The Dispersion Science of Papermaking

Paper is one of the most important inventions in the history of civilization, and it is an essential commodity to all people in the world. The fact that we make ubiquitous use of a score of paper products makes it easy to underestimate its value and significance. This review is intended to put into perspective the dispersion science involved in papermaking and to describe how our understanding of key processes has evolve since its conception, approximately 2000 years ago, from art to science. Paper is formed from a slurry of fibers and much smaller particles that are often called “fines” and other chemical additives. Ahead of the paper forming process the slurry is subjected to a series of steps, including treatment with polyionic species and passage through unit operations that impose shear forces on the papermaking suspension. These steps alternately disperse the solids apart or re-gather them back together. The overall process is optimized to achieve a highly uniform product, while at the same time achieving high efficiency in retaining fines in the sheet and allowing water to drain relatively quickly from the wet paper as it is being formed. As we approach the 1900-year anniversary of the first detailed account of the papermaking process, it is the goal of this review to explore the scientific principles that underlie the art of papermaking, emphasizing the state of dispersion of the fibrous slurries during various stages of the manufacturing process. Some concepts that arise out of the experience of papermakers have potential applications in other