Lignins and Lignin Derivatives as Dispersants for Copper Phthalocyanine Pigment Nanoparticles

Copper phthalocyanine (CuPc) is a widely used organic blue pigment with color brilliance, light fastness, and low cost. However, its poor dispersibility in aqueous solutions limits the water-borne application. Lignin's hyperbranched polymer structure makes it a potential dispersant. In this study, lignin is functionalized with carboxylic acid (−COOH) and amine (−NH2) to enhance the interaction with aqueous solutions. Their applications as dispersants for CuPc in aqueous solutions are investigated together with commercially available alkali lignin, dealkali lignin, and lignosulfonate. The effectiveness of dispersion stability is evaluated by the suspension stability. Lignin-NH2 enhanced the suspension stability of CuPc to allow 94 wt % CuPc particles to remain suspended in water for 24 h compared to 24.4 wt % with no dispersant added. The mechanism of dispersion is revealed by the measurements of zeta potential and particle size, as well as the calculation of lignin adsorption amount on CuPc. Moreover, the lignins are applied to disperse CuPc in acrylic resin as a water-based paint application. With the aid of lignin-NH2 dispersant, CuPc enhances the tinting strength to 110.75% without altering the blue color through color difference measurements. Lignin-NH2 contributes to both better suspension stability and tinting strength than a commercially available dispersant dioctyl sodium sulfosuccinate (DOSS).