Application of kraft lignin as a colorant for screen printing on cotton

This study presents the concept of utilizing kraft lignin, a forest industry side-stream, as a pigment colorant for textiles. While there are some previous works on using dissolved lignin for textile coloring, lignin particles have not previously been used for screen printing and the effect of biobased binders on color fastness of lignin remains unexplored. To answer this research gap, we used printing pastes containing either ultrasonicated or ball-milled lignin particles or colloidal lignin nanoparticles to screen print on cotton fabric. The morphology and size of the different types of particles used were characterized. Chitosan and methyl cellulose were used as a biobased binder and thickener, respectively, in the pastes. The printed fabrics exhibited colors ranging from beige to brown and the surface morphology and color fastness properties including wash, rub and light fastness were investigated. Wash fastness results clearly indicated the significance of chitosan in binding the lignin particles to the fabric. Moreover, the binding of colloidal lignin nanoparticles to cellulosic surfaces using chitosan was demonstrated by adsorption kinetics measurements via quartz crystal microbalance. Light fastness tests indicated an initial darkening of the color over a short period and a consecutive fading of the color over a longer period.