Fiber Suspensions Research Articles

Encapsulation of precipitated calcium carbonate fillers using carboxymethyl cellulose /polyaluminium chloride: preparation and its influence on mechanical and optical properties of paper

Inorganic fillers are usually used in papermaking industry to reduce production costs and enhance paper optical properties. As an attempt to improve fillers application in papermaking, carboxymethyl cellulose (CMC) and poly aluminum chloride (PAC) were used to encapsulate precipitated calcium carbonate (PCC) filler and modify its surfaces. In the first step, the optimum conditions for filler treatment (i.e. pH, CMC and PAC contents) were obtained. Through the second step, different amounts of CMC-encapsulated PCC were added to fiber suspension and some hand-sheets were made. Then, the effect of modified filler addition in different levels of 20, 25, and 35% on mechanical and optical properties of paper was investigated. The PAC dosage was found to be a critical factor for effective encapsulation of PCC fillers by carboxymethyl cellulose. When the dosages of CMC and PAC were 4% and 0.8% (based on the dry weight of PCC), respectively, filler modification caused to improve significantly the retention by more than twice. Strength properties of the hand-sheets fabricated with the CMC/PAC-modified PCC were also found to be significantly better than those obtained with the unmodified PCC at similar levels of filler content. In addition, the brightness and opacity of the filled papers at 30% addition of CMC-modified fillers were strikingly enhanced to 88.45 and 77%, respectively. SEM observations of the filled papers also demonstrated that CMC-encapsulated filler particles were clustered and retained efficiently onto the fiber network. The present method for modification of PCC may provide an alternative approach to increase the filler amount in the paper structure by alleviating filler drawbacks.

Rheological Behavior of Tomato Fiber Suspensions Produced by High Shear and High Pressure Homogenization and Their Application in Tomato Products.

This study investigated the effects of high shear and high pressure homogenization on the rheological properties (steady shear viscosity, storage and loss modulus, and deformation) and homogeneity in tomato fiber suspensions. The tomato fiber suspensions at different concentrations (0.1%–1%, w/w) were subjected to high shear and high pressure homogenization and the morphology (distribution of fiber particles), rheological properties, and color parameters of the homogenized suspensions were measured. The homogenized suspensions were significantly more uniform compared to unhomogenized suspension. The homogenized suspensions were found to better resist the deformation caused by external stress (creep behavior). The apparent viscosity and storage and loss modulus of homogenized tomato fiber suspension are comparable with those of commercial tomato ketchup even at the fiber concentration as low as 0.5% (w/w), implying the possibility of using tomato fiber as thickener. The model tomato sauce produced using tomato fiber showed desirable consistency and color. These results indicate that the application of tomato fiber in tomato-based food products would be desirable and beneficial.

The use of principal spatial tensor to predict anisotropic fiber orientation in concentrated fiber suspensions

The Phelps-Tucker anisotropic rotary diffusion (ARD) equation constitutes an important development in relation to concentrated fiber suspension rheology and is significant in its ability to predict transient, flow-induced fiber orientation, especially for long fiber composites in the industry. Within this model, a critical spatial tensor was assumed to be a polynomial tensor-valued function depending on both the orientation tensor and the rate-of-strain tensor. However, it can be difficult to derive a large number of fitting ARD parameters. For simplification, we newly defined the spatial tensor as coaxial with the orientation tensor's principal directions, while the spatial tensor's principal components are to control anisotropic changes in the orientation tensor. Such a principal spatial tensor used in the Phelps-Tucker ARD model is demonstrated in accurately predicting the shell-core structure of fiber orientation distributions for injection molding simulation of long fiber composites, supported with e...

