Epoxy resins are used as adhesives in construction and marine repair. They can bond in three ways: mechanically, through roughened surfaces; chemically; and ionically.
They turn from liquids to solids through a curing process that is exothermic (gives off heat). Epoxy and hardeners must be mixed precisely. Once the chemical reaction is complete, the mixture can be dry-sanded and shaped. You should be able to dent it with your thumbnail.
Resin
Epoxy is a liquid substance that contains a mixture of resins and hardeners for residential use in areas like kitchens, basements, and garages. Once mixed in a specific ratio, the chemical reaction transforms the liquid into a solid that is extremely durable and possesses some incredible properties. Epoxy can be used to create strong and long-lasting structures that can withstand heavy weight, are impervious to water exposure for short periods of time and exhibit high levels of resistance to corrosion. It is also easy to clean and provides a beautiful sheen that can look like marble or granite.
The chemistry of epoxy resins was invented near the beginning of World War II. The adhesive strength of epoxy was used to replace the rivets on the wings of American bombers. This allowed for a much lighter aircraft that could hold more bombs and achieve higher ranges than traditional planes. The versatility of the resins led to their use in a variety of applications including construction, flooring and coatings.
Typical epoxy resins are polymeric and contain both epoxide groups and anhydrides. The epoxide groups react with reactive hydrogen molecules to form a crosslinking network which gives the epoxy its strength. Anhydrides react with the epoxides to produce a covalent bond. These reactions occur in the presence of an acid catalyst and heat.
There are many different types of epoxy resins available for industrial use. The most common are vinyl ester, phenolic and acrylate. The chemistry of these differs, but all offer excellent durability and chemical resistance. The type of epoxy used in a floor coating depends on the substrate and the application.
A wide variety of additives can be incorporated into epoxy systems in order to change their properties. These additives can include plasticizers, fillers, accelerators and thickeners. The choice of these additives can change the viscosity, color, appearance and other properties of the epoxy system.
The final properties of an epoxy resin can be influenced by the choice of curing agent, the temperature during the cure process and the amount of heat applied to the resin during curing. The curing system also influences the rate at which the epoxy dries and hardens.
Hardener
Epoxy is a class of thermoset plastic materials. This is a type of material that sets under heat, and once it has set it cannot be softened or separated. Epoxy has a high tensile strength and flexural strength, and it is also water-resistant. Epoxy is used in the construction of many different types of structures, including floors.
Epoxies are cured by reacting them with polyfunctional curatives (or hardeners) in order to cross-link them and produce the properties that they have. These can be reacted with the epoxy resin itself through catalytic homopolymerisation, or they can be reacted with a wide range of co-reactants. The most common are polyfunctional amines, acids (and acid anhydrides), phenols and thiols (also called mercaptans). These have differing levels of reactivity with the epoxy resin, and when they are reacted together they form a three-dimensional cross-linked network that offers excellent chemical resistance and durability.
The curing of epoxy is a very slow reaction, and the precise conditions needed vary from one resin to another. It is important to use the correct hardener for the resin, and to be aware of how much to add, in order to achieve a full stoichiometric reaction. In the case of epoxies this is very important, as a stoichiometric reaction produces the best physical properties.
In order to speed up the reaction and get an epoxy floor back into service, some contractors choose to add more of the active ingredients than is recommended. This can cause problems in the long run, as the resulting material will not have the proper properties for the application and may not have the required strength.
Another factor that can cause a problem with an epoxy system is using the wrong solvent. Most commercial epoxies are formulated with solvents that can be toxic to humans. In addition, these solvents can degrade the chemistry of the epoxy and reduce its performance. This can lead to poor adhesion, brittleness or discoloration. The toxicity of the solvent is also an issue when it comes to the environment, and some manufacturers formulate their products with environmentally friendly solvents.
Curing Process
The chemical reaction between epoxy resin and hardener produces a solid substance that dries into a strong and durable material. When applied correctly, cured epoxy is suitable for use as an industrial flooring material. It can withstand heavy loads and is designed to withstand temperature changes without warping or cracking. This is due to the fact that cured epoxy is formed by covalent bonds, which are strong chemical bonds in which electrons are shared between atoms.
Epoxy is a versatile material and can be mixed with various ingredients to achieve different characteristics. For example, epoxies can be mixed with carbon fiber or fullerene to increase conductivity. The addition of these materials allows epoxy to be used for electrical applications, including conductive traces on printed circuit boards and as an antistatic material. Conductive epoxy is also commonly used for electronics repair.
Another way that epoxies can be modified is by using halogenated chemicals to provide specific flame and corrosion resistance. For instance, halogenated epoxy can be used for coatings in oil and gas drilling operations where high temperatures are frequently encountered. The halogenated chemicals, such as brominated bisphenol A or fluorinated compounds, are mixed with the epoxide to create a special compound.
Before applying epoxy to a surface, it must be thoroughly mixed to ensure that the chemical reaction takes place. It is recommended that the ratio of resin to hardener should be between 3:1 and 10:1. A roller pan and a mixing stick are typically used for mixing to prevent spills and ensure a thorough mixture. This process is crucial for achieving the best results and maximum performance.
The curing process for epoxy is an exothermic reaction that produces a great deal of heat. It is important to take this into account when choosing the right type of epoxy for a particular job. If the temperature is too low, the reaction may not be complete and the final product might not be as durable or as strong as intended.
Epoxy is a very versatile material with many uses and can be customized for specific applications by adding additional ingredients or changing the ratio of resin to hardener. The most important factor in ensuring that an epoxy resin or coating will cure properly is to allow adequate time for the curing process. The drying time can vary based on the type of epoxy and other factors, such as the temperature and humidity.
Applications
Epoxy is one of many forms of polymers, a group of manmade materials that are found in almost everything around us, including wool, rubber, and Styrofoam. They are durable, flexible, and highly versatile. These characteristics make them ideal for use in construction applications, where they are used to bind and seal surfaces.
While other adhesives rely on porous substrates to adhere, epoxy bonds with any material, making them suitable for application over smooth, even surfaces like concrete and metals. This allows for the creation of seamless joints, preventing moisture and other contaminants from penetrating into the interior of a building or structure. In addition, the chemical resistance of epoxy provides an effective barrier against a wide range of chemicals.
The chemistry of epoxy resins is complex, but the basic idea is simple: epoxide functional groups are reactive enough to react chemically with other molecules. These chemical reactions, known as cross linking, transform the epoxides into a hardened network of polymer strands. This process is called curing, and it is essential to achieving the full range of epoxy’s impressive properties.
Commodity epoxy resins are available from a number of major producers. These are generally prepared from olefins (via epoxidation of double bonds) or from aromatic or polyol compounds that have been reacted with epichlorohydrin. In either case, the resulting products are polymerized with monofunctional diluents to create low-medium viscosity resin systems that can be cured with a variety of co-reactants.
These co-reactants can be amines, acids, or other polar molecules, which are then combined with the epoxy resin to form a cross-linked system. A broad spectrum of diluents are available, from monofunctional glycidyl ethers to difunctional aliphatic alcohols or polyols with higher functionality (e.g., methylolpropane triglycidyl ether). Halogenated ingredients can also be added to provide flame resistance and electrical conductivity.
The resulting combinations of resins and hardeners are known as epoxy systems, which can then be applied to specific projects. Some epoxy systems can be cured in ambient temperature, but the majority require heat to reach their glass transition temperature and fully cure. Inadequate heat during curing can result in a network with incomplete cross-linking, and reduced mechanical and chemical resistance.