Epoxies are also used in producing fiber-reinforced or composite parts. Dicarboxylic acids such as hexahydrophthalic acid are used for diglycide ester resins. In general, epoxy adhesives cured with heat will be more heat- and chemical-resistant than those cured at room temperature. Many properties of epoxies can be modified (for example silver-filled epoxies with good electrical conductivity are available, although epoxies are typically electrically insulating). Over 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. [19] They are rarely used alone, but are rather employed to modify (reduce) the viscosity of other epoxy resins. The resulting material has ether linkages and displays higher chemical and oxidation resistance than typically obtained by curing with amines or anhydrides. 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. While it is common to associate polyester resins and epoxy resins, their properties are sufficiently different that they are properly treated as distinct materials. [1] The IUPAC name for an epoxide group is an oxirane. The only variable available to the user is to change the rate of this process using a catalyst, often Methyl-Ethyl-Ketone-Peroxide (MEKP), which is very toxic. [11] Devoe&Raynolds, which was active in the early days of the epoxy resin industry, was sold to Shell Chemical; the division involved in this work was eventually sold, and via a series of other corporate transactions is now part of Hexion Inc.[12]. 30,00070,000 g/mol) form a class known as phenoxy resins and contain virtually no epoxide groups (since the terminal epoxy groups are insignificant compared to the total size of the molecule). [34] In general, epoxies are known for their excellent adhesion, chemical and heat resistance, good-to-excellent mechanical properties and very good electrical insulating properties. This parameter is used to calculate the mass of co-reactant (hardener) to use when curing epoxy resins. Tertiary amines, carboxylic acids and alcohols (especially phenols) are effective accelerators. Higher molecular weight diglycidyl ethers (n 1) are formed by the reaction of the bisphenol A diglycidyl ether formed with further bisphenol A, this 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. Epoxies have been researched and used for construction for a few decades. Glycidylamine epoxy resins are higher functionality epoxies which are formed when aromatic amines are reacted with epichlorohydrin. The technique is named "water shut-off treatment".[28]. High purity grades can be produced for certain applications, e.g. Epoxy homopolymerisation is often used when there is a requirement for UV curing, since cationic UV catalysts may be employed (e.g. All quantities of mix generate their own heat because the reaction is exothermic. Epoxy resins diluents are typically formed by glycidylation of aliphatic alcohols or polyols and also aromatic alcohols. [37] Epoxy coatings have also been used in drinking water applications.[38]. and Siregar, S. Polymer modified cements and repair mortars. For the chemical group, see. 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). In this case, the peracids can also be formed in situ by reacting carboxylic acids with hydrogen peroxide. Since many novolacs are solids, this class of hardeners is often employed for powder coatings. 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). dodecanol glycidyl ether), difunctional (1,4-Butanediol diglycidyl ether), or higher functionality (e.g. for domestic DIY adhesives and chemical rock bolt anchors. [16] 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 Tg. Epoxies can be used to plug selective layers in a reservoir which are producing excessive brine. Until they are mixed the two elements are relatively inert, although the 'hardeners' tend to be more chemically active and should be protected from the atmosphere and moisture. There are two main areas of marine use. The cured epoxy is an electrical insulator and a much better conductor of heat than air. The rate of cure of polyesters can therefore be controlled by the amount and type of catalyst as well as by the temperature. Use of a difunctional or polyfunctional amine forms a three-dimensional cross-linked network. As it has a low surface tension, it is added as a wetting agent (surfactant) for contact with glass fibres. One-component products generally have shorter shelf-lives than standard 2-component systems, and products may require cooled storage and transport. These co-reactants are often referred to as hardeners or curatives, and the cross-linking reaction is commonly referred to as curing. By contrast, polyester resins are usually made available in a 'promoted' form, such that the progress of previously-mixed resins from liquid to solid is already underway, albeit very slowly. This process is known as "advancement". One particular risk associated with epoxy resins is sensitization. [62] Safe disposal also needs considering but usually involves deliberate curing to produce solid rather than liquid waste. Also known as mercaptans, thiols contain a sulfur which reacts very readily with the epoxide group, even at ambient or sub-ambient temperatures. These companies are known as "formulators". [23] Biobased epoxy diluents are also available.