Microfibrillated Cellulose Suspensions Research Articles

Enhancing the dispersibility of Gelidium amansii-derived microfibrillated cellulose through centrifugal fractionation

Hydrothermal pretreatment is useful for microfibrillated cellulose (MFC) preparation due to its safety, but the remaining hemicellulose might affect MFC properties. This study aimed to investigate the effect of centrifugation time on hemicellulose removal and the physicochemical properties of MFC obtained after hydrothermal pretreatment and micro-fibrillation. In this study, centrifugation was applied to the MFC suspension at varying duration times. Composition analysis and Fourier transform infrared spectra indicated that fractionated MFC has no hemicellulose content after 10, 20, and 30 min centrifugation. It also showed an approximately 5 times higher than 0.5 % g/g of initial solid concentration, indicated by a lower gel concentration point, than unfractionated MFC. Scanning electron microscope images of the fractionated MFC for 30 min (MFC2C) presented thin, long cellulose fibrils of 517 nm in average diameter and 635–10,000 nm in length that induced a slower sedimentation rate. MFC2C dispersion was also improved by autoclave sterilization by regulating cellulose structure, rheology, and crystallinity. As a result, MFC dispersibility can be enhanced by removing hemicellulose through simple centrifugation.

Microfibrillated cellulose (MFC) barrier coating for extending banana shelf life

This study evaluated, for the first time, the feasibility of using 100% microfibrillated cellulose (MFC) for a barrier coating to preserve the shelf life of bananas. MFC was produced from a commercial bleached kraft hardwood pulp through mechanical milling. Barrier coating was accomplished by dipping bananas into aqueous MFC suspensions. Performance of the barrier coating on the banana peel surface was evaluated from visual observations, weight loss, firmness, and dissolved soluble sugars content of the bananas. The results indicated that coating the banana peel surface with MFC delayed the browning and softening of the banana and the conversion of banana carbohydrates into soluble sugars. Furthermore, the extent of mechanical fibrillation in producing MFC affected MFC suspension wettability of banana peel surface, as well as the effectiveness of banana preservation. Casting-made MFC films were used to understand various factors of MFC barrier coating performance. The extent of MFC fibrillation was found to be more effective than increasing the amount of coating in reducing water vapor permeation for better fruit protection.

Enhancing the flexural properties of CFRP with vacuum-assisted deposition of cellulose microfibrils to create a multiscale reinforcement network

ABSTRACT Carbon fiber (CF) was coated with micro-fibrillated cellulose (MFC) using vacuum-assisted deposition in aqueous suspensions at concentrations of 0.1%, 0.2%, and 0.4%. The impact of distribution mesh configurations (DM arrangements) and fabric layer configuration on cellulose deposition was examined. Multiscale CF-MFC-Epoxy composites were created using resin infusion under flexible tooling, forming a 3D network of MFC between CFs that transferred stress and acted as a node at the intersection of 0–90 bundles. The addition of 0.1% MFC suspensions improved flexural properties, using no distribution media enhanced deposition and penetration efficiency, and drying stacked layers of CF fabrics improved load transference between them. This combination of parameters resulted in composites with a 16% increase in flexural modulus and 45% increase in flexural strength.

Characterizing lignin-containing microfibrillated cellulose based on water interactions, fibril properties, and imaging

Morphological characterization of microfibrillated cellulose (MFC) is critically important to process control in production and product specification for trade and product development yet is extremely difficult. This study evaluated several indirect methods for relative comparison of the morphology of lignin-free and lignin-containing ((L)MFCs). The (L)MFCs studied were produced using a commercial grinder through different passes from a dry lap bleached kraft eucalyptus pulp, a virgin mixed (maple and birch) unbleached kraft hardwood pulp, and two virgin-unbleached kraft softwood (loblolly pine) pulps with one bleachable grade (low lignin content) and one liner grade (high lignin content). The (L)MFCs were indirectly characterized using techniques based on water interactions, i.e., water retention value (WRV) and fibril suspension stability, as well as fibril properties, i.e., cellulose crystallinity and fine content. Optical microscopy and scanning electron microscopy were also applied to directly visualize the (L)MFCs to provide some objective measure of the morphology of the (L)MFCs. The results indicate that most measures such as WRV, cellulose crystallinity, fine content cannot be used to compare (L)MFCs from different pulp fibers. Measures based on water interactions such as (L)MFC WRV and suspension stability appeared can provide some degree of indirect assessment. This study provided the utilities and limits of these indirect methods for relative comparison of the morphologies of (L)MFCs.

