Effects of high treatment levels in a dry-strength additive program based on deposition of polyelectrolyte complexes : How much glue is too much?

Paper dry strength increased considerably when polyelectrolyte complexes deposited on fibers in large amounts. Substantial gains in breaking length were achieved through the sequential addition of balanced amounts of positively and negatively charged polymers to bleached kraft fibers. Strength increased strongly with increasing dosages up to 40%. The polymers were retained efficiently on the fibers even up to a level of equal amounts of polymer and fiber. The stickiness of undried paper handsheets increased with increasing polymer dosage, indicating practical upper limits. Other problems encountered at polymer dosages of 40% or more included polymer deposition onto the forming fabric, reduced dewatering rates, and reduced opacity of the paper. Results were affected primarily by the ratio of the two polymers and the manner in which the polyelectrolyte solutions were added. Application: Poly-DADMAC and CMC can be added in sequence to achieve stronger paper than possible with cationic starch.