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76-508: Throughout history, metal casting has been used to make tools, weapons, and religious objects. Metal casting history and development can be traced back to Southern Asia (China, India, Pakistan, etc). Southern Asia traditions and religions relied heavily on statue and relic castings. These items were frequently made from a copper alloy laced with lead. Since the beginning of metallurgy the majority of castings were simple one to two piece molds fashioned from either stone or ceramics. However, there

152-440: A copolymer with polyfunctional curatives or hardeners . This curing is what produces the qualities of the substance such as resistance, durability, versatility, and adhesion. In principle, any molecule containing a reactive hydrogen may react with the epoxide groups of the epoxy resin. Common classes of hardeners for epoxy resins include amines, acids, acid anhydrides, phenols, alcohols and thiols. Relative reactivity (lowest first)

228-456: A calculated amount of bisphenol A and then a catalyst is added and the reaction heated to circa 160 °C (320 °F). This process is known as "advancement". As the molecular weight of the resin increases, the epoxide content reduces and the material behaves more and more like a thermoplastic . Very high molecular weight polycondensates (ca. 30,000–70,000 g/mol) form a class known as phenoxy resins and contain virtually no epoxide groups (since

304-418: A catalyst. The resulting material has ether linkages and displays higher chemical and oxidation resistance than typically obtained by curing with amines or anhydrides. Since many novolacs are solids, this class of hardeners is often employed for powder coatings . Also known as mercaptans, thiols contain a sulfur which reacts very readily with the epoxide group, even at ambient or sub-ambient temperatures. While

380-498: A clay cylinder so molten metal could be poured down the center, filling and solidifying in the open spaces. This process allowed one hundred coins to be produced simultaneously. In the Middle East and West Africa the lost wax technique was used very early in their metallurgy traditions while China adopted it much later. In Western Europe lost wax techniques are considered to have been hardly used especially in comparison to that of

456-578: A cured network. This process is known as catalytic homopolymerisation. The resulting network contains only ether bridges, and exhibits high thermal and chemical resistance, but is brittle and often requires elevated temperature for the curing process, so finds only niche applications industrially. Epoxy homopolymerisation is often used when there is a requirement for UV curing, since cationic UV catalysts may be employed (e.g. for UV coatings ). Polyfunctional primary amines form an important class of epoxy hardeners. Primary amines undergo an addition reaction with

532-402: 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 : 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. The epoxide group

608-424: A large extent as secondary plasticizers and cost stabilizers for PVC . Aliphatic glycidyl epoxy resins of low molar mass (mono-, bi- or polyfunctional) are formed by the reaction of epichlorohydrin with aliphatic alcohols or polyols (glycidyl ethers are formed) or with aliphatic carboxylic acids (glycidyl esters are formed). The reaction is carried out in the presence of a base such as sodium hydroxide, analogous to

684-399: A lesser extent, monoanhydrides, non-stoichiometric, empirical determinations are often used to optimize dosing levels. In some cases, blends of dianhydrides and monoanhydrides can improve metering and mixing with liquid epoxy resins. Polyphenols, such as bisphenol A or novolacs can react with epoxy resins at elevated temperatures (130–180 °C, 266–356 °F), normally in the presence of

760-911: A low surface tension, it is added as a wetting agent (surfactant) for contact with glass fibres. Its reactivity to hardeners is comparable to that of bisphenol A. When cured, the epoxy resin leads to a thermosetting plastic with high chemical resistance and low water absorption. However, the commercial use of fluorinated epoxy resins is limited by their high cost and low T g . Epoxy resins diluents are typically formed by glycidylation of aliphatic alcohols or polyols and also aromatic alcohols. The resulting materials may be monofunctional (e.g. dodecanol glycidyl ether), difunctional ( 1,4-Butanediol diglycidyl ether ), or higher functionality (e.g. trimethylolpropane triglycidyl ether ). These resins typically display low viscosity at room temperature (10–200 mPa.s) and are often referred to as reactive diluents. They are rarely used alone, but are rather employed to modify (reduce)

