond pieces of Wood together Its main advantage over more traditional wood glues is its water resistance. It was introduced in the general North American market in the 1990s as Gorilla Glue and Excel, but has been used much longer in Europe. Gorilla Glue is a Brand of multipurpose Polyurethane Adhesive.

On the way to a new and better glue for bookbinders, a new adhesive system was introduced for the first time in 1985. Bookbinding is the process of physically assembling a Book from a number of folded or unfolded sheets of Paper or other material The base for this system is polyether or polyester, whereas polyurethane (PUR) is used as prepolymer. Its special feature is the coagulation at room temperature and the reacting to moisture.

1st Generation (1988 at the drupa)

• Low starting solidity
• High viscosity
• Cure time of more than 3 days

2nd Generation (1996 at the drupa)

• Low starting solidity
• High viscosity
• Cure time of less than 3 days

3rd Generation (2000 at the drupa)

• Good starting solidity
• Low viscosity
• Cure time between 6 and 16 hours

4th 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 real wonder compared to hotmelt and cold glue. Drupa, held every four years at the Messe Düsseldorf, Germany, is the largest printing equipment exhibition in the world Because of the missing moisture in the glue, papers with wrong grain direction can be processed without problems. Even printed and supercalandered paper can be bound without problems. It is the most economical glue with an application thickness of theoretical 0. 01 mm. But in reality it is not possible to apply less than 0. 03 mm. The PUR glue is very weather-proof and stable at temperatures from -40 °C to 100 °C.

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.

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 effieciently. Polyurethanes have been proven to last in excess of 25 years in abrasisive environments where non-coated steel would erode in less than 8 years. Polyurethanes are used in industries such as:

• Mining & Mineral Processisng
• Aggregate
• Transportation
• Concrete
• Paper Processing
• Power

Testing

Effects of visible light

Polyurethanes, especially those made using aromatic isocyanates, contain chromophores which interact with light. A chromophore is part (or moiety) of a Molecule responsible for its Color. 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. Light, or visible light, is Electromagnetic radiation of a Wavelength that is visible to the Human eye (about 400–700 In Organic chemistry, compounds composed of Carbon and Hydrogen are divided into two classes Aromatic compounds which contain Benzene rings 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. ^{[27] [28]} 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. ^[29] Increasing exposure time and/or light intensity during the storage of foam samples under ambient laboratory conditions increased the amount of permanent set induced in some compression set tests (the samples did not fully return to their original size and/or shape). Variability resulted from uncontrolled light exposure of cut samples prior to being compressed. Other foam properties were not substantively affected. It was recommended that specimen preparation and testing be done rapidly to minimize variation in results or if specimens are prepared but not tested for a week or more, that the samples should be protected from light exposure.

Higher-energy UV radiation promotes chemical reactions in foam, some of which are detrimental to the foam structure. Ultraviolet ( UV) light is Electromagnetic radiation with a Wavelength shorter than that of Visible light, but longer than X-rays ^[30]

See also

• Firestop
• Great Stuff sprayable foam
• Passive fire protection
• Penetrant
• Silicone

References

External links

• Center for the Polyurethanes Industry: information for EH&S issues related to polyurethanes
• Polyurethane synthesis