Molecular Mechanisms Involved in Creep Phenomena of Paper

摘要

The phenomenon of mechanosorptive creep (i.e., the increasing creep occurring in some hygroscopic materials subjected to moisture cycling) was studied for paper form a molecular point of view. Paper was tested in creep at different loading levels in a constant high humidity of 90% relative humidity (RH) and in a cyclic climate between 30 and 90% RH. Throughout the creep ests, spectra from the mid- and near-IR, as well as dynamic mechanical data, were recorded to determine molecular changes occurring with time. In tensile stress scans the instantaneous, dynamic elastic modulus was found to increase. It is suggested that this increase was due to orientation of the cellulose molecules, which was detected as changes in the mid-IR spectra at 1160 cm~(-1) assigned to the C_1-O-C_4 stretching. During creep in constant and cyclic humidity, the modulus was found to increase with time, more so for the cyclic humidity. Changes in the mid-IR spectra at 1184 and 1030 cm~(-1), which is assigned to CH_2, CH, and C-O, may indicate sliding between the celluose chanis. The near-IR measurements mainly showed differences in the mositure content. In stress scans the moisture content increased with increasing tensile load. In creep at constant 90% RH, the moisture content was also found to increase in a manner similar to the stress scan. In the cyclic humidity with a conditioning time of 70 min at 90% RH the moisture contentdecreased sucessively with increasing numbers of cycles.