Influence of Octyl Diamine as Chain Extenders in the Castor Oil‐Based Waterborne Polyurethane‐Urea Dispersions and Films

Waterborne polyurethane (WPU) and polyurethane‐urea (WPUU) dispersions synthesized through environmentally friendly approaches have been widely accepted in the coating applications. Here, waterborne polyurethane‐urea (WPUU) dispersions and their films were synthesized using castor oil as a renewable polyol, diisocyanate, and 1,8‐octyl diamine (OA) as a long‐chain aliphatic chain extender. The influence of varying OA contents (0.1–1.0 wt%) on the properties of castor oil‐based WPUU dispersions and their films was studied. For WPUU dispersions, the addition of OA resulted in the decrease in particle sizes (130.9–109.6 nm) and enhanced colloidal stability (> 12 months). The WPUU films showed better resistance against water, organic solvents, acids, and salts; improved the tensile strength (53.20–69.03 MPa) and Young's modulus (98.40–155.14 MPa); increased glass transition temperature (36.8°C–57.4°C); and also enhanced activation energies (76.47–123.98 kJ/mol) with increasing OA contents by forming a flexible cross‐linked structure. Also, the films remained thermally stable up to 200°C. Overall, the present work confirmed that chain extension with OA compared to short chain diamines in the WPUU dispersions and films improves the chemical, mechanical, and thermal properties with adequate flexibility, which can be an effective alternative for low‐gloss coating applications.