836-414: A lower electron density than aromatics, cycloaliphatic epoxies react less readily with nucleophiles than bisphenol A-based epoxy resins (which have aromatic ether groups). This means that conventional nucleophilic hardeners such as amines are hardly suitable for crosslinking. Cycloaliphatic epoxides are therefore usually homopolymerized thermally or UV-initiated in an electrophilic or cationic reaction. Due to

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912-610: A network with incomplete polymerisation, and thus reduced mechanical, chemical and heat resistance. Cure temperature should typically attain the glass transition temperature (T g ) of the fully cured network in order to achieve maximum properties. Temperature is sometimes increased in a step-wise fashion to control the rate of curing and prevent excessive heat build-up from the exothermic reaction. Hardeners which show only low or limited reactivity at ambient temperature, but which react with epoxy resins at elevated temperature are referred to as latent hardeners . When using latent hardeners,

988-566: A variety of ways, including reacting with fatty acids derived from oils to yield epoxy esters, which were cured the same way as alkyds. Typical ones were L8 (80% linseed) and D4 (40% dehydrated castor oil). These were often reacted with styrene to make styrenated epoxy esters, used as primers. Curing with phenolics to make drum linings, curing esters with amine resins and pre-curing epoxies with amino resins to make resistant top coats. Organic chains maybe used to hydrophobically modify epoxy resins and change their properties. The effect of chain length of

1064-581: A wide range of applications, including metal coatings , composites, use in electronics, electrical components (e.g. for chips on board ), LEDs, high-tension electrical insulators , paintbrush manufacturing, fiber-reinforced plastic materials, and adhesives for structural and other purposes. The health risks associated with exposure to epoxy resin compounds include contact dermatitis and allergic reactions, as well as respiratory problems from breathing vapor and sanding dust, especially from compounds not fully cured. Condensation of epoxides and amines

1140-494: A wide range of co-reactants including polyfunctional amines, acids (and acid anhydrides ), phenols, alcohols and thiols (sometimes 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 polymer , often with favorable mechanical properties and high thermal and chemical resistance. Epoxy has

1216-444: Is a common means of making washstands, washstand tops and shower stalls, with the skilled working of multiple colors resulting in simulated staining patterns as is often found in natural marble or travertine . Raw castings often contain irregularities caused by seams and imperfections in the molds, as well as access ports for pouring material into the molds. The process of cutting, grinding, shaving or sanding away these unwanted bits

1292-542: Is a common phenomenon for epoxy materials and is often of concern in art and conservation applications. Epoxy resins yellow with time, even when not exposed to UV radiation. Significant advances in understanding yellowing of epoxies were achieved by Down first in 1984 (natural dark aging) and later in 1986 (high-intensity light aging). Down investigated various room-temperature-cure epoxy resin adhesives suitable for use in glass conservation, testing their tendency to yellow. A fundamental molecular understanding of epoxy yellowing

1368-616: Is a further term, mostly used for coins with a very high copper content. Today the term copper alloy tends to be substituted for all of these, especially by museums. Copper deposits are abundant in most parts of the world (globally 70 parts per million), and it has therefore always been a relatively cheap metal. By contrast, tin is relatively rare (2 parts per million), and in Europe and the Mediterranean region, and even in prehistoric times had to be traded considerable distances , and

1444-421: Is a highly effective and widely used accelerator, but is now increasingly replaced due to health concerns with this substance. The most widely used accelerator is 2,4,6-Tris(dimethylaminomethyl)phenol . Epoxy resin may be reacted with itself in the presence of an anionic catalyst (a Lewis base such as tertiary amines or imidazoles) or a cationic catalyst (a Lewis acid such as a boron trifluoride complex) to form

