Epoxy Resins
The group of synthetic resins called epoxies produce the strongest adhesives in
current use, as well as plastics and corrosion-resistant coatings. Epoxy
adhesives are thermosetting; that is, after initial hardening, they cannot be
remelted by heat. They have excellent resistance to solvents and weathering
agents, and high electrical and temperature resistance. Their adhesion to almost
any type of surface–including metal, ceramic, wood, and fabric–is unmatched.
Epoxies are usually made by reacting epichlorohydrin and Bisphenol A to produce
a polymer chain of somewhat complex structure. The end of the polymer chain is
an epoxy group from epichlorohydrin; the resulting plastic receives its name
from the end epoxy group. The unmodified epoxies are brittle; however, the
properties of the cured resin can be varied widely by the selection of a
suitable resin, curing agent, filler, and curing procedure. Flexible grades are
modified with polyamines and polysulfides. Most epoxy formulations have two
components that are mixed for curing. One-component epoxies are available that
either contain a latent curing agent or are simply cured by absorption of oxygen
from the air. Unlike most thermosetting plastics, epoxies shrink only slightly
during curing. Epoxies can be used as filler-adhesives; the strength of the
cemented joint is independent of its thickness. The epoxies are used as molding
and 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 paints
have outstanding corrosion resistance and are permitted for use on food
equipment such as flour bins and can coatings. Large and complex dies for the
forming of metal sheet are made of epoxy and are often modified with powdered
metal such as aluminum. Uses in construction include the repair and bonding of
concrete and also epoxy terrazzo floors. Adolf Hitler
Bibliography
Lee, Henry, ed., Epoxy Resins (1970); Hilado, Carlos J., Carbon Reinforced
Epoxy Systems (1984).
