WHAT IS AN EPOXY ADHESIVE?
In the simplest form, an epoxy adhesive is a copolymer (a polymer made by the reaction of two different monomers, w/ units of more than 1 kind) formed by mixing resin and hardener together.
How Are Epoxy Adhesive Made?
Epoxies are made by first mixing together two different starting compounds, which are resin and a hardener. Curing begins after mixing the resin with the catalyst. The curing process is when molecular chains react to chemically active sites and the results is an exothermic reaction. The resin has epoxide groups and the hardener (catalyst) has amine groups and the covalent bonds that come from the combination of these two which creates a linkage consisting of the polymer, and this is what decides how rigid and strong the epoxy is going to be.
The alteration of the mechanical strengths of the properties, electrical, thermal, and chemical resistance, is done during the curing process by monitoring the conditions of the mixture throughout the process using temperature, resin choice, and the hardener compounds. This allows epoxy adhesives to be developed in a wide range of different applications, as well as operating conditions.
What Will Epoxy Adhesives Adhere To?
Epoxy adhesives will adhere to a wide range of different materials, with their properties being dependent on its specified chemistry us within the system and the nature of its available linkage. A few of the more important requirements in performance is the heat and chemical resistance, good adhesion, water resistance, including insulated mechanical and electrical properties.
What Are Epoxy Adhesives Used For?
Epoxy adhesives are used as a type of structural adhesive and it is commonly provided as either a one-component system or a two-component system. The one-component epoxy adhesive system generally uses a temperature ranging between 2500–3000 F when curing, these conditions produce a higher strength, with excellent adhesion to all metals, is good environmentally and has a harsh chemical resistance. Furthermore, an epoxy adhesive is often chosen as an alternative for welding or the usage of rivets.
What Are The Different Types Of Epoxy Adhesives?
The systems consisting of one component have been formulated using the pre-catalyzed method, which only requires a moderate amount of heat for curing, this improves its efficiency, avoiding any errors that could occur from the entrapment of air. What’s more, and the speed for the one-component systems are much quicker than that of the two-component systems.
The epoxy system consisting of two-components is different than the one-component system because the catalyzation can occur when at ambient temperatures, and it can also be accelerated with heat. When additional heat is added it will also promote even more cross-linkages that can result in more superior properties. Whereas, the system with two components is suitable to bond most surfaces. Since these have the ability to withstand continuous weight/force for an extended amount of time they are considered to be highly stable, and they have a resistance to chemical and physical influences. This is why the two-component epoxy system is thought to be a highly stable product. Both are very versatile, so they are usable for sealing, bonding, coating, and used by many industries for numerous products, including medical devices, electronics, and aerospace. There are some special formulations that make products cryogenically serviceable, flame retardant, resists high temperatures, cures fast, and much more.
What Is Epoxy Resin?
Epoxy resin is thermosetting polymers that have unique resistance and mechanical properties.
How Are Epoxy Resins Made?
Epoxy resins are made by curing, a process that consists of an exothermic reaction which is achieved by either the epoxy resins reacting with themselves or cross-linking with a hardener. This creates epoxy thermoset polymers, with good versatility, resistance, durability, and adhesion.
Epoxy Resin Uses
Encapsulating or potting media
Industrial epoxy coatings
Solidifying surfaces that are sandy in oil drilling
Non-skit epoxy coatings
As a binder in mortar and cement
Decorative flooring applications
Structural or engineering adhesives
Structural matrix material
Manufacturing of casts and molds
Different Types Of Epoxy Resin
Fiberglass, Aramid (Kevlar), and Carbon Fiber, all use three main kinds of Resins, which are Polyester Resins, Epoxy, and Vinylester. They all vary in cost and they all have individual characteristics. We will be discussing each of the Resins below. You should be aware of all Resins and Hardeners, as they all have issues related to safety. It would be wise for you to research each of the products you plan on using and make certain that you understand completely about the manufacturer’s information on its safety, and be sure to follow the recommendations they give to you.
1. Epoxy resins
Though these are the highest priced of the three Resins, they are all going to be worth what they cost. Epoxy Resins are going to be nearly three times stronger than the Resin type that is in line to be stronger. It will adhere very well to Fiberglass Aramid (Kevlar), and Carbon Fiber, and it forms a practically leak-proof barrier. Epoxy will also stick to the older Epoxy’s, as well as the majority of materials very well. The majority of epoxies tend to turn yellow if exposed to water. If you are buying Epoxy to be used under duress of extreme temperature changes or where it will get exposed to water, be sure that you are buying the “all-weather” Epoxy Hardener. For instance, one such hardener is referred to as the “West System’s 207 Hardener.”
Note that the majority of epoxies are going to be the color of amber. Anytime a typical amount of a Resin is applied on a composite, but just enough to wet the composite, it is going to turn out clear. There is an exception to the rule if it is applied to wet-out a yellow Kevlar, including Fiberglass that is white in color. In cases like this, the yellow Kevlar will turn slightly darker, and it will appear that the white Fiberglass has a slightly yellow tint. You can also buy Epoxy Resins that is totally clear. One of the totally clear one’s is the West System’s 207 Hardener, and it also includes UV protection. In fact, this s the only Epoxy Hardener that we know of that consists of both characteristics. However, do not confuse the ‘yellowing’ of Epoxy’s that occur over a period of time with the slightly amber in color of nearly all of them have. You can find around four Epoxies on the market that does not turn yellow after a certain period of time. No matter if the application is used indoors, the UV will still yellow your Epoxy over time. Should you not have any plans to paint your piece or application and/or you would like for it to have a nice appeal and last a while, you need to plan on using either a UV coating to protect it (like UV Urethane) and/or the 207 Hardener.
2. Vinylester Resins
These Resins will typically be nearly one-third of what the strength of Epoxy Resins is. They are going to adhere very badly to Aramid (Kevlar), and Carbon Fiber, however, they can still be used as aesthetic applications of the fibers. Primarily used with Fiberglass, but Vinylester Resins are commonly used mostly with Carbon when it is for cosmetic applications, whereas, a Polyester based gel coat or Polyester clear coat will be needed. However, a Resin of this type should never be used with Carbon or Aramid fabrics, not if strength is going to be a primary requirement. Also, note that Urethane based on clear coats is alright to use with Epoxies.
3. Polyester Resins
These are the Resin types that will cost the least. These kinds have a very poor capability when it comes to bonding and they should not ever be used for a structural work consisting of Carbon or Aramid. However, they will typically work fairly well with Fiberglass. No one should so much as consider using these Resins on a structural application that will contain Carbon Fiber or Aramid.