Alternative methods to evaluate flocculation of particles in papermaking suspensions

When dealing with papermaking fibre suspensions, particle aggregation takes place already before the paper web is formed. The particle aggregation depends on several aspects including particle mass concentration (consistency), particle collisions, electrochemical interactions promoted by chemical additives, etc. Due to its importance, fibre suspension aggregation (or flocculation) has been studied for a long time in papermaking, and several methods have been developed for this purpose. The traditional techniques include e.g. Focused Beam Reflectance Microscopy (FBRM) and High Speed Video Imaging (HSVI). Recently, a new optical method, Optical Coherence Tomography (OCT) has emerged for flocculation and aggregation analysis. The advantages of OCT are the possibility to study opaque suspensions, its micron-level resolution and its high data acquisition speed. OCT measurements can be combined with rheological measurements, allowing simultaneous measurement of both the time evolution of the aggregate size and the suspension viscosity. In this work, we used this approach to study the flocculation of suspensions of various papermaking furnishes. We analyzed the time evolution of the aggregate size and the fibre suspension viscosity when the studied papermaking suspensions were treated with a Highly Refined Furnish (HRF, this furnish contains a significant amount of MFC type fibrils) together with chemical additives. We show how such studies can lead to a better understanding of the impact of flocculation on the produced paper web on such quantities as formation, drainage potential and strength behavior.