Mini-Encyclopedia of Papermaking Wet-End
Part Three: Equipment & Unit Operations
The word flocculation has two meanings. When used by colloidal chemists, the word implies a process by which either colloidal materials or other suspended materials are brought together by the action of high-mass polyelectrolytes. Usually the term flocculation implies a mechanism in which polyelectrolytes bridge between the suspended particles or fibers. When used by papermakers, the word flocculation also can mean the grouping of fibers into bunches that have enough strength to persist after flow is stopped. Flocculation occurs in shear flow due to the fact that wood fibers have a length-to-thickness ratio of about 50 to 100. The action of charge-neutralizing additives such as alum or polyamines tends to increase fiber flocculation by a modest amount. Severe flocculation can be caused by excessive use of very high-mass polyelectrolytes, i.e. retention aids.
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