Page 566 - Handbook of Adhesives and Sealants

Sealant Families 487

13.3.3 Chlorosulfonated
polyethylene (Hypalon)
Hypalon is the DuPont tradename for chlorosulfonated polyethylene
resin, and it is used as the base for a one part sealant. A typical
formulation for a sealant of this type is as follows: 5
Composition Parts by weight

Blend of chlorosulfonated polyethylene 17.5
Chlorinated paraffins 17.5
Thixotropic fillers 20
Titanium dioxide 14
Curing agents, e.g., litharge 7.5
Dibutyl phthalate plasticizer 19
Solvents, e.g., isopropyl alcohol 4.5

These compositions are cured by cross-linking at ambient tempera-
tures to produce flexible sealants with good adhesion.
Hypalon-based sealants have excellent weathering properties, good
resistance to ozone, oxygen, and ultraviolet light, and excellent resis-
tance to strong acids. These systems generally have limited shelf sta-
bility. They also require extended cure time to reach the ultimate elas-
tomeric properties. Hypalon sealants are used in exterior joints where
movement is moderate. Construction applications include doors, win-
dows, and roofing.

13.3.4 Hot-melt sealants
In addition to butyl rubber and bitumens, several other polymers are
used as hot-melt sealants. Among these are the copolymers of ethylene
and vinyl acetate (EVA), atactic polypropylene, and mixtures of par-
affin wax and polyolefins. Being 100% solids, there is very little
shrinkage.
The set time of hot-melt sealants is much shorter than the conven-
tional sealant system. Thus, hot-melt sealants are finding their way
into high volume, production operations such as car manufacture. The
introduction of UV stable styrenic thermoplastic elastomers, such as
styrene-ethylene/butylene-styrene (SEBS), and thermally stable tack-
ifying resins have accelerated the development and commercialization
of hot-melt sealants.

13.4 High Performance Sealants
High performance sealants have movement capability of greater than
12% and generally excellent resistance to environmental extremes.