Epoxy is one of the basic or cured end products of epoxy resin , as well as the daily name for the epoxide functional group. The epoxy resin, also known as polyepoxides , is a class of prepolymers and a reactive polymer containing epoxide groups. The epoxy resin may be cross-linked either by itself through catalytic homopolymerization, or by various co-reactants including polyfunctional amines, acids (and acid anhydrides), phenols, alcohols and thiols (usually called mercaptans). These co-reactants are often referred to as hardener or curative, and crosslinking reactions are commonly referred to as curing. The reaction of polyepoxides by themselves or by polyfunctional functional hardener forms thermosetting polymers, often with favorable mechanical properties and high heat and chemical resistance. Epoxy has a variety of applications, including metal plating, used in electronic/electrical/LED components, high voltage electrical insulators, manufacturing paint brushes, fiber-reinforced plastic materials and structural adhesives.
Video Epoxy
Resin epoksi
Epoxy resins are low molecular weight pre-polymers or high molecular weight polymers which usually contain at least two groups of epoxides. Epoxide groups are also sometimes referred to as glycidyl or oxyane groups.
A wide variety of industrial epoxy resins are manufactured. The raw material for the production of epoxy resins is currently mostly derived from petroleum, although several available plant sources are now commercially available (eg plant glycerol used to make epichlorohydrin).
The epoxy resin is a polymeric or semi-polymer or oligomeric material, and is therefore rarely present as a pure substance, since the length of the variable chain results from the polymerization reaction used to produce it. High purity values ​​can be produced for certain applications, e.g. using a distillation distillation process. One disadvantage of high levels of purity of liquids is their tendency to form crystalline solids because of their highly ordered structure, which requires smelting to permit processing.
An important criterion for epoxy resins is epoxide group content. This is correctly stated as the specific amount of substance of the epoxide group in the material B under consideration, calculated as the ratio of the amount of substance of the epoxide group in this material B, n (EP), subdivided with mass m (B) of the B material under consideration, in this case, the resin mass. The SI unit for this quantity is "mol/kg", or multiples thereof. The abandoned amount still used is called the "epoxide number" which (not a number and therefore should not be referred to as such, but) the ratio of the group epoxide group, n (EP), and the mass m (B) of the material B, with units SI "mol/kg", or so-called " the weight of epoxide equivalent" , which is the ratio of the sample mass B of the resin and the amount of substance of the epoxide group present in sample B, with SI unit "kg/mol". The so-called "equivalent epoxide weight" is just the opposite of the so-called "epoxide number".
Specific quantities of epoxide group substances are used to calculate the mass of co-reactants (hardener) for use when curing epoxy resins. Epoxies are usually cured with stoichiometric amounts or near curative stoichiometrics to achieve maximum physical properties.
Like other classes of thermoset polymer materials, mixing of various classes of epoxy resins, as well as the use of additives, plasticizers or fillers is common to achieve desired processing or final properties, or to reduce costs. The use of mixing, additives and fillers is often referred to as formulate .
Bisphenol A epoxy resin
An important epoxy resin results from the incorporation of epichlorohydrin and bisphenol A to give bisphenol A diglycidyl ethers.
Increasing the ratio of bisphenol A to epichlorohydrin during preparation produces a higher molecular weight linear polyether with a glycidyl end group, which is a solid to dense semi-solid crystalline material at room temperature depending on the molecular weight attained. As the molecular weight of the resin increases, the epoxide content is reduced and the material behaves more and more like a thermoplastic. Very high molecular-weight polycondensates (about 30,000 - 70 000 g/mol) form a class known as phenoxy resin and contain almost no epoxide groups (since terminal epoxy groups are insignificant compared to the total size of the molecule). However, this resin contains hydroxyl groups throughout the spine, which may also undergo other crosslinking reactions, eg. with aminoplasts, phenoplasts and isocyanates.
