Viscoelastic mapping of SBS PSAs: Anti-plasticization and plasticization windows tuned by phenolic resin

In styrene–butadiene–styrene (SBS) pressure-sensitive adhesives (PSAs), tackifier-induced changes in chain mobility strongly influence viscoelastic behavior and the resulting adhesion–cohesion balance. In this study, phenolic resin was investigated as a concentration-dependent modifier for defining distinct viscoelastic windows in SBS PSAs. At low resin loading, phenolic–polymer interactions restricted segmental relaxation, producing an anti-plasticized regime characterized by higher cohesion, slower relaxation, and improved thermal shear resistance. At intermediate loading, a balanced viscoelastic window emerged in which sufficient energy dissipation was achieved without substantial loss of network integrity, resulting in the most favorable adhesion–cohesion balance and maximum peel performance. At high resin loading, the system shifted toward a plasticized regime with lower viscosity, faster relaxation, greater viscous dominance, and reduced shear adhesion failure temperature (SAFT). The results show that phenolic resin acts as a viscoelastic regulator rather than a simple tackifier, providing a practical framework for designing SBS-based PSAs with application-specific balances of adhesion, cohesion, and thermal resistance.