FRC Symposium Proceedings
FRC Symposium Proceedings
Oxfordpp 27-41Enhanced Test Devices for the Development of Novel Paper-like Materials for Sandwich-StructuresAbstractPDF
High performance sandwich components have a great significance in aerospace applications. Particularly, lightweight sandwich structures made of honeycomb or foldcores show excellent load carrying capabilities. Both types of cores are usually made of aramid paper coated with phenolic resin. Therefore, the development of improved paper-like materials seems to be a promising approach to improve the mechanical performance of this kind of cores. An essential part of this development process is the evaluation of the new materials by the complete characterisation of the mechanical properties. This is still a challenging task, since the resulting papers are orthotropic and most of the existing testing procedures and devices are not suitable for very thin sheet materials. This is particularly true for investigating stiffness and strength properties under compressive and shear loading.
The paper presents a novel single-curved compression test device as well as an adapted shear-frame for the in-plane characterisation of very thin specimens. These devices have been applied in the development process of a new paper-like material that consists of three layers in order to increase the stiffness and strength of honeycomb- and foldcores. The performance of this material was evaluated by comparing relevant mechanical properties to that of state of the art paper materials. Based on the experimental results the benefits of the new paper-like material could be shown.
Motivated by sustainability arguments there is a recent interest in forming of advanced structures in paper and paperboard. Therefore, in this paper, hydro-forming of papers and the effect of different fibre raw materials, beating, strength additives (PVAm), grammage and wet and dry papers have been investigated experimentally and numerically.
The experiments were carried out in laboratory hydro-forming device. Softwood sheets performed better than hardwood sheets, since they had higher strain at break. The ability of paper to withstand hydro-forming successfully was primarily dependent of the strain at break of the paper in relation to the straining required to fill the mould. Forming of wet sheets were also investigated; overall the wet sheets formed better than the dry sheets, which was due to higher strain at break and lower elastic energy. Since the forming was displacement controlled, there was no significant difference in the effects of beating, amount of PVAm or grammage.
Finite element modelling was performed to identify local strains and predict problematic regions. Simulations were also performed to determine how anisotropic sheets would behave, as well as to compare the process of hydro-forming with press-forming. The papers could be strained to higher strain levels than the measured strain at break because the paper is supported by the membrane and mould during the forming operation. The maximum strain a paper can withstand can be increased if the paper can slide into the mould, i.e. by having a lower coefficient of friction between the steel mould and the paperboard.
During hydro-forming the paper is supported by a rubber membrane, which gives lower strain levels than the corresponding press-forming operation due to the difference in how the paper is deformed. Press-forming therefore required paper with higher strain at break. Higher friction results in more paper being pulled into the mould, which contributes to wrinkling of the paper. Simulation of tray forming of a creased sample was performed, which showed that high friction or compliant creases decreased the circumferential compression.
Curl is unwanted dynamic behaviour that appears already in the manufacturing process and evolves through the end-use of paper or board due to moisture content changes and mechanical treatments. In this paper, the analytical and numerical approaches are used to reveal the sensitivity of the curl tendency to fundamental variables affecting deformation behaviour of paper. Good agreement between the measured curvatures induced into the sheet by the photocopying process and the simulated curvatures is achieved. Paper is treated as a multi-layered material, and finite element simulations are performed by using hygro-elasto-plastic and hygro-viscoelastic material models. Also analytical calculations are carried out to support the conclusions. The results show that the prediction and control of curl is not straightforward; curl depends not only on the fibre orientation structure but interacts in a complex way with the through-thickness dry solids content profiles during moisture content changes and external mechanical forces acting on paper. Despite the complexity of the phenomenon, the simplified computational approaches presented in this paper can be used for analysing and optimising the paper structure and process parameters to prevent detrimental curl.
