Commercial joint sealants

Table I. The main types of commercial joint sealants...

As early as 1982, Riesen and Bartelst ] demonstrated the usefulness of dynamic load thermomechanical analysis (DLTMA) for the characterization of commercial joint sealants for building construction. They used DLTMA to study the viscoelastic behavior of four different sealant types polysulfide, polyurethane, silicone, and polyacrylate. The difference in viscoelastic behavior of the sealants can be seen from Fig. 8. 

Uses Commercial building sealant for crack repair, cove bead expansion Joint sealant Features Nonsag... 

The average shore A hardness of the cured sealant is 20 to 25 but increases with ageing. Resistance to ultraviolet radiation is excellent, but this is not important for indoor applications. The maximum movement accommodation factor (MAF) can be 15% of the total joint width. Joints should be designed so that movement due to shrinkage and thermal changes does not exceed the maximum MAF, related to the joint width. Table 5.4 lists the properties in general for acrylic emulsion sealants. These properties are summarised from the commercial literature of several acrylic emulsion sealant manufacturers and should not be considered as specifications. Table 5.5 lists the standard specifications for these sealants. 

This is made primarily on the basis of the intended joint movement (see Sealant joint design), though other criteria are important such as compatibility with joint surface materials. To achieve a satisfactory bond to certain surfaces under the prevailing site conditions, it may be essential to employ an appropriate primer (see Primers for sealants). Table 1 summarizes the types of sealants available commercially and indicates their performance characteristics. 

Most of these systems use the one-shot technique and are based on MDI with either a polyether or a polyester. Crude or polymeric MDI or other liquid variants of MDI predominate. Formulations usually contain high catalyst concentrations of either tin or mercury salts to give a very rapid cure at room temperature within a few minutes. It is usual to use additives to provide specific properties of density and lower the cost. Applications are commercial vehicle floor mats, cable jointing and potting compounds, sealants, moulds and the like. 

Adhesives are used extensively by the aerospace industry for bonding structural components of aircraft (both military and commercial), missiles, and satellites. Sealants are used in joints around windows, in fuel tanks, etc. hot melts and pressure sensitive adhesives are utilized in aircraft interiors (primarily in fabricating decorative panels) while thermosetting adhesives are used to bond load bearing structural components. 

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