1520-806: Is a key technology used for toughening. Two part epoxy coatings were developed for heavy duty service on metal substrates and use less energy than heat-cured powder coatings . These systems provide a tough, protective coating with excellent hardness. One part epoxy coatings are formulated as an emulsion in water, and can be cleaned up without solvents. Epoxy coatings are often used in industrial and automotive applications since they are more heat resistant than latex-based and alkyd-based paints. Epoxy paints tend to deteriorate, known as "chalking out", due to UV exposure. Epoxy coatings have also been used in drinking water applications. Epoxy coatings find much use to protect mild and other steels due to their excellent protective properties. Change in color, known as yellowing,

1596-489: Is also sometimes referred to as an oxirane group. The most common epoxy resins are based on reacting epichlorohydrin (ECH) with bisphenol A ,  resulting in a different chemical substance known as bisphenol A diglycidyl ether (commonly known as BADGE or DGEBA). Bisphenol A-based resins are the most widely commercialised resins but also other bisphenols are analogously reacted with epichlorohydrin, for example Bisphenol F . In this two-stage reaction, epichlorohydrin

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1672-406: Is approximately in the order: phenol < anhydride < aromatic amine < cycloaliphatic amine < aliphatic amine < thiol. While some epoxy resin/ hardener combinations will cure at ambient temperature, many require heat, with temperatures up to 150 °C (302 °F) being common, and up to 200 °C (392 °F) for some specialist systems. Insufficient heat during cure will result in

1748-457: Is called "fettling" in UK english. In modern times robotic processes have been developed to perform some of the more repetitive parts of the fettling process, but historically fettlers carried out this arduous work manually, and often in conditions dangerous to their health. Fettling can add significantly to the cost of the resulting product, and designers of molds seek to minimize it through the shape of

1824-453: Is called prepolymerization: A product comprising a few repeat units ( n = 1 to 2) is a viscous, clear liquid; this is called a liquid epoxy resin. A product comprising more repeating units ( n = 2 to 30) is at room temperature a colourless solid, which is correspondingly referred to as solid epoxy resin. Instead of bisphenol A, other bisphenols (especially bisphenol F ) or brominated bisphenols (e. g. tetrabromobisphenol A ) can be used for

1900-573: Is common to achieve the desired processing or final properties, or to reduce cost. Use of blending, additives and fillers is often referred to as formulating . All quantities of mix generate their own heat because the reaction is exothermic. Large quantities will generate more heat and thus greatly increase the rate of the reaction and so reduce working time (pot-life). So it is good practice to mix smaller amounts which can be used quickly to avoid waste and to be safer. There are various methods of toughening them, as they can be brittle. Rubber toughening

1976-406: Is connected to 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. Epoxies are typically cured with stoichiometric or near-stoichiometric quantities of hardener to achieve

2052-475: Is degraded at temperatures above 350 °F (177 °C). Some epoxies are cured by exposure to ultraviolet light. Such epoxies are commonly used in optics , fiber optics , and optoelectronics . Epoxy systems are used in industrial tooling applications to produce molds , master models, laminates , castings , fixtures , and other industrial production aids. This "plastic tooling" replaces metal, wood and other traditional materials, and generally improves

2128-532: Is evidence of lost wax castings in numerous ancient civilizations. The lost wax process originated in ancient Mesopotamia . The earliest known record of lost-wax casting is a clay tablet written in cuneiform in the ancient city of Sparta, Babylon, which specifically records how much wax is needed to cast a key. The earliest-known castings in the global archaeological record were made in open stone molds. There are two types of lost wax methods, direct lost wax method and indirect lost wax method. The direct molding method

2204-433: Is first added to bisphenol A (bis(3-chloro-2-hydroxy-propoxy)bisphenol A is formed), then a bisepoxide is formed in a condensation reaction with a stoichiometric amount of sodium hydroxide. The chlorine atom is released as sodium chloride (NaCl) and the hydrogen atom as water. Higher molecular weight diglycidyl ethers (n ≥ 1) are formed by the reaction of the bisphenol A diglycidyl ether formed with further bisphenol A, this

