Effect of cationic PVA characteristics on fiber and paper properties at saturation level of polymer adsorption

The characteristics of dry strength additives affect their efficiency in improving fiber bonding. In this work, the influence the charge density and molecular weight, MW, of cationic poly (vinyl alcohol), CPVAs, in improving the strength of papers was investigated at equilibrium level of CPVA adsorption. In the case of CPVAs with the charge density of 0.75 meq/g, the small CPVAs (hy < 8 nm) did not alter the paper properties, though they adsorbed more than the large CPVAs. The large CPVAs (hy > 8 nm) improved the paper properties to some extent, but the hydrodynamic size of CPVAs did not affect their efficiency in improving the paper properties. Also, the low-charged (0.4 meq/g) high molecular weight (MW) CPVA improved the paper properties more than the high-charged high MW ones, even though the total charges introduced to fibers were less by applying low-charged CPVA than by applying high-charged ones. Similar trends were obtained by adsorbing various CPVAs on refined fibers. However, the properties of papers made from unmodified refined fibers were generally superior to those of papers made from CPVA-modified refined fibers, probably due to the coverage of fibrils on the fiber surface.