A COMPARATIVE STUDY OF THE EFFECT OF REFINING ON FIBER CHARGE OF VARIOUS PULPS

Abstract

The aim of this work was to study the influence of beating on various pulp properties such as freeness, specific surface area, Specific volume, surface charge and total charge. The beating operation is conducted in PFI mill with various revolutions at 10% consistency of the pulp. The results indicated that specific surface area and specific volume of the pulps as determined by permeability tester increased and increased with beating. The fibre surface charge, as determined . by particle charge detector and titration with poly-DADMAC (Polydiallyldimethylammonium chloride), is also increased with beating. However, the total fibre charge, as determined by conductometric titration, is not affected by beating operation. It is also evident that increase in specific surface area of pulps by beating resulted in a higher fibre surface charge and also better fibre—fibre bonding. Water retention value (WRV) is a measure of fibre flexibility and swelling. Water retention value (WRV) as determined by centrifuge method, increased with beating. The classification of fibres gives the amount of fines get drained through fibres as determined by Bauer Mcett fibre Classifier._ Different paper properties are determined at different beating levels and how different pulps at various freeness levels affect the drainage was studied. The experimental data are subjected to statistical analysis from graphs and then subjected to statistical regression analysis. Least square techniques have been used to develop some linear univariate regression models, which are found to be very accurate as the regression coefficients, R2 are close to unity (on an average above 0.98) and the percentage error does not exceed in any case f 7%. The comparison of model predicted data and the experimental data and also the comparison of residuals and model predicted value shows an excellent agreement between them. Therefore statistical predictions are claimed to be very good and reproducible with a reasonable degree of accuracy permitted in engineering estimates. Therefore the statistical regression can be used reliably for analysis purposes. From the detailed analysis of data and their interpretation it can be certainly stated without any doubt that the surface area of fibres plays an important role in the bonding of the fibres. A large fibre surface area provided higher fibre surface charge and more areas for Fibre—Fibre contacts and, subsequently, more number of bonds is developed between fibres. The experimental results also showed strong linear correlations between the surface charge and the hand sheets properties.