Deposition of cationic polymeric pigments on pulp fibers

Abstract

The potential advantage of using cationic pigments as wet-end additives in papermaking is in their expected ready deposition on anionic pulp fibers. The deposition characteristics of cationic polystyrene latex particles onto pulp fibers in a stirred system provide an information of the general behavior. The deposition proceeds at maximum rate in the pH region where the latex particles and the fibers have electrophoretic mobility of opposite sign. A departure from the expected behavior is observed in the pH region of latex destabilization. The failure of the coagulating latex to deposit indicates that hydrodynamic forces (introduced by mixing) acting on latex aggregates may prevent a deposition. An addition of neutral salt to the stirred system after deposition of latex particles was completed may result in a partial removal of latex particles from the fibers. The explanation for this reversible deposition is sought in an interplay of attractive forces between latex particles and fiber, the distance of their closest approach, and the size of particles upon which the hydrodynamic forces act. The behavior suggests that although the mutual attraction promotes deposition an intimate contact between latex particles and fiber is not established.