Cambridgepp 3-39Local Structural Orientation of Towel and Tissue Grades in Two and Three DimensionsAbstractPDF
This paper describes the study of new methods for characterizing the orientation of fiber segments in low density paper towel from two- and three-dimensional X-radiographic data sets. The end use properties of the absorbent hygiene grades such as paper towels and tissues stem from an open porous structure where stochastically distributed fibers are contorted by post forming processes to increase bulk, stretch, flexibility and softness, while maintaining adequate strength. The orientation of free fiber segments that form the network are kinked and curved in three dimensions by processes including creping, through air drying and embossing. Providing a linkage between process conditions and the end use properties through the characterization of the network structure is the overarching goal of this investigation. A method is presented for mapping the 2D, in-plane orientation of fiber segments using soft (6kV) X-radiographs and an algorithm for calculating the image moments for circular sub-regions that surround each point. The eigenvectors form the major and minor axes of the inertial ellipse from which the principal orientation may be extracted. Colorized maps representing the local orientation are used to examine the effects of embossing and creping, as well as comparing different forming processes. A method for characterizing fiber segment orientation in three dimensions uses a similar approach applied to binarized X-ray micro-computed tomographic data sets. The inertial ellipsoid is determined by performing principal component analysis on the covariance matrix of the voxels contained within a spherical region surrounding each solid voxel within the structure. The eigenvectors are used to extract the shape and principal orientation of the ellipsoids which are plotted as colorized representations in 3D space. The 2D and 3D plots demonstrate the sensitivity of the method to orientation of fiber segment mass, while mean fiber orientation plots reveal differences between samples.
Oxfordpp 139-158Development of Cellulose Nanofibre Quality with Mechanical Energy: Effect of Starting MaterialAbstractPDF
Energy efficient production of nanocellulose fibres is key to establishing this highly-promoted materials in an industrial scale. In this work, we attempt to explain how the mechanical energy input and the chemical composition of the raw materials affect the quality of nanofibres. Bleached eucalyptus Kraft (BEK) pulp, a commercially availble microfibrillated nanocellulose from cotton, and whitewater fines collected from a radiata pine thermomechanical pulping (TMP) mill were used to produce cellulose nanofibres. BEK was the most responsive to mechanical fibrillation due to low crystallinity and it produced high aspect ratio nanofibres, while TMP whitewater fines were the most difficult to process and resulted in low aspect ratio nanofibres. Nanofibres were then added to TMP newsprint to evaluate the effect on tnesile strength. Nanofibres produced from BEK were able to increase the tensile strength the most, while nanofibres from TMP whitewater fines had the least effect. The results showed that a high aspect ratio and a surface chemical composition favouring more hydrogen bonds i.e. pure cellulose, are the key criteria when selecting nanofibre for strength improvement in paper.
Oxfordpp 159-173The Effect of Fibrous Materials on the Rheology of Aqueous FoamsAbstractPDF
We studied fully developed pipe flow of fibre-laden aqueous foams and decoupled their bulk rheological properties boundary effects like slippage at the pipe wall. The air volume fraction of the foams varied between 70% and 75%. The addition of hardwood fibres at the consistency 20 g/kg to plain aqueous foam increased viscosity more than 100%, while with microfibrillated cellulose at a consistency of 25 g/kg the increase was about 30%. The effect of synthetic (cellulosic)rayon fibres was negligible at the consistency of 20 g/kg. All the studied foams could be described as shear-thinning power-law fluids with significant slippage at the pipe wall by particles size and interactions between particles and bubbles.
Oxfordpp 175-194Refining Impulse Controls the Morphological Modifications of FibersAbstractPDF
Considering the analogy between the pressing of a paper sheet and the refining of a pulp suspension, the refining impulse is introduced. For beaters, disc or conical refiners, whatever the running mode (continuous or batch), the refining impulse is found to be a controlling variable for the pulp properties, and consequently for the paper properties. In a Valley beater, different normal forces were applied. The SR evolution versus the refining impulse exhibits a unique curve whatever the experimental conditions. For disc and conical refiners, the refining impulse depends on the net power, the rotation speed, the bar width, or the average bar angle. A unique parameter is used to fit each set of trials to obtain a single curve of the SR evolution. This parameter corresponds to the global friction coefficient f. he fiber length and the swelling (WRV) depend also on the refining impulse. However, as in pressing theories, the applied pressure has also to be introduced as a complementary parameter. Consequently, the paper properties are shown to depend also on both the refining impulse and the applied pressure.
