1st Nordic Drying Conference - NDC'01, Trondheim, Norway, June 27-29, 2001

LIQUID REDISTRIBUTION PHENOMENA IN PULP AND PAPER SHEETS David Wessman, and Stig Stenström Chemical Engineering I, Chemical Center, Lund University, P.O. Box 124, SE-221 00 Lund, Sweden. E-mail: David.Wessman@kat.lth.se Keywords: liquid redistribution, pulp quality, capillary, moisture ratio ABSTRACT In an attempt to investigate the liquid redistribution phenomena, two test samples of kraft, sulfite, ground wood, recycled and thermomechanicalpulp differing in moisture content were placed together between two plates at a pressure of 10000 Pa. The basis weight of the test samples were 63-90 g/m2. Several combinations of pulps, contact times, temperatures and moisture ratios in the sample sheets were tested. The amount of redistributed liquid was determined gravimetrically. After approximately 1 hour no major changes in the moisture ratios were observed. Two sheets with initially two different moisture ratios did not reach the same moisture ratios even after 1 week. The liquid fluxes from a moist to a dryer sheet of the same quality were in the range of 0.3-0.09 g/m2s, regardless of the initial difference in moisture ratio used in the experiments. The redistribution seems to be independent of basis weight and difference in moisture ratio for the tested qualities. In combinations of different pulp qualities the unbleached kraft paper had a lower potential for redistribution than the bleached kraft paper but also a stronger influence on the liquid redistribution phenomena. The temperature dependence for the redistribution appears to follow the Lucas-Washburn relation for capillary transport.

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