The Impact of Liquid Components on Alteration of the Adhesion of Polyacrylate and Silicone Patches

Abstract

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.

Figure 1

Procedure used for preparation of the adhesive patches from acrylic (A1, A2, A3) and silicone (S1) polymers.

Figure 2

Probes used in the tack test: (A)—spherical probe (P5S) in contact with the A1 patch, (B)—cylindrical probe (C6).

Figure 3

The setup for the 90° peel test with dedicated attachment to texture analyzer.

Figure 4

Scheme of the swelling test setup.

Figure 5

Sample images of incompatibilities in acrylate and silicone patches: droplets of the liquid additives are dispersed in the polymeric matrix, which is visualized by optical microscopy but not seen when the surface of the patch is observed with SEM. A sample of a visually homogenous structure (A3-TA) is also presented.

Figure 6

Comparison of the results collected with a spherical (PS5) and cylindrical (C5) probe in the tack test for the A2-TA patch.

Figure 7

Results of probe tack test (force and work of adhesion) in acrylate PSA formulations: A2 and A3 with liquid additives (average ± SD; n = 10). P5S—spherical probe, C6—cylindrical probe. The reference values (respective patches without liquid additives) are marked as dashed lines.

Figure 8

Results of probe tack test in silicone PSA formulations: S1 and S2 with liquid additives (average ± SD; n = 10). P5S—spherical probe, C6—cylindrical probe. The reference values (respective patches without liquid additives) are marked as dashed lines.

Figure 9

Results of the peel test for acrylate (A2, A3) and silicone (S1, S2) patches—the effect of liquid additives (acrylates: n = 6, except for A3 where n = 3; S1: n = 5, S2 n = 3). The reference values (blank patch without liquid additives) are marked with dashed lines.

Figure 10

The 90° peel test for silicone patches S1-SO and S1-TA—comparison of the results obtained in vitro and in vivo.

Figure 11

Hardness of acrylate (A2, A3) and silicone (S1, S2) matrices—the effect of liquid additives (n = 6, except for S1-MIP: n = 2 and S2-GP: n = 3). The reference values (for the respective patch without liquid additives) are marked with dashed line.

Figure 12

Change in the mass (absorption of water) during submersion of the patches in phosphate buffer for 96 h and the residue mass after drying (erosion – the initial mass is marked with red line and the limit ±10% is marked with a blue area).