Direct measurement of rheological properties of microfibrillated cellulose using different measurement techniques

Fiber suspensions, such as MFC (Micro Fibrillated Cellulose), are a challenge for conventional rheometers. The cause of these problems is due to rheometer small flow channel dimensions that may restrict flocculation and due to often-questionable assumptions of the fluid behavior in the gap. One can instead use a pipe rheometer in combination with UVP-PD concept (Ultrasound Velocity Profiling - Pressure Difference) where the real flow behavior is used for the rheological analysis of the bulk properties of the suspension. Unfortunately the resolution of UVP is too low for studying near-wall phenomena, such as lubrication layer, that are often very important for understanding the rheology and to upscale the results to industrial flows. To address this problem we have widened the UVP-PD concept with OCT (Optical Coherence Tomography) measurements. This enables us to measure both the bulk and the wall-layer behavior simultaneously. Our results demonstrate the benefits of having direct detailed measurement of the velocity profile inside the rheometer.