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. Primary amines undergo an addition reaction with the epoxide group to form a hydroxyl group and a secondary amine. Ciba's epoxy business was spun off as Vantico in the late 1990s, which was subsequently sold in 2003 and became the Advanced Materials business unit of Huntsman Corporation of the United States. An important criterion for epoxy resins is the Epoxy value which is connected to the epoxide group content. [62] Safe disposal also needs considering but usually involves deliberate curing to produce solid rather than liquid waste. Large quantities will generate more heat and thus greatly increase the rate of the reaction and so reduce working time (pot-life). Novolaks are produced by reacting phenol with methanal (formaldehyde). The resins are low to medium viscosity at room temperature, which makes them easier to process than EPN or ECN resins. The resulting material has ether linkages and displays higher chemical and oxidation resistance than typically obtained by curing with amines or anhydrides. Instead of a hydroxy group, also the nitrogen atom of an amine or amide can be reacted with epichlorohydrin. While it is common to associate polyester resins and epoxy resins, their properties are sufficiently different that they are properly treated as distinct materials. They are therefore added to other epoxy resins as reactive diluents or as adhesion promoters. Epoxies were modified in a variety of ways, Reacted with fatty acids derived from oils to yield epoxy esters, which were cured the same way as alkyds. 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. Bisphenol A is a highly effective and widely used accelerator, but is now increasingly replaced due to health concerns with this substance. Normal gelcoat formulated for use with polyester resins and vinylester resins does not adhere to epoxy surfaces, though epoxy adheres very well if applied to polyester resin surfaces. Its reactivity to hardeners is comparable to that of bisphenol A. They are also used for radiation-cured paints and varnishes. printed circuit boards). 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). Most of the commercially used epoxy monomers are produced by the reaction of a compound with acidic hydroxy groups and epichlorohydrin. [48], In the aerospace industry, epoxy is used as a structural matrix material which is then reinforced by fiber. They can be made flexible or rigid, transparent or opaque/colored, fast setting or slow setting. The chemistry of epoxies and the range of commercially available variations allows cure polymers to be produced with a very broad range of properties. These highly viscous to solid resins typically carry 2 to 6 epoxy groups per molecule. Common classes of hardeners for epoxy resins include amines, acids, acid anhydrides, phenols, alcohols and thiols. Epoxy resins are applied using the technology of resin dispensing. It has been used and studied for art and historic structure preservation.[54][55][56]. [20] This has led to the term modified epoxy resin to denote those containing viscosity-lowering reactive diluents. This process is commonly referred to as curing or gelation process. 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). They can be used as adhesives for wood, metal, glass, stone, and some plastics. As it has a low surface tension, it is added as a wetting agent (surfactant) for contact with glass fibres. 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. 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. A fundamental molecular understanding of epoxy yellowing was achieved, when Krauklis and Echtermeyer discovered the mechanistic origin of yellowing in a commonly used amine epoxy resin, published in 2018. The global epoxy resin market was valued at approximately 9.1 (USD Billion) in 2021 and is predicted to gain revenue of about 14.7 (USD Billion) by 2028, is set to record a CAGR of nearly 6.8% over the period from 2022 to 2028. 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. 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. This process is known as catalytic homopolymerisation. Epoxy resins are used as bonding matrix along with glass or carbon fiber fabrics to produce composites with very high strength to weight characteristics, allowing longer and more efficient rotor blades to be produced. 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. [25] The study of epoxy curing is usually caried out by using Differential scanning calorimetry. [63], This article is about the thermoset plastic materials. 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. Because aliphatic epoxies have a lower electron density than aromatics, cycloaliphatic epoxies react less readily with nucleophiles than bisphenol A-based epoxy resins (which have aromatic ether groups). Fusion Bonded Epoxy Powder Coatings (FBE) are extensively used for corrosion protection of steel pipes and fittings used in the oil and gas industry, potable water transmission pipelines (steel), and concrete reinforcing rebar. The risk has been shown to be more pronounced in epoxy resins containing low molecular weight epoxy diluents. This last is substantially the strongest of the three. Also aliphatic glycidyl epoxy resins usually have a low viscosity compared to aromatic epoxy resins. By using vacuum impregnation on uncured epoxy, winding-to-winding, winding-to-core, and winding-to-insulator air voids are eliminated. 