The standard method of representing refining data is to plot fibre or sheet properties as a function of refiner Specific Energy Consumption (SEC), for separate refining trials done at different Specifics EDG Loads (SEL). This approach does not allow for refining outcomes to be predicted when refining at other values of SEL and does not allow for refining conditions to be optimized to satisfy multiple constraints. In addition, the change in fibre properties is determined by the number of impacts on a fibre and the energy used in each impact, while SEC is the product of number and energy used in each impact. The paper describes a new representation of refining data where the two axes of the plot are SEC/SEL, which is proportional to the number of impacts, and 1/SEL, which is proportional to the inverse of the energy used in each impact. Data from refining trials are then plotted as lines of equal value. The paper shows how flow and power limited for a low consistency refiner are represented on such a plot. The utility of the approach is demonstrated with refining data of a CTMP pulp with three different refining plates and three different speeds.
Oxfordpp 209-228Fractionation of Bifer Pulp in a Hydrodynamic Fractionation Device: Influence of Reynolds Number and Accept Flow RateAbstractPDF
Fibre fractionation in the Hydrodynamic Fractionation Device (HDF) was studied for changing suspension flow parameters, i.e. different channel Reynolds numbers Re and accept flow rates up to 20% of the feed flow rate. The suspension flow behaviour was described using images recored with a high-speed camera system. Fractionation performance was determined based on mass balances for a variety of length fractions of the pulp. Low Reynolds number flow characterised by Re = 1300 led to the formation of a fluid gap between the wall and the fibres located at the chaneel centre. Best fractionation performance was achieved for flow at this Reynolds number: no fiber removal was observed at 10% accept flow rate, and only 1% of the fibres were removed at 20% accept flow rate. A design space was established that highlights the optimum settings for fractionation in an HDF, which at low Re and high accept flow rate. Surprisingly, we found a significant increase of fines mass flow rate in the accept upon an increase of the Reynolds number. We speculate that a flow regime-dependent interaction of fines with the fibres exists in the HDF that critically affects the amount of fines in the fluid gap near the wall.
Oxfordpp 231-254The Effect of Microfibrillated Cellulose on the Strength and Light Scattering of Highly Filled PapersAbstractPDF
There has been much recent interest in the use of microfibrillated and nanofibrillated cellulose as additives to improve the mechanical properties of paper. Most of the original methods used to make these materials are to costly for this purpose, but now purely mechanical processed are becoming available which have been made it a more practical possibility. The tensile strength of unfilled paper and its relation to light scattering have been the subject of extensive theoretical and experimental research a, and the effect of addition of fibrillated cellulose have been considered by several authors in the light of this work. However, much less theoretical work have been dedicated to the properties of papers with high filler contents.
In the FiberLean process, fibres are mixed with filler and found together until fibres are converted into microfibrillated cellulose, a few percent of which can be added to paper to increase its strength and allow a substantially higher filler content. We build on the work of Bown to develop a model for the effect of filler on paper tensile strength and light scattering, and use this to investigate mechanism by which mfc improves these in highly filled paper. We further demonstrate some of the advantages of its use over the conventional refining approach. There include process flexibility and some specific paper properties such as increased elasticity and higher resistance to tearing.
Oxfordpp 255-280Experimental Study of Filtration of Fiber Suspensions: Part I: Time-resolved Measurements of the Formation of a Fiber NetworkAbstractPDF
We present a new laboratory apparatus designed to study the filtration of a fiber suspension in a parameter range close to that of the real papermaking process. An experimental procedure that combines index-of-refraction matching, high-speed imaging, and article Image Velocimetry (PIV) is used to measure glow and particles dynamics. In particular we presents results for: flow above a mesh similar to that used for paper forming; flow above and in the forming fiber network; evolution of the structure of the fiber network itself. Experiments are performed varying filtration velocity and fiber length. The results show that flow perturbations in the proximity of the mesh and the forming network are confined in a thin region and the height of this region are likely to scale with the pore size. Snapshot reveal qualitative difference between the networks formed by fibers of different lengths.
