Synthesis of blocked and branched waterborne polyurethanes for pigment printing applications

A series of blocked and branched waterborne polyurethanes (BBPUs) have been successfully synthesized and applied in pigment printing of cellulosic substrate. The branched structure was based on an “A2 + CB2” approach with diisocyanate prepolymer and diethanol amine. The terminal isocyanate groups were blocked by sodium bisulfite to lower curing temperature and improve the color fastness. The prepolymerization and chain extending could be considered as the end at 70°C after 90 min and at 80°C after another 90 min, respectively. It was suitable for sodium bisulfite to block isocyanate groups at 0°C–5°C for 40 min. The microphase separation of BBPU based on the longest polyethylene glycol (PEG) soft segment appeared. Both curing rate and pencil hardness of BBPU films distinctly reduced as the molecular mass of PEG soft segment ascended. The moisture rate increased from 18.1% to 49.2% with increasing the molecular weight of PEG, indicating that water resistance of the film became poor. Excellent acid and alkali resistances of the BBPU films were obtained. Color fastness to washing, rubbing, and light of the printed cotton fabrics was remarkably enhanced as the BBPU amount ascended to 10% which were cured at 85°C for 6 min.