High Content Microfibrillated Cellulose Suspensions Produced from Deep Eutectic Solvents Treated Fibres Using Twin-Screw Extruder

High Content Microfibrillated Cellulose Suspensions Produced from Deep Eutectic Solvents Treated Fibres Using Twin-Screw Extruder

A comparative study of the nonlinear rheological properties of three different cellulose nanofibril suspensions

This study focused on the nonlinear rheological characterization of three types of cellulose nanofibril (CNF) suspensions under large amplitude oscillatory shear (LAOS) flow. Three different CNFs were produced, two by mechanical fibrillation alone under different conditions [here named microfibrillated cellulose (MFC) and U-CNF] and the other by mechanical fibrillation after carboxymethylation (CM-CNF). MFC and U-CNF had broad width distributions, whereas CM-CNF had narrower fibril width and width distribution due to the presence of charged carboxymethyl groups. Nonlinear stress responses of the prepared suspensions were analyzed using the sequence of physical processes method. All CNF suspensions exhibited intracycle rheological transitions composed of three physical processes: (1) structure recovery, (2) elastic deformation to early stage yielding, and (3) late-stage yielding. MFC and U-CNF suspensions exhibited similar rheological transitions overall. However, CM-CNF suspension had a higher network recovery rate within a shorter time and showed an additional yielding step due to the complex interplay between recovery and yielding dynamics. This result originated from complete nanofibrillation and charged functional groups on fibril surfaces. Rapid reformation of effective fibril–fibril contacts in CM-CNF suspension was attributed to electrostatic repulsions and complete nanosized lateral dimensions. In addition, excitation frequency was found to influence intracycle rheological transitions. A range of intracycle rheological transitions became narrower on increasing frequency because the time period for each transition was not enough under faster flow conditions. In particular, the characteristic yielding step of CM-CNF suspension disappeared on increasing frequency, which suggested that high-frequency excitation might be unfavorable for the nonlinear viscoelastic characterization of soft materials under LAOS flow.

Microfibrillated cellulose films for mending translucent paper: an assessment of film preparation and treatment application options

Mending tears in translucent papers is a challenging task that requires mending materials with specific mechanical and optical properties. Recently, translucent films from microfibrillated cellulose have been suggested as an attractive alternative to traditional repair materials. We prepared custom films from a commercial microfibrillated cellulose suspension and compared their mechanical and optical properties as mending supports with commercially manufactured microfibrillated cellulose films and Japanese tissue. Tear mending of modern and historic translucent paper samples using the custom-made films and Klucel G or isinglass as adhesives showed satisfactory strength and resilience, and accelerated ageing tests yielded acceptable visual results. A case study on a translucent paper document from the collection of The National Archives, UK, is detailed. We conclude that custom-made tear mending materials from commercially available microfibrillated cellulose suspensions present a cost-effective and attractive approach for the mending of translucent papers.

Microdesigned Nanocellulose-Based Flexible Antibacterial Aerogel Architectures Impregnated with Bioactive Cinnamomum cassia.

