Adsorption kinetics of dyes and yellowing inhibitors on pulp fibers

The yellowing of mechanical pulps is a major drawback that limits them mainly to the production of lower value products. To prevent the yellowing, one method consists in applying specific molecules, yellowing inhibitors, directly onto the pulp. Yellowing inhibitors can be added in the pulp stock, on the wet-web or even at the size press of the papermaking process. The affinity of yellowing inhibitors for pulp and their adsorption kinetics are important in the determination of the optimal process strategy. It is the objective of this study to quantify the adsorption of inhibitors on pulp and to elucidate their adsorption mechanism.First, a method for characterising the affinity of model yellowing inhibitors for pulp has been tested. Two inhibitors were used: a sulfonated inhibitor and a quaternary ammonium inhibitor.The sorption of two dyes was investigated to elucidate the adsorption mechanism. Brilliant yellow, an anionic direct dye, has a low affinity for pulp fibers while toluidine blue, a cationic basic dye, has a high affinity for pulp fibers. (Abstract shortened by UMI.