Abstract

More and more bio-based materials are used in waterborne polyurethanes (WPUs) due to their non-toxic and pollution-free advantages. In this paper, waterborne polyurethanes (WPU) were synthesised from 2, 4-Toluene diisocyanate (TDI-80) and polypropylene glycol (PPG, Mn=1000). Four kinds of WPU leather finishing agents (WPU0, WPU1, WPU2, WPU3) were prepared by adding different contents of the bio-based material tannic acid (TA) as a cross-linking agent. After a series of tests, the results showed that the thermal degradation temperature of WPU films and their tensile strength increased with the rise of TA content. When 0.6g TA was added, the tensile strength and thermodynamic stability reached the highest values, but the elongation at break was the lowest at the same time. The addition of the cross-linking agent TA reduced the hydrophilicity of the WPU film from 40.8% to 16.2%. In the application of leather finishing, both dry and wet rubbing increased 1 to 2 grades through the introduction of TA and the folding fastness also improved significantly. The molecular chains were more closely arranged, and the distances between the molecules were also reduced on account of the incorporation of TA, resulting in a decrease in water vapour permeability. Based on this, the water contact angle of the finished leather has also increased from 68° to 99°.