This work is strategically premeditated to study the potential of a herbal medicinal product as a natural bioactive ingredient to generate nanocellulose-based antibacterial architectures. In situ fibrillation of purified cellulose was done in cinnamon extract (ciE) to obtain microfibrillated cellulose (MFC). To this MFC suspension, carboxylated cellulose nanocrystals (cCNCs) were homogeneously mixed and the viscous gel thus obtained was freeze-dried to obtain lightweight and flexible composite aerogel architectures impregnated with ciE, namely, ciMFC/cCNCs. At an optimal concentration of 0.3 wt % cCNCs (i.e., for ciMFC/cCNCs_0.3), an improvement of around 106% in compressive strength and 175% increment in modulus were achieved as compared to pristine MFC architecture. The efficient loading and interaction of ciE components, specifically cinnamaldehyde, with MFC and cCNCs resulted in developing competent antibacterial surfaces with dense and uniform microstructures. Excellent and long-term antimicrobial activity of the optimized architectures (ciMFC/cCNCs_0.3) was confirmed through various antibacterial assays like the zone inhibition method, bacterial growth observation at OD600, minimum inhibitory concentration (MIC, here 1 mg/mL), minimum bactericidal concentration (MBC, here 3-5 mg/mL), and Live/Dead BacLight viability tests. The changes in the bacterial morphology with a disrupted membrane were further confirmed through various imaging techniques like confocal laser scanning microscopy, FESEM, AFM, and 3D digital microscopy. The dry composite architecture showed the persuasive capability of suppressing the growth of airborne bacteria, which in combination with antibacterial efficiency in the wet state is considered as an imperative aspect for a material to act as the novel biomaterial. Furthermore, these architectures demonstrated excellent antibacterial performance under real "in use" contamination prone conditions. Hence, this work provides avenues for the application of crude natural extracts in developing novel forms of advanced functional biomaterials that can be used for assorted biological/healthcare applications such as wound care and antimicrobial filtering units.

Tailoring of rheological properties and structural polydispersity effects in microfibrillated cellulose suspensions

Industrial production of low-charge microfibrillated cellulose (MFC) typically results in wide fibril size distributions. This polydispersity influences viscosity, overall colloidal stability, and rheological properties of MFC suspensions and gels in aqueous systems. In this work, a systematic rheological analysis is performed for industrially prepared MFC and fractions of different size distributions. Gel formation and flow characteristics (e.g., shear-thinning) of each fraction are examined under neutral and acidic conditions and compared with the unfractionated MFC suspension. The effects of size, aspect ratio, and surface charge on the rheology of semi-dilute MFC suspensions are discussed. The results demonstrate that particle size and aspect ratio distribution control the viscoelasticity and shear-thinning properties of MFC suspensions. An increased fraction of small diameter nanofibrils, by ex situ addition of the fine particles with high aspect ratio or removal of the coarsest particles (with lower aspect ratio) by fractionation, significantly enhances the storage modulus and the yield stress of the complex mixture, compared to the properties of the coarser fractions. New insights are also reported on the tailoring of the rheology of highly polydisperse fibrillar mixtures, where the rheological contributions of each fraction are discussed.Graphic abstract

Microfibrillated Cellulose Suspension and Its Electrorheology.

Microfibrillated cellulose (MFC) particles were synthesized by a low-pressure alkaline delignification process, and their shape and chemical structure were investigated by SEM and Fourier transformation infrared spectroscopy, respectively. As a novel electrorheological (ER) material, the MFC particulate sample was suspended in insulating oil to fabricate an ER fluid. Its rheological properties—steady shear stress, shear viscosity, yield stress, and dynamic moduli—under electric field strength were characterized by a rotational rheometer. The MFC-based ER fluid demonstrated typical ER characteristics, in which the shear stresses followed the Cho–Choi–Jhon model well under electric field strength. In addition, the solid-like behavior of the ER fluid was investigated with the Schwarzl equation. The elevated value of both dynamic and elastic yield stresses at applied electric field strengths was well described using a power law model (~E1.5). The reversible and quick response of the ER fluid was also illustrated through the on–off test.

Pipe rheology of microfibrillated cellulose suspensions

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.