[24]. [61] Exposure to epoxy resins can, over time, induce an allergic reaction. Research is ongoing to investigate the use of epoxies and other recycled plastics in mortars to enhance properties and recycle waste. [57] The epoxy resin market is dominated by the Asia-Pacific region, which contributes 55.2% of the total market share. Hofer, Arnold; Schneider, Hildegard, and Siegenthaler, Nikolaus (1996) "Epoxy resin mixtures containing advancement catalysts". Epoxy resins yellow with time, even when not exposed to UV radiation. by secondary hydroxyl groups in the epoxy resin. Very high molecular weight polycondensates (ca. Di- and polyols lead to glycidyl ethers. Polyester epoxies are used as powder coatings for washers, driers and other "white goods". Overall reactivity potential for different hardeners can roughly be ordered; aliphatic amines > cycloaliphatic amines > aromatic amines, though aliphatic amines with steric hindrance near the amino groups may react as slowly as some of the aromatic amines. Curing with phenolics to make drum linings, curing esters with amine resins and pre-curing epoxies with amino resins to make resistant top coats. There are various methods of toughening them.[36]. They can be made flexible or rigid, transparent or opaque/colored, fast setting or slow setting. Homopolymerization may also occur between epoxide and hydroxyl groups. Depending on the properties required, the ratio may be anything from 1:1 or over 10:1, but in usually they must be mixed exactly. China is the major producer and consumer globally, consuming almost 35% of the global resin production. for UV coatings). They are also sold in boat shops as repair resins for marine applications. There are hundreds of ways that these formulators can modify epoxiesby adding mineral fillers (talc, silica, alumina, etc. Flexible epoxy resins are used for potting transformers and inductors. As a result, a typical formulator sells dozens or even thousands of formulationseach tailored to the requirements of a particular application or market. for high voltage electrical insulators. [41] They found that the molecular reason for epoxy yellowing was a thermo-oxidative evolution of carbonyl groups in the polymeric carboncarbon backbone via a nucleophilic radical attack. Amine type hardeners will alter both the processing properties (viscosity, reactivity) and the final properties (mechanical, temperature and heat resistance) of the cured copolymer network. Curing may be achieved by reacting an epoxy with itself (homopolymerisation) or by forming a copolymer with polyfunctional curatives or hardeners. First a hydroxy group reacts in a coupling reaction with epichlorohydrin, followed by dehydrohalogenation. This "plastic tooling" replaces metal, wood and other traditional materials, and generally improves the efficiency and either lowers the overall cost or shortens the lead-time for many industrial processes. [60] Solid epoxy resins are generally safer than liquid epoxy resins, and many are classified non-hazardous materials. One of the best examples was a system of using solvent free epoxies for priming ships during construction, this used a system of hot airless spray with premixing at the head. Castan's work was licensed by Ciba, Ltd. of Switzerland, which went on to become one of the three major epoxy resin producers worldwide. Most of the commercially used epoxy monomers are produced by the reaction of a compound with acidic hydroxy groups and epichlorohydrin. This process is commonly referred to as curing or gelation process. Epoxies generally out-perform most other resin types in terms of mechanical properties and resistance to environmental degradation. This means that conventional nucleophilic hardeners such as amines are hardly suitable for crosslinking. The second area is that their strength, gap filling properties and excellent adhesion to many materials including timber have created a boom in amateur building projects including aircraft and boats. They are also used for radiation-cured paints and varnishes. This class also displays lower viscosity at room temperature, but offers significantly higher temperature resistance than the aliphatic epoxy diluents. [20] This has led to the term modified epoxy resin to denote those containing viscosity-lowering reactive diluents. [31] The applications include coatings, adhesives[32][33] 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). 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.) The chemistry of epoxies and the range of commercially available variations allows cure polymers to be produced with a very broad range of properties. There are several dozen chemicals that can be used to cure epoxy, including amines, imidazoles, anhydrides and photosensitive chemicals. The epoxide group is also sometimes referred to as a oxirane group. [4][5], 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 when not fully cured. Epoxies are sold in hardware stores, typically as a pack containing separate resin and hardener, which must be mixed immediately before use. Electric generators, connected via the drivetrain with the rotor blades, convert mechanical wind energy in usable electric energy, and rely on epoxies electrical insulation and high thermal resistance properties. While 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. Epoxies typically are not used in the outer layer of a boat because they deteriorate by exposure to UV light. 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 anhydrides), phenols, alcohols and thiols (usually called mercaptans). [21] The use of the diluent does effect mechanical properties and microstructure of epoxy resins. using a distillation purification process. Polyols can be compounds such as 1,4-butanediol. 