Cyanoacrylate Adhesive Environmental Resistance
It doesn’t seem logical, but cyanoacrylate adhesives have more chemical resistance to gasoline than they do to water. One customer who normally used acetone to remove excess adhesive wanted to speed up the process. So he tried what is normally considered a stronger solvent, toluene. The toluene didn’t seem to have much effect at all. The bottom line is cyanoacrylates have poor resistance to polar solvents and better resistance to non-polar solvents.
The dielectric constant of each solvent provides a general measure of a solvent’s polarity. Water is very polar and (at 70°F the dielectric constant is 80. Gasoline is non-polar at 70°F the dielectric constant is 2. Although water will remove cyanoacrylate over time, manufacturers recommend removing cyanoacrylate adhesive with acetone which has a dielectric constant of 21 and nitromethane which is 36. Both acetone and nitromethane are polar aprotic solvents.
Other factors that affect the chemical resistance of the bond include temperature and bond design.
The following chart shows the % strength retention of cyanoacrylates. Standard cyanoacrylates retain about 50% of original strength at 80°C. Enhanced grades retain 50% strength to 120°C. Special high temperature grades have been designed to resist much higher temperatures. To activate the high temperature resistance the following secondary curing mechanism is used -this enables additional cross linking of the polymer allowing the cured adhesive to resist higher temperatures. Note: this procedure will only activate the high temperature resistance designed in to specialty grades. It is not recommended and will not improve temperature resistance of other grades.
1) Parts are bonded and clamped at room temperature for four hours.
2) The clamped parts are then heated at 150°C (302°F) for two hours.
3) After the two hours, the bond will be thermally resistant up to 250°C (482°).
For further help and advice, please contact Permabond.