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Katarina Dimic-Misic, Kari Vanhatalo, Olli Dahl, Patrick Gane
Rheological properties comparison of aqueous dispersed nanocellulose derived from a novel pathway-produced microcrystalline cellulose or by conventional methods

Appl. Rheol. 28:6 (2018) 64474 (15 pages)

Novel-produced never-dried and dried microcrystalline cellulose (MCC) was previously compared with a commercial MCC. The novel MCC was shown to be a suitable starting material for producing cellulose nanofibrils, in turn having similar molecular weight Mw, crystallinity, and particle size comparable to those from sequentially enzymatic and mechanically treated softwood sulphite pulp, but at lower cost. The study here presents a rheological parameterisation of the aqueous suspension throughout the process, aimed at delivering a correlation between specific surface area, at equal material particle size, and adsorptive coupling between neighbouring cellulose particles and interstitial water under flow. We conclude that combining dynamic viscosity with an independent measure of particle size provides a suitable quality control of MCC-derived cellulose nanofibrils, obviating the need for individual property-raw material relationships to be evaluated, and this principle may provide a generalised method for use in the production of cellulose nanofibrils.

Cite this publication as follows:
Dimic-Misic K, Vanhatalo K, Dahl O, Gane P: Rheological properties comparison of aqueous dispersed nanocellulose derived from a novel pathway-produced microcrystalline cellulose or by conventional methods, Appl. Rheol. 28 (2018) 64474.

Katarina Dimic-Misic, Kaarlo Nieminen, Patrick A.C. Gane, Thad Maloney, Herbert Sixta, Jouni Paltakari
Deriving a process viscosity for complex particulate nanofibrillar cellulose gel-containing suspensions

Appl. Rheol. 24:3 (2014) 35616 (9 pages)

Phase-separable particulate-containing gel structures constitute complex fluids. In many cases they may incorporate component concentration inhomogeneities within the ensemble matrix. When formulated into high consistency suspensions, these can lead to unpredictable time-dependent variations in rheological response, particularly under shear in simple parallel plate and cylindrical rotational geometries. Smoothing function algorithms are primarily designed to cope with random noise. In the case studied here, namely nanocellulose-based high consistency aqueous suspensions, the system is not randomised but based on a series of parallel and serial spatial and time related mechanisms. These include: phase separation, wall slip, stress relaxation, breakdown of elastic structure and inhomogeneous time-dependent and induced structure re-build. When vacuum dewatering is applied to such a suspension while under shear, all these effects are accompanied by the development of an uneven solid content gradient within the sample, which further adds to transitional phenomena in the recorded rheological data due to spatial and temporal differences in yield stress distribution. Although these phenomena are strictly speaking not noise, it is nevertheless necessary to apply relevant data smoothing in order to extract apparent/process viscosity parameters in respect to averaging across the structural ensemble. The control parameters in the measurement of the rheological properties, to which smoothing is applied, are focused on parallel plate gap, surface geometry, shear rate, oscillation frequency and strain variation, and relaxation time between successive applications of strain. The smoothing algorithm follows the Tikhonov regularisation procedure.

Cite this publication as follows:
Dimic-Misic K, Nieminen K, Gane PA, Maloney T, Sixta H, Paltakari J: Deriving a process viscosity for complex particulate nanofibrillar cellulose gel-containing suspensions, Appl. Rheol. 24 (2014) 35616.


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