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By George Waddill, Durcon Technical Services
The curing of an epoxy resin system normally takes place
in stages. The first of these is the combining of the two
reactive materials - the epoxy resin and the curing agent.
Normally, these two components are kept apart until reaction
is desired. The resin is normally a viscous liquid and
the curing agent may be a liquid or a low-melting solid.
When combined and a catalyst and heat are added, the resin
and curing agent react with a release of additional heat.
Reactive epoxy systems always release heat when curing,
thus, they are classified as exothermic reactions. The
exothermic heat acts to speed reaction. This second stage
of reaction results in formation of linear chains of combined
epoxy resin and curing agent. As the linear chains form,
the material is still in a liquid form but viscosity is
increasing rapidly.
Heat and catalyst promote further reaction. The linear
polymer chains are combined through chemical reactions
in a cross-linking process to form a polymerized system
approaching an extremely high molecular weight. During
this third stage of reaction, the material changes from
a viscous liquid to a solid gel. In this stage, the material
is developing strength. It is at this stage that, at LTI,
the material is removed from the mold and placed in a cure
oven. This material, just strong enough to be moved, is
at a stage of incomplete cure, relatively weak and unsuitable
for the intended use.
The final stage of curing, a lengthy process carried out
at an elevated temperature at LTI, results in completion
of the cross-linking process. The final product is a very
strong, chemically resistant material which is suitable
for a variety of applications.
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Chemical
Resistance