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. [citation needed], Epoxy resins may be thermally cured with anhydrides to create polymers with significant property retention at elevated temperatures for extended periods of time. Aromatic amines were widely used as epoxy resin hardeners, due to the excellent end properties when mixed with a parent resin. While some epoxy resin/ hardener combinations will cure at ambient temperature, many require heat, with temperatures up to 150C (302F) being common, and up to 200C (392F) for some specialist systems. Epoxies are also used as a structural glue. printed circuit boards). [17][18] The resulting materials may be monofunctional (e.g. The risk has been shown to be more pronounced in epoxy resins containing low molecular weight epoxy diluents. 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. [22] Mechanical properties of epoxy resins are generally not improved by use of diluents. Sensitization generally occurs due to repeated exposure (e.g. As adhesives, epoxies bond in three ways: a) Mechanically, because the bonding surfaces are roughened; b) by proximity, because the cured resins are physically so close to the bonding surfaces that they are hard to separate; c) ionically, because the epoxy resins form ionic bonds at an atomic level with the bonding surfaces. [40] Down investigated various room-temperature-cure epoxy resin adhesives suitable for use in glass conservation, testing their tendency to yellow. In Europe, wind energy components account for the largest segment of epoxy applications, about 27% of the market.[44]. for chips on board ), LEDs, high-tension electrical insulators, paint brush manufacturing, fiber-reinforced plastic materials, and adhesives for structural[3] and other purposes. As with other classes of thermoset polymer materials, blending different grades of epoxy resin, as well as use of additives, plasticizers or fillers is common to achieve the desired processing or final properties, or to reduce cost. Epoxies are typically cured with stoichiometric or near-stoichiometric quantities of hardener to achieve the best physical properties. Compared with LERs (liquid epoxy resins) they have very low viscosities. Cycloaliphatic epoxides are therefore usually homopolymerized thermally or UV-initiated in an electrophilic or cationic reaction. [47] Although they increase cost of mortars and concrete when used as an additive, they enhance properties. Epoxy resins are also used for decorative flooring applications such as terrazzo flooring, chip flooring, and colored aggregate flooring. with aminoplasts, phenoplasts and isocyanates. 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. Epoxy resins are used to bond copper foil to circuit board substrates, and are a component of the solder mask on many circuit boards. When cured, the epoxy resin leads to a thermosetting plastic with high chemical resistance and low water absorption. 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. It has been used and studied for art and historic structure preservation.[54][55][56]. Materials like wood, and others that are 'low-tech' are glued with epoxy resin. These resins do however contain hydroxyl groups throughout the backbone, which may also undergo other cross-linking reactions, e.g. Epoxy systems are used in industrial tooling applications to produce molds, master models, laminates, castings, fixtures, and other industrial production aids. [26], In general, uncured epoxy resins have only poor mechanical, chemical and heat resistance properties. [6][7][8], Condensation of epoxides and amines was first reported and patented by Paul Schlack of Germany in 1934. Epoxy has a wide range of applications, including metal coatings, composites,[2] use in electronics, electrical components (e.g. 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexane carboxylate). The strength of epoxy adhesives is degraded at temperatures above 350F (177C).[42]. Epoxy resin formulations are important in the electronics industry, and are employed in motors, generators, transformers, switchgear, bushings, insulators, printed wiring boards (PWB), and semiconductor encapsulants. Increasingly, water-based polyamines are also used to help reduce the toxicity profile among other reasons. Due to their high price, however, their use has so far been limited to such applications. German Patent 676117. These modifications are made to reduce costs, to improve performance, and to improve processing convenience. Novolaks are produced by reacting phenol with methanal (formaldehyde). Large scale epoxidized vegetable oils such as epoxidized soy and lens oils are used to a large extent as secondary plasticizers and cost stabilizers for PVC.[13]. The usual route to higher molecular weight epoxy resins is to start with liquid epoxy resin (LER) and add a calculated amount of bisphenol A and then a catalyst is added and the reaction heated to circa 160C (320F). In principle, any molecule containing a reactive hydrogen may react with the epoxide groups of the epoxy resin. The majority of the epoxy systems sold are produced by these formulators and they comprise over 60% of the dollar value of the epoxy market. Important epoxy resins are produced from combining epichlorohydrin and bisphenol A to give bisphenol A diglycidyl ethers. 