Molecular Mechanisms Involved in Creep Phenomena of Paper, 1999 International Paper Physics Conference Proceedings

Anne-Mari Olsson, Lennart Salmén

The phenomenon of mechanosorptive creep was studied from a molecular point of view. Paper was tested in creep at different loading levels in a constant high humidity of 90 %RH and in a cyclic climate between 30 and 90 % RH. Throughout the creep tests spectra from mid and near IR as well as dynamic mechanical data were recorded to determine molecular changes occurring with time. The local, instantaneous, elastic modulus during the creep in constant and cyclic humidity was found to increase with time, more so for the cyclic humidity. This increase was suggested to be due to orientation of the cellulose molecules, detected from changes in the mid IR spectra at 1160 cm -1 , assigned to the C1-O-C4 stretching. The near IR measurements showed mainly differences in moisture content. In stress scans the moisture content increased with increased tensile load. Also in creep at constant 90 %RH the moisture content was found to increase in similarity with the stress scan. In the case of cyclic humidity with a conditioning time of 70 min at 90 %RH the moisture content decreased successively with the number of cycles.