Polyurethane/Cellulose Nanocrystals Nanocomposites for High‐Performance Waterborne Adhesives

ABSTRACT Waterborne polyurethane (PU) adhesives are considered one of the most promising classes of waterborne adhesives due to their wide application potential in various fields, including packaging, footwear, automotive, and construction. However, compared to their solvent‐based counterparts, waterborne PU adhesives exhibit inferior chemical resistance, thermal stability, and mechanical properties, which limit their widespread application. To address these limitations, the present study explores the incorporation of cellulose nanocrystals (CNCs) as a reinforcing biobased nanofiller into PU dispersions, likely to be used in waterborne PU adhesives. The effects of CNC addition to the PU dispersion and films were investigated using tensile testing, dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), and rheological measurements. The results demonstrated a significant enhancement in both tensile strength and modulus, without severely compromising ductility. This is consistent with the well‐documented strong reinforcing effect of CNCs. The application of these nanocomposite PU dispersions as waterborne adhesives was also investigated, providing a sustainable alternative to solvent‐based adhesives. At an optimal CNC concentration of 4 wt%, substantial improvements in adhesive performance were achieved without compromising processability.