Bio-hydrophilic chain extenders with amphiphilic character for waterborne polyurethane derived from castor oil/tea seed oil: separation, synthesis, and application

Unsaturated vegetable fatty acids, as a renewable resource, are abundantly present in vegetable oils, exhibiting significant potential for the synthesis of bio-polyols and bio-based polyurethanes (PUs). Herein, castor oil (CO) and tea seed oil (TSO) were selected as feedstocks to fabricate bio-based hydrophilic chain extenders (HCEs) for water-based polyurethane (WPU). Firstly, the raw oils were treated through a three-step process involving saponification, acidification and urea inclusion purification, yielding unsaturated ricinoleic acid (RA) and oleic acid (OA) with high purities of 93.99% and 92.72%, respectively. Subsequently, an efficient thiol-ene click reaction was carried out to prepare amphiphilic ricinoleic acid-based chain extender (RACE) and amphiphilic oleic acid-based chain extender (OACE) under ambient conditions (1 h, room temperature) with relatively lower molecular weight ( M w ) and accurate functionality ( f − OH = 2 ). The activation energies for the reactions of RACE/OACE and dimethylolpropionic acid (DMPA) with isophorone diisocyanate (IPDI) were evaluated via non-isothermal DSC kinetic analysis (Kissinger method and Ozawa method), and the apparent activation energy ( Ea from Kissinger/ Eo from Ozawa) values were found to be 76.66/78.88 kJ·mol − ¹ for RACE and 74.58/76.91 kJ·mol − ¹ for OACE, respectively, which were slightly higher than that of DMPA (Ea/Eo = 73.01/75.32 kJ·mol − ¹). Application of these bio-HCEs for preparing WPU revealed that the particle size and absolute zeta potential of emulsion with more than 0.0248 mol bio-HCEs were equivalent to those of the emulsion with 0.0192 mol DMPA, and the resultant WPU films showed enhanced broken elongation, increased water contact angles, and reduced water absorption ratio. Collectively, the significance of this work resides in providing a feasible and potentially universal strategy for fabricating bio-HCEs from natural unsaturated oils and offering a sustainable alternative for the advancement of WPU.