Epoxy resins also known as polyepoxides, are a class of reactive prepolymers and polymers which contain epoxide groups, is an extremely versatile synthetic resin, which consists of two components: The actual resin and the hardener. When these two components are mixed together, the material hardens within a few hours. Usually, the mixing ratio of resin and hardener is 1:1 -4:1.
In general, epoxies are known for their excellent adhesion, chemical and heat resistance, good-to-excellent mechanical properties and very good electrical insulating properties. It has a particularly high level of flexural strength and is suitable for both domestic and commercial purposes.
Chemistry
Epoxies are thermosetting polymer resins where the resin molecule contains one or more epoxide groups. The chemistry can be adjusted to perfect the molecular weight or viscosity as required by the end-use. Epoxy resins may be reacted either with themselves through catalytic homopolymerisation, or with a wide range of co-reactants including polyfunctional amines, acids (and acid anhydrides), amino phenols and aliphatic diols, etc.
One of the most common glycidyl epoxy resins is created using Bisphenol A (BPA) and is synthesized in a reaction 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.
Feature
- Durable and structurally stable
- Low moisture absorption
- Bonds well, strong and durable
- Effective electrical insulation
- Room temperature cure
- Corrosion-resistant and resistant to acids
- Excellent gloss and clarity
- Excellent chemical resistance
- Excellent fatigue strength and flexural strength
- Low-viscosity, The consistency helps prevent air bubbles, Self-leveling, deep-level penetration and filling small cavities.Low shrinkage after curing.
- NOT UV resistant; will yellow in sunlight
- Absence of VOCs (volatile organic compounds)
Types of Epoxy Resin
There are two primary types of epoxies: glycidyl epoxy and non-glycidyl. Glycidyl epoxy resins can be further defined as either glycidyl-amine, glycidyl ester, or glycidyl ether. Non-glycidyl epoxy resins are either aliphatic or cyclo-aliphatic resins.
Bisphenol Epoxy Resins
Bisphenol-A diglycidyl ether (DGEBA) is a commonly used variety of commercial epoxy resin. It is produced as a result of the reaction of bisphenol-A on contact with epichlorohydrin in the presence of a basic catalyst. This variety of epoxy resin has the lowest molecular weight.
Aliphatic Epoxy Resins
These types of epoxy resins are produced either as a result of double bond epoxidation (involving cycloaliphatic epoxides and epoxidized vegetable oils) or reaction with epichlorohydrin (glycidyl ethers and esters). Cycloaliphatic epoxides feature one or more aliphatic ring in the molecule containing the oxirane ring. They have a defined aliphatic structure, high oxirane content, and absence of chlorine. This makes for low levels of viscosity, good weather resistance, low dielectric constants, and high Tg.
Novolac Epoxy Resins
These types of resins are produced as a result of contact and reaction between phenol and methanol (formaldehyde). The reaction of epichlorohydrin and novolacs results in the formation of novolacs with glycidl residues including epoxyphenol novolac (EPN) or epoxycresol novolac (ECN). Such epoxies do not contain solvents or volatile organic compounds. Being free of VOCs, they are extremely safe to use and respirators aren’t required. They have a relatively high level of adhesive strength, making for good levels of coverage. Protection and durability are also assured in the application of these resins.
Halogenated Epoxy Resins
These epoxy resins are admixed for special properties. This involves the application and mixture of brominated and fluorinated varieties. Brominated bisphenol A is the preferred option for flame resistance and electrical applications. However, the commercial production and use of such resins is limited due to the associated cost and low Tg.
Epoxy Resin Diluents
The creation of epoxy diluents involves the glycidylation of aliphatic alcohols or polyols. The materials produced as a result of such processes may be either monofunctional (e.g. dodecanol glycidyl ether), difunctional (butanediol diglycidyl ether), or higher functionality (e.g. trimethylolpropane triglycidyl ether).
Glycidylamine Epoxy Resins
These epoxy resins have relatively high levels of functionality and are formed as a result of the contact reaction between aromatic amines and epichlorohydrin. Industrial grades include triglycidyl-p-aminophenol (functionality 3) and N,N,N′,N′-tetraglycidyl-bis-(4-aminophenyl)-methane (functionality 4). They have a low-medium viscosity at room temperature, making them easier to process than EPN or ECN varieties.
Application
Epoxy resin materials has a wide range of applications, including coatings, adhesives, potting electronics/electrical components/LEDs, high tension electrical insulators, paint brush manufacturing, fiber-reinforced plastic materials.
Adhesives
One of the most common uses of epoxy resin is for adhesive purposes. That’s because the strong-properties of the epoxy allow for structural and engineering adhesives. 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. In general, epoxy adhesives cured with heat will be more heat- and chemical-resistant than those cured at room temperature.
Electrical systems and electronics
As epoxy resins are fantastic insulators and offers protection from dust, moisture and short circuits it remains one of the primary resins used in circuit creation too. Widely used in insulators, motors, transformers, generators, transformers, switchgear, bushings, insulators, printed wiring boards (PWB), and semiconductor encapsulants.
Painting
Known as powder coatings, epoxy paint is found on many household goods like dryers, washers, stoves and similar white goods. Typically, this type of paint is used in more commercial settings. With a water clean-up and tough, protective coating, epoxy paint is an excellent option for appliances. Likewise, cast iron, cast aluminium and cast steel are also other metals which work well with this painting application.
Coatings and Sealant
Epoxy is also known for its corrosion prevention properties, making it an ideal solution to many household objects which may normally rust with time. Items including paint cans, metal containers, and foods which are typically acidic are normally coated before use.
Aerospace applications
In the aerospace industry, epoxy is used as a structural matrix material which is then reinforced by fiber. Epoxy resins satisfy a variety of non-metallic composite designs in commercial and military aerospace applications including flooring panels, ducting, vertical and horizontal stabilizers, wings etc.
Biology
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.
Art restoration
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. It is also used in jewelry, as a doming resin for decorations and labels, and in decoupage type applications for art, countertops, and tables.
Safety Precautions
Epoxy resin and the hardener contain substances that should not come into direct contact with the skin. Direct skin contact can cause allergies and irritation of the skin. Note that some aromatic amine curing agents may be carcinogenic. A properly cured epoxy resin system usually presents no health problems relating to skin irritation.
There is a variety of safety precautions that should be taken into account when using epoxy resin.
Firstly, you should wear gloves to protect your hands against exposure to the resin and hardener liquids. Nitrile gloves are recommended as they are quite unlikely to react upon contact with the skin or resin. Any remaining resin can be removed with a mixture of soap and water.
Secondly , you are also advised to wear safety goggles to protect your eyes. If there is any contact with the eyes, you should flush repeatedly with water for a period of 15 minutes and avoid rubbing. Medical attention should be sought at the earliest opportunity.
Lastly, it’s important to ensure that there is sufficient ventilation whenever you are working with epoxy resin. This may be achieved by opening the windows or switching on the ceiling fan in your work area. Alternatively, a respirator may be worn if you are unable to achieve a good level of ventilation.