Specific Surface Area - An Important Property of Mechanical Pulps, 1991 International Mechanical Pulping Conference Proceedings

Optical and mechanical properties of mechanical pulps are normally evaluated by testing unfilled laboratory handsheets. This method of evaluation may however be incorrect if the pulp is to be used in paper products with a high filler loading. This is particularly true of the optical properties, since these properties depend not only on the optical properties of the pulp and the filler, but also on the extent to which the structure of the sheet can be changed when fibers are replaced by filler. An example of a situation in which incorrect judgements can be made is in the evaluation of post-treated mechanical pulp fibers. Chemically post-treatment often leads to an increase in sheet density and a reduction in handsheet light scattering, but the increase in light scattering coefficient for a given amount of added filler is greater after the post-treatment because the specific surface area of the pulp measured in the pulp suspension before drying has been increased.

This paper describes the method of determining the specific surface area of a pulp suspension under wet conditions using the CP-cell technique (Compressibility-Permeability), and illustrates the importance of this specific surface area as a property of mechanical pulps intended for use in filler-containing papers.