Stress Development in a Cellulose-Nanofibril-Containing Pigment Coating Layer during Drying

The effects of cellulose nanofibrils (CNFs) and carboxymethyl cellulose (CMC) on the shrinkage and surface characteristics of a pigment coating layer were compared. The shrinkage of the coating layer caused by evaporation of the aqueous phase during the drying process was measured using the beam-deflection method. CMC increased drying stress via rapid immobilization of the wet coating with precipitation of the CMC molecules. However, the coating that contained CNF had a much lower stress level because the coating layer experienced less shrinkage after the immobilization point and because of the diminished shrinkage characteristics of CNF in the length direction. The water-absorbent CNF formed a collapsed structure on the coating surface, resulting in lower gloss, because it was formed under low shear and dried at a low temperature. Coated paper made under high shear and at a high drying …