PCC Fillers for Groundwood Papers, 1991 Papermakers Conference Proceedings

Paper produced from mechanical pulps has been traditionally made under acidic papermaking conditions because of "fiber alkaline darkening" that occurs as pH is increased. The degree of darkening depends on many chemical and physical variables including pulp type, wet end pH, and water quality. Because precipitated calcium carbonate (PCC) and other calcium carbonate fillers normally buffer wet end pH in the 7.5 - 8.2 range, excessive fiber darkening has precluded their use in most wood containing grades.

Now a new, "acid-tolerant" form of PCC has been developed that readily allows PCC to be used at pH 5.0 - 7.0 on the papermachine. This new PCC can be used in groundwood papers without significant fiber darkening. This permits the papermaker to cost-effectively utilize the very high brightness and opacity attainable with PCC compared to traditional groundwood paper fillers. Some experiences with specific groundwood grades are illustrated.