The Effect of Contact Time Between CPAM and Colloidal Silica on the Flocculation Behaviour in the Approach Flow, 2021 TAPPICon Live (21TAPL)

Multi-component wet-end systems have become increasingly common in papermaking with the objective of improving the retention-formation-dewatering relationship.  It is quite common to use at least a cationic polymer, often in combination with an anionic micro-particle.  In some cases, a fixative is also used.  However, there is still debate on the optimal implementation of these systems.  In particular, optimizing the contact time of the cationic polymer prior to addition of the anionic micro-particle is still poorly understood.  In this work, we investigate the effect of the contact time of a cationic polyacrylamide (CPAM) prior to addition of colloidal silica on the flocculation response in a flowing fiber suspension. The effect of using a fixative is also investigated.  Focused beam reflectance measurements (FBRM) are combined with z-potential measurements for optimizing the addition levels of a 2- and 3-component system, as well as for elucidating the effect of contact time on CPAM performance. Trials are then performed on a pilot scale flow loop, where the time between addition of these two components is varied and the resulting flocculation response characterized using high speed filming and image analysis techniques.  It is shown that the efficacy of CPAM can be improved significantly through use of a fixative and that a longer CPAM contact time may be beneficial in terms of flocculation, however hydrodynamic shear tends to dominate the flocculation response regardless of contact time due to floc rupture. 

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