Key role of anionic trash catching system on the efficiency of lignocellulose nanofibers in industrial recycled slurries

The processing of recycled paper into packaging materials is becoming one of the most important activities of paper mills. However, the use of recycled paper as a raw material causes an important increase of dissolved colloidal substances in industrial waters, known as anionic trash, which greatly increases water conductivity and cationic demand disturbing the function of commonly used retention agents (cationic starch, cationic polyacrylamides). On the other hand, several investigators showed that lignocellulosic nanofibers (LCNF) can be used as reinforcement in papermaking, but their retention can be affected by anionic trash. This work aims to study the technical viability of the application of triticale straw lignocellulose nanofibers in recycled fiber suspensions at industrial scale. For this purpose, a complex retention system of LCNF was proposed to improve the reinforcement efficiency of LCNF. Results show that, with the addition of only 1.5% (w/w) of LCNF, it is possible to fulfill the physical–mechanical requirements of the commercial test liner, and the addition of 4.5% of LCNF would allow the reduction of basis weight and additives or the development of applications with higher mechanical requirements.

Numerical simulation and visualization of fiber suspension in a turbulent round jet

The turbulent properties of the fiber suspension in a turbulent round jet are numerically simulated and visualized, and some of the results are compared with the experimental data. The effects of the Reynolds number, fiber volume fraction, and aspect ratio are analyzed. The results show that the fiber injection in the flow has a delay effect on the streamwise velocity decay along the jet axis, and such an effect becomes more obvious with the increases in the fiber volume fraction and aspect ratio and the decrease in the Reynolds number. The flow with fibers shows an increase in the streamwise velocity along the radial direction, and the increase magnitude is directly proportional to the fiber volume fraction and aspect ratio and inversely proportional to the Reynolds number. The presence of fibers makes the turbulent kinetic energy and Reynolds stress increase, and the extent increases with the fiber volume fraction, Reynolds number, and fiber aspect ratio.

Correction to: Effect of various refining processes for Kenaf Bast non-wood pulp fibers suspensions on heat transfer coefficient in circular pipe heat exchanger

Heat transfer coefficients were obtained for a range of non-wood kenaf bast pulp fiber suspensions flowing through a circular pipe heat exchanger test loop. The data were produced over a selected temperature and range of flow rates from the flow loop. It was found that the magnitude of the heat transfer coefficient of a fiber suspension is dependent on characteristics, concentration and pulping method of fiber. It was observed that at low concentration and high flow rates, the heat transfer coefficient values of suspensions were observed higher than that of the heat transfer coefficient values of water, on the other hand the heat transfer coefficient values of suspensions decreases at low flow rates and with the increase of their concentration. The heat transfer were affected by varying fiber characteristics, such as fiber length, fiber flexibility, fiber chemical and mechanical treatment as well as different pulping methods used to liberate the fibers. Heat transfer coefficient was decreased with the increase of fiber flexibility which was also observed by previous researchers. In the present work, the characteristics of fibers are correlated with the heat transfer coefficient of suspensions of the fibers. Deviations in fiber properties can be monitored from the flowing fiber suspensions by measuring heat transfer coefficient to adjust the degree of fiber refining treatment so that papers made from those fibers will be more uniform, consistent, within the product specification and retard the paper production loss.

Characteristics and environmentally friendly extraction of cellulose nanofibrils from sugarcane bagasse

This study reports an environmentally friendly process to prepare cellulose nanofibrils (CNFs) from sugarcane bagasse (SCB), by ultrasonication combined with various mechanochemical pretreatments. The pretreatments included continuous steam explosion, dilute alkali-catalyzed (0.4wt% NaOH) hydrothermal treatment, and bleaching with hydrogen peroxide. The morphology and physiochemical properties of the fibers obtained after each stage of treatment were characterized by various techniques. Suspensions of fibers subjected to different pretreatments were prepared by the same mechanical process. The result proved that continuous steam explosion pretreatment could strip the primary wall and the binding materials related to middle lamella, loosen the structure of fiber cell wall, and promote sequent nanofibrillation of the cellulose fibers. Therefore, the total energy consumption is reduced. The current pretreatments effectively removed non-cellulosic constituents of the raw fibers, using very small amount of chemical reagents. Individual CNFs typically had diameters of 20–40nm, high aspect ratios, a fine web-like structure, and good thermal stability.