Bisphenol F epoxy resin
Bisphenol F may undergo the formation of epoxy resins in the same manner as bisphenol A. These resins usually have lower viscosities and higher mean epoxy content per gram than bisphenol A resins, which (once healed) give them increased chemical resistance.
Novolac epoxy resin
The phenol reaction with formaldehyde and subsequent glycidylation with epichlorohydrin result in novitable epoxy, epoxy phenol novolak (EPN) and epoxy cresol novolak (ECN). It is very thick with solid resins with an average epoxide function of about 2 to 6. The high epoxide functionality of this resin forms a highly crosslinked polymer network featuring high temperature and chemical resistance, but low flexibility.
Aliphatic epoxy resin
Aliphatic epoxy resins are usually formed by aliphatic alcohol glycidylation or polyols. The resulting resin may be monofunctional (eg dodecanol glycidyl ether), difunctional (butanediol diglycidyl ether), or higher functionality (eg trimethylolpropane triglycidyl ether). These resins typically show a 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 used to modify (reduce) the viscosity of other epoxy resins. This leads to the term 'modified epoxy resin' to denote those containing reactive viscosity-lowering diluents. The associated class is a cycloaliphatic epoxy resin, containing one or more cycloaliphatic rings in the molecule (eg 3,4-epoxycyclohexylmethyl-3,4-epoxyclohydexane carboxylate). This class also displays low viscosity at room temperature, but offers significantly higher temperature resistance than an aliphatic epoxy diluent. However, its reactivity is rather low compared to other epoxy resin classes, and high temperature drying using suitable accelerators is usually required.
Epoxy glycidhylamine resin
Glycidhylamine epoxy resin is a higher epoxy functionality that is formed when the aromatic amine is reacted with epichlorohydrin. The important industrial values ​​are triglycidyl- p -aminophenol (functionality 3) and N , N , N ?, N ? - tetraglycidyl-bis- (4-aminophenyl) -methane (function 4). Resins have a low to moderate viscosity at room temperature, which makes it easier to process than EPN or ECN resins. This coupled with high reactivity, plus the high temperature resistance and mechanical properties of the resulting cured tissue make them an important material for aerospace composites applications.
Maps Epoxy
Curing epoxy resin
In general, uncured epoxy resins have only low mechanical, chemical, and thermal resistance properties. However, good properties are obtained by reacting a linear epoxy resin with an appropriate curative to form a three-dimensional thermoset cross-bond structure. This process is usually referred to as a curing or gelation process. Curing epoxy resins is an exothermic reaction and in some cases generates enough heat to cause thermal degradation if not controlled.
The curing process can be carried out by reacting the epoxy by itself (homopolymerization) or by forming a copolymer with polyfunctional curative or hardeners . In principle, any molecule containing reactive hydrogen can react with the epoxide group of epoxy resins. Common classes of hardeners for epoxy resins include amines, acids, acid anhydrides, phenols, alcohols and thiols. The relative reactivity (the first low) is roughly in the order of: phenol & lt; anhydride & lt; aromatic amine & lt; cycloaliphatic amine & lt; aliphatic amine & lt; thiols.
While some combinations of epoxy resins will cure at room temperature, many require heat, with temperatures up to 150 ° C common, and up to 200 ° C for some specialist systems. Insufficient heat during the healer will result in tissue with imperfect polymerization, and thereby reduce mechanical, chemical and thermal resistance. The healing temperature should normally reach the glass transition temperature (Tg) of fully restored tissue to achieve maximum properties. Temperature sometimes increases gradually to control the preservation rate and prevent excessive heat formation from exothermic reactions.
Hardener that only shows low or limited reactivity at room temperature, but which reacts with epoxy resin at high temperatures is referred to as latent hardener . When using latent speakers, epoxy resins and hardener can be mixed and stored for some time before use, which is advantageous for many industrial processes. A very active latent hardener enables a single component product (1K) to be produced, in which resins and hardener are provided pre-mixed to the end user and require only heat to start the preservation process. One-component products generally have a shorter shelf life than standard 2-component systems, and the product may require refrigerated storage and transportation.
