Modification of fiber passage ratio model in order to assess OCC pulp fiber length fractionation using pressure screen

Fractionation is an efficient process to produce more uniform pulp from the initially non-uniform OCC pulp and consequently improve paper strength properties. In this study, the previous screening model (fiber passage ratio model) used in virgin pulp screening to predict fractionation efficiency and pulp consistency changes, extended for OCC pulp fractionation. As fiber length fractionation and consistency changes are related to volumetric reject ratio by fiber passage ratio, so here, the effects of several key variables i.e. volumetric reject ratio, screen aperture velocity, and pulp type on P(l) were determined.The new modified equations calculated by using of experimental P(l) obtained in OCC pulp fractionation have more accuracy in predicting above variables effects on fiber length fractionation and consistency changes. In comparison with virgin pulp, OCC have lower fractionation efficiency and higher reject thickening factor. It was shown that fiber length fractionation and reject thickening factor increase with increasing volumetric reject ratio.