Nanofibrillated cellulose (NFC) and microfibrillated cellulose (MFC) can be obtained by the mechanical breakdown of natural fibers. These materials have the potential to be produced at low cost and may give many novel...
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ISBN:
(纸本)9781622768431
Nanofibrillated cellulose (NFC) and microfibrillated cellulose (MFC) can be obtained by the mechanical breakdown of natural fibers. These materials have the potential to be produced at low cost and may give many novel properties to paper, paper coatings, paints, or other products. However, suspensions of these materials have a complex rheology even at low solids. To be able to coat, pump, or mix NFC at moderate solids, it is critical to understand the rheology of these suspensions and how they flow in process equipment. Only a limited number of reports have been published in the literature on NFC rheology at moderate solids. The rheological properties of NFC were characterized with parallel-disk geometry in a controlled stress rheometer. The solids of the material were changed by a filtration process in the range of 3.5 to 10.5%. A laboratory size press device was used to apply NFC to the paper surface at various solids using two different application methods. The coat weight of NFC was reported as a function of speed, nip loading and solids. A model was developed to predict the coat weight obtained in the device that accounts for the non-Newtonian aspects of the suspension as well as dewatering effects. NFC was found to be a highly shear thinning material with a power law index of around 0.1. Oscillatory tests gave consistent results and showed a linear viscoelastic region at low strains. The complex viscosity, the storage modulus, and the yield stress were determined for the range of solids. The variation in coat weight as a function of speed and nip loading was minimal. While solids of 10.5% gave higher coat weights than solids of 3.5%, the increase is much less than what would be expected for the same volumetric application of the suspension. A pre-metered method of applying NFC using steel and rubber rolls resulted in a non-uniform application from side to side. While glycerin and other Newtonian fluids gave rise to an even film split, NFC suspensions in the de
Recent work on the prediction of activity for single wire papermachine showed promising results in terms of the time and length scale of the drop formation event. However, the results were based on a single increase i...
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ISBN:
(纸本)1595100350
Recent work on the prediction of activity for single wire papermachine showed promising results in terms of the time and length scale of the drop formation event. However, the results were based on a single increase in the wire radius of curvature, not a series of foils as practiced in the industrial setting. The work here is based on the same model as described by Wildfong and Bousfield (2003), but now looks at what happens after a single foil and a series of foils and includes inertial terms. The wire profile is assumed to follow a sinusoidal path for this work, but this restriction can be relaxed for future work once a better understanding of wire deflection is obtained. The deflection and frequency of the wire profile is important in terms of activity generation. The size of the spouts that form is a strong function of the wire velocity relative to the spacing of the table elements. The thickness of the fluid layer on the wire is minor parameter, but thicker fluid layers are more prone to form spouts. The shear stress in the fluid layer is often small, but when ripples or spouts form, the stress levels are in the 1 - 10 Pa range. The model agrees with industrial observations.
The short time uptake of a fluid by porous media is important in a number of processes such as in coating and printing operations. Past theoretical work ranges from simple expressions to complex three dimensional netw...
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The short time uptake of a fluid by porous media is important in a number of processes such as in coating and printing operations. Past theoretical work ranges from simple expressions to complex three dimensional network models. A three dimensional control volume method is described here. Various regions of the paper can be described in terms of void fraction, pore size, permeability, and surface energy. The various merits of different models are described. The model is compared to experimental data. The results are good for most systems, but for others, unexpected results are obtained. Results for a region of low permeability are presented as well as implications for print mottle issues.
The effect of coating methods on the coating layer and print uniformity was investigated. A new laboratory device to emulate forward roll coating was developed. A method to characterize coating uniformity using a stai...