Oxfordpp 281-298Experimental Study of Filtration of Fiber Suspensions: Part II: Combined PIV and Pressure Drop Measurements.AbstractPDF
The filtration of a fiber suspension has been studied experimentally. Typical application where pressure filtration occurs are: papermaking, air cleaners, production of composite materials, etc. In particular, in papermaking, the quality of the final product depends on the fiber orientation and mass distribution in the filtered materials Micro-variations of there properties can strongly affect the quality of the final product and they can occur during filtration, thus it is important to predict how this can happen. However, this is not an easy task, first because the filtered cake is a non-homogeneous compressible porous media, second because the filtration flow is non-stationary, since the cake is continuously evolving in time. Therefor in this work we focus on the filtration flow through formed steady fiber networks. For each grammage (i.e. mass of fibers per unit area), we simultaneously measure the pressure drop across the network and velocity field on top and below the fiber network using Particle Image Velocimetry (PIV). Compression of the fiber network can also be extracted form the PIV images normalized filtration resistance was found to be decreasing with increasing network thickness, as well as network compressibility. From the PIV data the influence of the formed fiber network on the flow field was analyzed and characteristic scales of the flow structure are quantified.
Oxfordpp 299-322Characterization of Fines Quality and Their Independent Effect on Sheet PropertiesAbstractPDF
It is widely accepted that pulp fines (particles passing a 200 mesh screen) largely affect pulp properties, sheet consolidation and the final paper properties. Especially fines produced during refining – so called secondary fines- showing a more fibrillar character compared to primary fines already present after the pulping process, have a positive effect on strength properties. Although this is common knowledge within the paper physics community, it is still largely unclear which detailed properties of fines influence pulp and paper properties to what extent. As fines show some similarity to MFC, this question is also of interest regarding the sue of MFC as an additive in papermaking. We apply established and new methods for fines characterization, such as the secondary fines content, the swelling ability and data on fibrillation and fibrillary material together with a suitable experimental setup t isolate the technological impact of fines in the final product Thus we are able to evaluate the technological effect of fines with different characteristics in therms of the above mentioned properties. Our results clearly show that categorizing primary and secondary fines is not sufficient when it comes to their technological impact and only in depth analysis of the fines present in a given pulp allows to understand their effect on paper properties.
Oxfordpp 323-343The Effect of Press Nip Geometry on Dryness, Density and Paper PropertiesAbstractPDF
Oxfordpp 345-365Chemical Modification of Pulp Fibres for the Production of Thermoformable PaperAbstractPDF
Enhancing the usability of paper based materials in forming processes is one major objective to pave the way for a sustainable and bio-based economy. Therefore, modifications of either the forming process or the paper material will provide future opportunities. The present study focuses on the concept of chemical pulp fibre modification as a factor influencing the formability of paper materials made thereof.Specifically, covalent attachment of ester moieties with different chain lengths onto cellulose onto fibres, a surface polymer grafting and a two-step glycol cleavage-reduction approach were characterised regarding their chemical composition and thermomechanical properties. To evaluate their formability, a temperature controlled tensile test was used.
Microfibrillated cellulose (MFC) has unique properties which can lead to interesting new paper applications. Some applications strongly rely on defined pore structure, like filter paper for water purification or separator paper in batteries. The pore structure modification of a paper sheet through MFC is investigated, the combination of MFC and polyelectrolytes (PEs) enables a pore dimension reduction of an existing softwood softwood base layer. In both handsheet and pilot paper machine trials this effect was accomplished and reproducible. It was shown that MFC grammage, MFC consistency and PE type are significant factors that affect the pore dimension.
Oxfordpp 383-407Simulation of Sloshing of Condensate Water Inside a Drying Cylinder Using Particle Finite Element MethodAbstractPDF
Energy consumption is a key issue in paper making due to its high costs and for ecological reasons. In this paper, we focus on the simulation of the drying section, with a special emphasis on the heat transfer inside a steam-heated drying cylinder, accounting for the sloshing of condensate water inside the cylinder. It is known that the condensate creates a barrier reducing the efficiency of heat transfer through the cylinder surface, a shortcoming that can be overcome by the addition of turbulator bars that increase the convective heat transfer through the water layer. In this study, we simulate the fluid flow and heat transfer in the drying roll for both the water and steam phase, but for simplicity, neglect the phase change.The Particle Finite Element Method with a fixed mesh (PFEM-2) is used to compute the numerical solution. Our aim is to show the capability of this method for solving complex sloshing phenomena with adequate qualitative accuracy and computational efficiency.
