Some Considerations on Measurement of the Beating Degree of Paper Pulp

Abstract

To compare the beating degree measured by various methods, and to investigate the changes of pulp properties caused by Lampen mill beating, softwood sulfite and kraft pulps and hardwood kraft pulp at various beating time were fractionated by Tappi Standard classifier. Each fraction was obtained on the wire of 12, 24, 40 and 80 meshes, and the effluent was collected on the 300 meshes wire to obtain the shortest fraction (Fr V). Canadian Standard freeness, water retention value and specific surface area by the permeability method of the fractionated pulp were measured at the various beating time.In regard to the freeness values of unbeaten pulps, there is little difference among the fractions except Fr V. Though the beating decreases rapidly freeness of the whole pulp, the freeness of Fr IIV of the beaten pulp remained at nearly the same level as that of Fr IIV of unbeaten pulp. Only Fr V showed relatively large decrease in freeness after the beating. The results of the fractionation of beaten pulps revealed that the freeness of beaten pulp was mainly dependent on the amount and the freeness of Fr V. The difference of pulp properties between the fractions of unbeaten and beaten pulps is clearly recognized by the measurement of the water retention value of pulps. As can bee seen from the linear correlation between specific surface area and freeness of various pulps, the results of both methods show the same tendency. Among these three methods, it could be said that the water retention value represents the relative difference of the pulp properties most characteristically. Kraft pulp has a higher resistance to the cutting action by beating than sulfite pulp. So there happens a different fiber length distribution corresponding to based on the type of pulp and the beating time. Summarizing the results described above the following conclusion is drawn that for the accurate evaluation of the properties of the beaten pulp, it is necessary to measure the yield and the water retention value of each fraction.