Cationic cellulose nanofibers with efficient anionic dye adsorption: adsorption mechanism and application in salt-free dyeing of paper

Cationic modification of cellulose fibers is an effective strategy to improve the absorptive capacity of anionic dyes and promote wastewater treatment. In this study, cationic cellulose nanofibers (CCNFs) with different degrees of substitution (DS) were prepared by grafting cellulose fibers with 2, 3-epoxypropyltrimethylammonium chloride (EPTMAC) and homogenizing. The synthesized CCNFs were employed in salt-free dyeing of ultra-lightweight paper. It showed that the maximum adsorption capacity of CCNFs for anionic dye was 1281.74 mg/g, and the dye uptake was as high as 90% under mild conditions without NaCl. Dyeing adsorption dynamics and isotherm analyses revealed that the dyeing process was monomolecular chemical adsorption. Moreover, compared with the control group and blank group, the dyed ultra-lightweight paper added with CCNFs not only had better color fixation and dye uptake, but also possessed higher breaking stress. This study fully confirmed the great potential of CCNFs in the salt-free dyeing of cellulose.