Deconstruction of microfibrillated cellulose into nanocrystalline cellulose rods and mesogenic phase formation in concentrated low-modulus sodium silicate solutions

This work demonstrates for the first time the deconstruction of microfibrillated cellulose (MFC) into rod-like cellulose nanocrystals (CNCs) in concentrated low modulus sodium silicate solutions. To this aim, MFC suspensions at different concentrations were first treated in sodium hydroxide solutions and then amorphous silica powder was added. Optical microscopy and transmission electron microscopy observation showed how MFC was efficiently deconstructed into CNCs, evidencing the occurrence of a phase separation into an isotropic and mesogenic phase. The extracted CNCs were characterized by a remarkably higher length (600–1200 nm) in comparison with the plant-derived ones commonly reported in literature. FT-IR spectroscopy and 29Si MAS NMR confirmed that the Qn equilibrium of the suspended silicate species was affected, proportionally to the amount of MFC. It was also shown, that due to the excluded volume effect exerted by silicate anions, nematic or smectic ordering could be achieved for CNC concentrations far below the critical rod concentration predicted by the Doi-Edwards model.

Rheology of microfibrillated cellulose (MFC) suspensions: influence of the degree of fibrillation and residual fibre content on flow and viscoelastic properties

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.

Rheological and Flocculation Analysis of Microfibrillated Cellulose Suspension Using Optical Coherence Tomography

A sub-micron resolution optical coherence tomography device was used together with a pipe rheometer to analyze the rheology and flocculation dynamics of a 0.5% microfibrillated cellulose (MFC) suspension. The bulk behavior of the MFC suspension showed typical shear thinning (power-law) behavior. This was reflected in a monotonously decreasing floc size when the shear stress exceeded the yield stress of the suspension. The quantitative viscous behavior of the MFC suspension changed abruptly at the wall shear stress of 10 Pa, which was reflected in a simultaneous abrupt drop of the floc size. The flocs were strongly elongated with low shear stresses. With the highest shear stresses, the flocs were almost spherical, indicating a good level of fluidization of the suspension.

The use of a pilot-scale continuous paper process for fire retardant cellulose-kaolinite nanocomposites

Nanostructured materials are difficult to prepare rapidly and at large scale. Melt-processed polymer-clay nanocomposites are an exception, but the clay content is typically below 5 wt%. An approach for manufacturing of microfibrillated cellulose (MFC)/kaolinite nanocomposites is here demonstrated in pilot-scale by continuous production of hybrid nanopaper structures with thickness of around 100 μm. The colloidal nature of MFC suspensions disintegrated from chemical wood fiber pulp offers the possibility to add kaolinite clay platelet particles of nanoscale thickness. For initial lab scale optimization purposes, nanocomposite processing (dewatering, small particle retention etc) and characterization (mechanical properties, density etc) were investigated using a sheet former (Rapid Köthen). This was followed by a continuous fabrication of composite paper structures using a pilot-scale web former. Nanocomposite morphology was assessed by scanning electron microscopy (SEM). Mechanical properties were measured in uniaxial tension. The fire retardancy was evaluated by cone calorimetry. Inorganic hybrid composites with high content of in-plane oriented nanocellulose, nanoclay and wood fibers were successfully produced at pilot scale. Potential applications include fire retardant paperboard for semi structural applications and as reinforcement mats in molded thermoset biocomposites.

Influence of shear rheometer measurement systems on the rheological properties of microfibrillated cellulose (MFC) suspensions

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.

Experimental investigation of the flow dynamics and rheology of complex fluids in pipe flow by hybrid multi-scale velocimetry

A hybrid multi-scale velocimetry method utilizing Doppler optical coherence tomography in combination with either magnetic resonance imaging or ultrasound velocity profiling is used to investigate pipe flow of four rheologically different working fluids under varying flow regimes. These fluids include water, an aqueous xanthan gum solution, a softwood fiber suspension, and a microfibrillated cellulose suspension. The measurement setup enables not only the analysis of the rheological (bulk) behavior of a studied fluid but gives simultaneously information on their wall layer dynamics, both of which are needed for analyzing and solving practical fluid flow-related problems. Preliminary novel results on rheological and boundary layer flow properties of the working fluids are reported and the potential of the hybrid measurement setup is demonstrated.

