Synthesis of Castor Oil‐Based Waterborne Polyurethane with Improved Properties via Adjusting PBA/CO Soft Segment Ratio

Abstract In this study, dimethylol propionic acid (DMPA) and ethoxylated polymer diol (N120) are incorporated as composite hydrophilic groups to synthesize a series of castor oil‐based waterborne polyurethane (CWPU) nano‐emulsions. The properties of the nano‐emulsions with different ratio of polybutylene adipate (PBA) and castor oil (CO) soft segments as well as their film are investigated systematically. Fourier infrared spectroscopy (FTIR) confirms that CO was successfully introduced into the waterborne polyurethane (WPU) structure. The result indicates that the maximum contact angle of the film is 75.51° with a 7/3 molar ratio of PBA/CO. Thermal Gravimetric Analyzer (TGA) and Dynamic thermomechanical analysis (DMA) tests show that the thermal stability of the films has gradually improved with the increase of castor oil content. The content of castor oil in CWPU also affects the mechanical properties of the film. The tensile strength of the film reaches 23.2 MPa, and the elongation at break is 1460.7 %, when the molar ratio of PBA/CO is 9/1. Atomic force microscopy (AFM) is used to express the surface morphology of CWPU films. The films surface become rougher due to the introduction of CO. This work combines castor oil and water‐based systems to provide a relatively simple preparation method to synthesize CWPU nano‐emulsions, which can be used in environmental protection coatings and adhesives, and has broader application prospects.