Preparation of sulfomethylated lignin grafted by pyrrolidone for utilization as a dispersant in nano pigment paste

In this work, sulfomethylated lignin (SAL) was firstly synthesized using alkali lignin (AL) as raw materials, and then grafted with pyrrolidone as adsorption groups to prepare sulfomethylated lignin grafted by pyrrolidone (SALN). Results showed that SALN had a lower sulfonic group content than SAL but additionally contained 0.79 mmol/g of pyrrolidone groups. SAL and SALN were separately used as dispersants to prepare 20 wt% of cobalt blue nano pigment paste, and the minimum particle size of 82 nm and 52 nm was achieved when the dispersant dosage was 10 wt% and the grinding time was 4 h. After 7 days of thermal storage at 60 °C, the particle size of nano pigment paste prepared by SALN nearly remained unchanged, but that prepared by SAL increased from 82 nm to 285 nm, and there was obvious precipitation. Therefore, the thermal storage stability of cobalt blue nano pigment paste prepared by SALN was much better than that of SAL. Adsorption isotherm and infrared spectra experimental results indicated a firm multi-point anchoring complexing adsorption was formed between the pyrrolidone group of SALN and Co–O on cobalt blue surface, which made SALN not easy to desorb during collisions caused by Brownian motions. SAL was adsorbed through –C(=O)O−, and thus easy to desorb. Therefore, the stability of the nano pigment paste prepared by SALN was superior to that of SAL.