Analysis of rheology and wall depletion of microfibrillated cellulose suspension using optical coherence tomography

A rheometric method based on velocity profiling by optical coherence tomography (OCT) was used in the analysis of rheological and boundary layer flow properties of a 0.5% microfibrillated cellulose (MFC) suspension. The suspension showed typical shear thinning behaviour of MFC in the interior part of the tube, but the measured shear viscosities followed interestingly two successive power laws with an identical flow index (exponent) and a different consistency index. This kind of viscous behaviour, which has not been reported earlier for MFC, is likely related to a sudden structural change of the suspension. The near-wall flow showed existence of a slip layer of 2–12 μm thickness depending on the flow rate. Both the velocity profile measurement and the amplitude data obtained with OCT indicated that the slip layer was related to a concentration gradient appearing near the tube wall. Close to the wall the fluid appeared nearly Newtonian with high shear rates, and the viscosity approached almost that of pure water with decreasing distance from the wall. The flow rates given by a simple model that included the measured yield stress, viscous behavior, and slip behavior, was found to give the measured flow rates with a good accuracy.

Substrate role in coating of microfibrillated cellulose suspensions

Interest in nanocellulose-based coatings for packaging applications has been growing due to their excellent oil and gas barrier properties combined with their sustainable, recyclable, biodegradable, and non-toxic nature. Coating of nanocellulose materials such as microfibrillated cellulose (MFC) on paper/paperboard is challenging compared to traditional paper coating materials due to excessively high viscosity and yield stress of MFC suspensions at rather low solids content, typically below 5%. Possessing large amounts of water and a distinct rheological behavior such suspensions set tough demands on the substrate to be coated. It is important to understand and quantify substrate requirements in order to coat these suspensions successfully and achieve a satisfactory coating quality. A custom-built slot geometry is used herein to enable coating of highly viscous MFC suspensions on different paper-based substrates in a roll-to-roll process. The impact of substrate properties, such as surface chemistry and surface energy, surface roughness and surface porosity, and water absorption capacity on MFC coatability and coating quality is reported. Coating adhesion to the substrate was quantified with surface strength testing of MFC coated substrates. Various techniques, such as Scanning Electron Microscopy, IGT print penetration tests, and air permeability tests were employed for measuring coating coverage and surface porosity. MFC coating was found to adhere best to a highly hydrophilic surface, whereas the most uniform and defect-free film at low coat weights was formed on a smooth surface. It was also found that the MFC coat weight needed for full coverage, and therefore potentially good barrier, needs to exceed the surface roughness volume of the substrate. Water absorption capacity of the substrate also determines the final MFC coating quality obtained. The results clearly highlight the role of paper-based substrate for successful and effective coating of the micro and nanocellulose suspension.

Novel aqueous spongy foams made of three-dimensionally dispersed wood-fiber: entrapment and stabilization with NFC/MFC within capillary foams

This article describes the preparation of novel aqueous spongy foams that are composed of three-dimensionally distributed wood-fiber networks stabilized with nanofibrillate cellulose (NFC) and/or microfibrillated cellulose (MFC). The free standing aqueous spongy foams were prepared with the entrapment of NFC and/or MFC—stabilized air-in-water (A/W) capillary foams using “gel trapping technique”. The stability of spongy foams could be controlled by manipulating the volume fraction of NFC and/or MFC and a secondary liquid immiscible with the continuous phase of the NFC and/or MFC suspension. Possible morphology and mechanical distribution of NFC and/or MFC within spongy foams were verified with optical microscope, SEM, and functional load-bearing method. Owing to three-dimensionally dispersed wood-fiber structure, ultra-lightweight (0.01–0.06 g/cm3), high porosity (>90%), and microporous (10–80 μm), the NFC and/or MFC reinforced spongy foams, improved compressional strength-vertical direction obviously, from 0.0 to more than 13.78 kPa.