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100-490: Epoxy resins may be reacted ( cross-linked ) either with themselves through catalytic homo polymerisation , or with 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

200-626: A Bresle test . Salinization (increasing salinity, aka freshwater salinization syndrome ) and subsequent increased metal leaching is an ongoing problem throughout North America and European fresh waterways. In highway de-icing, salt has been associated with corrosion of bridge decks, motor vehicles, reinforcement bar and wire, and unprotected steel structures used in road construction. Surface runoff , vehicle spraying, and windblown salt also affect soil, roadside vegetation, and local surface water and groundwater supplies. Although evidence of environmental loading of salt has been found during peak usage,

300-440: 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)

400-432: A face-centered cubic (fcc) lattice with a two-atom basis or as two interpenetrating face centered cubic lattices. The first atom is located at each lattice point, and the second atom is located halfway between lattice points along the fcc unit cell edge. Solid sodium chloride has a melting point of 801 °C and liquid sodium chloride boils at 1465 °C. Atomic-resolution real-time video imaging allows visualization of

500-423: A permanent wave to hair involves the breaking and reformation of disulfide bonds. Typically a mercaptan such as ammonium thioglycolate is used for the breaking. Following this, the hair is curled and then "neutralized". The neutralizer is typically an acidic solution of hydrogen peroxide, which causes new disulfide bonds to form, thus permanently fixing the hair into its new configuration. Compromised collagen in

600-696: A thermosetting polymer , often with favorable mechanical properties and high thermal and chemical resistance. Epoxy has 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

700-455: 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

800-399: A change in the polymers' physical properties. When "crosslinking" is used in the biological field, it refers to the use of a probe to link proteins together to check for protein–protein interactions , as well as other creative cross-linking methodologies. Although the term is used to refer to the "linking of polymer chains" for both sciences, the extent of crosslinking and specificities of

900-578: 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

1000-400: 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

1100-423: 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

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1200-623: 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 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

1300-908: 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)

1400-414: 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

1500-632: A major source of food spoilage. Even though more effective desiccants are available, few are safe for humans to ingest. Many microorganisms cannot live in a salty environment: water is drawn out of their cells by osmosis . For this reason salt is used to preserve some foods, such as bacon, fish, or cabbage. In many dairy industries, salt is added to cheese as a color-, fermentation-, and texture-control agent. The dairy subsector includes companies that manufacture creamery butter, condensed and evaporated milk, frozen desserts, ice cream, natural and processed cheese, and specialty dairy products. In canning, salt

1600-677: A much wider range of properties than conventional cross-linked elastomers because the domains that act as cross-links are reversible, so can be reformed by heat. The stabilizing domains may be non-crystalline (as in styrene-butadiene block copolymers) or crystalline as in thermoplastic copolyesters. Alkyd enamels , the dominant type of commercial oil-based paint, cure by oxidative crosslinking after exposure to air. In contrast to chemical cross-links, physical cross-links are formed by weaker interactions. For example, sodium alginate gels upon exposure to calcium ions, which form ionic bonds that bridge between alginate chains. Polyvinyl alcohol gels upon

1700-610: 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,

1800-459: A polymer depend strongly on the cross-link density. Low cross-link densities increase the viscosities of polymer melts . Intermediate cross-link densities transform gummy polymers into materials that have elastomeric properties and potentially high strengths. Very high cross-link densities can cause materials to become very rigid or glassy, such as phenol-formaldehyde materials. In one implementation, unpolymerized or partially polymerized resin

1900-461: A preservative, salt inhibits the growth of bacteria. Salt acts as a binder in sausages to form a binding gel made up of meat, fat, and moisture. Salt also acts as a flavor enhancer and as a tenderizer . It is used as a cheap and safe desiccant because of its hygroscopic properties, making salting an effective method of food preservation historically; the salt draws water out of bacteria through osmotic pressure , keeping it from reproducing,

2000-454: A problem in any coating application, because trapped salts cause great problems in adhesion. Naval authorities and ship builders monitor the salt concentrations on surfaces during construction. Maximal salt concentrations on surfaces are dependent on the authority and application. The IMO regulation is mostly used and sets salt levels to a maximum of 50 mg/m soluble salts measured as sodium chloride. These measurements are done by means of