Simplified bead-chain model for direct fiber simulation in viscous flow

For efficient simulation of the motion of fibers during processing of fiber-reinforced thermoplastics, we propose a simplification of the bead-chain model (BCM), in which each fiber is modeled as a chain of spheres. The proposed simplified bead-chain model (SBCM) solves only one equation of translational motion, whereas the BCM requires three equations. The effects of bending and hydrodynamic torques, which are considered in the equation of rotational motion in the BCM, are expressed in the SBCM by adding terms to the equation of translational motion, although twisting motion is ignored. The validity of the SBCM is examined by comparing the results of both models when simulating the behavior of a single fiber and fiber suspensions in a simple shear flow. The SBCM provides results comparable to those of the BCM with lower computation time. This suggests that the SBCM could be an efficient alternative to the BCM.

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.

From dilute to entangled fibre suspensions involved in the flow of reinforced polymers: A unified framework

Most suspension descriptions nowadays employed are based on Jeffery model and some of its phenomenological adaptations that do not take into account the possible existence of a relative velocity between the fibres and the suspending fluid when the fibre interactions increase. It is expected that at very low density of contacts, as predicted by standard suspension models, fibres move with the suspending fluid velocity. When the density of fibre interactions becomes extremely high and a percolated network of fibre contacts is established within the suspension, fibres cannot move anymore and then the fluid flows throughout the rigid or moderately deformable entangled fibre skeleton, like a fluid flowing through a porous medium. In between these two limit cases, one could expect that fibres move but with a velocity lower than the one of the suspending fluid. Thus, two contributions are expected, one coming from standard suspension theory in which fibres and fluid move with the same velocity, and the other resulting in a Darcy contribution consisting of the relative fibre/fluid velocity. In this paper, we elaborate a general model able to adapt continuously to all these flow regimes.

Effect of various refining processes for Kenaf Bast non-wood pulp fibers suspensions on heat transfer coefficient in circular pipe heat exchanger

Effect of various refining processes for Kenaf Bast non-wood pulp fibers suspensions on heat transfer coefficient in circular pipe heat exchanger

Electrophoretic deposition of fiber hydroxyapatite/titania nanocomposite coatings

Hydroxyapatite/titania nanocomposite coatings were electrophoretically deposited from ethanolic suspensions of titania and fiber shaped hydroxyapatite (FHA) nanoparticles. Triethanolamine (TEA) was used to enhance the colloidal stability of particles in suspensions. Electrophoretic deposition (EPD) was performed using the suspensions with different concentrations (wt%) of titania/FHA particles. EPD rate decreased more rapidly with time for suspensions with higher wt% of FHA due to the higher voltage drop over the deposits shaped from them. Stacking of long FHA particles on the substrate during EPD resulted in the formation of coarse pores in the deposits. It was found that titania nanoparticles can more efficiently infiltrate through and fill the pores in TEA containing suspensions due to the stronger electrostatic repulsion force between pore walls (FHA) and titania nanoparticles in them. The coatings deposited from the suspensions with 50wt% of FHA or more did not crack during drying due to the significant reinforcement action provided by high wt% of FHA in them. Nanocomposite coatings deposited from TEA containing (2mL/L) suspensions with 50 and 75wt% of FHA had the best corrosion resistance in simulated body fluid (SBF) solution due to their crack-free microstructure and efficiently filled pores.

