Flocculation of microfibrillated cellulose in shear flow

Anni Karppinen,Tapio Saarinen,Jukka Seppälä,Antti Laukkanen,Markus Nuopponen,Juha Salmela

doi:10.1007/s10570-012-9766-5

Anni Karppinen, Tapio Saarinen + Show 4 more

Open Access

https://doi.org/10.1007/s10570-012-9766-5

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Abstract

AbstractIn this work, the rheological properties of microfibrillated cellulose suspensions under stepped flow and constant shear were studied using a combination of rotational dynamic rheometer and digital imaging. During each rheological measurement, the structure of the suspension was monitored through a transparent outer cylinder with a digital camera. This enabled simultaneous analysis of the suspension floc size distribution and traditional rheological characterization. In stepped flow conditions, a good correlation between suspension floc structure and flow curve measurement was found. At constant shear, the suspension structure was dependent on the shear rate and concentration of the suspension. A low shear rate resulted in heterogeneous floc structure, which was also detected by an increase in the ratio of the viscous component to elastic component in the rheological measurement. At low concentrations and 0.5 s−1shear rate, flow induced a formation of floc cylinders between the rotating cylinder and stationary cup surface.

Highlights

Microfibrillated cellulose (MFC) is a unique nanomaterial that is prepared by the disintegration of wood or other cellulosic fibers into fibrils
The plateau in the flow curve at intermediate shear rates has been reported earlier for MFC (AgodaTandjawa et al 2010; Iotti et al 2011; Karppinen et al 2011), and it has been observed with different measuring geometries, like plate-and-plate (AgodaTandjawa et al 2010; Iotti et al 2011) and concentric cylinders (Karppinen et al 2011)
Some suspensions underwent network breaking in the flow curve at shear rate 5 s-1, and in these cases the floc size was much higher in the flow curve than after constant shear

Summary

Introduction

Microfibrillated cellulose (MFC) is a unique nanomaterial that is prepared by the disintegration of wood or other cellulosic fibers into fibrils. A low shear rate resulted in heterogeneous floc structure, which was detected by an increase in the ratio of the viscous component to elastic component in the rheological measurement. We use the photographing system combined with floc size analysis of the images to explain the shape of the flow curve at different MFC concentrations.

Results

Conclusion