Synthesis of branched waterborne polyurethane and its application in the preparation of liquid indigo dispersion

In order to solve the problems of low dye-uptaking and serious environmental pollution in the dyeing process of indigo dye. A branched waterborne polyurethane dispersant (WPU) was successfully synthesized from isophorone diisocyanate, trimethylolpropane and 2,4′-dihydroxybenzophenone. The structure and properties of WPU were characterized to prove that it could be used as a new dispersant to prepare liquid indigo dispersion. It could be clearly found that the D50 of the prepared liquid indigo dispersion with WPU2 dispersant was less than 500 nm, D90 was also less than 500 nm. Compared with powdered indigo dye, the K/S value of liquid indigo dispersion dyed fabric under the same conditions was about 11, which was twice that of powdered indigo dyed fabric. The UV resistance (UPF value) of the dyed fabric was about 272.72, which was triple that of powdered indigo dyed fabric, and its washing fastness was grade 3–4 and rubbing fastness was grade 4–5, demonstrating it also has excellent fastness like traditional powdered indigo, even slightly improved the staining fastness.