Rheological Behavior of Cellulose Fiber Suspensions: Application to Paper-Making Processing (original) (raw)
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Rheology of pulp fibre suspensions: A critical review
Chemical Engineering Science, 2011
This paper reviews past studies on the measurement of rheological properties of pulp fibre suspensions. Such suspensions are complex fluids important in the manufacture of many pulp-fibre based products, such as communication papers, hygiene products, packaging, as well as other fibre-based materials. Pulp suspensions play a role in other biomass conversion processes as well. This review focuses on key properties
This paper reviews past studies on the measurement of rheological properties of pulp fibre suspensions. Such suspensions are complex fluids important in the manufacture of many pulp-fibre based products, such as communication papers, hygiene products, packaging, as well as other fibre-based materials. Pulp suspensions play a role in other biomass conversion processes as well. This review focuses on key properties of fibre suspensions, such as regimes of behaviour based on inter-fibre contact, apparent yield stress, apparent viscosity, and viscoelasticity. Difficulties encountered in measurement of these properties due to flow regime changes, heterogeneous mass distribution, and formation of depletion layers at solid boundaries is discussed and methods to overcome them are reviewed.
Pipe rheology of microfibrillated cellulose suspensions
Cellulose
The shear rheology of two mechanically manufactured microfibrillated cellulose (MFC) suspensions was studied in a consistency range of 0.2–2.0% with a pipe rheometer combined with ultrasound velocity profiling. The MFC suspensions behaved at all consistencies as shear thinning power law fluids. Despite their significantly different particle size, the viscous behavior of the suspensions was quantitatively similar. For both suspensions, the dependence of yield stress and the consistency index on consistency was a power law with an exponent of 2.4, similar to some pulp suspensions. The dependence of flow index on consistency was also a power law, with an exponent of − 0.36. The slip flow was very strong for both MFCs and contributed up to 95% to the flow rate. When wall shear stress exceeded two times the yield stress, slip flow caused drag reduction with consistencies higher than 0.8%. When inspecting the slip velocities of both suspensions as a function of wall shear stress scaled wi...
Cellulose, 2018
The influence of the degree of fibrillation (DoF), i.e. the fibril width distribution, on the rheological properties of microfibrilated cellulose (MFC) suspensions was investigated. To extend the understanding of the dominating effect of either fibril diameter alone or diameter size distribution, flow curves (viscosity against shear rate) and viscoelastic measurements were performed on single, double and ternary component mixtures of medium and highly fibrillated MFCs and pulp fibres across a range of solids content. The data were quantified using classical and recently introduced descriptors, and presented in comprehensive 3D/ternary contour plots to identify qualitative trends. It was found that several rheological properties followed the trends that are generally described in the literature, i.e. that an increasing DoF increases the MFC suspension network strength. It was, however, also found that coarse pulp fibres can have additional effects that cannot be explained by the increased fibril widths alone. It is hypothesised that the increased stiffness (directly caused by the larger fibril width) as well as the reduced mobility of the pulp fibres are additional contributors. The data are discussed in relation to recent findings in the field of rheology and related morphological models of MFC suspension flow behaviour.
Cellulose, 2017
Flow curve and viscoelastic measurements were performed on microfibrillated cellulose (MFC) suspensions of different solids content using both cylinder and cup (smooth and rough) as well as vane in cup geometries. To compare the data quantitatively from amplitude sweep measurements and dynamic flow curves several descriptors were newly introduced to parameterize the observed two-zone behaviour separated by a transition region. It was observed that the cylinder cup geometries are prone to erroneous effects like slip, wall depletion and/or shear banding. However, those effects were not observed when the MFC suspension was not stressed beyond the dynamic critical stress (yield) point, i.e. when still in the linear viscoelastic regime. The vane in cup system on the other hand, seems to be less affected by flow inhomogeneities. By following the rheological properties as a function of the MFC suspension solids content, it could be shown that the global property trends remained alike for all investigated measurement systems, despite the presence of erroneous effects in some geometries. The observed effects were linked to recent model hypotheses in respect to the morphology of MFC suspensions under changing shear situations.
