Restoring Adhesion–Cohesion Balance in High Bio-Content Waterborne Pressure-Sensitive Adhesives through Itaconate Chemistry and Nanocellulose Reinforcement

Abstract

High biobased content waterborne pressure-sensitive adhesives (PSAs) were developed via seeded semi-continuous emulsion polymerization using renewable monomers including dibutyl itaconate (DBI), 2-octyl acrylate (2-OA), isobornyl acrylate (IBOA), and isobornyl methacrylate (IBOMA), achieving biobased contents up to 78%. The incorporation of DBI significantly altered the polymer microstructure, as evidenced by changes in gel fraction and soluble molar mass, promoting greater molecular flexibility and improved fibril formation. In conventional systems, shear resistance decreased due to reduced network density. A similar balance of adhesive properties was observed in biobased formulations. To restore cohesion while preserving pressure-sensitive behavior, sulfated cellulose nanocrystals (sCNCs) were incorporated at low loadings (0.25–1.0 phm). Rheological analysis revealed an increased storage modulus (G′) while maintaining compliance below the Dahlquist criterion, enabling reinforcement without compromising tack. At 0.5–1.0 phm sCNC, shear adhesion failure temperature (SAFT) values of the high biobased systems doubled and approached those of the petroleum-based reference (∼10,000 min) while maintaining balanced peel performance (10–14 N/25 mm). These results demonstrate that combining DBI with renewable cellulose nanocrystal reinforcement provides an effective strategy for developing highly biobased waterborne PSAs that maintain balanced performance.