bonding between cellulosic fibers in the absence and presence of dry-strength agents - a review

Various hydrophilic polyelectrolytes, including cationic starch products, are used by papermakers to promote inter-fiber bonding and increase paper’s dry-strength. Thus, papermakers can meet customer require-ments with a lower net cost of materials, more recycled fibers, or higher mineral content. In the absence of polymeric additives, key mechanisms governing bond development between cellulosic fibers include capillary action, three-dimensional mixing of macromolecules on facing surfaces, conformability of the materials, and hydrogen bonding. Dry-strength additives need to adsorb efficiently onto fibers, have a hydrophilic character, and have a sufficiently high molecular mass. Though it is possible to achieve significant strength gains by optimal usage of individual polyelectrolytes, greater strength gains can be achieved by sequential addition of oppositely charged polyelectrolytes. Superior strength can be achieved by in-situ formation of polyelectrolyte com-plexes, followed by deposition of those complexes onto fiber surfaces. Polyampholytes also hold promise as efficient dry-strength additives. Opportunities for further increases in performance of dry-strength agents may involve fiber surface modification, self-assembled layers, and optimization of the dry film characteristics of dry-strength polymers or systems of polymers.