Preparation of degradable castor oil-based waterborne polyurethane with tannic acid as crosslinking agent and its application on leather surface coating

In recent years, the types and quantities of polyurethane products have increased day by day. However, traditional petroleum-based water-based polyurethanes not only have the problem of difficult waste disposal, but also accelerate the depletion of petroleum materials. Herein, an eco-friendly polymer was successfully prepared by introducing tannic acid (TA) into castor oil-based waterborne polyurethane (WPU). The effects of the incorporation of TA, a bio-based material, on the particle size of the resulting polyurethane (PU) dispersion, and the thermal performance, mechanical properties, and hydrophobicity of PU membranes were systematically investigated. Finally, ATR-FTIR and SEM of cured films after degradation were measured to characterize the degradation ability of the membranes. It was found that the tensile strength of the samples is improved from 12.67 to 19.57 MPa with the TA content increasing from 0 to 1.5%, nevertheless their elongation at break declines from 306.51 to 237.12%. A noteworthy increase in the glass transition temperature (Tg) was exhibited by using DSC and DMA for the resulting PU films with increasing the TA content. Besides, the improvement in the water absorption of the blend films decreases from 14.5 to 10.2% according to the advantage of TA increasing the degree of cross-linking of the system. After 120 days of degradation, it can be seen that the urethane bond and the aliphatic ester bond played a vital role in the degradation process through the infrared of the degraded films. At the same time, the introduction of TA improves the degradation performance of WPU films. What is more, the application of WPU dispersions containing tannins on the leather surface shows excellent comprehensive performance, which means that WPU dispersions have potential applications as leather finishing agents. This work takes advantage of two kinds of bio-based materials, the mass of bio-based materials accounts for 57% of the total mass, which not only shortens the utilization of petroleum resources, but also effectively resolved the problem that poor quality of castor oil-based WPU and traditional waste is difficult to degrade, improving the commercial value of castor oil-based PU.