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

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 rheologi...

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Bibliographic Details
Published in:Cellulose (London) 2012-06, Vol.19 (3), p.647-659
Main Authors: Saarikoski, Eve, Saarinen, Tapio, Salmela, Juha, Seppälä, Jukka
Format: Article
Language:English
Subjects:
Bioorganic Chemistry
Cellulose
Cellulose fibers
Ceramics
Chemistry
Chemistry and Materials Science
Composites
Cylinders
Depletion
Disintegration
Flocculation
Glass
Natural Materials
Organic Chemistry
Physical Chemistry
Polymer Sciences
Rheological properties
Rheology
Shear rate
Shear stress
Shearing
Size distribution
Sodium chloride
Sustainable Development
Viscosity
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Summary: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.
ISSN:0969-0239
1572-882X
DOI:10.1007/s10570-012-9661-0