2280-693: Is flat and lacks transparency. Often topical treatments are applied to the surface. For example, painting and etching can be used in a way that give the appearance of metal or stone. Alternatively, the material is altered in its initial casting process and may contain colored sand so as to give an appearance of stone. By casting concrete, rather than plaster, it is possible to create sculptures, fountains, or seating for outdoor use. A simulation of high-quality marble may be made using certain chemically-set plastic resins (for example epoxy or polyester which are thermosetting polymers ) with powdered stone added for coloration, often with multiple colors worked in. The latter

2356-434: Is happening inside the mold or die during the casting process. List of copper alloys Copper alloys are metal alloys that have copper as their principal component. They have high resistance against corrosion . Of the large number of different types, the best known traditional types are bronze , where tin is a significant addition, and brass , using zinc instead. Both of these are imprecise terms. Latten

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2432-497: Is kept under 15%, it does not markedly decrease corrosion resistance of copper. Brasses can be sensitive to selective leaching corrosion under certain conditions, when zinc is leached from the alloy ( dezincification ), leaving behind a spongy copper structure. A bronze is an alloy of copper and other metals, most often tin, but also aluminium and silicon. Copper is often alloyed with precious metals like gold (Au) and silver (Ag). † amount unspecified Epoxy Epoxy

2508-671: Is not present in these materials as it is in Bisphenol A and F resins, the UV stability is considerably improved. Halogenated epoxy resins are admixed for special properties, in particular brominated and fluorinated epoxy resins are used. Brominated bisphenol A is used when flame retardant properties are required, such as in some electrical applications (e.g. printed circuit boards ). The tetrabrominated bisphenol A (TBBPA, 2,2-bis(3,5-dibromophenyl)propane) or its diglycidyl ether, 2,2-bis[3,5-dibromo-4-(2,3-epoxypropoxy)phenyl]propane, can be added to

2584-448: Is the family of basic components or cured end products of epoxy resins . Epoxy resins, also known as polyepoxides , are a class of reactive prepolymers and polymers which contain epoxide groups. The epoxide functional group is also collectively called epoxy . The IUPAC name for an epoxide group is an oxirane . Epoxy resins may be reacted ( cross-linked ) either with themselves through catalytic homo polymerisation , or with

2660-602: Is to make the wax material into the same wax mold as the casting by hand or other tools; the indirect molding method is to make the wax mold through the mold. The direct molding method requires craftsmen to have a high technical level, otherwise the quality of castings cannot be guaranteed. However, the limitation of manual direct molding is that its efficiency is too low to achieve mass production. In this regard, indirect moulding has advantages. In indirect moulding, artisans usually make moulds from stone, wood, clay or other plastic materials. Early civilizations discovered lead aided in

2736-518: The Indus valley civilization. There were no pieces of lost wax found in the capital of Anyang during the Shane dynasty (1600-1040 BC) while a large amount (100,000 pieces) of piece-mould fragments were found. This led to the conclusion that lost wax was not performed in the capital during this dynasty. However, the discovery of a mask made using the investment moulding dated at around 1300 BC indicated that

2812-401: The amino groups may react as slowly as some of the aromatic amines. Slower reactivity allows longer working times for processors. Temperature resistance generally increases in the same order, since aromatic amines form much more rigid structures than aliphatic amines. Aromatic amines were widely used as epoxy resin hardeners, due to the excellent end properties when mixed with a parent resin. Over

2888-489: The best physical properties. Novolaks are produced by reacting phenol with methanal ( formaldehyde ). The reaction of epichlorohydrin and novolaks produces novolaks with glycidyl residues , such as epoxyphenol novolak (EPN) or epoxycresol novolak (ECN). These highly viscous to solid resins typically carry 2 to 6 epoxy groups per molecule. By curing, highly cross-linked polymers with high temperature and chemical resistance but low mechanical flexibility are formed due to