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 the epoxy formulation. Some epoxies are cured by exposure to ultraviolet light. Some (non-crosslinked) epoxy resins with very high molar mass are added to engineering thermoplastics, again to achieve flame retardant properties. The largest volume type of circuit boardan "FR-4 board"is a sandwich of layers of glass cloth bonded into a composite by an epoxy resin. The epoxy curing reaction may be accelerated by addition of small quantities of accelerators. These were often reacted with styrene to make styrenated epoxy esters, used as primers. Temperature resistance generally increases in the same order, since aromatic amines form much more rigid structures than aliphatic amines. The rate of the reaction can be changed by using different hardeners, which may change the nature of the final product, or by controlling the temperature. Epoxies, by contrast, are inherently strong, somewhat flexible and have excellent adhesion. Densifying plastic materials such as PET and plastic bags and then using them to partially replace aggregate and depolymerizing PET to use as a polymeric binder in addition to epoxy to enhance concrete are actively being studied. Typical ones were L8 (80% linseed) and D4 (40% dehydrated castor oil). Use of blending, additives and fillers is often referred to as formulating. As aromaticity is not present in these materials as it is in Bisphenol A and F resins, the UV stability is considerably improved. Reaction and subsequent crosslinking occur only after opening of the anhydride ring, e.g. Epoxy resins produced from such epoxy monomers are called glycidyl-based epoxy resins. Relative reactivity (lowest first) is approximately in the order: phenol < anhydride < aromatic amine < cycloaliphatic amine < aliphatic amine < thiol. Polyfunctional primary amines form an important class of epoxy hardeners. The global market is made up of approximately 50100 manufacturers of basic or commodity epoxy resins and hardeners. Instead of a hydroxy group, also the nitrogen atom of an amine or amide can be reacted with epichlorohydrin. Epoxy materials tend to harden somewhat more gradually, while polyester materials tend to harden quickly, particularly if a lot of catalyst is used. In the electronics industry epoxy resins are the primary resin used in overmolding integrated circuits, transistors and hybrid circuits, and making printed circuit boards. The presence of the catalyst in the final product actually detracts from the desirable properties, so that small amounts of catalyst are preferable, so long as the hardening proceeds at an acceptable pace. Thiols have a characteristic odour, which can be detected in many two-component household adhesives. So it is good practice to mix smaller amounts which can be used quickly to avoid waste and to be safer. The chlorine atom is released as sodium chloride (NaCl) and the hydrogen atom as water. These highly viscous to solid resins typically carry 2 to 6 epoxy groups per molecule. Daniels LJ, PhD thesis Lancaster University 1992, 3,4-Epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate, 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexane carboxylate, "Electrical Resistance Sensing of Epoxy Curing Using an Embedded Carbon Nanotube Yarn", "The Influence of Mixing Methods of Epoxy Composition Ingredients on Selected Mechanical Properties of Modified Epoxy Construction Materials", "US Patent Application for FIRE-RESISTANT GLAZING Patent Application (Application #20130196091 issued August 1, 2013) - Justia Patents Search", "Epoxy resins thermosetting for mechanical engineering", "Health Effects from Overexposure to Epoxy WEST SYSTEM", "Allergic Contact Dermatitis from a Nonbisphenol A Epoxy in a Graphite Fiber Reinforced Epoxy Laminate", "Occupational Contact Dermatitis Due to Epoxy Resin in a Fiberglass Binder", "Diluting Agent - an overview | ScienceDirect Topics", "Diluents and viscosity modifiers for epoxy resins", "Developments in reactive diluents: a review", "Effect of reactive and non-reactive diluents on thermal and mechanical properties of epoxy resin", "The effect of reactive diluent on mechanical properties and microstructure of epoxy resins", "Synthesis and Application of Polyepoxide Cardanol Glycidyl Ether as Biobased Polyepoxide Reactive Diluent for Epoxy Resin", "The application of differential scanning calorimetry (DSC) to the study of epoxy resin curing reactions", "Epoxy Resin - an overview | ScienceDirect Topics", "Benefits and Applications of BTDA and Other Dianhydrides in Polyimide and Epoxy Resins", "Structural Adhesives - Improvements in Vehicle Crash Performance", "Effects of CNBR Modification on Mode I Fracture of Epoxy Adhesives for Automotive Application", "Preparation and Research of Solvent-Free Epoxy Coating for Drinking Water Tank", "Mechanism of Yellowing: Carbonyl Formation during Hygrothermal Aging in a Common Amine Epoxy", Preliminary Study on Epoxy-Based Polymer for Water Shut-Off Application, "Mechanical Properties and Microstructure of Epoxy Mortars Made with Polyethylene and Poly(Ethylene Terephthalate) Waste", "A new embedding technique for electron microscopy, combining a water-soluble epoxy resin (Durcupan) with water-insoluble Araldite", "A Modification of the Water-miscible Epoxy Resin "Durcupan" Embedding Method for Ultrathin Sectioning", "Improvements in epoxy resin embedding methods", "The Yellowing of Epoxy Resin Adhesives: Report on Natural Dark Aging", "The Application of Epoxy Resins for the Restoration of Historic Structures", "The Use of Epoxy Resins for the Stabilization of Deteriorated Masonry", "Epoxy Resin Market- By Application (Paints & Coatings, Wind Energy, Composites, Construction, and Electrical & Electronics): Global Industry Perspective, Comprehensive Analysis, and Forecast, 20222028", "Synthesis and characterization of bio-based epoxy blends from renewable resource based epoxidized soybean oil as reactive diluent", "Synthesis and Properties of Organosilicon-Grafted Cardanol Novolac Epoxy Resin as a Novel Biobased Reactive Diluent and Toughening Agent", https://en.wikipedia.org/w/index.php?title=Epoxy&oldid=1101140406, Short description is different from Wikidata, Articles with unsourced statements from March 2021, Creative Commons Attribution-ShareAlike License 3.0, This page was last edited on 29 July 2022, at 14:20.

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