The epoxy preservation reaction can be accelerated by the addition of a small amount of accelerator. Tertiary amines, carboxylic acids and alcohols (especially phenols) are effective accelerators. Bisphenol A is a very effective and widely used accelerator, but is now increasingly replaced due to health problems with this substance.
Homopolymerization
The epoxy resin can be reacted by itself in the presence of anionic catalyst (Lewis base such as tertiary amine or imidazole) or cationic catalyst (Lewis acid such as boron trifluoride complex) to form preserved tissue. This process is known as catalytic homopolymerization. The resulting network contains only ether bridges, and exhibits high thermal and chemical resistance, but is fragile and often requires high temperatures for preservation processes, thus only finding industry niche applications. Homopolymerization of epoxy is often used when there is a requirement for UV curing, because cationic UV catalysts can be used (eg for UV coatings).
Amina
Primary Polyfunctional primers form an important class of epoxy hardener. Primary amines undergo addition reactions with epoxide groups to form hydroxyl groups and secondary amines. The secondary amine may then react with the epoxide to form a tertiary amine and an additional hydroxyl group. The kinetic studies show the primary amine reactivity to be about twice that of the secondary amine. The use of dysfunctional or polyfunctional amines forms a three-dimensional cross-linked network. Aliphatic, cycloaliphatic and aromatic amines are all used as epoxy hardener. This type of amine will change both the processing properties (viscosity, reactivity) and the final properties (mechanical, temperature and heat resistance) of the copolymer network to be preserved. Thus the amine structure is usually chosen according to the application. Reactivity is broadly in the order of aliphatic amines & gt; cycloaliphatic amine & gt; aromatic amines. Temperature resistance generally increases in the same order, since aromatic amines form a much more rigid structure than aliphatic amines. While aromatic amines used to be widely used as epoxy resin binders due to their excellent final properties, health problems with the handling of these materials mean that they are now largely replaced by safer aliphatic or cycloaliphatic alternatives.
Anhydride
Epoxy resins can be cured with cyclic anhydrides at high temperatures. The reaction occurs only after the opening of the anhydride ring, eg. by the secondary hydroxyl group in the epoxy resin. Possible side reactions may also occur between the epoxide and hydroxyl groups, but these can be suppressed by addition of tertiary amine. Low viscosity and high latency of anhydride coatings make it suitable for processing systems requiring the addition of mineral fillers prior to drying, for example for high voltage electrical insulators.
Phenol
Polyphenols, such as bisphenol A or novolak, may react with epoxy resins at high temperatures (130-180 ° C 266-356 ° F), usually in the presence of a catalyst. The resulting material has an ether linkage and exhibits higher chemical and oxidation resistance than is normally obtained by healing with amines or anhydrides. Since many novolac are solids, this hardener class is often used for powder coating.
Thiols
Also known as mercaptan, Thiols contain sulfur which is very easy to react with epoxide groups, even at ambient or sub-ambient temperatures. While the resulting tissue does not typically display high temperatures or chemical resistance, the high reactivity of the thiol groups makes it useful for applications where heat treatment is not possible, or very rapid healing is needed for example. for domestic DIY adhesives and chemical stone bolt anchors. Tiol has a distinctive odor, which can be detected in many adhesives of two household components.
History
Epoxide and amine condensation was first reported and patented by Paul Schlack of Germany in 1934. The claims of the bisphenol A-based epoxy resin invention included Pierre Castan in 1943. Castan's work was licensed by Ciba, Ltd. from Switzerland, which goes on to become one of three major epoxy resin producers worldwide. Ciba's epoxy business was separated and then sold in the late 1990s and is now the Advanced Materials business unit of Huntsman Corporation of the United States. In 1946, Sylvan Greenlee, working for Devoe & amp; Raynolds Company, a patented resin derived from bisphenol-A and epichlorohydrin. Devoe & amp; Raynolds, active in the early days of the epoxy resin industry, was sold to Shell Chemical; the divisions involved in this work are eventually sold, and through a series of other corporate transactions are now part of Hexion Inc.
