Page 567 - Handbook of Adhesives and Sealants

488 Chapter Thirteen

They are often used in exterior, high movement applications. Sealants
of this type generally cure by the chemical crosslinking of elastomeric-
base resins. They are available as either single part or two part sys-
tems. The single part systems generally require atmospheric moisture
to cause cure either by inducing oxidation or condensation of a reactive
end group.
High performance sealant families include fluoropolymers, fluoro-
carbons, polysulfides, urethanes, and silicones. By far the polysulfides,
polyurethanes, and silicones make up the bulk of the high perform-
ance sealant market. Table 13.4 compares properties of these three
sealants. High performance sealants have a higher price than other
sealants and due to their chemically reactive nature tend to be more
difficult to apply.

13.4.1 Fluorosilicone and
fluoropolymer sealants
Fluorosilicone polymers are intermediate in cost and performance be-
tween the fluoropolymers and silicones. They have unusually high re-
sistance to chemicals and maintain elastomeric properties over a very
wide temperature range ( 80 to 450 F). Fluorosilicone sealants are
available as single component sealants or as two component systems
that are peroxide cured. They are used as sealants for aircraft, auto-
mobiles, and oil well heads in cold climates.
Fluoropolymers are used in small volume, high temperature and
fuel resistant applications. They are also available in single- and two-
part systems. Cured fluoroelastomers can withstand prolonged expo-

TABLE 13.4 Comparison of Properties of Polysulfide, Silicone, and Urethane
Sealants 7
Property Polysulfide Silicone Urethane
Recovery from stress
Ultraviolet resistance
Cure rate a to
Cure rate, two component b
Cure rate, latent hardener NA NA
Low temperature gunnability
Tear resistance
Cost
Paintability
Available in colors
Unprimed adhesion to concrete
Resistance to hydrolysis
Non-bubbling
Self levelling available c
a One component sealant.
b Silicone is available only as one component
c Desirable for plaza decks and pavements.