Chemical Modification of Chemithermomechanical Pulps Part 1: Mechanical, Optical, and Aging Properties of Propionylated Spruce CTMP

Abstract

The effect of propionic anhydride on the optical, mechanical, and aging properties of hydrogen-peroxide-bleached spruce (Picea abies) chemithermomechanical pulp (CTMP) has been examined. The aging properties were evaluated using different aging conditions simulating aging behind window-glass, ambient storage (in the dark), and dry heat exposure. The propionylation treatment was carried out on paper sheets.

Chemical modification with propionic anhydride strongly reduced light-induced yellowing: Up to 80% of the discoloration (calculated from the post color number) could be hindered, although 50% of the free phenolic hydroxyl groups were still present in the propionylated sample. The stability against storage in the dark under ambient conditions (23°C, 50% relative humidity) or exposure to dry heat (105°C) was, however, not improved to the same extent. Propionylation did not extensively change the optical or dry strength properties of the treated paper sheets, whereas the wet tensile strength was substantially improved.