Flocculation of cellulose fibre suspensions: the contribution of percolation and effective-medium theories

The concept of crowding factor applied to the flocculation of cellulose fibres is revisited through the application of percolation and effective medium theories. It is shown that, even if the crowding factor allows predicting the critical concentration of fibre suspension above which flocculation occurs, and indeed leads to acceptable results in most cases, percolation and effective medium theories are most rigorous and much less empirical. Examples of calculation are given for fibres assumed to behave either like rigid rods or like elongated prolate ellipsoids, and compare very correctly with experimental measurements found in the literature. Finally, beyond the purely geometrical aspects, the roles of several physico-chemical parameters on the onset of flocculation are also discussed, and shown to be perfectly explained by percolation predictions.