2100-566: 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

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2200-421: Is deicing of roadways in sub-freezing weather. In addition to the many familiar domestic uses of salt, more dominant applications of the approximately 250 million tonnes per year production (2008 data) include chemicals and de-icing. Salt is used, directly or indirectly, in the production of many chemicals, which consume most of the world's production. It is the starting point for the chloralkali process ,

2300-540: 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

2400-471: Is a highly crosslinked polymer that comprises the main structural material of higher plants. A hydrophobic material, it is derived from precursor monolignols . Heterogeneity arises from the diversity and degree of crosslinking between these lignols. Intrastrand DNA crosslinks have strong effects on organisms because these lesions interfere with transcription and replication . These effects can be put to good use (addressing cancer) or they can be lethal to

2500-419: 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

2600-801: 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,

2700-399: Is added to animal hides to inhibit microbial activity on the underside of the hides and to attract moisture back into the hides. In rubber manufacture, salt is used to make buna , neoprene , and white rubber types. Salt brine and sulfuric acid are used to coagulate an emulsified latex made from chlorinated butadiene . Salt also is added to secure the soil and to provide firmness to

2800-467: Is added to food, either by the food producer or by the consumer, as a flavor enhancer, preservative, binder, fermentation -control additive, texture-control agent, and color developer. The salt consumption in the food industry is subdivided, in descending order of consumption, into other food processing, meat packers, canning , baking, dairy, and grain mill products. Salt is added to promote color development in bacon, ham and other processed meat products. As

2900-489: 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

3000-477: Is also used a seasoning agent, e.g. in potato chips, pretzels , and cat and dog food. Sodium chloride is used in veterinary medicine as emesis -causing agent. It is given as warm saturated solution. Emesis can also be caused by pharyngeal placement of small amount of plain salt or salt crystals. For watering plants to use sodium chloride ( NaCl ) as a fertilizer, moderate concentration is used to avoid potential toxicity: 1–3 grams (0.035–0.106 oz) per liter

3100-406: 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

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3200-453: 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

3300-572: 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

3400-550: Is commonly used to prepare antibody-hapten conjugates for antibody development. An in-vitro cross-linking method is PICUP ( photo-induced cross-linking of unmodified proteins ). Typical reagents are ammonium persulfate (APS), an electron acceptor, the photosensitizer tris-bipyridylruthenium (II) cation ( [Ru(bpy) 3 ] ). In in-vivo crosslinking of protein complexes, cells are grown with photoreactive diazirine analogs to leucine and methionine , which are incorporated into proteins. Upon exposure to ultraviolet light,

3500-406: 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

3600-474: 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

3700-433: 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

3800-486: Is found in the Earth's crust as the mineral halite (rock salt), and a tiny amount exists as suspended sea salt particles in the atmosphere. These particles are the dominant cloud condensation nuclei far out at sea, which allow the formation of clouds in otherwise non-polluted air . Salt is currently mass-produced by evaporation of seawater or brine from brine wells and salt lakes . Mining of rock salt

3900-578: Is generally safe and effective for most plants. Sodium chloride is used together with water as one of the primary solutions for intravenous therapy . Nasal spray often contains a saline solution. Sodium chloride is also available as an oral tablet, and is taken to treat low sodium levels. Sodium chloride is the principal extinguishing agent in dry-powder fire extinguishers that are used on combustible metal fires, for metals such as magnesium, zirconium, titanium, and lithium (Class D extinguishers). The salt forms an oxygen-excluding crust that smothers

4000-990: Is near 108.7 °C (227.7 °F). The pH of a sodium chloride solution remains ≈7 due to the extremely weak basicity of the Cl ion, which is the conjugate base of the strong acid HCl. In other words, NaCl has no effect on system pH in diluted solutions where the effects of ionic strength and activity coefficients are negligible. Common salt has a 1:1 molar ratio of sodium and chlorine. In 2013, compounds of sodium and chloride of different stoichiometries have been discovered; five new compounds were predicted (e.g., Na 3 Cl, Na 2 Cl, Na 3 Cl 2 , NaCl 3 , and NaCl 7 ). The existence of some of them has been experimentally confirmed at high pressures and other conditions: cubic and orthorhombic NaCl 3 , two-dimensional metallic tetragonal Na 3 Cl and exotic hexagonal NaCl. This indicates that compounds violating chemical intuition are possible, in simple systems under non-ambient conditions. Salt

