Synthesis of blocked waterborne polyurethane polymeric dyes with tailored molecular weight: thermal, rheological and printing properties

Abstract

A series of polymeric dyes based on blocked waterborne polyurethanes (BWPUs) with varied molecular weights have been synthesized successfully. The influence of molecular weight on the thermal, rheological, and printing properties of the BWPUs are mainly investigated. The molecular weight of the BWPUs are tailored in the range of 2860–24 600 by selecting different chain lengths of polyethylene glycol (PEG0/400/600/1000/2000) as soft segments. The glass transition temperature (T_g) of the BWPUs decreased from 5.1 °C to −52.6 °C with increasing molecular weight of the soft segment, which implied a better film-forming property. Additionally, BWPUs with higher molecular weight offered better thermal stability. It is also found that BWPUs with a higher molecular weight show a more distinct shear thinning behavior and viscous behavior. The synthesized BWPUs were further applied in textile printing as both a colorant and adhesive to investigate their application performances. The printing viscosity index (PVI) values of all BWPUs pastes are below 0.3, suggesting that they are preferred for printing fine patterns on hydrophilic fibers. The color fastness of the printed cotton fabrics was found to be improved to 4–5 grade as the molecular weight of the BWPUs and baking temperature were increased. Consequently, the polymeric dyes could provide a novel route for obtaining high-quality printing products and shortening the textile coloring process.