Generally, the methyls offer better bond strengths on metals, the ethyls providing better strengths on everything else. Substrate selection and bondline configuration directly infleuence adhesive performance. For example, two polished bare metal surfaces are best bonded with a methyl grade. By comparison, better results would be generated by an ethyl grade when bonding a single barE metal surface, such as an emblem to an automobile fender. The automobile fender is painted, and while composed of metal, the adhesive is in contact with the acrylic paint layer, a plastic surface.
Surface chemistry plays an important role in the cure of the classic cyanoacrylate adhesives.
Instantbond TM grades cure as the result of contact with trace amounts of moisture. The reaction is called ionic polymerization. Any surface capable of absorbing moisture is a good surface for bonding. Instantbond TM cyanoacrylates require sufficient atmospheric moisture to cure or catalyze the liquid adhesive. The Instantbond TM formulations cure best when surface pH is slightly alkaline or over 7.0.