THE EFFECT OF PAPER FORMATION AND GRAMMAGE ON ITS PORE-SIZE DISTRIBUTION

The pore size distribution in paper, measured by fluid permeation perp endicular to the plane of the sheet, is known to be approximately logn ormal with standard deviation proportional to the mean. Also, this cor responds quite well to the polygonal size distribution arising from a random array of lines in a piano, which may be approximated using the negative exponential distribution for inter-crossing distances in rand om networks. We use the gamma distribution to generalize to the distri bution of inter-crossing distances in flocculated networks and so obta in a family of pore size distributions indexed by the degree of floccu lation in the network. This new analytic work helps understand the hit herto-explained observation that the standard deviation of pore size i ncreases with the mean for manifestly non-random papers, when measured by laminar flow. A comparison with data from the literature is provid ed. Coefficients of variation of free-fibre-length and pore radius bot h increase with flocculation but decrease with increasing grammage.