Degradable, anticorrosive, and fluorescent waterborne polyurethanes from vegetable oil internal emulsifiers for adhesives and strain sensor

In this work, three soybean oil internal emulsifiers with different −OH functionalities (203.03 ∼ 219.45 mg KOH·g−1) were prepared via the ring-opening reaction of epoxidized soybean oil (ESO) attacked by phosphoric acid. The soybean oil internal emulsifiers and castor oil (C.O) were employed to produce an array of DMPA- (dimethylol propanoic acid-) free anionic waterborne polyurethane dispersions (PUDs) with high bio-based content (69.2%) by utilizing the phosphoryl groups in ionic form. The curing films exhibited good mechanical properties, thermal stability, and multifunctionality (degradability, fluorescence, and anticorrosion). The films (WPU-P5, WPU-P10, and WPU-P15) can be completely degraded in 4.5 wt% NaOH solution for 10 h at room temperature. In addition, the films also displayed fluorescence under 365 nm UV irradiation, and the change of fluorescent intensity during material stretching and damage, which hence could be used to detect material tensile behavior and material damage. Due to the corrosion inhibition performance of the phosphoryl group and its excellent adhesion to the metal substrate, the WPU-P15 film had the best corrosion resistance. The adhesive capacity of the films as pressure sensitive adhesive was characterized by the shear strength test, hanging weight time and peeling test. The WPU-P10 film had a shear strength of 1.66 MPa, a hanging time of 1 kg weight up to 10 h, and a peel stress of 0.67 MPa. The WPU-P15 film was also applied in strain sensing to detect human activity. These studies are bound to further expand the application range of vegetable oil-based WPU materials.