Polyurethane hardener chemistry

Polyurethanes are linear polymers that have a molecular backbone containing carbamate groups -NHCO2. These groups, called urethane, are produced through a chemical reaction between a diisocyanate and a polyol. First developed in late s, polyurethanes are some of the most versatile polymers.

They are used in building insulation, surface coatings, adhesives, solid plastics, and athletic apparel. Polyurethanes, also known as polycarbamates, belong to a larger class of compounds called polymers. Polymers are macromolecules made up of smaller, repeating units known as monomers.

Generally, they consist of a primary long-chain backbone molecule with attached side groups. Polyurethanes are characterized by carbamate groups -NHCO 2 in their molecular backbone. Synthetic polymers, like polyurethane, are produced by reacting monomers in a reaction vessel.

In order to produce polyurethane, a step—also known as condensation—reaction is performed. In this type of chemical reaction, the monomers that are present contain reacting end groups. The first step of this reaction results in the chemical linking of the two molecules leaving a reactive alcohol OH on one side and a reactive isocyanate NCO on the other.

These groups react further with other monomers to form a larger, longer molecule. This is a rapid process which yields high molecular weight materials even at room temperature.

Polyurethanes that have important commercial uses typically contain other functional groups in the molecule including esters, ethers, amides, or urea groups. Polyurethane chemistry was first studied by the German chemist, Friedrich Bayer in He produced early prototypes by reacting toluene diisocyanate reacted with dihydric alcohols. From this work one of the first crystalline polyurethane fibers, Perlon U, was developed.

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The development of elastic polyurethanes began as a program to find a replacement for rubber during the days of World War II. Inthe first polyurethane elastomers were produced. These compounds gave millable gums that could be used as an adequate alternative to rubber.

When scientists found that polyurethanes could be made into fine threads, they were combined with nylon to make more lightweight, stretchable garments.Epoxy refers to any of the basic components or cured end products of epoxy resinsas well as a colloquial name for the epoxide functional group. Epoxy resins may be reacted cross-linked either with themselves through catalytic homopolymerisation, or with a wide range of co-reactants including polyfunctional amines, acids and acid anhydridesphenols, alcohols and thiols usually called mercaptans.

These co-reactants are often referred to as hardeners or curatives, and the cross-linking reaction is commonly referred to as curing. Reaction of polyepoxides with themselves or with polyfunctional hardeners forms a thermosetting polymeroften with favorable mechanical properties and high thermal and chemical resistance.

Most of the commercially used epoxy monomers are produced by the reaction of a compound with acidic hydroxy groups and epichlorohydrin :. Epoxy resins produced from such epoxy monomers are called glycidyl -based epoxy resins. The hydroxy group may be derived from aliphatic diolspolyols polyether polyolsphenolic compounds or dicarboxylic acids.

Phenols can be compounds such as bisphenol A and novolak. Polyols can be compounds such as 1,4-butanediol. Di- and polyols lead to diglycid polyethers. Dicarboxylic acids such as hexahydrophthalic acid are used for diglycide ester resins. Instead of a hydroxy group, also the nitrogen atom of an amine or amide can be reacted with epichlorohydrin.

The other production route for epoxy resins is the conversion of aliphatic or cycloaliphatic alkenes with peracids : [2] [3]. As can be seen, in contrast to glycidyl-based epoxy resins, this production of such epoxy monomers does not require an acidic hydrogen atom but an aliphatic double bond. Bisphenol A-based resins are the most widely commercialised resins but also other bisphenols are analogously reacted with epichlorohydrin, for example Bisphenol F. Instead of bisphenol A, other bisphenols especially bisphenol F or brominated bisphenols e.

polyurethane hardener chemistry

Bisphenol F may undergo epoxy resin formation in a similar fashion to bisphenol A. These resins typically have lower viscosity and a higher mean epoxy content per gram than bisphenol A resins, which once cured gives them increased chemical resistance. Important epoxy resins are produced from combining epichlorohydrin and bisphenol A to give bisphenol A diglycidyl ethers. Increasing the ratio of bisphenol A to epichlorohydrin during manufacture produces higher molecular weight linear polyethers with glycidyl end groups, which are semi-solid to hard crystalline materials at room temperature depending on the molecular weight achieved.

This route of synthesis is known as the "taffy" process.

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This process is known as "advancement". Very high molecular weight polycondensates ca. These resins do however contain hydroxyl groups throughout the backbone, which may also undergo other cross-linking reactions, e.

Epoxy resins are polymeric or semi-polymeric materials or an oligomerand as such rarely exist as pure substances, since variable chain length results from the polymerisation reaction used to produce them.

High purity grades can be produced for certain applications, e. One downside of high purity liquid grades is their tendency to form crystalline solids due to their highly regular structure, which then require melting to enable processing. An important criterion for epoxy resins is the epoxide group content. This is expressed as the " epoxide equivalent weight ", which is the ratio between the molecular weight of the monomer and the number of epoxide groups.

