STUDIES OF FLOCCULATION IN CELLULOSE FIBER SUSPENSIONS BY NMR IMAGING

In this study the effects of retention aids on the flow behaviour of p ulp suspensions were investigated using flow-encoded nuclear magnetic resonance (NMR) imaging. A cationic polymer and a two-component microp article system were studied. Both axial velocity profiles and pressure drops were measured simultaneously as a function of the mean bulk flo w rate after addition of retention aid. The shear stress at the fibre plug surface was also determined. It is demonstrated that, at low flow rate adding polymeric flocculant to a dilute hardwood fibre suspensio n can induce a slip velocity between the dense fibre aggregates and th e remainder of the suspension. Introducing retention aids at fully tur bulent flow results in the formation of plug flow immediately after th e addition. The disruption of fibre networks flocculated by retention aids was also monitored as a function of the shearing time at constant flow rate.