The influence of consistency and fibre length on the yield stress of OCC pulp fibre suspensions

The effect of fibre length on the yield stress of recycled old corrugated containers (OCC) pulp fibre suspensions was investigated. Two types of OCC pulps were divided into four fractions based on the fibre length with a Bauer-McNett classifier. The yield stress of each fraction was measured using the shear stress ramp method at pulp consistency ranging from 0.5% to 2.5% (w/v). The results showed that both pulp consistency and fibre length had significant effects on the yield stress of OCC pulp suspensions, and the yield stress was greater with increasing fibre length and pulp consistency. Moreover, the effect of consistency in OCC pulp suspension with long fibres on the yield stress was stronger than in the slurry with short fibres.

Flow-induced gelation of microfiber suspensions

The flow behavior of fiber suspensions has been studied extensively, especially in the limit of dilute concentrations and rigid fibers; at the other extreme, however, where the suspensions are concentrated and the fibers are highly flexible, much less is understood about the flow properties. We use a microfluidic method to produce uniform concentrated suspensions of high aspect ratio, flexible microfibers, and we demonstrate the shear thickening and gelling behavior of such microfiber suspensions, which, to the best of our knowledge, has not been reported previously. By rheological means, we show that flowing the suspension triggers the irreversible formation of topological entanglements of the fibers resulting in an entangled water-filled network. This phenomenon suggests that flexible fiber suspensions can be exploited to produce a new family of flow-induced gelled materials, such as porous hydrogels. A significant consequence of these flow properties is that the microfiber suspension is injectable through a needle, from which it can be extruded directly as a hydrogel without any chemical reactions or further treatments. Additionally, we show that this fiber hydrogel is a soft, viscoelastic, yield-stress material.

Comparative health effects in mice of Libby amphibole asbestos and a fibrous amphibole from Arizona

This project developed from studies demonstrating that Libby Amphibole Asbestos (LAA) causes a non-typical set of health outcomes not generally reported for asbestos, including systemic autoimmunity and an unusual and devastating lamellar pleural thickening that progresses to severe pulmonary dysfunction and death. Further, mineral fiber mixtures with some similarities to LAA have recently been discovered in southern Nevada and northwestern Arizona, where the material exists in extensive recreational areas and is present in yards, roads, parking lots and school yards. The objective was to compare the health outcomes in mice exposed to either LAA or the fibrous amphiboles collected in Arizona at the Lake Mead National Recreational Area at very low doses to represent environmental exposures. In this study, the fibrous amphibole asbestos sample from Arizona (AzA) is composed of winchite (69%), actinolite (22%), and non-amphibole minerals (9%) and has a mean aspect ratio of 16.7±0.9. Fibrous amphibole asbestos from Libby (LAA) is composed of winchite (70%), richterite (9%), tremolite (5%), and non-amphibole minerals (16%) with a mean aspect ratio of 8.4±0.7. C57BL/6 mice were exposed by oropharyngeal aspiration to fiber suspensions at a very low dose of 3μg/mouse. After seven months, both LAA- and AzA-exposed mice had indices of chronic immune dysfunction related to a TH17 cytokine profile, with B cell activation, autoantibody production and proteinuria, suggesting kidney involvement. In addition, both exposures led to significant lung and pleural fibrosis. These data suggest that there is risk of pulmonary disease and autoimmune outcomes with environmental exposure to amphibole asbestos, and that this is not limited to Libby, Montana.

Charge reversal system with cationized cellulose nanocrystals to promote dewatering of a cellulosic fiber suspension

A surface-modified form of cellulose nanocrystals (CNC) was employed to explore mechanisms related to the release of water from cellulosic fiber suspensions during papermaking. The CNC surface was rendered partly cationic (forming CCNC) by adsorption of poly-(diallyldimethylammonium chloride) (poly-DADMAC), a high charge density cationic polymer. Meanwhile, a suspension of cellulosic fibers and calcium carbonate particles was prepared from recycled copy paper, which was treated sequentially with poly-DADMAC and a very-high-mass anionic acrylamide copolymer (aPAM). Subsequent addition of CCNC strongly promoted water release, whereas ordinary CNC had the opposite effect. The effect of the CCNC was achieved with ten times less poly-DADMAC, as the final additive, compared to when adding the polymer alone. Results were consistent with a model of nanoparticle-enabled bridging, based on an assumption of non-equilibrium or slowly equilibrating processes of adsorption.