Oxfordpp 409-449Quantitative Studies of Ambient Gases in Pulp and Paper Mills and Their Degradation with Photo-catalytic Oxidation Technology.AbstractPDF
In order to reduce gaseous pollution emissions and achieve the goal of cleaner production in paper industry, in this study, (I) First, the concentrations of four potential compositions of gaseous pollutants, TVOC, HCHO, H2S and CxHy, in the ambient air on 30 sampling sites in 5 pulp and paper mills were analysed. The analysed results were discussed in the following aspects: (a) the levels of four gaseous pollutants on all the sampling sites in five mills; (b) gaseous pollution differences due to different production processes; (c) gaseous pollution comparisons on the common sites. (II) Secondly, the compositions of VOCs in a secondary fiber paper mill were determined with GC-MS method. The main identified substances in the four sites were as follows: (a) waste paper sorting room: alkanes, phenols and esters; (b) paper machine hall: benzene homologues, alkanes, ethers and phenols; (c) vacuum pulp outlet: benzene homologues and phenols; (d) office area: benzene homologues and phenols. (III) Third and last, aiming a the detected formaldehyde and benzene pollutants, a photo-catalytic reactor was developed and its performance with respect to degradation was studied. The performance tests of reactor showed that both formaldehyde and benzene could be completely degraded, but the degradation time for benzene was much longer than that for formaldehyde.
Oxfordpp 451-485Prediction of Mineral Deposits in Kraft Pulp Bleaching Lines Through Chemical Process SimulationAbstractPDF
The general tendency in the pulp industry towards reduced fresh water consumption and minimum effluent causes major deposit problems in mills. Chemical pulp bleach plants are affected by several types of mineral deposits, the most frequent being calcite, calcium oxalate and barite. We present a coupled chemical process simulation of kraft pulp bleaching line, which handles chemical equilibria, together with dissolution and precipitation effects. The simulation could adequately predict formation of mineral deposits throughout a D0(EP)D1D2 bleaching line. Strategies to help reduce formation of calcium oxalate and barite scales could be evaluated. Partial substitution of sodium hydroxide by a magnesium source at extraction stage is anticipated to inhibit formation of calcium oxalate throughout the line. Also, using sulfuric acid instead of spent acid for pH regulation at D0 would reduce but not suppress barite deposits.
Oxfordpp 489-594Three-dimensional Deformation and Damage Mechanisms in Forming of Advanced Structures in PaperAbstractPDF
There is a large potential for wood-fiber based materials such as paper and board to contribute to lightweight structures in several applications, particularly packaging. Fiber-based packaging materials have important advantages in comparison to fossil-based plastics regarding biodegradability, recyclability and renewability. Individualisation has become a crucial criterion for the use of packaging solutions and forming of advanced paperboard structure is a key technology for manufacturing of such packaging shapes. New sustainable packaging concepts are creating a need for paper materials with considerably enhanced properties.
Paper and board are in manufacturing of geometrically advances structures in general subjected to complex and often little known multi-axial states of loading and deformation that are necessarily quantified by conventional measures for paper performance. Today, commercial paperboard is optimised for folding and printing, and not for applications involving forming of advanced structures. It is like-wise important to design the manufacturing process to meet the particular properties of paperboard. Manufacturing methods that are suitable for metals and plastics are inevitably not suitable for paper and board since the deformation and damage mechanisms of fibre network materials are different from metals and plastics.
In this paper recent findings in the literature on 3D forming of paper and paperboard structures are reviewed. In particular, deformation and damage mechanisms involved in pertinent forming operations and how they are related to paper and board properties in order to enhance the development of new advanced paper materials and structure are analysed.
