Ask Dr. Dave
October 1, 2009
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Adhesives and sealants troubleshooting tips from Dr. Dave Dunn.
Question: I am looking for sealants for sealing the joints in a steel structural insulated panel building that will be assembled in the Arctic at temperatures below zero degrees. Would you recommend using RTV silicones or polyurethanes for the job?
Answer: It depends on whether you simply need a sealant that will have sufficient flexibility at low temperatures to withstand the climate or whether you need to actually apply the sealant at these temperatures. The cured silicone or urethane will certainly be suitable for the low temperatures. However, if you want to apply them in situ then there are two potential problems. First, you will need to ensure that there is not frozen water on the joint surfaces that will cause adhesion problems; you may need to use a heat gun to get rid of any ice. Secondly, the sealants require atmospheric moisture for curing, and the humidity may be extremely low. Be aware that full cure may take weeks under these conditions. An alternative would be to use two-component mixable versions of these sealants that do not require moisture for curing, and then heat the sealant after application to speed up the cure.
Question: In general, is it safe to freeze cyanoacrylate adhesives to extend shelf life? Can I store them at -18 to -22°C?
Answer: Yes, cooling is a very common way of extending the shelf life of cyanoacrylates. In fact, that is how I store them at home in my kitchen refrigerator, which doesn’t make me too popular! At low temperatures, the adhesive becomes very viscous, molecular mobility is slowed and the speed of all chemical reactions (including curing) is reduced to virtually zero. Storing the adhesives at around -20°C will keep the adhesives stable for years. You just have to make sure that you let them thaw with the bottle sealed to avoid condensation of moisture into the adhesives when you want to use them.
Any views or opinions expressed in this column are those of the author and do not represent those of Adhesives & Sealants Industry, its staff, Editorial Advisory Board or BNP Media.
Question: I am looking for sealants for sealing the joints in a steel structural insulated panel building that will be assembled in the Arctic at temperatures below zero degrees. Would you recommend using RTV silicones or polyurethanes for the job?
Answer: It depends on whether you simply need a sealant that will have sufficient flexibility at low temperatures to withstand the climate or whether you need to actually apply the sealant at these temperatures. The cured silicone or urethane will certainly be suitable for the low temperatures. However, if you want to apply them in situ then there are two potential problems. First, you will need to ensure that there is not frozen water on the joint surfaces that will cause adhesion problems; you may need to use a heat gun to get rid of any ice. Secondly, the sealants require atmospheric moisture for curing, and the humidity may be extremely low. Be aware that full cure may take weeks under these conditions. An alternative would be to use two-component mixable versions of these sealants that do not require moisture for curing, and then heat the sealant after application to speed up the cure.
Question: In general, is it safe to freeze cyanoacrylate adhesives to extend shelf life? Can I store them at -18 to -22°C?
Answer: Yes, cooling is a very common way of extending the shelf life of cyanoacrylates. In fact, that is how I store them at home in my kitchen refrigerator, which doesn’t make me too popular! At low temperatures, the adhesive becomes very viscous, molecular mobility is slowed and the speed of all chemical reactions (including curing) is reduced to virtually zero. Storing the adhesives at around -20°C will keep the adhesives stable for years. You just have to make sure that you let them thaw with the bottle sealed to avoid condensation of moisture into the adhesives when you want to use them.
Any views or opinions expressed in this column are those of the author and do not represent those of Adhesives & Sealants Industry, its staff, Editorial Advisory Board or BNP Media.
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