A mathematical model for the effects of volume fraction and fiber aspect ratio of biomass mixture during enzymatic hydrolysis

Renewable energy or biofuel from lignocellulosic biomass is an alternative way to replace the depleting fossil fuels. The production cost can be reduced by increasing the concentration of biomass particles. However, lignocellulosic biomass is a suspension of natural fibres, and processing at high solid concentration is a challenging task. Thus, understanding the factors that affect the rheology of biomass suspension is crucial in order to maximize the production at a minimum cost. Our aim was to develop a mathematical model for enzymatic hydrolysis of cellulose by combining three scales: the macroscopic flow field, the mesoscopic particle orientation, and the microscopic reactive kinetics. The governing equations for the flow field, particle stress, kinetic equations, and particle orientation were coupled and were simultaneously solved using a finite element method based software, COMSOL. One of the main results was the changes in rheology of biomass suspension were not only due to the decrease in volume fraction of particles, but also due the types of fibres. The results from the simulation model agreed qualitatively with the experimental findings. This approach has enables us to obtain better predictive capabilities, hence increasing our understanding on the behaviour of biomass suspension.

Numerical modeling of high aspect ratio flexible fibers in inertial flows

A numerical model for the behavior of flexible fibers under inertial flows was developed by coupling discrete element method and finite volume method. The fibers were discretized into several beam segments, and the equations of motion were integrated with a 2nd order accurate explicit scheme. The 3D Navier-Stokes equations were discretized by a 4th order accurate (space and time) unstructured finite volume scheme. Momentum exchange between the fluid and fibers was enforced by including a source term of the fiber hydrodynamic force in the Navier-Stokes equations. The choice of an appropriate model for the hydrodynamic force on a fiber in a fluid flow depending on the Reynolds number is discussed and covers a range of Reynolds number between 10−2 and 102. The current numerical model is validated against different experimental studies, including deflection of fiber in uniform flow, fibers in isotropic turbulent flow, and concentrated fiber suspension in channel flow. The numerical model was able to reproduce the damping/enhancement phenomena of turbulence in a channel flow as a consequence of the micro-structural evolution of the fibers.

Rheology of concentrated suspensions of non-colloidal rigid fibres

Pressure- and volume-imposed rheology is used to study suspensions of non-colloidal, rigid fibres in the concentrated regime for aspect ratios ranging from 3 to 15. The suspensions exhibit yield stresses. Subtracting these apparent yield stresses reveals a viscous scaling for both the shear and normal stresses. The variation in aspect ratio does not affect the friction coefficient (ratio of shear and normal stresses), but increasing the aspect ratio lowers the maximum volume fraction at which the suspension flows. Constitutive laws are proposed for the viscosities and the friction coefficient close to the jamming transition.

Formability and flow front observation of carbon/polyamide 6 randomly oriented strand composites during compression molding

Chopped carbon fiber tape-reinforced thermoplastics are randomly oriented strand materials that are easy to process and have good mechanical properties. Studying the formability and flow evolution during compression molding is essential; in particular, clarifying the relationship between the forming parameters and mold-filling characteristics of highly concentrated fiber suspensions. Here, we investigated the key parameters of strand size and effective pressure and demonstrated filling a complex mold cavity under practical processing conditions. In addition, a simplified method for observing the progression of the flow front using a video camera was proposed, where the dependence of the applied load on the mold-filling time could be observed. Filling complex-shaped mold cavity using chopped carbon fiber tape-reinforced thermoplastics is achievable using shorter strands and higher pressures. Also, the degradation of mechanical performance should be carefully considered when the material undergoes large deformation to form complex-shaped products.