Retention aids for high-speed paper machines

The use of microparticles in retention-aid systems is a well- established practice. Bentonite clays and silica particles are widely used as flocculants. The problem is that increasing machine speeds create higher shear forces that break the flocs and impair retention. Consequently, chemical suppliers are continually searching for ways to increase floc strength. A fifth generation of colloidal silica microparticles is now being used in retention systems designed for the intense shear conditions that exist in highspeed gap formers. Used in concert with cationic polymers or starches, these particles help create smaller, denser, and much stronger flocs. Developments in microparticle technology over the past five years have broadened the range of potential applications to include the more challenging papermaking systems, including lightweight coated papers, supercalendered papers, recycled test liner and recycled corrugated board. Five case studies highlight the potential for gains in productivity, product quality, and cost efficiency for papermakers who have modified their retention strategies to include this latest generation of colloidal silica microparticles.