Epoxies
are synthetic thermosetting resins. These Resins which
are liquids or brittle solids would be of use only
when they are cured by the additions of hardener also
called curing agent or catalyst. Once cured by the
addition of hardener they become hard irreversible
systems. It is the hardener, which controls the properties
of an epoxy system. Thermosets do not melt but decomposes
at high temperature. Thermosets are phenol formaldehyde
urea formaldehydes, melamine, Epoxy Resins, Unsaturated
polyesters, Silicon’s etc.
Thermosetting resins
display good creep resistance and exposure to serve
environmental condition such as heat, cold, radiation,
humidity and chemical atmosphere. The cured epoxies
possess excellent mechanical, physical and chemical
properties and can be used up to about 80°C. once
the resin and hardener are mixed, curing begins and
proceeds at a rate depended upon the factors such
as temperature and reactivity of resin and hardener
towards each other. Usually the curing agent is exothermic.
Many a times other materials are required to be added
so as to modify the properties of the cured resin.
There are about 15 to 20 different types of resins
in market and over 300 hardeners so that the possible
number of combination of resin and hardener is very
high. The formulators can make various formulations
suitable for the required application.
Epoxy resins and hardeners
are supplied by manufacturers in the form of a liquid
in separate packings. A combination of Resin &
Hardener is referred to as the epoxy resin system.
Epoxide resins, if desired, are modified by the addition
of dilutents, fillers & flexibilizing modifiers
to suit the purpose for which they are to be used. |
