Moisture sorption response of paper subjected to ramp humidity changes: Modeling and experiments

Moisture has a profound effect on the physical properties of paper and thus determines the performance characteristics of paper products including the so-called mechanosorptive effect where the creep behavior of paper is acce ntuated by cyclic humidity variations. Moisture transport in a paper sheet exposed to ramp changes in the external humidity has been studied. Our tran sport model considers a paper sheet as a composite medium of fibers and voi d spaces with moisture transported by diffusion through each one. Diffusion in the fibers is approximated by a lumped linear relaxation process. The i mportant dimensionless parameters consist of the Blot, fiber, and void diff usion numbers. A comparison of the model predictions with experimental tran sient moisture uptake of a bleached kraft paper board sample showed that a single value of the fiber relaxation parameter, k(i), was sufficient to giv e good estimates of transient moisture sorption data.