This report appeared, in slightly different form, on P. 183 of the August 1992 Tappi Journal. It is reprinted here with the permission of Tappi Journal.
The Spring Grove, Pennsylvania, pulp and paper mill of the P. H. Glatfelter Company undertook research and development studies regarding alkaline sizing in the late 1960's. Management decided to switch to alkaline sizing for cost savings and better paper permanence.
The Spring Grove Glatfelter mill is over 100 years old and one of the industry's most profitable. Pine and hardwood chips are stored outside in piles. They are then bleached and digested for pulp to be used in the paper mill.
The switch to alkaline sizing was made on one machine at a time, starting in 1972 on a 30-year-old machine. The balance of the machines were converted by 1974. Most of P. H. Glatfelter's Spring Grove production is for quality hardbound books. Today, approximately 50,000 tons per day, at approximately 100 mills in the United States are being produced with alkaline sizing.
The trend from alum rosin to alkaline sizing can be explained by the better filler content loading, better brightness with calcium carbonate, and cost reductions in sizing.
The P. H. Glatfelter Company considered both ASA (alkenyl succinic anhydride) and AKD (alkyl ketene dimer) sizing methods. ASA sizing was chosen for its economic benefits and on-machine sizing control. The fact that calcium carbonate pigments were readily available began a new papermaking era in the United States.
The method of change involves adding alkaline sizing emulsions at or near the same point at which alum and rosin are added. The pH is then raised to 8 or more with the addition of caustic and calcium carbonate, as the alum and rosin are slowly backed out. This is the easiest part of conversion to alkaline sizing.
Once the change from alum rosin sizing to alkaline sizing is completed, there are many areas of concern. The ASA sizing conversion at Glatfelter in Spring Grove required review of the following concerns:
The choice of method depends upon the mills' products and the results desired. Calcium carbonate pigments are chosen with these and other factors in mind: scattering value, net titanium dioxide replacement value, and relative costs for alternate pigments. Handling costs must also be included.
The switch to alkaline ASA sizing at Glatfelter's Spring Grove, Pennsylvania, mill has been beneficial in many ways. There have been, of course, new learning requirements, but time has proven this alkaline conversion successful.