THE INFLUENCE OF THE BLEACHING MEDIUM ON CAUSTIC EXTRACTION EFFICIENCY .1. THE ROLE OF FIBER SWELLING

Delignification of a chlorine-dioxide-treated kraft pulp was inhibited when the alkaline extraction medium contained >50% (v/v) ethanol. Alk aline extraction experiments were performed with various media at a gi ven fibre swollen volume to determine if fibre deswelling caused the e ntrapment of lignin fragments. Extractions conducted with ethanol and aqueous BaCl2 solutions showed similar levels of delignification. Howe ver, extractions performed with aqueous NaCl solutions yielded conflic ting results. Estimates of the effective diffusion coefficients did no t differ appreciably among the media investigated Further analyses ind icated that the average lignin fragment diameter is smaller than the r educed average pore. width. These results suggested that factors other than fibre deswelling are responsible for the lower extent of deligni fication in ethanol-water and aqueous BaCl2 media.