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. [26], In general, uncured epoxy resins have only poor mechanical, chemical and heat resistance properties. This route of synthesis is known as the "taffy" process. Use of blending, additives and fillers is often referred to as formulating. Polyphenols, such as bisphenol A or novolacs can react with epoxy resins at elevated temperatures (130180C, 266356F), normally in the presence of a catalyst. The hydroxy group may be derived from aliphatic diols, polyols (polyether polyols), phenolic compounds or dicarboxylic acids. In principle, any molecule containing a reactive hydrogen may react with the epoxide groups of the epoxy resin. Epoxy resins diluents are typically formed by glycidylation of aliphatic alcohols or polyols and also aromatic alcohols. Epoxy coatings are often used in industrial and automotive applications since they are more heat resistant than latex-based and alkyd-based paints. [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. However, the commercial use of fluorinated epoxy resins is limited by their high cost and low Tg. [45] The chemical reactions in both cases are exothermic. This parameter is used to calculate the mass of co-reactant (hardener) to use when curing epoxy resins. They have been extensively used with concrete and cementitious systems. [43] In addition, for offshore and onshore wind energy installations, epoxy resins are used as protective coatings on steel towers, base struts and concrete foundations. Such epoxies are commonly used in optics, fiber optics, and optoelectronics. However, aliphatic epoxy resins polymerize very slowly at room temperature, so higher temperatures and suitable accelerators are usually required. This process is known as "advancement". This means that conventional nucleophilic hardeners such as amines are hardly suitable for crosslinking. Epoxy resins are used to bond copper foil to circuit board substrates, and are a component of the solder mask on many circuit boards. 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]. Aliphatic, cycloaliphatic and aromatic amines are all employed as epoxy hardeners. Instead of bisphenol A, other bisphenols (especially bisphenol F) or brominated bisphenols (e. g. tetrabromobisphenol A) can be used for the said epoxidation and prepolymerisation. [47] Although they increase cost of mortars and concrete when used as an additive, they enhance properties. 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. Change in color, known as yellowing, is a common phenomenon for epoxy materials and is often of concern in art and conservation applications. One particular risk associated with epoxy resins is sensitization. These companies are known as "formulators". 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. As there is a general trend to renewable and "green" sources and greater use of biobased materials, research is ongoing in the epoxy arena too. In some cases, blends of dianhydrides and monoanhydrides can improve metering and mixing with liquid epoxy resins.[30]. through poor working hygiene or lack of protective equipment) over a long period of time. Epoxy has a wide range of applications, including metal coatings, composites,[2] use in electronics, electrical components (e.g. In Europe, wind energy components account for the largest segment of epoxy applications, about 27% of the market.[44]. In Europe, about 323,000 tonnes of epoxy resin were manufactured in 2017 generating some 1,055 million in sales. trimethylolpropane triglycidyl ether). 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. [57] The epoxy resin market is dominated by the Asia-Pacific region, which contributes 55.2% of the total market share. Halogenated epoxy resins are admixed for special properties, in particular brominated and fluorinated epoxy resins are used.[13]. All quantities of mix generate their own heat because the reaction is exothermic. 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate). This is expressed as the "epoxide equivalent weight", which is the ratio between the molecular weight of the Rorar and the number of epoxide groups. They are also sold in boat shops as repair resins for marine applications. Polyester resins are typically low strength unless used with a reinforcing material like glass fibre, are relatively brittle unless reinforced, and have low adhesion. Tertiary amines, carboxylic acids and alcohols (especially phenols) are effective accelerators. The reaction is carried out in the presence of a base such as sodium hydroxide, analogous to the formation of bisphenol A-diglycidyl ether. Temperature resistance generally increases in the same order, since aromatic amines form much more rigid structures than aliphatic amines. 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexane carboxylate). Epoxy resins made of (long-chain) polyols are also added to improve tensile strength and impact strength. However, polyester resins are much cheaper. Important epoxy resins are produced from combining epichlorohydrin and bisphenol A to give bisphenol A diglycidyl ethers. Castan's work was licensed by Ciba, Ltd. of Switzerland, which went on to become one of the three major epoxy resin producers worldwide. Research is ongoing to investigate the use of epoxies and other recycled plastics in mortars to enhance properties and recycle waste. [6][7][8], Condensation of epoxides and amines was first reported and patented by Paul Schlack of Germany in 1934. Schlack, P. (1938) "Manufacture of amines of high molecular weight, which are rich in nitrogen". 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. 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. 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 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. [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. For dianhydrides, and to a lesser extent, monoanhydrides, non-stoichiometric, empirical determinations are often used to optimize dosing levels. Flexible epoxy resins are used for potting transformers and inductors. Epoxies have been researched and used for construction for a few decades. 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). Because of the better mechanical properties relative to the more common polyester resins, epoxies are used for commercial manufacture of components where a high strength/weight ratio is required. 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.) Curing may be achieved by reacting an epoxy with itself (homopolymerisation) or by forming a copolymer with polyfunctional curatives or hardeners. [27] However, good properties are obtained by reacting the linear epoxy resin with suitable curatives to form three-dimensional cross-linked thermoset structures. Polyols can be compounds such as 1,4-butanediol. Epoxy is the family of basic components or cured end products of epoxy resins. The global market is made up of approximately 50100 manufacturers of basic or commodity epoxy resins and hardeners. 