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Questions and Answers

October 5, 2000
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Questions and answers in the Adhesives Sealants Industry.

Question: We have been purchasing super glue from local retail stores to assemble small, plastic parts. We recently discovered through an industrial distributor that all super glues are not the same. Now we are confused. Are we using the best super glue for the job?

Answer: “Super glues” are the most common name for cyanoacrylate adhesives. When super glues were first introduced in the early 1950s, they were quite revolutionary.

The early super glues were based on ethyl and methyl cyanoacrylate, and although they worked well under many conditions, some substrates and bonding conditions stymied them. More recently, advancements have been made that make these brittle adhesives tougher, more temperature resistant and able to work on difficult substrates with minimal or no surface preparation. Perhaps one of the most exciting developments in recent years has been the development of higher-molecular-weight versions that have gained FDA acceptance for bonding human tissue.

There are a number of manufacturers of industrial grades of cyanoacrylate adhesives. Any one of these manufacturers can evaluate your particular needs and suggest both an adhesive grade, as well as potential application devices that may enhance your assembly process.

-Robert Smith

Question: Recently, I have encountered problems using contact cement. For years I used solvent-based adhesives, but recently needed to change to aqueous versions and have had nothing but problems. They just seem to take too long to dry, and even when they do, the grab just doesn’t seem to be there. What alternative do I have?

Answer: You have identified a common problem in making the switch from solvent-based adhesives to water-based versions. Water does take longer to evaporate than most solvents. You may wish to consider other adhesives than contact types, depending upon the nature of your application. In some instances, hot melt adhesives or moisture-cure polyurethane adhesives have been successfully used as substitutes in applications formerly using solvent-based contact adhesives. There are a number of suppliers of these types of adhesives who could evaluate your particular circumstances and likely recommend a suitable alternative.

-Robert Smith

Question: In making fiberglass boats, we often need to adhere various things to the hulls during manufacture. We have been using a two-component polyurethane adhesive, but it gives us sporadic and unpredictable results. Are we using the wrong type of adhesive?

Answer: Fiberglass constructions are really a matrix or composite of unsaturated polyester resin and glass-fiber reinforcements. The unsaturated polyester resin is cured via a free-radical polymerization process, usually using a peroxide catalyst or “hardener.” As in most free-radical polymerizations, the cure is actually inhibited by atmospheric oxygen. This can result in a small, uncured, “oily” layer on the surface of the fiberglass part. The residue can interfere with the bonding process. You will most likely need to clean the surface thoroughly and rough it up a bit before bonding, particularly with polyurethane adhesives. There are also structural acrylic adhesives available that will actually bond through some of this film, but even then, it is good practice to clean the surface thoroughly before trying to use any adhesive system.

-Roger Lohman

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