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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.

Michel Schenker, Joachim Schoelkopf, Patrick Gane, Patrice Mangin
Quantification of flow curve hysteresis data . a novel tool for characterising microfibrillated cellulose (MFC) suspensions

Appl. Rheol. 28:2 (2018) 22945 (13 pages)

A novel method is introduced to describe quantitatively hysteresis seen in flow curves of microfibrillated cellulose suspensions. Also, a data normalisation procedure is presented that allows a direct comparison of data from suspensions of different solids contents. The discussion of the flow curve hysteresis of an MFC suspension is proposed to provide a lot of information on the suspension morphology under flow. Such information is not only useful for process design, but also may serve as a quality control tool. Hysteresis data as a function of the suspension solids content are provided, and considered with reference to an overview made of peer work in the field. Two discrete hysteresis loop areas were found in the flow curves presented in this work, each associated with a distinct shear rate region, one where the viscosity of the flow curve during shear rate increase is higher than that of the shear rate flow curve at decreasing shear rate (named positive hysteresis) and another where it is the opposite (named negative hysteresis). This behavior seems to have been rarely reported, and where reported we offer an explanation, based on morphological models and rheometer measurement set up, as to why other researchers may find a variety of hysteresis forms. It is hypothesised that the negative normalised hysteresis is mainly depending on the excessive flocculation/ structuration induced at intermediate shear rates during the shear rate increase, and that it is necessarily less with increasing solids content because of the reduced availability of free water. The positive normalised hysteresis, however, is considered to originate from the different morphologies at lower shear rates, i.e. the initial, homogeneous structure vs. the structure that was previously induced by the intermediate shear during shear rate decrease. The positive normalised hysteresis appears not to depend on the solids content, indicating a self-similarity or scaling behavior of the structuring with respect to the underlying network structure.

Cite this publication as follows:
Schenker M, Schoelkopf J, Gane P, Mangin P: Quantification of flow curve hysteresis data . a novel tool for characterising microfibrillated cellulose (MFC) suspensions, Appl. Rheol. 28 (2018) 22945.

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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