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. [15] As the molecular weight of the resin increases, the epoxide content reduces and the material behaves more and more like a thermoplastic. Two part epoxy coatings were developed for heavy duty service on metal substrates and use less energy than heat-cured powder coatings. Epoxies are typically cured with stoichiometric or near-stoichiometric quantities of hardener to achieve the best physical properties. Aromatic amines were widely used as epoxy resin hardeners, due to the excellent end properties when mixed with a parent resin. Very high molecular weight polycondensates (ca. 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. This curing is what produces the qualities of the substance such as resistance, durability, versatility, and adhesion. These commodity epoxy manufacturers mentioned above typically do not sell epoxy resins in a form usable to smaller end users, so there is another group of companies that purchases epoxy raw materials from the major producers and then compounds (blends, modifies, or otherwise customizes) epoxy systems from these raw materials. 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. [28] Curing of epoxy resins is an exothermic reaction and in some cases produces sufficient heat to cause thermal degradation if not controlled.[29]. German Patent 676117. The strength of epoxy adhesives is degraded at temperatures above 350F (177C).[42]. These modifications are made to reduce costs, to improve performance, and to improve processing convenience. Cycloaliphatic epoxides contain one or more aliphatic rings in the molecule on which the oxirane ring is contained (e.g. for chips on board ), LEDs, high-tension electrical insulators, paint brush manufacturing, fiber-reinforced plastic materials, and adhesives for structural[3] and other purposes. Important industrial grades are triglycidyl-p-aminophenol (functionality 3) and N,N,N,N-tetraglycidyl-bis-(4-aminophenyl)-methane (functionality 4). Epoxy resins are excellent electrical insulators and protect electrical components from short circuiting, dust and moisture. China is the major producer and consumer globally, consuming almost 35% of the global resin production. These co-reactants are often referred to as hardeners or curatives, and the cross-linking reaction is commonly referred to as curing. "Flocoat" that is normally used to coat the interior of polyester fibreglass yachts is also compatible with epoxies. Epoxy resins yellow with time, even when not exposed to UV radiation. [61] Exposure to epoxy resins can, over time, induce an allergic reaction. 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. Compared with LERs (liquid epoxy resins) they have very low viscosities. Epoxy systems are used in industrial tooling applications to produce molds, master models, laminates, castings, fixtures, and other industrial production aids. One-component products generally have shorter shelf-lives than standard 2-component systems, and products may require cooled storage and transport. Typical fiber reinforcements include glass, carbon, Kevlar, and boron. 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. Epoxies generally out-perform most other resin types in terms of mechanical properties and resistance to environmental degradation. The high latency of anhydride hardeners makes them suitable for processing systems which require addition of mineral fillers prior to curing, e.g. Epoxies can be used to plug selective layers in a reservoir which are producing excessive brine. This class also displays lower viscosity at room temperature, but offers significantly higher temperature resistance than the aliphatic epoxy diluents. As a result, a typical formulator sells dozens or even thousands of formulationseach tailored to the requirements of a particular application or market. In the electronics industry epoxy resins are the primary resin used in overmolding integrated circuits, transistors and hybrid circuits, and making printed circuit boards. plant derived glycerol used to make epichlorohydrin). This obviated the problem of solvent retention under the film, which caused adhesion problems later on. dodecanol glycidyl ether), difunctional (1,4-Butanediol diglycidyl ether), or higher functionality (e.g. As aromaticity is not present in these materials as it is in Bisphenol A and F resins, the UV stability is considerably improved. Epoxy use is a main source of occupational asthma among users of plastics. Allergic reaction sometimes occurs at a time which is delayed several days from the exposure. for domestic DIY adhesives and chemical rock bolt anchors. [17][18] The resulting materials may be monofunctional (e.g. There are two main areas of marine use. Epoxies are also used in producing fiber-reinforced or composite parts. The same applies to transformers, bushings, spacers, and composites cables connecting the windmills to the grid. [21] The use of the diluent does effect mechanical properties and microstructure of epoxy resins. Relative reactivity (lowest first) is approximately in the order: phenol < anhydride < aromatic amine < cycloaliphatic amine < aliphatic amine < thiol. They are more expensive than polyester resins and vinyl ester resins, but usually produce stronger and more temperature-resistant thermoset polymer matrix composite parts. Epoxy materials tend to harden somewhat more gradually, while polyester materials tend to harden quickly, particularly if a lot of catalyst is used. They are produced by the reaction of a cyclic alkene with a peracid (see above). 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). [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. [22] Mechanical properties of epoxy resins are generally not improved by use of diluents. The other production route for epoxy resins is the conversion of aliphatic or cycloaliphatic alkenes with peracids:[13][14] 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. 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 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. 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. [49], Water-soluble epoxies such as Durcupan[50][51] are commonly used for embedding electron microscope samples in plastic so they may be sectioned (sliced thin) with a microtome and then imaged. There are various methods of toughening them.[36]. The secondary amine can further react with an epoxide to form a tertiary amine and an additional hydroxyl group. The final product is then a precise thermoset plastic. [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.