Apps
Applications for epoxy-based materials are extensive and include coatings, adhesives and composite materials such as those using carbon fiber and fiberglass reinforcement (although polyester, vinyl ester, and other thermoset resins are also used for glass-reinforced plastics). Epoxy chemistry and various commercially available variations allow the healing polymer to be produced with a wide variety of properties. In general, epoxies are known for their adhesive strength, excellent chemical and heat resistance, excellent mechanical properties to excellent and excellent electrical insulation properties. Many epoxy properties can be modified (for example, silver filled epoxy with good electrical conductivity available, although epoxies typically isolate electrically). Variations that offer high thermal insulation, or thermal conductivity combined with high electrical resistance to electronic applications, are available.
Paint and coating
Two parts epoxy coatings are developed for heavy-duty service on metal substrates and use less energy than a heat-preserved powder layer. This system provides a hard protective layer with excellent hardness. Some epoxy coatings are formulated as an emulsion in water, and can be cleaned without solvent. Epoxy coatings are often used in industrial and automotive applications because they are more heat resistant than latex and alkyd based paints. Epoxy paints tend to get worse, known as "Leaving traces", due to UV exposure.
Polyester epoxies are used as powder coatings for washing machines, dryers and other "white goods". Fusion Bonded Epoxy Powder Coatings (FBE) are extensively used for corrosion protection of steel pipes and fittings used in the oil and gas industry, pipeline transmission pipes (steel), and concrete reinforcement concrete. Epoxy coatings are also widely used as primers for improving the adhesion of automotive and marine paints especially on metal surfaces where corrosion (rusting) resistance is important. Cans and metal containers are often coated with epoxy to prevent rusting, especially for foods such as acidic tomatoes. Epoxy resins are also used for decorative floor applications such as terrazzo flooring, chip flooring, and colored aggregate flooring. Epoxies are modified in various ways, treated with fatty acids derived from oil to produce epoxy esters, which are healed in the same way as alkyds. The typical is L8 (80% flax seed, D4 (40% dry castor oil).This is often reacted with styrene to make epoxy esters of stirrenate, used as a primer.Cure with phenolic to create a drum layer, cure ester with amine resin and pre heal epoxies with amino resins to create a top coat that holds one of the best examples is a system using solvent-free epoxy for priming vessels during construction, it uses an airless spray system with a hot spray on the head.This eliminates the solvent problem of retention under the film, causing adhesion problems later on.
Glue
Epoxy adhesives are a major part of an adhesive class called "structural adhesive" or "adhesive engineering" (which includes polyurethane, acrylic, cyanoacrylate, and other chemicals.) These high-performance adhesives are used in the construction of aircraft, cars, bikes, boats, clubs golf, skiing, snowboards, and other applications that require high strength bonding. Epoxy adhesives can be developed to fit 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 blur/colored, quick settings or slow settings. Epoxy adhesives have better heat and chemical resistance than other common adhesives. In general, heat-treated epoxy adhesives will be more heat-resistant and chemical resistant than those cured at room temperature. The strength of the epoxy adhesive is degraded at temperatures above 350 Â ° F (177 Â ° C).
Some epoxies are cured by exposure to ultraviolet light. Such epoxies are commonly used in optics, optical fibers, and optoelectronics.
Industrial tools and composites
The epoxy system is used in industrial tooling applications to produce molds, parent models, laminates, castings, fixtures, and other industrial production aids. These "plastic tools" replace metal, wood and other traditional materials, and generally improve efficiency and lower overall costs or shorten lead-time for many industrial processes. Epoxies are also used in producing fiber or composite reinforced components. They are more expensive than polyester resins and vinyl ester resins, but usually produce stronger and more temperature-resistant composite parts of polymer thermosetting matrices.
