Penetration of high-charge cationic polymers into silica gel particles and cellulosic fibers

The gradual penetration of positively charged polymeric additives below the outer surfaces of cellulosic fibers can play an important role in the selection of addition points and optimization of chemical dosages on a paper machine. The present work was undertaken to help understand the role of high and low-molecular-mass fractions of a cationic polyelectrolyte, in determining the charge behavior of the outer surfaces of fibers. Commercial polyelectrolyte samples typically contain a broad range of molecular masses. A dialysis procedure was used to selectively remove the low-mass fraction of poly-diallyldimethylammonium chloride (poly-DADMAC) from aqueous solutions of the polymer. Only cationic polymer samples having a very-low-mass component exhibited penetration into the interior spaces of silica gel, which has a well-defined, narrow pore size distribution. The presence of low-mass components of the polymer also affected the electrical potential associated with the outer surfaces of solids treated with high-mass poly-DADMAC. Preliminary observations showed related behavior in the case of cellulosic fibers. The wide range of time required for measured streaming potential values to decrease to zero, depending on the amount of poly-DADMAC added at time zero, was consistent with a gradual diffusion of the macromolecules below the outer surfaces of the fibers.