STUDIES OF ANISOTROPIC PERMEABILITY WITH APPLICATIONS TO WATER REMOVAL IN FIBROUS WEBS .2. WATER REMOVAL AND OTHER FACTORS AFFECTING PERMEABILITY

An extensive set of data for in-plane and transverse permeability of p aper to water has been obtained In Part 1, experimental methods and da ta were presented on anisotropic permeability in paper, as well as the relation between freeness and Darcian permeability. Part 2 presents a dditional data on the effects of water removal on sheet permeability i ncluding the effect of recycling. Drying a wet sheet of never-dried fi bers to above 70% solids permanently increases the permeability of the fibers through hornification. Lower levels of water removal by wet pr essing (or mild blotting and air drying) can also increase sheet perme ability. This change may represent a temporary collapse of fibrils and rearrangement of fines by capillary forces. Also presented are data o n the effect of fines content and the role of basis weight in measured sheet permeability. Included is a discussion on the nature of anisotr opic permeability the factors that cause it, and their implications fo r the papermaking process.