Stress Development in a Cellulose-Nanofibril-ContainingPigment Coating Layer during Drying

The effects of cellulose nanofibrils (CNF) 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 temperature showed fewer surface defects because the CNF gel structure was destroyed under the high-shear condition.