Surface Modification of SBS Rubber by Low-Pressure Inert Gas Plasma for Enhanced Adhesion to Polyurethane Adhesive

Low-Temperature Plasma Modification of Styrene–Butadiene Block Copolymer Surfaces for Improved Adhesion—A Kinetic Approach

“…Indeed, it has already been found several times that changes in the concentration of functional groups responsible for reactions with PU adhesives (C−OH, C−Cl, >C=O), measured directly by FTIR and XPS spectroscopies as a function of plasma treatment time, demonstrate a good correlation with an analogous dependence for the peel strength of adhesive joints [4,8,13,18]. Curves showing the theoretical relationships between the peel strength and the plasma treatment time in the proposed kinetic model, for example, with assumed values of parameters similar to those determined experimentally (see Table 1): (curve 1) according to Equation 1 Indeed, it has already been found several times that changes in the concentration of functional groups responsible for reactions with PU adhesives (C−OH, C−Cl, >C=O), measured directly by FTIR and XPS spectroscopies as a function of plasma treatment time, demonstrate a good correlation with an analogous dependence for the peel strength of adhesive joints [4,8,13,18]. The relative concentrations of −OH groups are expressed by normalized surface areas of the characteristic IR bands in the range of 3650 to 3710 cm −1 , which are assigned to O−H stretching vibrations [23].…”

“…A more detailed analysis of the model allowed showing of the differences between the action of reactive and inert plasmas, Figure 8. Dependence of the rate constant k 1 on the discharge power for all types of plasma tested, plotted according to Equation (4). The values of the parameter n were calculated based on the linear regression of the plots.…”

“…Usually, after the plasma treatment, a pronounced increase in the adhesion of the polymer surfaces to adhesives was observed. In some cases, only a few seconds of plasma exposure was enough to obtain several times higher peel strength than that of the non-treated samples [4]. There is no doubt that the observed improvement in adhesive properties results from changes in the chemical structure and nanomorphology of the polymer surface.…”

“…The strength and quality of such adhesive-bonded joints depend, to a great extent, on the chemical structure and morphology of the polymer surface, and therefore can be controlled by various surface treatments. It is already known for more than 20 years that a particularly useful method in this respect is the low-temperature (non-equilibrium), both low pressure and atmospheric pressure, plasma treatment [1][2][3][4][5][6][7]. Such treatment, which can be performed either in inert plasmas (generated e.g., in Ar or He) or chemically reactive (but non-polymerizable) plasmas (generated e.g., in O 2 , CO 2 , or H 2 O), causes changes in the chemical structure of the polymer surface by two fundamental processes.…”

“…The radical centers are also responsible for the formation of cross-linking bonds (for example, C−C, C−O−C), the number of which increases with the concentration of these centers. In turn, the second process involves bombarding the surface with ions, which leads to the preferential etching of the surface by removing certain atoms or their groups and, consequently, increases the surface roughness [4].…”