Polymer Engineering & Science, 2021
Processing of concentrated lignocellulosic biomass suspensions typically involves the conversion of the cellulose into sugars and sugars into ethanol. Biomass is usually preprocessed (i.e. via comminution, steam explosion, etc.) to form fine cellulosic fibers to be dispersed into an aqueous phase for further treatment. The resulting cellulose suspensions need to be pressurized and pumped into and out of various processing vessels without allowing the development of flow instabilities that are typically associated with the "demixing", i.e., the segregation of the cellulosic biomass from the aqueous phase. Here, it is demonstrated that the use of a gelation agent, hydroxypropyl guar gum (HPG) at the relatively low concentration of 0.5 wt% significantly affects the development of viscoelastic material functions of cellulosic suspensions, and improves the dispersive mixing of the cellulose fibers within the aqueous phase. This results in the reduction of the flow instabilities and associated demixing effects that are ubiquitously observed during the pressurization of cellulosic suspensions in Poiseuille and compressive squeeze flows.
The vane method and kinetic modeling: shear rheology of nanofibrillated cellulose suspensions
Cellulose, 2014
We conduct rheological characterization of nanofibrillated cellulose (NFC) suspensions, a highly non-Newtonian complex fluid, at several concentrations. Special care is taken to cope with the prevalent problems of time scale issues, wall depletion and confinement effects. We do this by combining the widegap vane geometry, extremely long measurement times, and modeling. We take into account the wide-gap related stress heterogeneity by extending upon mainstream methods and apply a gap correction. Furthermore, we rationalize the experimental data through a simple viscous structural model. With these tools we find that, owing to the small size of the particles subjected to Brownian motion, the NFC suspensions exhibit a critical shear rate, where the flow curve experiences a turning point. This makes the steady state of these suspensions at low shear rates non-unique. To optimize various mixing and pumping applications, such history dependent tendency of NFC suspensions to shear band needs to be taken into account. Keywords Rheology Á Nanofibrillated cellulose Á Modeling Recently, chemical (Saito et al. 2006) or enzymatic (Pääkkö et al. 2007) pretreatments have been developed to introduce new surface properties to the fibers and to enhance the fibrillation process. Flow properties of NFC suspensions are important for the applications, storage, and processing of the material. NFC suspensions are strongly shear-thinning and their viscosity is dependent on the concentration (
Viscoelastic properties and flow instabilities of aqueous suspensions of cellulosic fibers
2019
Processing of concentrated lignocellulosic biomass suspensions typically involves the conversion of the cellulose into sugars and sugars into ethanol. Biomass is usually preprocessed (i.e. via comminution, steam explosion, etc.) to form fine cellulosic fibers to be dispersed into an aqueous phase for further treatment. The resulting cellulose suspensions need to be pressurized and pumped into and out of various processing vessels without allowing the development of flow instabilities that are typically associated with the "demixing", i.e., the segregation of the cellulosic biomass from the aqueous phase. Here, it is demonstrated that the use of a gelation agent, hydroxypropyl guar gum (HPG) at the relatively low concentration of 0.5 wt% significantly affects the development of viscoelastic material functions of cellulosic suspensions, and improves the dispersive mixing of the cellulose fibers within the aqueous phase. This results in the reduction of the flow instabilities and associated demixing effects that are ubiquitously observed during the pressurization of cellulosic suspensions in Poiseuille and compressive squeeze flows.
Shear rheology of diluted solutions of high molecular weight cellulose
Journal of Applied Polymer Science, 1986
A steady-state and dynamical rheological study was performed with dilute solutions (1-4%) of high molecular weight cellulose (M, = 350,000). The solutions are strongly viscoelastic. The steady-state viscosity and the first normal stress difference have a power law dependence on the shear rate. T h e power law indices have the same dependence on temperature and concentration. These results as well as the correlation between the steady-state viscosity and the real part of the complex viscosity are in good agreement with the Spriggs model. The 4% concentrated solution shows the beginning of a rubber-like storage modulus plateau, suggesting the existence of an entanglement network. EXPERIMENTAL Materials Menoufi cotton cellulose (DP 2000) was dewaxed by alcohol-benzene extraction. MMNO from Texaco was purified by recrystallization of the monohy
Rheological characterization of fibrillated cellulose suspensions via bucket vane viscometer
Cellulose, 2014
This paper discusses the practical application of a bucket vane viscometer in the characterization of novel nanofibrillated cellulose suspensions. Specifically, we use two different grades of nanocellulose, Masuko grinded and TEMPO oxidized ones. We work at the consistency range of 1-2.3 % w/w. We find, in agreement to more accurate rheometer based experiments, that both these materials behave in a highly non-linear manner. Thus, as we discuss in this paper, using a wide gap device necessitates the use of a correction algorithm in the conversion of the angular velocity to global shear rate to access the materials intrinsic, geometry independent, flow behavior. Furthermore, from the application viewpoint, we find that the classically measured low shear rate viscosity is not a good quantity to characterize these materials.