Synthesis of an amino-terminated waterborne polyurethane-based polymeric dye for high-performance dyeing of biomass-derived aldehyde-tanned chrome-free leather

An amino-terminated waterborne polyurethane-based polymeric dye (AWPUD) was synthesized for the high-performance dyeing of chrome-free leather tanned by biomass-derived aldehyde (BAT). Fourier transform infrared spectroscopy (FTIR) and ¹H NMR spectra illustrated the successful synthesis of AWPUD via incorporating small-molecule dyes (SMDs) (C.I. Acid Red 14) and sodium 2,4-diaminobenzenesulfonate into the polyurethane skeleton. The amino group content of AWPUD was tested to be 1.34 wt% (based on dry weight), which included 0.65 wt% of terminal amino groups. The characteristic absorption peaks of AWPUD were observed at 538 nm and 573 nm, similar to those of SMDs. AWPUD-dyed crust leathers exhibited better dyeing performances than SMD-dyed crust leather in terms of comparable dye penetration degree, lower chroma of wastewater, and higher filler-dye uptake ratio. In addition, AWPUD-dyed crust leathers had higher dyeing uniformity, dry-wet rubbing resistance, and thermal stability. Meanwhile, AWPUD-dyed crust leathers had better comprehensive physical properties in terms of higher mechanical strengths, comparable softness, and smooth grain surface. These results suggest that AWPUD has the great potential to be used in the high-performance dyeing of BAT-tanned leather.