Recovered Kraft Fibers and Wet-End Dry-Strength Polymers, 2005 Papermakers Conference

The drying and recycling of paper profoundly affects the bulk and surface properties of kraft fibers. Recovered kraft fibers tend to be less porous on a sub-microscopic scale, less flexible, and less able to swell with water, compared to never-dried, refined fibers. Recovered fibers also tend to be less able to form inter-fiber bonds. This review considers how changes associated with the drying and recycling of kraft fibers affect their interactions with dry-strength polymers such as cationic starch, copolymers of acrylamide, and high-charge cationic polymers. A key finding of recent research is that the listed changes in fiber properties occur independently of whether or not dry-strength polymers are present. There are two main ways that strength-enhancing additives can compensate for losses in bonding ability. First, drystrength polymers present in the original paper can contribute to bonding when the same material is recycled. Second, additional wet-end polymers applied during production of the recycled paper can help compensate for deficiencies of bonding ability. Recently a dual-polymer dry-strength program was adjusted to match the ability of recovered kraft fibers to retain cationic polymers. This approach makes it possible to tailor a treatment system to the type of furnish that is being used.