This parameter is used to calculate the mass of co-reactant hardener to use when curing epoxy resins.Click here - YouTube video. EMAIL CALL or email. We're available when you are. We form a personal relationship with our customers and freely share technical information, how to-advice, product information and tips-and-tricks. Floors, tables, boats, leaks, rot repair. We handle it all!

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Epoxy adducts. Read about epoxy web site fibs, half truths, fake facts, and misleading statements before you buy from any online vendor. Knowledge is power! Epoxy Only Web Google Search. Your Host and Tour Guide:. We go the extra mile for your respect and support.

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Who are we? Watch our company video. In effect, the 'mixture' has started to cure even before the two parts are mixed. They perform much like other epoxies, but have improved overall physical properties. These include, but are not limited to better color stability and curing at slightly cooler temperatures. Cure time can be much faster than with 'regular' epoxies. Compare your suppliers and not just the products. If you know of any other epoxy company that shares as much technical.

Part 1: Epoxies Epoxies consist of two components that react with each other forming a hard, inert material.The polymeric materials known as polyurethanes form a family of polymers which are essentially different from most other plastics in that there is no urethane monomer and the polymer is almost invariably created during the manufacture of a particular object. Polyurethanes are made by the exothermic reactions between alcohols with two or more reactive hydroxyl -OH groups per molecule diols, triols, polyols and isocyanates that have more than one reactive isocyanate group -NCO per molecule diisocyanates, polyisocyanates.

For example a diisocyanate reacts with a diol:. The group formed by the reaction between the two molecules is known as the 'urethane linkage'. It is the essential part of the polyurethane molecule. The physical properties, as well as the chemical structure, of a polyurethane depend on the structure of the original reactants, in particular the R 1 and the R 2 groups.

polyurethane hardener chemistry

The characteristics of the polyols - relative molecular mass, the number of reactive functional groups per molecule, and the molecular structure - influence the properties of the final polymer, and hence how it is used. There is a fundamental difference between the manufacture of most polyurethanes and the manufacture of many other plastics. Polymers such as poly ethene and poly propene are produced in chemical plants and sold as granules, powders or films.

Products are subsequently made from them by heating the polymer, shaping it under pressure and cooling it. The properties of such end-products are almost completely dependent on those of the original polymer. Polyurethanes, on the other hand are usually made directly into the final product. Much of the polyurethanes produced are in the form of large blocks of foam, which are cut up for use in cushions, or for thermal insulation. The chemical reaction can also take place in moulds, leading to, for example, a car bumper, a computer casing or a building panel.

Polyurethanes

It may occur as the liquid reactants are sprayed onto a building surface or coated on a fabric. The combined effects of controlling the polymer properties and the density lead to the existence of a very wide range of different materials so that polyurethanes are used in very many applications Table 1. Polyurethanes can be rigid or rubbery at any density between, say 10 kg m -3 and kg m The overall range of properties available to the designer and the manufacturer is clearly very wide and this is reflected in the many, very different, uses to which polyurethanes are put.

In Expected to be Research and Markets, Plastics - the Facts PlasticsEurope, As polyurethanes are made from the reaction between an isocyanate and a polyol, the section is divided into three parts: a production of isocyanates b production of polyols c production of polyurethanes.

Although many aromatic and aliphatic polyisocyanates exist, two are of particular industrial importance. They are:. TDI was developed first but is now used mainly in the production of low density flexible foams for cushions. The starting material is methylbenzene toluene. When it reacts with mixed acid nitric and sulfurictwo isomers of nitromethylbenzene NMB are the main products.

If this mixture is nitrated further, a mixture of dinitromethylbenzenes is produced. In industry they are known by their trivial names, 2,4-dinitrotoluene and 2,6-dinitrotoluene DNT. In turn, the amines, known commercially as Toluene Diamines or TDA, are heated with carbonyl chloride phosgene to produce the diisocyanates and this process can be carried out in the liquid phase with chlorobenzene as a solvent at about K:.

Alternatively, these reactions are carried out in the gas phase by vaporizing the diamines at ca K and mixing them with carbonyl chloride. This is an environmental and economic improvement over the liquid phase process as no solvent is needed. It is expensive to produce this mixture in different proportions.While most polyurethanes are thermosetting polymers that do not melt when heated, thermoplastic polyurethanes are also available.

Polyurethane polymers are traditionally and most commonly formed by reacting a di- or triisocyanate with a polyol. Since polyurethanes contain two types of monomers, which polymerise one after the other, they are classed as alternating copolymers. Both the isocyanates and polyols used to make polyurethanes contain, on average, two or more functional groups per molecule. Polyurethanes are used in the manufacture of high-resilience foam seating, rigid foam insulation panels, microcellular foam seals and gasketsspray foamdurable elastomeric wheels and tires such as roller coasterescalatorshopping cartelevatorand skateboard wheelsautomotive suspension bushingselectrical potting compounds, high-performance adhesivessurface coatings and sealants, synthetic fibers e.

