Effect of surface contamination on the durability and strength of stainless steel – polyisobutylene pressure-sensitive adhesive bonds

Abstract Cleaning of substrate's surface with a solvent is a standard step in a procedure of adhesive joints preparation while carrying out adhesion tests. However, is cleanliness of substrates really so important? The effect of contamination of substrate's surfaces with vegetable (sunflower) and mineral (naphthenic) oils on the strength and durability of adhesive joints formed by neat and organoclay-filled polyisobutylene-based PSAs with a stainless steel substrate was studied. For the filled composition, the strength of the adhesive joints was higher, even with the contaminated surface, than for the system with the neat PIB. Contamination of the surface leads to the formation of a weak layer of plasticized polymer, which contributes to decreasing of the adhesion strength and durability. These parameters, however, are restored over time, which could be connected with the absorption of the contaminants by the adhesive material, as a result of polymer swelling, and their migration to the bulk of the adhesive. The ability of contaminants that can be absorbed and removed from the surface into the bulk of the adhesive is determined by their solubility in the adhesive. It was demonstrated using laser microinterferometry method that PIB is miscible with naphthenic oil, whereas PIB − sunflower oil system exhibits upper-critical-solution-temperature behavior. These observations provide an explanation to the growth trends of durability and strength of the joints over time in the cases of sunflower and naphthenic oil contamination of the substrate's surface.