Flocculated flow of microfibrillated cellulose water suspensions: an imaging approach for characterisation of rheological behaviour

Eve Saarikoski,Juha Salmela,Tapio Saarinen,Jukka Seppälä

doi:10.1007/s10570-012-9661-0

Eve Saarikoski, Juha Salmela + Show 2 more

Open Access

https://doi.org/10.1007/s10570-012-9661-0

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Abstract

Abstract Our aim was to characterise the suspension rheology of microfibrillated cellulose (MFC) in relation to flocculation of the cellulose fibrils. Measurements were carried out using a rotational rheometer and a transparent cylindrical measuring system that allows combining visual information to rheological parameters. The photographs were analyzed for their floc size distribution. Conclusions were drawn by comparing the photographs and data obtained from measurements. Variables selected for examination of MFC suspensions were degree of disintegration of fibres into microfibrils, the gap between the cylinders, sodium chloride concentration, and the effects of changing shear rate during the measurement. We studied changes in floc size under different conditions and during network structure decomposition. At rest, the suspension consisted of flocs sintered together into a network. With shearing, the network separated first into chain-like floc formations and, upon further shear rate increase, into individual spherical flocs. The size of these spherical flocs was inversely proportional to the shear rate. Investigations also confirmed that floc size depends on the geometry gap, and it affects the measured shear stress. Furthermore, suspension photographs revealed an increasing tendency to aggregation and wall depletion with sodium chloride concentration of 10−3 M and higher.

Highlights

Microfibrillated cellulose (MFC) water suspensions have been investigated since the 1980s when Turbak et al (1983) and Herrick et al (1983) reported a route for defibrillation of cellulose into its constituent components and suggested very promising applications in thickening foodstuff and suspending solids
We show how the degree of disintegration of fibres into microfibrils, the gap between the cylinders, sodium chloride concentration, and the effects of changing shear rate during the measurement are reflected in the floc structure and the suspension rheology
During the characterisation of microfibrillated cellulose water suspensions, rheological measurements were supplemented by visual examination of the floc structure

Summary

Introduction

Microfibrillated cellulose (MFC) water suspensions have been investigated since the 1980s when Turbak et al (1983) and Herrick et al (1983) reported a route for defibrillation of cellulose into its constituent components and suggested very promising applications in thickening foodstuff and suspending solids. Besides using MFC in suspension form, have been proposed in composites utilizing the transparency of the most defibrillated MFC grades (Ono et al 2001; Ono et al 2004; Saito et al 2006) and the low thermal expansion of fibrils in e.g. optoelectronics (Yano et al 2005). Even for these purposes, the manufacturing still includes steps in which the fibrils are in a suspension. Understanding how to control the rheological behaviour of MFC suspensions is crucial for fully exploiting the capabilities of the material

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