These materials were also used to produce rigid foams, gum rubber, and elastomers. In DuPont introduced polyether polyols, specifically poly tetramethylene ether glycoland BASF and Dow Chemical started selling polyalkylene glycols in Polyether polyols were cheaper, easier to handle and more water-resistant than polyester polyols, and became more popular.

Union Carbide and Mobaya U. 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.

Inurethane-modified polyisocyanurate rigid foams were introduced, offering even better thermal stability and flammability resistance. During the s, automotive interior safety components, such as instrument and door panels, were produced by back-filling thermoplastic skins with semi-rigid foam.

Parts of this car, such as the fascia and body panels, were manufactured using a new process called reaction injection molding RIMin which the reactants were mixed and then injected into a mold.

The addition of fillers, such as milled glass, micaand processed mineral fibres, gave rise to reinforced RIM RRIMwhich provided improvements in flexural modulus stiffnessreduction in coefficient of thermal expansion and better thermal stability. This technology was used to make the first plastic-body automobile in the United States, the Pontiac Fieroin Further increases in stiffness were obtained by incorporating pre-placed glass mats into the RIM mold cavity, also known broadly as resin injection moldingor structural RIM.

Starting in the early s, water-blown microcellular flexible foams were used to mold gaskets for automotive panels and air-filter seals, replacing PVC polymers.

Polyurethane foams have gained popularity in the automotive realm, and are now used in high-temperature oil-filter applications. In the early s, because of their impact on ozone depletionthe Montreal Protocol restricted the use of many chlorine -containing blowing agents, such as trichlorofluoromethane CFC By the late s, blowing agents such as carbon dioxidepentane1,1,1,2-tetrafluoroethane HFCa and 1,1,1,3,3-pentafluoropropane HFCfa were widely used in North America and the EU, although chlorinated blowing agents remained in use in many developing countries.

Polyurethane products often are simply called "urethanes", but should not be confused with ethyl carbamatewhich is also called urethane. Polyurethanes neither contain nor are produced from ethyl carbamate. Non-isocyanate based polyurethanes NIPUs have been developed to mitigate health and environmental concerns associated with the use of isocyanates to synthesize polyurethanes. Polyurethanes are in the class of compounds called reaction polymerswhich include epoxiesunsaturated polyestersand phenolics.

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, elastic polymer. High amounts of crosslinking give tough or rigid polymers. Long chains and low crosslinking give a polymer that is very stretchy, short chains with many 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. 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. Polyols are polymers in their own right and have on average two or more hydroxyl groups per molecule.

Polyether polyols are mostly made by co-polymerizing ethylene oxide and propylene oxide with a suitable polyol precursor. Polyols used to make polyurethanes are mixtures of similar molecules with distinct molecular weights, which is why the "average functionality" is often mentioned.E-Mail us and let us know what you think.

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polyurethane hardener chemistry

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Classifieds Exchange. Notify Me Of New Listings. Request A Quote.Our goal is to give those interested in learning the fundamentals of the chemistry the knowledge to empower themselves to make the best decision for their application. So, from a chemical perspective polyurethane is proper term to describe automotive paints that are often called urethane. The use of the polyurethane and urethane terminology has largely emerged as a need to differentiate products that have varying performance.

It is fact that the performance of polyurethanes can vary greatly depending on how the polyurethane is formed and the formulation of the finished product. The type of polyol and polyisocyanate largely determines the final performance.

However, the polyol portion varies widely. Polyol types vary greatly accounting for a wide range of performance properties and applications of polyurethanes ranging from soft and permanently flexible polyurethane membranes, to hard and impact resistant bowling balls.

polyurethane hardener chemistry

Performance form each can vary widely depending on the composition of the polyol itself. The reason to bring this up is that some would argue that acrylic polyurethane polyurethane built from acrylic polyol is a superior product but this is not universally the case as some acrylic polyols have horrible durability performance. This makes the terminology confusion since, as we discussed earlier, all urethane linkage containing coating systems are really polyurethanes whether built from acrylic or polyester polyols.

The performance of polyester polyols also varies widely making it difficult to generalize any performance based on the name. That is why it is best not to focus on the name of a product rather focus on the performance data a recommendations from fellow users. In summary we learned that urethane finishes are actually all polyurethanes from a chemistry perspective and that saying one polyurethane is better than another acrylic polyurethane for instance is not an advisable way to choose a product.

For best success long term focus on the performance data and unbiased reviews of a product to ensure you are getting what you expect. For most automotive coating name brands the price of the raw materials and manufacturing overhead is only a very small part of the total cost.

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