In the last decade, there have been major advancements in the development of geometrically advanced 3D paperboard structures including technological advances of various forming process, enriched understanding of the importance and influence of process parameters, and new paperboard materials with significant improved forming properties. However, there is still a lack of knowledge regarding the deformation mechanisms of these complex systems and particularly regarding the influence of friction. One remedy would be the enhancement of numerical simulation tools. Optimisation of existing forming processes and development of new ones as well as tailored paper and board materials with properties customised to the demands of exiting and new 3D forming processes will also play important roles. This development is only in its beginning and major progress is expected in the near future.
Oxfordpp 595-609Focused Ion Beam Tomography as A Means for Characterization of CNF in A Paper Matrix.AbstractPDF
A method to study Cellulose Nanofibril (CNF) distribution in three dimensions within a paper matrix-in-situ-was developed. Focused Ion Beam (FIB)/Scanning Electron Microscopy (SEM) tomography was used to investigate the distribution of cellulose nanofibres in thee dimensions within a paper structure. Sufficient resolution and material contrast was contained using both secondary and back-scattered electrons in volumes as large as 103 um3. Challenges and approaches to achieve this are discussed, both with respect to the microscopy technique and with respect to image processing and volume reconstruction. A range of recorded images and reconstructed 3D volumes show the technique capable of resolving CNF in a paper matrix. Results presented show CNF within the paper matrix forming capsules enclosing filler particles. These capsules are seen to only infrequently be in physical contact with the enclosed particles. Similar separation between CNF and enclosed filler particles was tested and confirmed in CNF films with 10 wt% added ground calcium carbonate.
Oxfordpp 611-625Synchroton Tomographic Imaging of Softwood Paper: A 4D Investigation of Deformation and Failure MechanismAbstractPDF
Fiber pull-out and fiber fracture are the two dominant failure mechanisms of softwood paper. For the first time, 4D synchrotron X-ray tomographic imaging (three spatial directions plus time) was performed to observe these mechanism in-situ during tensile deformation of softwood paper handsheets. The experiments were conducted on three handsheets, produced from pulp that was low consistency refined at 0 k Wh/t and 100 kWh/t and wither air-dried in restraint or freeze-dried. The fibre deformation was found to be highly complex; initially being accommodated via straightening of the fibres resulting in fibre separation and then complete fibre pull-out or fibre fracture. The 3D strain fields, computed by Digital Volume Correlation, revealed increasing out-of =plane deformation in samples with decreasing inter-fibre bonding. Further, the relation between the L2 norms of the out-of-lane strain fields with displacement was computed and found to follow a second order polynomial, with an increasing slope in samples with reduced inter-fibre bonding. It was then shown that the accumulated out-of plane deformations could be used as a metric to quantify the relative contribution of inter-fibre bond breakage, and subsequently, fibre pull-out during tensile deformation of handsheets. The results demonstrate that 4D imaging provides new insights into paper deformation mechanisms.
Oxfordpp 627-649A Micro-mechanical Modelling Study of Drying Restraint Effects on the Hygro-mechanics of Paper SheetsAbstractPDF
In this contribution we show how fibre activation and micro-buckling of fibre walls may explain, quantitatively, differences in the hydro-mechanical response of paper sheets due to the presence or absence of mechanical restraint during their fabrication. To this end, both effects are incorporated in an idealised micro-mechanical model of the fibre network. The model is used to predict the response of the network to wetting-drying cycles, as a function of the degree of restraint during production. Restrained-dried networks are predicted to exhibit an irreversible hydroscopic strain upon first wetting and a different reversible hygro-expansivity coefficient, compared with free-dried networks, which match well with experimental values reposted in the literature.
Oxfordpp 651-668Computational Design of Fibre Network by Discrete Element MethodAbstractPDF
Soft fibre networks, typically seen in bathroom tissues, kitchen towels, and personal-care products, have properties that are intricately affected by the details of fibre geometry, 3D-network structures, and processing conditions. Designing such materials and products for better performance, while controlling cost, is especially a challenge in today’s fast paced product development. This paper concerns the development of a new, robust computational design platform for the design of soft fibre networks.
We have used particle-based methods, particularly, Discrete Element Method (DEM), to model fibres, fibre networks, their properties and performance, and also unit processes for manufacturing. Unlike other computational methods, this method has advantages to model discrete and non-homogeneous materials, complex geometries, and highly non-linear dynamic problems, such as large deformation (flow), contact/non/contact, fracture, and fragmentation.
