The Mechanisms of Transport of Water and N-Propanol Through Pulp and Paper

Measurements have been made of transport rates of water, n-propanol, and mixtures of the two through samples of kraft pulp and filter paper. Comparison of the rates for the two components and the measured effects of temperature and relative humidity provide insight into the rate-limiting mechanisms of transport within these materials. Results show that gas-phase transport within pores and interstices dominates the mass-transfer process. Condensed-phase transport also occurs for water at high moisture contents, more so for paper than for pulp. The lesser contribution of condensed-phase transport for pulp may reflect the substantially lower bulk density of pulp. The dominance of gas-phase transport for pulp is also borne out by results of a second experiment, wherein pressure drops for gas permeation through pulp were measured following step changes in the humidity of the permeating gas.