Electrical and electronic systems
The epoxy resin formulation is important in the electronics industry, and is used in motors, generators, transformers, switchgear, bushing, and insulators. Epoxy resin is an excellent electrical insulator and protects electrical components from short circuits, dust and moisture. In industrial epoxy resin electronics is the main resin used in overmolding integrated circuits, transistors and hybrid circuits, and making printed circuit boards. The largest volume of circuit boards - "FR-4 board" - is a sandwich of a layer of glass cloth that is bonded into the composite by epoxy resin. Epoxy resins are used to attach copper foils to circuit board substrates, and are a component of soldering masks on many circuit boards.
Flexible epoxy resin is used for potted transformers and inductors. By using vacuum impregnation on uncooked epoxy, winding, twist, winding-to-core winding, and winding-to-insulator are removed. Preserved epoxy is an electrical insulator and heat conductor much better than air. Transformer and inductor hot spots are greatly reduced, providing stable and longer life components than unpotted products.
The epoxy resin is applied using resin channeling technology.
Petroleum & amp; petrochemicals
Epoxies can be used to connect selective layers in excessive saline-producing reservoirs. This technique is named "water shut-off treatment".
Consumer and marine applications
Epoxies are sold in hardware stores, usually as packages containing separate resins and hardener, which must be mixed immediately before use. They are also sold in boat shops as a repair resin for marine applications. Epoxies are not usually used in the outer layers of boats because they are worsened by UV exposure. They are often used during repairs and assembly of boats, and then over-coated with conventional polyurethane or two-piece or marine-varnish paints that provide UV protection.
There are two main areas of marine use. Due to better mechanical properties relative to the more common polyester resins, epoxies are used for the manufacture of commercial components where a high strength/weight ratio is required. The second area is that their strength, filling gap properties and excellent adhesion to many materials including wood have created an explosion in amateur building projects including aircraft and ships.
Normal gelcoates formulated for use with polyester resins and vinylester resins do not adhere to epoxy surfaces, although the epoxy adheses very well when applied to the surface of the polyester resin. "Flocoat" which is commonly used to coat the yacht polyester fiberglass interior is also compatible with epoxies.
The epoxy material tends to harden somewhat more gradually, while the polyester material tends to harden quickly, especially if many of the catalysts are used. The chemical reaction in both cases is exothermic. A large mixture will generate its own heat and speed up the reaction, so it usually mixes a small amount that can be used quickly.
Although it is common to associate polyester resins and epoxy resins, their properties are quite different so they are treated correctly as different materials. Polyester resins are typically low-strength unless used with reinforcing materials such as glass fibers, relatively fragile except reinforced, and have low adherence. Epoxies, on the other hand, are inherently strong, somewhat flexible and have excellent adhesion. However, polyester resins are much cheaper.
Epoxy resins usually require an exact mixture of the two components that make up the third chemical. Depending on the required property, the ratio can be anything from 1: 1 or more than 10: 1, but in each case must be mixed appropriately. The end product is the right thermo-setting plastic. Until both are mixed, the two elements are relatively inert, although the 'hardener' tends to be more chemically active and must be protected from atmosphere and humidity. The reaction rate can be changed by using different hardener, which can change the nature of the final product, or by controlling the temperature.
In contrast, polyester resins are usually available in a 'promoted' form, so the progress of the previously mixed resins from liquid to solid is already ongoing, albeit very slowly. The only variable available to users is to change the rate of this process using a catalyst, often methyl-ethyl-ketone-peroxide (MEKP), which is highly toxic. The presence of the catalyst in the final product actually reduces from the desired properties, so a small amount of catalyst is preferred, as long as the hardening takes place at an acceptable rate. The healing rate of the polyester can therefore be controlled by the amount and type of catalyst as well as by the temperature.
As an adhesive, epoxy binds in three ways: a) mechanically, due to a rough binding surface; b) By proximity, since the preserved resin is physically very close to the hard-to-break bond surface; c) Ionic, because the epoxy resin forms ionic bonds at the atomic level with the binding surface. The latter is the most powerful of the three. In contrast, polyester resins can only bind using the first two, which greatly reduce their use as adhesives and in marine repair.
