THE APPARENT DENSITY OF PAPER

A model of paper structure is presented which combines the apparent density model of Gorres and Luner [1] with the orientation function of Kallmes and Corte [2]. The model predicts that the apparent density of paper increases with increased fibre orientation. Experimental sheets with different fibre orientations were formed on a laboratory dynamic sheet former using five mechanical pulps. The densities of the sheets increased with fibre orientation as predicted by the model. The basic fibre properties of the five mechanical pulps were determined and used as input into the modified Interactive Multi-Planar Model (IMPM). The model predicted lower density values than those measured experimentally. The results indicated the importance of mechanical pulp fines in the development of sheet structure, and they suggest that some assumptions, which are implicit in the model, need to be re-examined regarding their applicability with mechanical pulps.