2964-408: The casting process (such as the runners and risers). Plaster and other chemical curing materials such as concrete and plastic resin may be cast using single-use waste molds as noted above, multiple-use 'piece' molds, or molds made of small rigid pieces or of flexible material such as latex rubber (which is in turn supported by an exterior mold). When casting plaster or concrete, the material surface

3040-462: The casting with iron bands. In metalworking, metal is heated until it becomes liquid and is then poured into a mold. The mold is a hollow cavity that includes the desired shape, but the mold also includes runners and risers that enable the metal to fill the mold. The mold and the metal are then cooled until the metal solidifies. The solidified part (the casting) is then recovered from the mold. Subsequent operations remove excess material caused by

3116-440: The categories: copper, high copper alloy, brasses, bronzes, cupronickel , copper–nickel–zinc (nickel silver), leaded copper , and special alloys. The similarity in external appearance of the various alloys, along with the different combinations of elements used when making each alloy, can lead to confusion when categorizing the different compositions. The following table lists the principal alloying element for four of

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3192-717: The commercially used epoxy monomers are produced by the reaction of a compound with acidic hydroxy groups and epichlorohydrin . First a hydroxy group reacts in a coupling reaction with epichlorohydrin, followed by dehydrohalogenation . Epoxy resins produced from such epoxy monomers are called glycidyl -based epoxy resins. The hydroxy group may be derived from aliphatic diols , polyols (polyether polyols), phenolic 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 glycidyl ethers . Dicarboxylic acids such as hexahydrophthalic acid are used for diglycide ester resins. Instead of

3268-405: The efficiency and either lowers the overall cost or shortens the lead-time for many industrial processes. Epoxies are also used in producing fiber-reinforced or composite parts. They are more expensive than polyester resins and vinyl ester resins , but usually produce stronger and more temperature-resistant thermoset polymer matrix composite parts. Machine bedding to overcome vibrations is a use in

3344-491: The entire casting manufacturing route. Casting process simulation was initially developed at universities starting from the early ' 70s , mainly in Europe and in the U.S. , and is regarded as the most important innovation in casting technology over the last 50 years. Since the late ' 80s , commercial programs (such as PoligonSoft, AutoCAST and Magma) are available which make it possible for foundries to gain new insight into what

3420-511: The epoxide group to form a hydroxyl group and a secondary amine. The secondary amine can further react with an epoxide to form a tertiary amine and an additional hydroxyl group. Kinetic studies have shown the reactivity of the primary amine to be approximately double that of the secondary amine. Use of a difunctional or polyfunctional amine forms a three-dimensional cross-linked network. Aliphatic, cycloaliphatic and aromatic amines are all employed as epoxy hardeners. Amine type hardeners will alter both

3496-462: The epoxy formulation . The formulation may then be reacted in the same way as pure bisphenol A. Some (non-crosslinked) epoxy resins with very high molar mass are added to engineering thermoplastics, again to achieve flame retardant properties. Fluorinated epoxy resins have been investigated for some high performance applications , such as the fluorinated diglycidether 5-heptafluoropropyl-1,3-bis[2-(2,3-epoxypropoxy)hexafluoro-2-propyl]benzene. As it has

3572-672: The epoxy resin and hardener may be mixed and stored for some time prior to use, which is advantageous for many industrial processes. Very latent hardeners enable one-component (1K) products to be produced, whereby the resin and hardener are supplied pre-mixed to the end user and only require heat to initiate curing. One-component products generally have shorter shelf-lives than standard 2-component systems, and products may require cooled storage and transport. The epoxy curing reaction may be accelerated by addition of small quantities of accelerators . Tertiary amines, carboxylic acids and alcohols (especially phenols) are effective accelerators. Bisphenol A

3648-420: The first civilizations to use casting methods to mass produce coins. Around the middle of the first millennium BC (1000 BC - 1 BC), coins used were made from silver but as the millennium progressed the coins shifted to a cast copper alloy. New technology was developed to mass produce the new copper coins. Introduced was a multi piece stackable coin template mold. Multiple molds were placed on top of one another into