With this approach, fibres are represented by a series of connected spherical particles in different lengths and geometries (curl, kinks, twists). Fiber networks are created by the deposition of those fibres under gravity, followed by the subsequent consolidation under pressure. here processes have shown an interesting transition phenomenon from a highly fluidic granular system to a fragile soft solid. The network is then subjected to a creping process, a critical process of tissue-making. The model was able, not only to reproduce unique crepe frequencies, but also unprecedented details of the destruction of fibre network structures and fibre failure (dusting) during creping. Typical tensile tests, thickness-direction compression tests, and softness tests have been also performed to demonstrate unique deformation characteristics of low-density, low-basis weight fibre networks.
This computational design system based on DEM provides a promising platform for exploring large parameter space of new material/product design.
Oxfordpp 669-682Linking Paper Structure to Local Distribution of Deformation and DamageAbstractPDF
A method for quantitatively investigating the relationship between local structural properties (local basis weight, local thickness, local density and local load carrying factor (local fiber orientation)) and local tensile deformation (local strain and local temperature increase (thermal energy dissipation)) was introduced. It was found by utilizing the method for 70 g/m2 sack paper strips that relative basis weight, relative thickness, relative density and relative load carrying factor combined explain 31% and 26% of total variation in relative strain and relative temperature increase, respectively. Best single predictors for relative strain were relative basis weight (R2=0.14) and relative load carrying factor (R2=0.11). On the other hand, relative basis weight alone was the best predictor for relative temperature increase deformation distribution parameters from the perspective that high relative temperature increase is preceded by the high relative strain, it could be said that the relative strain explains 45% of the total variation in the relative temperature increase (R2=0.45). Thus, these two parameters describe the deformation in partially different ways. Based on this study, it can be concluded that the introduced method offers a promising tool to quantitatively investigate the separate/combined influence of local structure properties on the local deformation accumulation initializing the failure of paper.
Oxfordpp 683-719The Effect of Geometry Changes on the Mechanical Stiffness of Fiber-fiber BondsAbstractPDF
In this work, we discuss the effect of geometry on the compliance of the fibre bond regions against normal and tangent loads. Since the fibre bonds play a key role in defining the paper strength, the compliance of the bond regions can affect the amount of elastic energy stored in the bonds and thus change not only the strength but also the stiffness of paper products under certain conditions. Using finite element simulation tools, we overcome the major difficulty of performing controlled mechanical testing of the isolated bond region and reveal the key geometrical factors affecting the compliance of the bond region. Specifically, we show that the compliance of the fiber-fiber bond is strongly governed by its geometric configuration after pressing. Among the strongest factors is the collapse of the lumen and the crossing angle.
Using the range of obtained stiffness values, we demonstrated the effect the bond stiffness has on the stiffness of the network using fiber-level simulation tools. We show how the dependence of tangent bond stiffness on fiber-to-fiber angle further softens the more compliance cross-machine direction.
Oxfordpp 751-773Paper-based Chemical Detecting Sensors for Surface-enhanced Raman ScatteringAbstractPDF
In this study, we fabricated a paper-based molecule-detecting sensor for the surface-enhanced Raman scattering (SERS) technique. SERS phenomenon is based on the face that the low intensity of Raman scattering is dramatically increased when the molecules are adsorbed on novel metal surface. To improve the applicability of paper substrate as a base for SERS several trials were made. The smoothness of the filter paper was improved through a calendaring process. To prevent the spreading of the chemical solution on the aper the hydrophobicity of paper was increased by treating with an alkyl ketene dimer (AKD). Onto the smooth and hydrophobic filter paper a silver nanoparticle (AgNP) solution was applied with a simple drop and dry method, and analyte was treated in the same manner on the AgNP decorated area for SERS measurement. To improve the reproducibility of the SERS intensity, an area scanning method that used a dual axis galvanometric mirror was introduced. A 4-aminothiophenol molecule could be detected at the femtomolar level using the hydrophobic-treated filter paper. Coating of cellulose nanofibrils (CNF) made from pulp fibers reduced the surface pore sizes and increased the uniformity of the surface of the filter paper, which improved the reproducibility and sensitivity of the molecule-detecting sensor. The use of a high magnification objective lens for increased SERS intensity allowed for the detection of a strong SERS signal, and the application of a CNF coating to the filter paper improved the reproducibility. Pesticides were detected using the paper-based substrate as SERS substrate.
