Abstract
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 with the yield stress, a good data collapse was obtained. The observed similarities in the shear rheology of both the MFC suspensions and the similar behavior of some pulp fiber suspensions suggests that the shear rheology of MFC suspensions might be more universal than has previously been realized.
Highlights
Micro/nanofibrillated cellulose (MNFC) is currently a material of high interest due to its sustainability and biodegradability, and its unique properties such as mechanical robustness, barrier properties, high specific surface area, lightness, and complex rheology
The MNFC suspensions produced using only mechanical treatment differ in size and morphology from MNFC suspensions produced using chemical, enzymatic, or carboxymethylation pretreatments followed by mechanical treatment (Desmaisons et al 2017)
In addition to yield stress and shear viscosity, we study the slip behavior of the microfibrillated cellulose (MFC) suspensions, as this topic has hitherto been mostly neglected in the existing literature
Summary
Micro/nanofibrillated cellulose (MNFC) is currently a material of high interest due to its sustainability and biodegradability, and its unique properties such as mechanical robustness, barrier properties, high specific surface area, lightness, and complex rheology. The fibrils may differ in physical properties depending on the production method and/or the raw material source. The MNFC suspensions produced using only mechanical treatment differ in size and morphology from MNFC suspensions produced using chemical, enzymatic, or carboxymethylation pretreatments followed by mechanical treatment (Desmaisons et al 2017). There has been an explosive growth in MNFC research, including improved MNFC production technologies, surface functionalization, characterization techniques, composites processing, self-assembly, optical properties, and barrier properties. The applications of MNFC are already numerous, varying from a rheology modifier in cements, inks, drilling fluids and cosmetics, to a wide spectrum of products such as supercapacitors, transparentflexible electronics, batteries, barrier/separation membranes, and antimicrobial films (Klemm et al 2011; Isogai 2013; Moon et al 2016; Naderi 2017)
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