EPOXY RESIN

~ also known as polyepoxides; EP 828 acrylate; ED 20 acrylate; E 44, acrylate; YD 128 acrylate; Pacrosir VE 196, etc. is a class of reactive prepolymers and polymers which contain epoxide groups.

Epoxy resins may be reacted either with themselves through catalytic homopolymerization, or with a wide range of co-reactants including polyfunctional amines, acids, phenols, alcohols, and thiols. These co-reactants are often called hardeners or curatives, and the cross-linking reaction is referred to as curing. Reaction of polyepoxides with themselves or with polyfunctional hardeners forms a thermosetting polymer. As of 2006, the epoxy industry amounts to more than US$5 billion in North America and about US$15 billion worldwide.

Chemical structure:  C₂₁H₂₅ClO_5. Epoxy resins are low molecular weight pre-polymers or higher molecular weight polymers which normally contain at least two epoxide groups. The epoxide group is also sometimes referred to as a glycidyl or oxirane group.

Properties:  Epoxy resin has great mechanical strength and is nearly always cheaper and faster than welding. It also has excellent resistance to chemicals. Its thermal and electrical properties, strength, and durability are what epoxy resin is noted for. In addition, it has resistance to immersion and hostile chemical vapor.

Production: 

A wide range of epoxy resins are produced. Today, the raw materials for epoxy resin production derived largely petroleum, although some plant-derived sources are now commercially available. 

1. Bisphenol A epoxy resin: essential epoxy resins are produced from combining epichlorohydrin and bisphenol A to give bisphenol A diglycidyl ethers. 
2. Bisphenol F epoxy resin: Bisphenol F may undergo epoxy resin formation in a similar way to bisphenol A. These resins usually have lower viscosity and a higher mean epoxy content per gram than bisphenol A resins, which (once cured) gives them increased chemical resistance.
3. Novolac epoxy resin: Reaction of phenols with formaldehyde and subsequent glycidylation with epichlorohydrin produces epoxidized novolacs, such as epoxy phenol novolacs (EPN) and epoxy cresol novolacs (ECN).
4. Aliphatic epoxy resins: are usually formed by glycidylation of aliphatic alcohols or polyols. The resins produced may be monofunctional (e.g. dodecanol glycidyl ether), difunctional (butanediol diglycidyl ether), or higher functionality (e.g. trimethylolpropane triglycidyl ether). These resins usually have 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 reduce the viscosity of other epoxy resins.
5. Glycidylamine epoxy resins: higher functionality epoxies created when aromatic amines are reacted with epichlorohydrin. The epoxy resins have low to medium viscosity at room temperature, which makes them easier to process than EPN or ECN resins.

Chemical reactions and Uses: Good properties of epoxy resins are procured by reacting the linear epoxy resin with suitable curatives to form 3D cross-linked thermo-set structures ,i.e. curing or gelation process. Uncured epoxy resins have only poor mechanical, chemical and heat resistance properties. Curing of epoxy resins is exothermic and in some cases produces sufficient heat to cause thermal degradation if not controlled. Epoxy resin can react with itself (homopolymerization) and other curatives including; amines, anhydrides, phenols, and thiols.

Epoxy resin are often used in metal coatings, electronics/electrical components/LEDs, high tension electrical insulators, paint brush manufacturing, fiber-reinforced plastic materials and structural adhesives. In medicine, Water-soluble epoxies such as Durcupan are commonly used for embedding electron microscope samples in plastic so they may be sectioned (sliced thin) with a microtome and then imaged. In art, Epoxy resin, mixed with pigment, may be used as a painting medium, by pouring layers on top of each other to form a complete picture.

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