Hydrophobic high-bio-based content waterborne polyurethane prepared by diols and high-molecular weight internal emulsifier

Vegetable oil-based waterborne polyurethanes (WPU) have gained significant attention in the leather industry as sustainable coatings, yet inherently suffer from limited bio-based content, hydrophobicity, and low-temperature resistance due to their reliance on low-molecular weight (Mw) hydrophilic chain extenders and highly functionalized bio-based polyols. To overcome these challenges, we developed a long fatty chain-based design strategy by synthesizing a high-Mw castor oil emulsifier (COE) and two bio-based diols, successfully preparing a novel series of WPU emulsions. When the COE content reached 30%, the emulsions demonstrated good stability while achieving a high-bio-based content of 70.94%. The incorporated long fatty chains endowed the WPU films with good hydrophobicity (water contact angle > 90°), exceptional water resistance (water absorption < 2%), chemical resistance, and self-cleaning properties. Moreover, these high-bio-based content films exhibited tunable thermomechanical performance, including enhanced low-temperature resistance ( T g = 2.8 °C) and improved elongation with increasing Mw, while maintaining excellent thermal stability ( T d5% > 200 °C). This work provides an effective approach for developing sustainable WPU for leather applications with balanced performance properties through strategic molecular design of long fatty chain structures.