Permeability of pulp fiber mats with filler particles

We studied the permeability of fibrous media composed of filler particles in addition to fibers which are often encountered in industrial practice. Bleached Kraft pulp wood fibers and different kinds of fillers used in papermaking were the focus of this study. The fillers consisted of (i) scalenohedral precipitated calcium carbonate (PCC-Albacar), (ii) prismatic PCC (Albafil), and (iii) kaolin clay particles. The composite permeability increased with the addition of smaller quantities of PCC but higher loadings lowered the permeability significantly. The kaolin particles decreased the permeability of the pulp mats at all loading levels. The initial permeability increase observed with PCC was also accompanied by a simultaneous increase in the drainage rates of the pulps. The higher permeability is due to flocculation caused by heterocoagulation of PCC particles and the pulp fibers. At higher filler loadings, the PCC particles clog the pore spaces and reduce the permeability. Kaolin particles do not cause flocculation and hence decreased the permeability at all loadings. A model for the permeability of such composites was developed based on the Kozeny–Carman equation, considering the specific surface area as composed of two contributions. The first, due to fibers alone can result in lower specific surface areas caused by flocculation. The second contribution was an increase in surface area due to clogging of the fiber mats. The specific volume of the composite pulp mats was modeled as a simple weighted mixture of the specific volumes of the individual components.