3724-481: The fluidity of molten copper, allowing them to cast more intricate designs. For example, the dancing girl of Mohenjo-daro is a copper alloy casting that most likely utilizes the lost wax technique. Lost wax casting can be dated back to 4000 BC or the Chalcolithic period. One of the oldest studied examples of this technique is a 6,000-year old amulet from Indus valley civilization . India is attributed as one of

3800-449: The formation of bisphenol A-diglycidyl ether. Also aliphatic glycidyl epoxy resins usually have a low viscosity compared to aromatic epoxy resins. They are therefore added to other epoxy resins as reactive diluents or as adhesion promoters . Epoxy resins made of (long-chain) polyols are also added to improve tensile strength and impact strength. A related class is cycloaliphatic epoxy resin, which contains one or more cycloaliphatic rings in

3876-401: The high functionality, and hence high crosslink density of these resins. There are two common types of aliphatic epoxy resins: those obtained by epoxidation of double bonds (cycloaliphatic epoxides and epoxidized vegetable oils ) and those formed by reaction with epichlorohydrin (glycidyl ethers and esters). Cycloaliphatic epoxides contain one or more aliphatic rings in the molecule on which

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3952-549: The linear epoxy resin with suitable curatives to form three-dimensional cross-linked thermoset structures. This process is commonly referred to as curing or gelation process. Curing of epoxy resins is an exothermic reaction and in some cases produces sufficient heat to cause thermal degradation if not controlled. Curing does induce residual stress in epoxy systems which have been studied. The induced stresses may be alleviated with flexibilisers. Curing may be achieved by reacting an epoxy with itself (homopolymerisation) or by forming

4028-474: The lost wax technique may have influenced other regions in China. Historians debate the origin of the development of the cannon but most evidence points to Turkey and Central Asia in the 18th and 19th century. The casting process of a cannon is a bit more complex with the use of a clay core, a template which has clay moulded around it and then broken out followed by an assembly in a casting pit that involves binding

4104-435: The low dielectric constants and the absence of chlorine, cycloaliphatic epoxides are often used to encapsulate electronic systems, such as microchips or LEDs. They are also used for radiation-cured paints and varnishes. Due to their high price, however, their use has so far been limited to such applications. Epoxidized vegetable oils are formed by epoxidation of unsaturated fatty acids by reaction with peracids. In this case,

4180-923: The modifiers has been studied. Epoxy adhesives are a major part of the class of adhesives called "structural adhesives" or "engineering adhesives" (that includes polyurethane , acrylic , cyanoacrylate , and other chemistries.) These high-performance adhesives are used in the construction of aircraft, automobiles, bicycles, boats, golf clubs, skis, snowboards, and other applications where high strength bonds are required. Epoxy adhesives can be developed to suit almost any application. They can be used as adhesives for wood, metal, glass, stone, and some plastics. They can be made flexible or rigid, transparent or opaque /colored, fast setting or slow setting. Epoxy adhesives are better in heat and chemical resistance than other common adhesives. In general, epoxy adhesives cured with heat will be more heat- and chemical-resistant than those cured at room temperature. The strength of epoxy adhesives

4256-484: The mold, the material being cast, and sometimes by including decorative elements. Casting process simulation uses numerical methods to calculate cast component quality considering mold filling, solidification and cooling, and provides a quantitative prediction of casting mechanical properties, thermal stresses and distortion. Simulation accurately describes a cast component's quality up-front before production starts. The casting rigging can be designed with respect to

4332-400: The molecule (e.g. 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate). This class also displays lower viscosity at room temperature, but offers significantly higher temperature resistance than the aliphatic epoxy diluents. However, reactivity is rather low compared to other classes of epoxy resin, and high temperature curing using suitable accelerators is normally required. As aromaticity

