Columbia Coronado 25 Owenrs Manual page 82

6.1.3 (continued)
are soluble in styrene monomers and are, in fact, sold as solid resins dissolved
in styrene monomer. Special-purpose resins can be made fire-retardant, flexible,
thixotropic (slow to drain off a vertical surface) or corrosion-resistant, to name
just a few.
Polyester resins vary considerably in their physical properties after cure. That is
why it is important to select the proper resin for each of the many fiber glass
products now being manufactured.
6.1.4 Catalysts, Promoters, and Polymerization
Polyester resins have to be cured before they can be useful to a manufacturer of fiber
glass products. The curing process is a chemical reaction called polymerization.
Chemically, this word implies the buildup of large groups of molecules held together
by chemical bonds. If many molecules group together in this fashion, the resulting
product is a hard, rigid solid that assumes the shape of its container.
For all practical purposes, the container is called a mold, and the
polymerization is called gellation, or, simply, a cure.
Two ingredients are essential to the successful polymerization of a polyester
resin: a catalyst and a promoter. A catalyst is a material that, by its presence,
aids a chemical reaction without actually taking part in the reaction itself. In
the classic case, a catalyst could be removed from the products of a chemical
reaction and used again and again. Polyester resin development, however, has lead
to the use of peroxide compounds as catalysts for the curing reaction. Being
somewhat unstable, though, these compounds tend to break dawn and thus yield other
products that actually do the catalyzation. The peroxide compounds also cannot be
recovered afterward because the product of a polyester cure is a solid resin mass.
Nevertheless, as the peroxides do not chemically enter the polyester reaction, they
are true catalysts.
A promoter is a material that enhances the action of a catalyst without actually
having any catalytic value itself. Most resin manufacturers supply resin either
with or without a promoter mixed in ("Promoted" or "Unpromoted"). All the
promoted forms have a reasonable long shelf life when stored as directed.
SECTION 6
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