Homogeneity of Kraft Pulps, 2000 Pulping / Process & Product Quality Conference Proceedings

J. Iribarne, L. R. Schroeder--Several authors have suggested that the higher strength of laboratory and liquor-displacement kraft pulp, when compared to conventional kraft pulp, is partly due to the higher homogeneity of the former. However, recent studies indicate that the distribution of lignin in single fibers is mainly controlled by chip size, suggesting that pulps from the same chip source should be equally homogeneous. The differences between mill and laboratory pulps were studied after a fractionation procedure. Four hydrocyclone stages followed by Bauer-McNett separation split the pulps into twelve fractions with distinct fiber length and coarseness. Kappa number did not change with fiber coarseness, while CED viscosity increased. Longer fibers were generally associated with higher CED viscosities, lower apparent densities and higher wet zero-span tensile indices. There were no consistent differences between the fiber lengths and CED viscosities of mill and laboratory pulp fractions. In general, mill pulp fractions had higher fiber coarseness and lower apparent densities than their laboratory counterparts, as well as somewhat higher kappa numbers. Estimated fiber strengths were higher in almost all laboratory pulp fractions than in the corresponding fractions of mill pulps. The fiber strength deliveries of all pulp fractions were similar, indicating that fiber strength loss in the mill pulping operations was relatively uniform. Within the resolution of the experiments, the laboratory pulps did not appear to be more homogeneous than the mill pulps.