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The effect of coating methods on the coating layer and print uniformity was investigated. A new laboratory device to emulate forward roll coating was developed. A method to characterize coating uniformity using a staining technique and a confocal laser scanning microscope (CLSM) was proposed. Burn out tests are compared to the CLSM technique in terms of coating layer evenness. The coating mass distribution was calculated using image analysis software from both methods. Samples were printed with a procedure to bring out back trap mottle issues. A reasonable correlation was found between the burn out test and CLSM observation when the fluorescent dye was not rinsed from the sample. The CLSM method made quantification of coating mass distribution more rapid than the burn out test. Laboratory roll coated samples and pilot scale spray coated samples had less uniform coating layers compared to bladed coated samples. This new CLSM observation method also gave some correlation with back-trap mottle. Therefore, the coating mass distribution seems to influence print mottle. As compared with other coating methods, the pilot spray coated papers had poor back-trap mottle, even when compared in terms of coating layer uniformity. This result suggests that some other parameter besides coating mass distribution may influence the printing uniformity.
The flow behavior of coatings under a blade is important in the design of coating systems and modifying coating formulations. Several types of rheometers are now used such as capillary slit devices or rotary equipment...
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ISBN:
(纸本)9781605605104
The flow behavior of coatings under a blade is important in the design of coating systems and modifying coating formulations. Several types of rheometers are now used such as capillary slit devices or rotary equipment, but these all are different from the actual blade geometry and situation. The motivation of the present work is to develop a laboratory blade device that may be used to characterize the flow behavior of coatings close to industrial conditions. A blade is loaded against a deformable roll with a known force. Coating is applied to a plastic film in front of the blade. After one revolution, the coat weight is measured. The relationship between blade force and wet coat thickness is obtained. A finite element method is used to predict the blade forces for a given shear thinning rheology. The predicted results for Newtonian test fluids are within experimental error of the measured results. However, coating formulations have predicted blade forces that are one third of the measured force. This error seems to be related to the viscoelastic nature of the coatings. The blade-roll combination could be thought of as a type of rheometer, not to obtain an absolute value of viscosity at high shear rates and low dwell time, but as an indicator of the performance during actual operation.
The penetration of hot melt adhesive into coated paperboard influences the efficient use of adhesive and the final bond strength in the production of boxes and other structures. However, little systematic work is repo...
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•Method is able to quantify concentrations of starch, latex, calcium carbonate, and kaolin dynamically. • Binder can migrate even after FCC. • Large pigment sizes enhances, not only latex migration, but starch migrati...
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ISBN:
(纸本)9781510801295
•Method is able to quantify concentrations of starch, latex, calcium carbonate, and kaolin dynamically. • Binder can migrate even after FCC. • Large pigment sizes enhances, not only latex migration, but starch migration. • CMC addition minimizes relative motion of pigment and latex.
As computer speeds have increased and software developed, our ability to describe complex coating flows has improved. The potential to improve the design and control of coating processes using computational fluid dyna...
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As computer speeds have increased and software developed, our ability to describe complex coating flows has improved. The potential to improve the design and control of coating processes using computational fluid dynamics (CFD) is good and has already been demonstrated. The basic techniques and methods of modern CFD are described. The developments of the use of CFD to solve paper coating problems are reviewed, especially the work focused on blade coating of paper. Examples of other coating flows are presented. Issues related to coating-paper interactions are discussed. The ease of use of a commercial package is demonstrated. Other modeling techniques that use computers are described.
Before cellulose nanofibers (CNF) can be used in paper furnishes or as a surface layer, the drainage characteristics of pulps that contain CNF must be determined. In addition, the influence of CNF addition on pressing...
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ISBN:
(纸本)9781510847286
Before cellulose nanofibers (CNF) can be used in paper furnishes or as a surface layer, the drainage characteristics of pulps that contain CNF must be determined. In addition, the influence of CNF addition on pressing needs to be understood. CNF was added to pulp furnishes at various levels and also applied as a curtain to the just formed web on the drainage table on a pilot paper machine. The couch solids and the final press solids, for various nip pressures is obtained. The final press solids is also predicted from an equation in the literature. In some cases, CNF addition is found to increase press solids instead of decreasing it.
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