Adhesives are the substances that are used to bind two substrates. They may be of various types but they basically belong to two categories - thermoplastic and thermosetting. Epoxy resins belong to the latter group. This means that once they are cured, they cannot be remolded. They are the polymers of endless numbers of smaller molecules; hence this epoxy adhesive is also the polymers of smaller molecules with at least two epoxide groups. Since there is no end to the chain reaction forming such high molecular weight polymers, these resins are rarely found in the pure form. Some very high grade pure varieties can be produced by applying certain applications like distillation purification process. But the problem with thishigh grade adhesive glue is that it readily forms crystalline solids owing to its highly regular structures.
The epoxide content forms an important criterion for the epoxy resins. This number determines the amount of co - reactants to be used for curing this adhesive glue. Stoichiometric or near - stoichiometric quantities of curative is used to cure epoxy resins for the best results. Blending of different grades of this glue, use of additives, and fillers, together called as formulating is usually done to get the desired result or to lower the cost of the product. The most common type of epoxies results from reacting epichlorhydrin with bisphenol. Bisphenol F epoxy, Novolac, Aliphatic, Anhydrides, Phenols, Thiols, are some of the classes of epoxy resins. Uncured epoxy resins do not have the chemical or heat resistance, but they can be cured to get all the good properties. For this they are reacted with suitable polyfunctional curatives or with themselves, also called as Homopolymerisation.
There are special epoxies which are waterproof and are capable of curing underwater. These adhesive products have a wide range of application in electronic or electrical components, metal coatings, high tension electrical insulators and many more. They are used in root canal procedure to bind guttapercha. This epoxy adhesive is available in liquid and paste forms. So before using them it is necessary to judge our own requirements. Since they are very strong, precaution should be taken while mixing the epoxy resins and should be used immediately. They should be applied sparingly but covering the entire surface that has to be bonded.
Epoxies have a wide range of applications in industries. They are used with the anti-corrosive paints for surface coating, marine coating, coating for steel pipes, etc. They are widely used in construction industries for adhesives and grouts in the buildings, grouts for leveling, floorings, and also in the construction of roads and bridges. In the field of electrical and electronics, they are used in rotating machines, cable jointing, etc. These adhesives are also used at our homes mainly in the field of art and craft. So we see that there may be various types of adhesives available in the market, but epoxies are the most widely used resins out of them all.