Page 520 - Handbook of Adhesives and Sealants

Chapter
12

Sealant Classification and

Composition

12.1 Introduction
Sealants are like adhesives in many ways. In fact, they are often con-
sidered together because many formulations can perform either as an
adhesive or as a sealant. Usually, a sealant must effectively bond to
a substrate in order for it to perform its function. However, a sealant
is normally used to exclude or contain while an adhesive is used to
hold. Sealants generally are used to exclude dirt, moisture, and chem-
icals or to contain a liquid or gas. Materials that are used as sealants
generally have lower strength than materials that are used as adhe-
sives. This is because sealant formulations contain large amounts of
inert filler material, primarily for cost reduction and gap filling pur-
poses. Sealant formulations also contain elastomeric resins to provide
flexibility and elongation rather than high tensile strength.
In addition to adhering to the substrate and providing a certain
degree of holding power, sealants can also be used to provide acoustical
insulation, vibration damping, and electrical insulation or conduction
depending on the conductivity of the fillers. Specialty sealants can also
be used for thermal insulation or even as a fire barrier. Certain sealant
formulations are also used for heavy surface coatings to protect
against mechanical or chemical attack or to improve the appearance
of a part. Therefore, like adhesives, sealants are often required to pro-
vide a multiplicity of functions in addition to their primary role.
This chapter describes methods of classifying sealant materials. The
various types of sealant materials are characterized. The components
used in common sealant formulations are identified and discussed in
relation to the final performance requirements. Common families of

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