Page 548 - Handbook of Adhesives and Sealants

Sealant Classification and Composition 473

long term performance and weatherability are important to an appli-
cation, contact the sealant manufacturers and ask for results of ac-
celerated testing performed on specific substrates and under specific
loading conditions. Such data are often available and can identify at
least a family of sealants that may be candidates for the application.
For more information on environmental resistance of sealants and ad-
hesives, the reader is directed to Chapter 17.
In many situations, the appearance of the sealant is almost as im-
portant as its physical properties. Thus, most sealants are available
in a variety of colors to match the environment in which they are used.
Several questions must be considered when determining the appear-
ance requirements of sealants: 7
Does a sealant cause discoloration of surrounding areas, initially or
over a period of time?
Does water runoff over the material cause unsightly residues?
Does one product cause discoloration of another?
Does the product itself change in appearance over time for any rea-
son?

Sealants may also need to be compatible with a specific environment
for certain applications. Examples of this may be a requirement for a
sealant to have USDA or FDA acceptance because food or drugs are
to be processed in the area near the sealant. It may be that in an
installation such as a food processor or clean room, the sealant cannot
outgas or liberate certain chemical components either during or after
cure. Another end-use requirement could be that the sealant must
meet certain fire resistance properties to meet code requirements in
housing construction or in a particular area of use.

12.5 Commercial Products and
Formulations
A wide range of materials and formulations are available for preparing
sealant products that meet a specific need. Most sealants, however,
are a compromise formulation. That is, manufacturers formulate their
products to meet a variety of applications. These products, then, meet
a majority of needs, while the final choice rests with the informed user.
Modern demands for increased productivity, higher performance, and
environmentally safer materials have led to a decline in the use of
some of the older chemistries, particularly solvent-based sealants.
Over the past several years, polyurethanes have become one of the
mainstays for sealing of building joints. Silicones have had success in