April 2007

Question:Would you please repeat some of the comments you made a few years ago about handling adhesives and sealants in cold temperatures?

Answer:Cold weather brings two potential problem areas as far as adhesives and sealants are concerned, namely low temperatures and low humidity. One of the critical things to do if you are using a water-based adhesive like an acrylic latex is to ensure that you prevent it from freezing. You should check drums at the receiving dock to make sure the adhesive has not frozen during shipment; this is often evidenced in a cottage cheese-like look. Also, ensure that drums are not left on the receiving dock in very cold weather. Although many latex adhesives can be formulated to be freeze-thaw stable, the industry is trending away from this because the anti-freeze additives, such as ethylene glycol, are quite toxic. When you receive or ship water-based adhesives, use a company that uses heated trucks, not merely one that gives you some sort of guarantee about non-freezing. Make sure that epoxy adhesives are stored in heated warehouses to prevent crystallization. If you are using adhesives and sealants outdoors, you should check carefully with your supplier because products tend to cure more slowly at low temperatures. Many epoxies, for example, won’t cure at all at low temperatures.

Most assembly and sealing operations carried out indoors take place in a controlled environment, but you can sometimes see winter-related problems. I have received many calls over the years from manufacturers who are using “instant” cyanoacrylate adhesives and finding that they are not instant anymore! Low humidity is the most common cause of this because moisture on surfaces catalyzes the cure of cyanoacrylates. The solution to this problem is to create a high-humidity environment, such as humidifying a fume-hood or small room. The cure rate of other products that depend on moisture for curing, such as RTV silicones and one-component polyurethanes, can also be affected by low humidity.

Question:What’s the difference between a latex adhesive and a dispersion adhesive?

Answer:Many companies have been using the term “dispersion” in place of latex to disassociate their water-based adhesives from adhesives based on natural rubber latex. This is due to the severe allergic reactions some people have to the residual proteins found in natural rubber. Although synthetic latex does not have this problem, and can also be eliminated in natural rubber by processing, the association of latex with allergies still lingers.