4100-670: 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

Epoxy - Misplaced Pages Continue

4200-410: 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 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

4300-586: Is primarily added as a flavor enhancer and preservative . It also is used as a carrier for other ingredients, dehydrating agent, enzyme inhibitor and tenderizer. In baking, salt is added to control the rate of fermentation in bread dough. It also is used to strengthen the gluten (the elastic protein-water complex in certain doughs) and as a flavor enhancer, such as a topping on baked goods. The food-processing category also contains grain mill products. These products consist of milling flour and rice and manufacturing cereal breakfast food and blended or prepared flour. Salt

4400-564: 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

4500-407: Is transparent or translucent, brittle, hygroscopic , and occurs as the mineral halite . In its edible form, it is commonly used as a condiment and food preservative . Large quantities of sodium chloride are used in many industrial processes, and it is a major source of sodium and chlorine compounds used as feedstocks for further chemical syntheses . Another major application of sodium chloride

4600-780: Is treated with a crosslinking reagent . In vulcanization , sulfur is the cross-linking agent. Its introduction changes rubber to a more rigid, durable material associated with car and bike tires . This process is often called sulfur curing. In most cases, cross-linking is irreversible, and the resulting thermosetting material will degrade or burn if heated, without melting. Chemical covalent cross-links are stable mechanically and thermally. Therefore, cross-linked products like car tires cannot be recycled easily. A class of polymers known as thermoplastic elastomers rely on physical cross-links in their microstructure to achieve stability, and are widely used in non-tire applications, such as snowmobile tracks, and catheters for medical use. They offer

4700-569: Is used to flocculate and increase the density of the drilling fluid to overcome high downwell gas pressures. Whenever a drill hits a salt formation, salt is added to the drilling fluid to saturate the solution in order to minimize the dissolution within the salt stratum. Salt is also used to increase the curing of concrete in cemented casings. In textiles and dyeing, salt is used as a brine rinse to separate organic contaminants, to promote "salting out" of dyestuff precipitates, and to blend with concentrated dyes to increase yield in dyebaths and make

4800-480: Is used to produce glass , sodium bicarbonate , and dyes , as well as a myriad of other chemicals. In the Mannheim process , sodium chloride is used for the production of sodium sulfate and hydrochloric acid . Sodium chloride is heavily used, so even relatively minor applications can consume massive quantities. In oil and gas exploration, salt is an important component of drilling fluids in well drilling. It

4900-615: The native state . Common crosslinkers include the imidoester crosslinker dimethyl suberimidate, the N-Hydroxysuccinimide -ester crosslinker BS3 and formaldehyde . Each of these crosslinkers induces nucleophilic attack of the amino group of lysine and subsequent covalent bonding via the crosslinker. The zero-length carbodiimide crosslinker EDC functions by converting carboxyls into amine-reactive isourea intermediates that bind to lysine residues or other available primary amines. SMCC or its water-soluble analog, Sulfo-SMCC,

5000-399: The addition of borax through hydrogen bonding between boric acid and the polymer's alcohol groups. Other examples of materials which form physically cross-linked gels include gelatin , collagen , agarose , and agar agar . Crosslinking is often measured by swelling tests. The crosslinked sample is placed into a good solvent at a specific temperature, and either the change in mass or

5100-401: 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

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5200-489: 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

5300-531: The change in volume is measured. The more crosslinking, the less swelling is attainable. Based on the degree of swelling, the Flory Interaction Parameter (which relates the solvent interaction with the sample), and the density of the solvent, the theoretical degree of crosslinking can be calculated according to Flory's Network Theory. Two ASTM standards are commonly used to describe the degree of crosslinking in thermoplastics. In ASTM D2765,

5400-461: The colors look sharper. One of its main roles is to provide the positive ion charge to promote the absorption of negatively charged ions of dyes. For use in the pulp and paper industry , it is used to manufacture sodium chlorate , which is then reacted with sulfuric acid and a reducing agent such as methanol to manufacture chlorine dioxide , a bleaching chemical that is widely used to bleach wood pulp . In tanning and leather treatment, salt