Aerospace application
In the aerospace industry, epoxy is used as a structural matrix material which is then reinforced by fibers. Strengthening of typical fibers includes glass, carbon, Kevlar, and boron. Epoxies are also used as structural glue. Materials such as wood, and other 'low-tech' are glued together with epoxy resins.
Biology
Water-soluble epoxies such as Durcupan are commonly used to insert electron microscope samples in plastic so that they can be cut (thinly sliced) with microtom and then imaged.
Art
Epoxy resins, mixed with pigments, can be used as a painting medium, by pouring layers on top of one another to form a complete picture.
Industry
In 2006, the epoxy industry totaled more than US $ 5 billion in North America and about US $ 15 billion worldwide. The Chinese market has grown rapidly, and accounts for more than 30% of the total world market. It consists of about 50-100 manufacturers of resin or epoxy amplifier or base class resin.
The commodity epoxy producer mentioned above usually does not sell epoxy resins in a form that can be used for smaller end users, so there are other groups of companies that buy epoxy raw materials from major manufacturers and then compounds (integrating, modifying, or customizing) epoxy system from this raw material. These companies are known as "formulators". Most of the epoxy systems sold are manufactured by these formulators and they comprise over 60% of the dollar value of the epoxy market. There are hundreds of ways in which this formulator can modify epoxy - by adding a mineral filler (talc, silica, alumina, etc.), by adding flexibilizer, viscosity reducer, dye, thickener, accelerator, adhesion promoter, etc. These modifications are made to reduce costs, to improve performance, and to improve processing convenience. As a result, a typical formulator sells dozens or even thousands of formulations - each tailored to specific application or market requirements.
Influenced by the global economic downturn, the size of the epoxy market declined to $ 15.8 billion in 2009, almost to 2005 levels. In some regional markets it even fell by nearly 20%. The epoxy market is currently experiencing positive growth as the global economy recovers. With an annual growth rate of 3.5-4% the epoxy market is expected to reach $ 17.7 billion in 2012 and $ 21.35 billion by 2015. Higher growth rates are forecasted thereafter due to stronger demands from the epoxy composite market and epoxy adhesive market.
Health risks
The main risks associated with the use of epoxy are often related to the hardening component and not to the epoxy resin itself. Amine hardeners are typically generally corrosive, but can also be classified as toxic or carcinogenic/mutagenic. Aromatic amines pose a particular health hazard (mostly known or suspected carcinogens), but their use is now limited to certain industrial applications, and safer aliphatic or cycloaliphatic amines are commonly used.
Liquid epoxy resins in an uncured state are largely classified as eye and skin irritation, as well as toxic to aquatic organisms. Solid epoxy resins are generally safer than liquid epoxy resins, and many are classified as non-hazardous materials. One of the specific risks associated with epoxy resins is sensitization. Risk has been shown more clearly in epoxy resins containing low molecular weight epoxy thinners. Exposure to epoxy resins can, over time, cause an allergic reaction. Sensitization generally occurs due to repeated exposure (eg through poor working hygiene or lack of protective equipment) over a long period of time. Allergic reactions occasionally occur at a delayed time of several days from exposure. Allergic reactions are often seen in the form of dermatitis, especially in areas where exposure is highest (usually the hands and forearms). The use of epoxy is a major source of work-related asthma among plastic users. Bisphenol A, used to produce the general class of epoxy resins, is a known endocrine disrupter.
See also
- Thermosetting Polymers
- Thermoset polymer matrix
- Plastics
References
External links
- health hazard Epoxy Resin (California Department of Health Services) April 21, 2008 @ Wayback Machine https://web.archive.org/web/20080421095718/http://www.dhs.ca.gov/ohb/HESIS/epoxy.htm
- Chemical epoxide, easy to understand
Source of the article : Wikipedia
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