The group of synthetic resins called epoxies produce the strongest adhesives incurrent use, as well as plastics and corrosion-resistant coatings.
Epoxyadhesives are thermosetting; that is, after initial hardening, they cannot beremelted by heat. They have excellent resistance to solvents and weatheringagents, and high electrical and temperature resistance. Their adhesion to almostany type of surface--including metal, ceramic, wood, and fabric--is unmatched.Epoxies are usually made by reacting epichlorohydrin and Bisphenol A to producea polymer chain of somewhat complex structure. The end of the polymer chain isan epoxy group from epichlorohydrin; the resulting plastic receives its namefrom the end epoxy group.
The unmodified epoxies are brittle; however, theproperties of the cured resin can be varied widely by the selection of asuitable resin, curing agent, filler, and curing procedure. Flexible grades aremodified with polyamines and polysulfides. Most epoxy formulations have twocomponents that are mixed for curing. One-component epoxies are available thateither contain a latent curing agent or are simply cured by absorption of oxygenfrom the air.
Unlike most thermosetting plastics, epoxies shrink only slightlyduring curing. Epoxies can be used as filler-adhesives; the strength of thecemented joint is independent of its thickness. The epoxies are used as moldingand potting compounds, reinforced plastics, surface finishes, and adhesives.Molding compounds are chiefly used by the electronic and electrical industries;potting compounds are poured to encapsulate small electronic parts. Epoxy paintshave outstanding corrosion resistance and are permitted for use on foodequipment such as flour bins and can coatings.
Large and complex dies for theforming of metal sheet are made of epoxy and are often modified with powderedmetal such as aluminum. Uses in construction include the repair and bonding ofconcrete and also epoxy terrazzo floors. Adolf HitlerBibliographyLee, Henry, ed., Epoxy Resins (1970); Hilado, Carlos J., Carbon ReinforcedEpoxy Systems (1984).