5500-717: 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

5600-552: The cornea, a condition known as keratoconus , can be treated with clinical crosslinking. In biological context crosslinking could play a role in atherosclerosis through advanced glycation end-products (AGEs), which have been implicated to induce crosslinking of collagen, which may lead to vascular stiffening. Proteins can also be cross-linked artificially using small-molecule crosslinkers. This approach has been used to elucidate protein–protein interactions . Crosslinkers bind only surface residues in relatively close proximity in

5700-414: The crosslinking agents vary greatly. Crosslinking generally involves covalent bonds that join two polymer chains. The term curing refers to the crosslinking of thermosetting resins, such as unsaturated polyester and epoxy resin, and the term vulcanization is characteristically used for rubbers . When polymer chains are crosslinked, the material becomes more rigid. The mechanical properties of

5800-412: The diazirines are activated and bind to interacting proteins that are within a few ångströms of the photo-reactive amino acid analog (UV cross-linking). Sodium chloride Sodium chloride / ˌ s oʊ d i ə m ˈ k l ɔːr aɪ d / , commonly known as edible salt , is an ionic compound with the chemical formula NaCl , representing a 1:1 ratio of sodium and chlorine ions. It

5900-405: 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

6000-456: The efficiency can have large economic paybacks. Some applications of chlorine include PVC thermoplastics production, disinfectants, and solvents. Sodium hydroxide is extensively used in many different industries enabling production of paper, soap, and aluminium etc. Sodium chloride is used in the Solvay process to produce sodium carbonate and calcium chloride . Sodium carbonate, in turn,

6100-511: 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

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6200-462: 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

6300-672: 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

6400-600: The fire. Since at least medieval times, people have used salt as a cleansing agent rubbed on household surfaces. It is also used in many brands of shampoo , toothpaste, and popularly to de-ice driveways and patches of ice. Sodium chloride crystals have a transmittance of at least 90% (through 1 mm) for infrared light having wavelengths in the range 0.2– 18  μm . They were used in optical components such as windows and lenses, where few non-absorbing alternatives existed in that spectral range. While inexpensive, NaCl crystals are soft and hygroscopic – when exposed to

6500-432: The form of epoxy granite . Cross-linked In chemistry and biology , a cross-link is a bond or a short sequence of bonds that links one polymer chain to another. These links may take the form of covalent bonds or ionic bonds and the polymers can be either synthetic polymers or natural polymers (such as proteins ). In polymer chemistry "cross-linking" usually refers to the use of cross-links to promote

6600-449: 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

6700-447: The formula [Na(H 2 O) 8 ] , with the Na–O distance of 250  pm . The chloride ions are also strongly solvated, each being surrounded by an average of six molecules of water. Solutions of sodium chloride have very different properties from pure water. The eutectic point is −21.12 °C (−6.02 °F) for 23.31% mass fraction of salt, and the boiling point of saturated salt solution

6800-476: The foundation on which highways are built. The salt acts to minimize the effects of shifting caused in the subsurface by changes in humidity and traffic load. Hard water contains calcium and magnesium ions that interfere with action of soap and contribute to the buildup of a scale or film of alkaline mineral deposits in household and industrial equipment and pipes. Commercial and residential water-softening units use ion-exchange resins to remove ions that cause

6900-447: The gritting vehicles despite being stockpiled prior to use. In recent years this additive has also been used in table salt. Other additives had been used in road salt to reduce the total costs. For example, in the US, a byproduct carbohydrate solution from sugar-beet processing was mixed with rock salt and adhered to road surfaces about 40% better than loose rock salt alone. Because it stayed on

7000-429: The hardness. These resins are generated and regenerated using sodium chloride. The second major application of salt is for deicing and anti-icing of roads, both in grit bins and spread by winter service vehicles . In anticipation of snowfall, roads are optimally "anti-iced" with brine (concentrated solution of salt in water), which prevents bonding between the snow-ice and the road surface. This procedure obviates

7100-690: The heavy use of salt after the snowfall. For de-icing, mixtures of brine and salt are used, sometimes with additional agents such as calcium chloride and/or magnesium chloride . The use of salt or brine becomes ineffective below −10 °C (14 °F). Salt for de-icing in the United Kingdom predominantly comes from a single mine in Winsford in Cheshire . Prior to distribution it is mixed with <100 ppm of sodium ferrocyanide as an anticaking agent , which enables rock salt to flow freely out of

