They have excellent electrical and thermal properties and good chemical resistance. They are low cost and used for electrical insulation, electronic components, putty fillers, and paints. Polycarbonate resins are thermoplastics generally developed from bisphenol A and phosgene.
They have a high refractive index, electrical and thermal dimensional stability, resistance to staining, and resistance to filtration. They are used for metal replacements, safety helmets, lenses, electrical components, photography film, and insulators. Polyamide resins contain an amide group as a recurring part of their molecular chains. They are easily molded, strong and resistant, and lightweight. They have a low friction coefficient and are abrasion and chemical resistant.
They are used for nonlubricated bearings, fibers, gears, sutures, tires, watchbands, packaging, and bottles. Polyurethane resins are copolymers made up of polyol and isocyanate components. They are very versatile when combined with other resins, and have a high film elasticity and adhesion to substrates. Polyurethane resins also have a good balance of elongation and hardness.
They are used for insulation, elastomers, adhesives, and foam liners for clothing. Silicone resins used to be created with sodium silicate and various chlorosilanes, but now they are often formed with the less reactive tetraethoxysilane or ethyl polysilicate and several disiloxanes.
They have good thermal and oxidative stability and are flexible and water repellent. Silicone resins form hard films because of their three-dimensional network structure. They are used for rubber, laminates, encapsulated resins, defoamers, and water-resistant applications.
Epoxy resins , also called polyepoxides, are a type of reactive prepolymers and polymers which contain epoxide groups. They have excellent chemical and heat resistance and strong adhesion properties. They are used for laminates, adhesives, flooring, linings, propellers, and surface coatings.
The formation of an epoxy polymer may be illustrated by the reaction between 2,2-bis 4-hydroxyphenyl propane I Bisphenol-A and epichlorohydrin II to initially form a prepolymer as follows:.
This is the diglycidyl ether of bisphenol-A DGEBA , where n represents the number of times the repeating unit occurs in the prepolymer. If n is 0 or 1, the product is a viscous liquid. If n is greater than 1 the product is a brittle solid. The relative amounts of the reactants determine the value of n, a large excess of epichlorohydrin favoring the formation of a liquid.
Crosslinking or curing giving a solid is illustrated with a general poly functional amine in Figure 1. Some anhydrides such as phthalic anhydride III are also used for curing agents. They first react with a free hydroxyl group on the chain, freeing a carboxylic acid group to react either with another chain hydroxyl or an epoxide group.
Epoxy resins are thermosetting materials as opposed to thermoplastic materials. Thermosetting plastics are cured or "set" into a form which is retained to the plastic's decomposition temperature without melting while thermoplastics have melting or liquefying temperatures.
Thermosetting plastics are also insoluble in their cured stated while thermoplastics usually have several solvents. The commercial introduction of epoxy resins was in Other used include adhesives, laminates, and casting resins.
The resins show low shrinkage in their curing reactions which make them extremely valuable in space filling applications. An epoxy resin system requires two components, a diepoxide or equivalent epichlorohydrin is equivalent to a diepoxide since another epoxide group is formed upon destruction of the first one and a reactive diol or polyol.
Epichlorohydrin is the most readily available and cheapest diepoxide equivalent, and almost all commercial epoxy systems employ it. Bisphenol-A is also widely used since the aromatic nature enhances the hydroxyl reactivity and adds strength to the resin formed. Aliphatic triol such as glycerol IV have been used to give denser crosslinking. Other polyhydroxylic compounds which find application in epoxy resin formulations are the novolaks, which are products of the reaction of phenols and formaldehyde in acid solution and may be represented by:.
The combination of the available diepoxides or equivalents and the polyhydroxy compounds gives a large number of possible epoxy pre-polymers. The number of possible resins is raised even higher by the number of possible curing agents which may be used for each of the prepolymers.
Epoxy is a type of polymer, a group of chemical compounds that consist of large molecules with repeating subunits.
The molecular structure of polymers give them their toughness and elasticity, making polymers both natural and manmade ones ubiquitous in daily life. Wool, rubber, Styrofoam, and epoxy are just a few of the polymers that you likely already know. This particular polymer plays an essential role in construction—as adhesives and in coatings.
Epoxy resins include epoxides—highly reactive groups of molecules—that harden or cure through chemical reactions, which are caused either by combining it with other substances or heating it to a high temperature. Versatile, long-lasting, and with a remarkable degree of heat resistance, epoxy adhesives can be used in almost any situation where you need to glue two materials together—think: binding sub floors, gluing a detail to a larger structure, or reinforcing a fastener.
Epoxy adhesives can be used with a wide range of materials: wood, metal, plastic, masonry, and more. Epoxies are one of many options when it comes to adhesives, though its strengths make it a popular choice in construction projects. There are two main types of epoxy adhesives, one-part or heat-cured and two-part epoxies. One-part epoxies cure faster, though they are often not as strong as two-part epoxies. Heat-cured epoxies have many industrial applications, but are not often used in construction, due to the high-heat requirement for them to cure—even those that react at the lowest level of heat will need to be exposed to temperatures of at least degrees Fahrenheit.
With its remarkable resilience, epoxy resin is used in products ranging from electronic components and medical devices to infrared telescopes and missile warning systems. With two-part epoxies, the two components needed to create the chemical reaction are packaged separately. Like their heat-cured counterparts, two-part epoxies have many industrial uses, in automotive, aeronautical, and other manufacturing areas, and they are also especially common in boat building.
They are also used in construction projects, with applications including attaching countertops to substrates, fastening concrete elements to others either also of concrete or of stone or metal, and securing decorative moldings in place. J-B Weld and competitors sell two-part epoxy systems in many different systems from simple tubes that require manually mixing the components to cartridges for specialized guns.
Learn all about the stuff that holds building materials together in the MT Copeland online Fasteners and Adhesives course.
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