4408-505: The more common types used in modern industry, along with the name for each type. Historical types, such as those that characterize the Bronze Age , are vaguer as the mixtures were generally variable. The following table outlines the chemical composition of various grades of copper alloys. A brass is an alloy of copper with zinc. Brasses are usually yellow in colour. The zinc content can vary between few % to about 40%; as long as it

4484-594: The oil and gas industry, potable water transmission pipelines (steel), and concrete reinforcing rebar . Epoxy coatings are also widely used as primers to improve the adhesion of automotive and marine paints especially on metal surfaces where corrosion (rusting) resistance is important. Metal cans and containers are often coated with epoxy to prevent rusting, especially for foods like tomatoes that are acidic . Epoxy resins are also used for decorative flooring applications such as terrazzo flooring, chip flooring, and colored aggregate flooring. Epoxies have been modified in

4560-602: The oxirane ring is contained (e.g. 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexane carboxylate ). They are produced by the reaction of a cyclic alkene with a peracid (see above). Cycloaliphatic epoxides are characterised by their aliphatic structure, high oxirane content and the absence of chlorine, which results in low viscosity and (once cured) good weather resistance, low dielectric constants and high T g . However, aliphatic epoxy resins polymerize very slowly at room temperature, so higher temperatures and suitable accelerators are usually required. Because aliphatic epoxies have

4636-400: The past few decades concern about the possible adverse health effects of many aromatic amines has led to increased use of aliphatic or cycloaliphatic amine alternatives. Amines are also blended, adducted and reacted to alter properties and these amine resins are more often used to cure epoxy resins than a pure amine such as TETA. Increasingly, water-based polyamines are also used to help reduce

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4712-444: The peracids can also be formed in situ by reacting carboxylic acids with hydrogen peroxide. Compared with LERs (liquid epoxy resins) they have very low viscosities. If, however, they are used in larger proportions as reactive diluents , this often leads to reduced chemical and thermal resistance and to poorer mechanical properties of the cured epoxides. Large scale epoxidized vegetable oils such as epoxidized soy and lens oils are used to

4788-453: The polymerisation reaction used to produce them. High purity grades can be produced for certain applications, e.g. using a distillation purification process. 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 Epoxy value which

4864-418: The processing properties (viscosity, reactivity) and the final properties (mechanical, temperature and heat resistance) of the cured copolymer network. Thus amine structure is normally selected according to the application. Overall reactivity potential for different hardeners can roughly be ordered; aliphatic amines > cycloaliphatic amines > aromatic amines, though aliphatic amines with steric hindrance near

4940-871: The range of commercially available variations allows cure polymers to be produced with a very broad range of properties. They have been extensively used with concrete and cementitious systems. In general, epoxies are known for their excellent adhesion, chemical and heat resistance, good-to-excellent mechanical properties and very good electrical insulating properties. Many properties of epoxies can be modified (for example silver -filled epoxies with good electrical conductivity are available, although epoxies are typically electrically insulating). Variations offering high thermal insulation , or thermal conductivity combined with high electrical resistance for electronics applications, are available. As with other classes of thermoset polymer materials, blending different grades of epoxy resin, as well as use of additives, plasticizers or fillers

5016-417: 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. The usual route to higher molecular weight epoxy resins is to start with liquid epoxy resin (LER) and add

5092-413: The required component properties. This has benefits beyond a reduction in pre-production sampling, as the precise layout of the complete casting system also leads to energy , material, and tooling savings. The software supports the user in component design, the determination of melting practice and casting methoding through to pattern and mold making, heat treatment , and finishing. This saves costs along

5168-491: The resulting cured network makes them important materials for aerospace composite applications. There are several dozen chemicals that can be used to cure epoxy, including amines , imidazoles, anhydrides and photosensitive chemicals. The study of epoxy curing is usually carried out by using differential scanning calorimetry . In general, uncured epoxy resins have only poor mechanical, chemical and heat resistance properties. However, good properties are obtained by reacting

