Cyanoacrylate, curing relative humidity

Moisture-curing adhesives are formulated with resins that react with atmospheric moisture to form a curedpolymer. Most ofthese 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 of curing is dependent on the relative humidity and the thickness of the adhesive. If there is too much moisture on the surface, curing of polyurethanes occurs so quickly that... 

The optimum cure condition for cyanoacrylates is when the relative humidity (RH) is between 40% RH and 60% RH. Lower RH, i.e., 20% RH, will result in a slower cure, and high RH (80% RH) result in a faster cure. A dry environment (low RH) often occurs when the work area heating system is switched on in the autumn months, thus drying out the local air adjacent to the work station. 

Cyanoacrylates are very dependent on the presence of small amounts of moisture on the surface and if the relative humidity in the working area is less than 25% RH, the cyanoacrylate will be slow to cure. Surface acidity can also interfere with the curing of cyanoacrylates (see Section 1.2). 

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