7200-400: 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

7300-500: The host organism. The drug cisplatin functions by formation of intrastrand crosslinks in DNA. Other crosslinking agents include mustard gas , mitomycin , and psoralen . In proteins , crosslinks are important in generating mechanically stable structures such as hair and wool , skin , and cartilage . Disulfide bonds are common crosslinks. Isopeptide bond formation is another type of protein crosslink. The process of applying

7400-419: The industrial process to produce chlorine and sodium hydroxide , according to the chemical equation This electrolysis is conducted in either a mercury cell, a diaphragm cell, or a membrane cell. Each of those uses a different method to separate the chlorine from the sodium hydroxide. Other technologies are under development due to the high energy consumption of the electrolysis, whereby small improvements in

7500-471: The initial stage of crystal nucleation of sodium chloride. The Thermal conductivity of sodium chloride as a function of temperature has a maximum of 2.03 W/(cm K) at 8 K (−265.15 °C; −445.27 °F) and decreases to 0.069 at 314 K (41 °C; 106 °F). It also decreases with doping . From cold (sub-freezing) solutions, salt crystallises with water of hydration as hydrohalite (the dihydrate NaCl·2 H 2 O ). In 2023, it

7600-546: 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

7700-434: 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,

7800-922: 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

7900-400: 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

8000-594: 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

8100-601: 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

8200-400: 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

8300-444: 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

8400-453: 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

8500-418: 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

8600-869: 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

8700-417: 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

8800-488: 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

8900-585: The road longer, the treatment did not have to be repeated several times, saving time and money. In the technical terms of physical chemistry, the minimum freezing point of a water-salt mixture is −21.12 °C (−6.02 °F) for 23.31 wt% of salt. Freezing near this concentration is however so slow that the eutectic point of −22.4 °C (−8.3 °F) can be reached with about 25 wt% of salt. Road salt ends up in fresh-water bodies and could harm aquatic plants and animals by disrupting their osmoregulation ability. The omnipresence of salt in coastal areas poses

9000-444: 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

9100-417: The sample is weighed, then placed in a solvent for 24 hours, weighed again while swollen, then dried and weighed a final time. The degree of swelling and the soluble portion can be calculated. In another ASTM standard, F2214, the sample is placed in an instrument that measures the height change in the sample, allowing the user to measure the volume change. The crosslink density can then be calculated. Lignin

9200-519: The spring rains and thaws usually dilute the concentrations of sodium in the area where salt was applied. A 2009 study found that approximately 70% of the road salt being applied in the Minneapolis-St Paul metro area is retained in the local watershed. Some agencies are substituting beer , molasses , and beet juice instead of road salt. Airlines utilize more glycol and sugar rather than salt-based solutions for deicing . Salt

9300-430: 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

9400-705: 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

9500-467: The vertices of a regular octahedron . In the language of close-packing , the larger chloride ions (167 pm in size ) are arranged in a cubic array whereas the smaller sodium ions (116 pm ) fill all the cubic gaps (octahedral voids) between them. This same basic structure is found in many other compounds and is commonly known as the NaCl structure or rock salt crystal structure. It can be represented as

9600-886: 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

9700-487: The water in ambient air, they gradually cover with "frost". This limits application of NaCl to dry environments, vacuum-sealed areas, or short-term uses such as prototyping. Materials that are mechanically stronger and less sensitive to moisture, such as zinc selenide and chalcogenide glasses , more widely used than NaCl. In solid sodium chloride, each ion is surrounded by six ions of the opposite charge as expected on electrostatic grounds. The surrounding ions are located at

9800-554: 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

9900-487: Was discovered that under pressure, sodium chloride can form the hydrates NaCl·8.5H 2 O and NaCl·13H 2 O. The attraction between the Na and Cl ions in the solid is so strong that only highly polar solvents like water dissolve NaCl well. When dissolved in water, the sodium chloride framework disintegrates as the Na and Cl ions become surrounded by polar water molecules. These solutions consist of metal aquo complex with

10000-539: 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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