Moisture curing adhesives

For all its benefits, the water/isocyanate reaction can be troublesome as well. All raw materials that go into a one-component moisture-cured adhesive must have very low moisture content, usually less than 0.05% water. If higher water levels are present, the adhesive can start curing in the reactor, causing an increase in viscosity, or, in extreme cases, gelation. 

The amorphous polyesters are becoming increasingly important for one-component 100% solid moisture-curing adhesives. These materials are usually viscous, amorphous liquids. Poly(2-methylpropane adipate), an example of an amorphous polyester, is a liquid even at a molecular weight of 2000. The amorphous polyesters are usually asymmetrical in structure. In the poly(2-methylpropane adipate) example, the pendant methyl group would be expected to interfere with chain packing, thereby preventing crystallization [27]. 

The soft segments made from asymmetrical (amorphous) polyols are important for two-component structural adhesives and one-component moisture-curing adhesives. These materials are applied and usually cured at room temperature. 

Property One-part moisture cure adhesive Two-part isocyanate (higher monomer)/ polyol Two-part isocyanate prepolymer (low monomer )/polyol... 

Moisture-curing adhesives are formulated with resins that react with atmospheric moisture to form a cured polymer. Most of these resins are one-part cyanoacrylates, silicones, or polyurethanes. The key advantage, of course, is their ability to cure without the use of heat or other external form of energy. However, in many cases, several days of ambient exposure are required to achieve full properties since the rate... 

Silicone adhesives were introduced commercially in 1944 [5, p. 213]. In 1960 the silicone sealants were introduced to the construction industry [11, p. 86]. Silicones are useful at both high and low temperatures and are available today as solvent-based moisture-curing adhesives, one-part moisture-curing adhesives and sealants, two-part curing adhesives and sealants, and pressure-sensitive adhesives. 

Moisture curing. Moisture-cured adhesives require only ambient moisture to cure. These adhesives contain functional groups that have been purposely blocked and rendered unreactive until exposed to humidity. Moisture reacts with the blocked groups releasing the functional (active)... 

Two-part systems Single-part, cured via catalyst or hardener Moisture-curing adhesives Radiation (hght, ultraviolet, election heam, etc.)-curing adhesives Adhesives catalyzed hy the substrate... 

Classification with respect to the methods of reaction is discussed in Sect. 12.3 to include thermosets, thermoplastics, high-temperature adhesives, elastomers, sealants, anaerobics, moisture curing adhesives, and primers. 

Important Moisture Curing Adhesives Cyanoacryiate Adhesives... 

As with the anaerobic adhesives, moisture-curing adhesives, such as cyanoacrylates, are typically applied using bottles, cartridges etc., made for specific applications. Since moisture exclusion is imperative for premature polymerization, metering and dispensing equipment is designed specially to prevent contact of moisture-curing adhesives with air, prior to use. 

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