12.1 Introduction

Sealants are like adhesives in many ways. In fact, they are often considered 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 chemicals or to contain a liquid or gas. Materials that are used as sealants generally have lower strength than materials that are used as adhesives. This is because sealant formulations contain large amounts of inert filler material, primarily for cost reduction and gap filling purposes. 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 provide 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...