Solvent‐Free, High Castor Oil Content‐Based Pressure‐Sensitive Adhesive: Synthesis and Performance

ABSTRACT With the growing demand for sustainable and biodegradable adhesives, castor oil has gained attention as a promising bio‐based raw material due to its hydroxyl functionality, low toxicity, and environmental benefits. In this study, a solvent‐free pressure‐sensitive adhesive (CO‐PSA) with a high castor oil content (55 wt%) was synthesized via controlled functionalization of castor oil (trifunctional to difunctional) and polymerization with isophorone diisocyanate (IPDI). FTIR confirmed the target chemical structure of CO‐PSA by comparing the structures of the starting material, intermediates, and final product. The optimal CO‐PSA formulation (CO‐PSA‐3) exhibited outstanding adhesive performance: initial tack for an 11# steel ball, 180° peel adhesion strength of 12.26 N/25 mm, and static shear holding power of 25 h. Wettability tests confirmed good surface interaction (water contact angle < 80° for all formulations), ensuring effective substrate bonding. Thermal analysis (DSC/TGA) indicated good thermal stability (initial thermal degradation temperature: 266°C) and flexibility at low temperatures (glass transition range: −70°C to −32°C). Degradation studies showed that CO‐PSA undergoes complete alkaline hydrolysis within 2 h, forming nanoscale degradation products (~90 nm in diameter). The high–castor‐oil (55 wt%), solvent‐free, and degradable CO‐PSA formulation developed in this study can serve as an environmentally friendly alternative to petroleum‐derived adhesives, advancing sustainable adhesive technologies for the packaging industry and related sectors.