Characterization of friction during pulping: An interesting tool to achieve good deinking

A parameter the shear factor has been introduced to characterize the effect of friction forces in a Helico pulper It is defined by mathematical analog y, as the viscosity of a Newtonian fluid that would require the same power consumption as a pulp suspension. The shear factor has been evaluated for s everal conditions of repulping of virgin pulp, old newspaper and old magazi ne grade. The results show that the lower the shear factor, the slower the ink fragmentation and ink redeposition kinetics, which would lead to better ink removal by flotation.