How does epoxy work?
Epoxy is thermosetting. That means that it cures depending on the surrounding temperature. Once epoxy is cured, it cannot be uncured. Epoxy is an epoxide, which simply means that it's more reactive to other chemicals. A polyepoxide such as epoxy is made up of unreacted epoxide. This basically means that pure epoxy is extremely susceptible to reactions with other chemicals. The other chemical in the case of epoxy is a hardening or curing agent which works to cure it into a very strong adhesive.
Epoxies are created through reacting an epoxy resin and a hardener or simply by reacting the resins themselves. The vast majority of epoxy resins are themselves an industrial product which are derived from petroleum and are also the result of an epoxide reactive process. All depending on the type of reaction that was used to produce them, cured epoxy resins can either be like honey, or something much more viscous. Their actual molecular weight will determine the uses that you can get out of them.
Epoxy resins are very stable at room temperature and only cure when reacting with some kind of curing agent. Epoxies are the most common coating that's used in the field of wastewater. These are based on reactions which are made with still further reactions. We will now take a look at the different types of epoxy that are out there.
This is the most commonly used resin when it comes to epoxy coatings. These are available in a very large range of molecular weights, which makes them particularly versatile when it comes to the application of the epoxies. The resulting product of this is a honey-like liquid, and it is largely used for solids coatings as well as flooring systems. Bisphenol A has good broad range chemical resistance as well as great physical properties. It's cured using a variety of curing agents at good ambient temperatures. Because of its high viscosity and the difficult applications of it, there have traditionally been dilutants added to the formula. Reactive dilutants can have a good effect on diluting the epoxy but could also have negative effects in other aspects of the epoxy as well.
These epoxies are far less viscous than Bisphenol A epoxies. They also provide strong solvent chemical resistance. These less viscous epoxies are quite a bit more expensive than Bisphenol A epoxies. They can be used in a wide variety of applications that secure them in the use of epoxies in general.
Novolac epoxies are similar in some ways to Bisphenol F epoxies in the way that they are both formed. Bisphenol F is actually the simplest form of Novolac resins. Novolacs, however, have more reactive groups in their overall subgroup and is more highly crosslinked than both Bisphenol A and Bisphenol F. You should note that Novolac has higher curing temperatures in general and is more of a delicate epoxy than some of the other ones we've looked at thus far.
Novolac epoxies are much more viscous than the others, and this results in what is called higher functionality. The higher the functionality, the greater the crosslink overall. Bisphenol F resins, for example, have a slightly higher functionality than Bisphenol A resins, and so they have a better resistance to a greater number of chemicals in general. Along with this, the chemical resistance of Bisphenol F resins is better because of its lower viscosity when compared with Bisphenol A resins.
Other Epoxy Coating Information
There is also 100 percent solid putty epoxies. These are formulated with liquid epoxies which are then added to other types of formulations. They are bulked up to the consistency of a putty by adding certain other ingredients that contribute to the putty consistency. These are high build solid epoxies that are commonly applied at 1/8 inch to 1/2 inch. These solventless solid putty epoxies are commonly used to seal over rivets or other similar areas, as splash zone compounds that can be mixed and cured underwater, and as full surfaces for the protection of concrete walls and floors.
The water resistance of 100 percent solid putty epoxies is very high, but the filler content that's required can degrade its reaction with certain other chemicals that are essential for good working order of the epoxy.
Epoxy powders provide performance of a similar quality to liquid epoxies. The epoxies are made by dry grinding the ingredients involved in the epoxy process in a pulverizing fashion. Thicker protective coatings are made by that dry grinding process.
Powder coatings are applied by heating up the item that's going to be coated and dipping it in the powder or by applying the powder with electrostatic spray. The surface has to be heated above what the fusion temperature of the powder is and kept there for long enough to allow the powder to adhere to the surface. Epoxy powders are commonly used as pipe coatings. These coatings have an advantage in that they provide very little waste and provide environmental advantages too.
Water-based epoxies typically consist of an emulsion in water as one component and some sort of solution as the second component. Water-thinned epoxies aren't emulsion coatings, but they have been designed to let in a little bit of water. The other benefit to water-based epoxies is that they can be safely applied over existing coatings.
While this list isn't exhaustive, it should give you a good idea as to how epoxy works.