ИСТИНА

A common recommendation before carrying out adhesion tests is cleaning the surface with a solvent. However, is cleaning of the substrate so important? The objective of our work was to investigate the effect of contamination of substrate’s surfaces with various oils (vegetable and mineral) on the strength and durability of adhesion joints formed by conventional and filled PSAs with a steel surface. As pressure-sensitive adhesives, polyisobutylene-based compositions (PIB) with wide molecular weight distribution were used. To suppress the cold flow, 40 wt % of organomodified montmorillonite Cloisite 15 was used as the filler. The contamination of the surface was modelled with sunflower and naphthenic oils. Generally, the adhesion characteristics correlated with the rheological properties: durability with a zero-shear viscosity of PSA, whereas strength with a spurt stress. For the filled composition, the strength of the adhesive compound was higher, even on the contaminated surface, than for the pristine system. Contamination of the surface leads to the formation of a weak layer, which contributes to decreasing of the adhesion strength and durability. These parameters, however, are restored over time, which could be connected with absorption of the contaminants with the adhesive material and their migration to the bulk of adhesive. The ability of contaminants to be absorbed and diffuse through the PSA material is determined by their solubility in the adhesive. It was demonstrated using microinterferometry method that PIB is miscible with naphthenic oil, whereas PIB − vegetable oil system exhibits upper critical solution temperature behavior. These observations provide an explanation to the trends of durability and strength of the joints over time in the cases of vegetable and naphthenic oil contaminations.