Dispersion of quinacridone pigments using cellulose nanofibers promoted by CH-pi interactions and hydrogen bonds

摘要

Organic pigments are prone to aggregate, resulting in decreasing of their properties. Therefore, pigment dispersants are demanded to have both high adsorption capacity and aggregation inhibiting property for pigment particles. In the present study, the suitability of cellulose nanofibers (CNFs) as a dispersant for quinacridone, a common red-violet organic pigment, was investigated. Quinacridone particles were well adsorbed on the CNFs. Scanning electron microscopy images of the quinacridone-CNF mixtures showed that the quinacridone primary particles were stacked along the cellulose fibers, and the aggregations were inhibited. In addition, the size of the quinacridone particles had an effect on their color. The interactions of quinacridone and cellulose were investigated by Fourier transform infrared (FTIR) and solution-state nuclear magnetic resonance (NMR) spectroscopies. FTIR spectra of the quinacridone-CNF mixtures indicated the intermolecular interactions between quinacridone and cellulose. Because quinacridone and CNFs were insoluble in the NMR solvents, gel-state NMR spectroscopy, which has been used for the whole plant cell wall analysis, was conducted on them. Consequently, whole signals arising from quinacridone and cellulose were enabled to be assigned, and the coupling constant of quinacridone has reported for the first time. The nuclear Overhauser effect spectroscopy (NOESY)-NMR spectrum of the quinacridone-CNF mixture revealed both NH group and aromatic moiety of quinacridone were interacted with glucose unit. The former was considered to be related to hydrogen bonding, and the latter to CH-pi interactions. These specific interactions might contribute to achieve the high adsorption capacity of CNFs for quinacridone. Graphic abstract