A simple microcalorimetry system to determine the adsorption behaviour of acids in large adhesive bond gaps using base-initiated solution polymerisation of ethyl-2-cyanoacrylate

This work presents the use of a simple microcalorimetry cyanoacrylate (CA) polymerisation system for investigating aspects of CA adhesive cure through gap and adsorption of adhesive acid stabiliser by a range of metal and glass substrates. It is well established that strong acid induced inhibition periods (IPs) are almost directly proportional to the acid concentration in weak base initiated polymerisations of alkyl CAs in tetrahydrofuran (THF). Ethyl cyanoacrylate (ECA) polymerisation IP measurements were used to determine the adsorption of methanesulfonic acid (MSA) in THF or ECA solutions by a range of metal, glass and polypropylene (PP) lap shears surfaces. The extent of substrate acid sorption was found to decrease in the order: Copper-zinc alloy (C23000) > grit blasted mild steel > aluminium alloy 2024T3 > mild steel > glass > aluminium > stainless steel alloy 304 > PP. Differences in the extent of acid adsorption were accounted for in terms of two effects: surface acidity/basicity and surface area (roughness). The decrease in MSA concentration following lap shear immersion in an MSA solution was related to the reactivity of the substrates for catalysing bond line polymerisations as described in a recently reported confocal Raman spectroscopic study of ECA/substrate reactivity.