Mini-Encyclopedia of Papermaking Wet-End
Part Two: Definitions and Concepts
The pH is the negative logarithm (base ten) of the hydrogen ion concentration in a solution. An increase of one pH unit implies a ten-fold increase in hydrogen ion concentration. At a neutral pH of 7 there are equal numbers of hydrogen ions and hydroxyl ions. The value of pH has a profound influence in papermaking because it affects the ionic character of fibers and many additives. Fibers tend to become increasingly anionic as the pH is increased in the range 3 to 8. Papermakers' alum is strongly cationic under acidic papermaking conditions (3.5 < pH < 5.5), but it quickly loses its cationic charge after addition to alkaline furnish (7 < pH < 9). The acidity of a furnish equals the amount of strong base such as NaOH needed to raise the pH to 8.3.
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