Mini-Encyclopedia of Papermaking Wet-End
Part Two: Definitions and Concepts
The word coagulation means that fine particles in a suspension collide with each other and stick together. Usually the particles are brought near to each other by Brownian motion or by flow. Brownian motion is a random migration of particles due to collisions with solvent molecules. The rate of Brownian motion can be predicted from the temperature, the size of the particles, and the viscosity of the solution. Flow effects tend to overwhelm Brownian migration rates in the case of particles larger than 1 micro-meter. Factors which tend to make fine particles stick together after a collision include (a) lack of strong electrostatic or steric repulsive forces, (b) London dispersion forces, a type of Van der Waals force, and (c) polyelectrolyte bridges or patches. The presence of water-loving hemicellulose and cellulose macromolecules extending from papermaking fibers tends to weaken coaguation effects in papermaking suspensions.
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