Fundamentals of hot-melt pressure-sensitive adhesive tapes: the effect of tackifier aromaticity

We revisit the effect of varying the tackifier aromaticity on adhesive performance in a styrenic block co-polymer (SBC)-based pressure-sensitive adhesive tape. Aromaticity strongly affects the compatibility between the tackifying resin and base polymer and is defined as the relative number of protons attached to an aromatic ring. Dynamic mechanical analysis, peel resistance, tack, shear resistance and atomic force microscopy were utilized to detect changes in adhesive performance due to resin aromaticity. The results indicate that increasing the aromaticity of the tackifier enhanced the compatibility between the tackifier and styrene domains. As a consequence, the high-temperature cohesive performance measured by the shear adhesion failure temperature decreased due to plasticization of the end-blocks by the aromatic resins. However, other properties of interest such as the glass transition of the rubbery matrix, tack, peel resistance and holding power were less affected by the resin aromaticity. We note that this paper is of limited scope because we have focused this research on styrene-isoprene-styrene, which is very compatible with a wide range of tackifiers. More significant differences would be expected in formulations based on styrene-butadiene-styrene or styrene-isoprene-butadiene-styrene polymers in which the compatibility between the resin and midblock would be more sensitive to the resin aromaticity. In addition to our results, we review the literature and some fundamentals of formulating SBC-based adhesives and PSA testing.