Question: I am trying to bond several rubber parts together. I would like to try a cyanoacrylate adhesive, but I hear they are very brittle when cured. Is that true?
Answer: Unfortunately, because some of the common cyanoacrylates tend to be somewhat brittle in comparison to other adhesives when used to bond rigid substrates, they are rarely considered for bonding rubbers. However, these adhesives have been widely used over the years for rubber bonding. For example, so-called “O-ring kits” are sold to make custom-sized O-rings from rubber cord stock, and some critical applications (like bonding rubber balloons on heart catheters) have always used cyanoacrylates. The rubber actually absorbs the stresses put on the bond, and the brittleness of the adhesive is not an important issue.
Cyanoacrylates give very good bond strengths on common rubbers like nitrile, neoprene and Buna N, with strengths often exceeding the strengths of the rubber. In fact, more rigid substrates can now be bonded with more flexible cyanoacrylates because of advancements in the technology over the years. Rubber-toughened cyanoacrylates are true impact-resistant structural adhesives. The first toughened cyanoacrylates were always black in color because they were toughened with rubbers containing carbon black filler, but white and colorless versions are now available.
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