THE EFFECT OF PH ON THE OPTICAL-PROPERTIES OF PAPER

Handsheets were made at four different pH levels ranging from 4 to 10 (and including the normal operating pH) from various mechanical and ch emical pulp furnishes obtained from several paper mills. The sheets we re dried using various temperatures, and their optical properties were measured. The brightness of sheets made from mechanical pulps decreas ed with increasing pH as a result of increased light absorption and de creased light scattering. A change of pH from 4 to 6, 8 and 10 caused a brightness drop of about 1, 2 and 4 points, respectively. No synergi stic effect between pH and drying temperature was observed. The bright ness of sheets made from bleached kraft pulp at pH 6, 8 and 10 was sim ilar and that of sheets made at pH 4 was slightly lower. Increased dry ing temperature had little effect on optical properties of kraft paper .