Thesis (M.Sc.) - Asian Institute of Technology

A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science

Paper formation has become an ever-important parameter in controlling strength properties of paper. Even though there has been some studies on this topic much of the things are unclear for softwood kraft pulp. In this study effect on formation was studied based on fiber fractionation. Unrefined as well as refined Finnish bleached softwood kraft pulp was fractionated using Bauer-McNett fiber classifier into four different fiber length groups. The fine fraction passing through 200-mesh screen was not collected. PFI refined pulp was used to represent the commercial paper making conditions as well as to see the effect of refining on formation where unrefined pulp was used to investigate the effect of formation on strength properties of natural fiber without any treatment. Handsheets in standard laboratory and headbox consistency were made from each unrefined fraction and the effect of formation on physical properties was measured. Refined fiber fractions were used to make standard laboratory handsheets and the effect of formation on strength properties were measured, there by compared the results with unrefined standard laboratory handsheet results. Different fiber fractions were mixed together to achieve a specific length weighted fiber length of a single fraction and results obtained by making standard laboratory and headbox consistency handsheets were compared to see the effect of coarseness on formation and there by the effect on strength properties. Paper with better formation demonstrated higher strength properties. Opposite relationship has achieved by the tear strength. Light scattering coefficient also improves with reducing fiber length where it also responds to the formation improvements in positive way. Increasing pulp consistency has adversely effect on formation and all the strength properties were suffered. Mixing different fiber fractions to achieve a specific fiber length has improved all the strength properties and also the light scattering coefficient, which is a very good sign to improve strength properties by mixing shorter fiber fractions with longer fibers. Mixing as short fibers as possible with longer fibers will pronounced the effect.