5244-784: The resulting network does not typically display high temperature or chemical resistance, the high reactivity of the thiol group makes it useful for applications where heated curing is not possible, or very fast cure is required e.g. for domestic DIY adhesives and chemical rock bolt anchors . Thiols have a characteristic odour, which can be detected in many two-component household adhesives. The applications for epoxy-based materials are extensive and they are considered very versatile. The applications include coatings, adhesives and composite materials such as those using carbon fiber and fiberglass reinforcements (although polyester , vinyl ester , and other thermosetting resins are also used for glass-reinforced plastic). The chemistry of epoxies and

5320-444: The said epoxidation and prepolymerisation. 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

5396-430: The terminal epoxy groups are insignificant compared to the total size of the molecule). These resins do however contain hydroxyl groups throughout the backbone, which may also undergo other cross-linking reactions, e.g. with aminoplasts, phenoplasts and isocyanates . Epoxy resins are polymeric or semi-polymeric materials or an oligomer , and as such rarely exist as pure substances, since variable chain length results from

5472-706: The toxicity profile among other reasons. Epoxy resins may be thermally cured with anhydrides to create polymers with significant property retention at elevated temperatures for extended periods of time. Reaction and subsequent crosslinking occur only after opening of the anhydride ring, e.g. by secondary hydroxyl groups in the epoxy resin. Homopolymerization may also occur between epoxide and hydroxyl groups. The high latency of anhydride hardeners makes them suitable for processing systems which require addition of mineral fillers prior to curing, e.g. for high voltage electrical insulators. Cure speed may be improved by matching anhydrides with suitable accelerators. For dianhydrides, and to

5548-891: The viscosity of other epoxy resins. This has led to the term modified epoxy resin to denote those containing viscosity-lowering reactive diluents. The use of the diluent does effect mechanical properties and microstructure of epoxy resins. Mechanical properties of epoxy resins are generally not improved by use of diluents. Biobased epoxy diluents are also available. Glycidylamine epoxy resins are higher functionality epoxies which are formed when aromatic amines are reacted with epichlorohydrin . Important industrial grades are triglycidyl- p -aminophenol (functionality 3) and N , N , N ′, N ′-tetraglycidyl-bis-(4-aminophenyl)-methane (functionality 4). The resins are low to medium viscosity at room temperature, which makes them easier to process than EPN or ECN resins. This coupled with high reactivity, plus high temperature resistance and mechanical properties of

5624-555: Was achieved, when Krauklis and Echtermeyer discovered the mechanistic origin of yellowing in a commonly used amine epoxy resin, published in 2018. They found that the molecular reason for epoxy yellowing was a thermo-oxidative evolution of carbonyl groups in the polymeric carbon–carbon backbone via a nucleophilic radical attack. Polyester epoxies are used as powder coatings for washers, driers and other "white goods". Fusion Bonded Epoxy Powder Coatings (FBE) are extensively used for corrosion protection of steel pipes and fittings used in

5700-571: Was expensive, sometimes virtually unobtainable. Zinc is even more common at 75 parts per million, but is harder to extract from its ores. Bronze with the ideal percentage of tin was therefore expensive and the proportion of tin was often reduced to save cost. The discovery and exploitation of the Bolivian tin belt in the 19th century made tin far cheaper, although forecasts for future supplies are less positive. There are as many as 400 different copper and copper alloy compositions loosely grouped into

5776-543: Was first reported and patented by Paul Schlack of Germany in 1934. Claims of discovery of bisphenol-A -based epoxy resins include Pierre Castan in 1943. Castan's work was licensed by Ciba , Ltd. of Switzerland, which went on to become one of the three major epoxy resin producers worldwide. In 1946, Sylvan Greenlee, working for the Devoe ;& Raynolds Company (now part of Hexion Inc. ), patented resin derived from bisphenol-A and epichlorohydrin . Most of

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