Architecture：Sealants and Adhesives.pdfVIP

579 14 Sealants and Adhesives 1.0 INTRODUCTION Most sealants are used in exterior applications, hence, they must be deformable, have good recovery properties, and should have good overall elastic properties. Many sealants used in the construction industry are required to maintain functional performance characteristics over many years. While in service, sealants are exposed to environmental factors such as UV radiation, water, oxygen, and thermal cycling. Depending on which face of the building sealants are placed, type of substrate, and geographic region, they may be exposed to extreme environmental conditions, stress, and strain gradients. Hence, sealants are susceptible to weather-induced degradation. In general, degradation involves both chemical and physi- cal processes with the chemical reactions usually preceding the physical [1] process. Weathering of construction sealants is an issue of importance not only to sealant formulators, manufacturers, and specifiers, but also to contractors and users. Sealants can fail due to weather exposure and aging. This type of failure is often characterized by discoloration and crazing and/or stiffness of the sealant surface and is a result of the individual or 579 580 Chapter 14 - Sealants and Adhesives combined effects of solvent evaporation, ozone attack, migration of plas- ticizers, UV radiation, water immersion, etc. To prevent failure and promote certain performance characteris- tics, additives, such as adhesion promoters, fillers, pigments, plasticizers, and thixotropic agents, can be introduced into the polymer. Typical fillers are carbon black, calcium carbonate, talc, clays, and ground silica. Primers, release agents, and backup materia