Polyacrylates and polysiloxanes are polymers used in pressure-sensitive adhesive (PSA) patches. Liquid additives are co-solvents of the active substances or permeation enhancers, and their compatibility with the polymeric matrix and the effect on adhesive properties should be considered. The patches were prepared from commercial polyacrylates (three types of Duro-Tak®) and siloxanes (Bio-PSA® and Soft Skin Adhesive®). Propylene glycol, polyoxyethylene glycol, isopropyl myristate, triacetin, triethyl citrate and silicone oil were added (10% w/w). Formulations were evaluated microscopically and with a texture analyzer in terms of in vitro adhesiveness and hardness. Only silicone oil was compatible with the silicone matrices. The best compatibility of acrylic PSA was observed with triethyl citrate; one out of three Duro-Tak matrices was incompatible with every additive. In all compositions, the adhesiveness was impaired by the liquid additives. A significant drop in adhesiveness was noted after immersion of the patches in buffer and drying. The probe tack test was considered as the most useful for evaluation of the effect of the liquid additive on adhesiveness, but the results obtained with a spherical and cylindrical probe were contradictory. The structural changes caused by the additives were also demonstrated by a 90° peel test, considered as complementary to the tack test.
Keywords: acrylates; adhesiveness; liquids; patches; pressure-sensitive adhesives; silicones.