Oxfordpp 739-749Paper-based Electronics and Sensors Fabricated by Using Printing TechnologyAbstractPDF
Paper is seen as a potential substrate for devices such as electronics and sensor because of environmental friendliness being a dualistic material with flexibility and rigidity, and a possibility for mass production at low cost. In this study, two such applications as devices will be introduced. First, a power generator has been developed to convert sonic vibration into electric energy. Secondly, a corona discharge-treated polytetrafluoroethylene sheet, as an electret, was attached to a paperboard with a back electrode. Another paperboard with a counter electrode was mechanically vibrated to simulate a sound. During vibration, electric power was successfully generated by electrostatic induction. Insertion of nano0cellulose paper further more enhanced the output voltage. A simple, quick, sensitive and ion species-selective paper-based sensor with a quinone derivative dye ink-jet printed has been developed to detect Cu2+ ions at 2 ppm, a maximum allowed for drinking water, by colour change observation. A fluorescence spectrum of the dye provided higher resolution to permit quantitative detection of Cu2+ concentrations.
Oxfordpp 777-784Developments of Manufacturing Techniques and Applications of Cellulose NanofibreAbstractPDF
Nippon Paper industries has been developing Cellulose Nanofibre (CNF) products prepared by the fibrillation of chemically modified pulp since 2007.
In November 2013 we started to operate a pre-commercial plant in order to provide CNF for the collaborators, potential users and internal use, after 5 years of fundamental research together with out collaborators with the aim of commercialization of products using CNF. In our pre-commercial plant, mainly TEMPO oxidized CNF is produced, a process developed by the research group of Prof. A. Isogai at The University of Tokyo. In addition t TEMPO oxidation, other chemical modifications such as carboxymethylation are carried out in out plant as well. Thus collaborators can choose the type of CNF samples, depending on their target applications.
In 2016, NPI announced the plan to install a CNF full-scale production facilities at the Ishinomaki Mill and the Gotsu Mill in Japan. At the Ishinomaki Mill, CNF prepared by TEMPO oxidation will be produced, and at the Gotsu Mill, CNF prepared by carboxymethylation will be produced.
In this brief paper we will present our developments of manufacturing techniques and applications of chemically modified CNF
Oxfordpp 785-800Preparation and Characterization of Spherical Nanosized Cellulose by Enzymatic Hydrolysis of Pulp FibersAbstractPDF
In this work, the pulp fibers were enzymolyzed to prepare the nano-sized cellulose (NC). The as-prepared samples were characterized by optical microscopy, electron microscopy, and Raman spectra. The experimental results indicated that enzymatic hydrolysis of pulp fibers could produce the spherical NC with a mean particle size of about 30 nm, which has the excellent monodispersity and uniformity. When the concentration of complex enzymes was 20 u/mL (cellulase: xylanase = 9:1), the yield of NC was 13.6%. The single cellulase was used, even if the concentration and time reached up to 200 u/mL, only a mixture of trip and granular flocculation were obtained. The positive synergistic effect between xylanase and cellulase could be due to the enzymolysis of hemicellulose located on the cellulose microfibers to favorable of cutting and splitting of the microfibers by the endoglycannase in cellulase. Otherwise, the additive copper sulfate could decrease formation of reducing sugar effectively.
Using a recently proposed concept of cell wall structure based on a multiplicity of lamellae coaxial with the cell, the effect of drying on the structure of the cell wall of bleached spruce sulphite tracheids has been examined by means of nitrogen adsorption. The data suggest that in the fully water-swollen wall there are up to several hundred lamellae, each of the order of 100 Å thick, with a median separation of about 35 Å. During drying, the lamellae draw together progressively into thicker and thicker aggregates, decreasing the total pore volume, but leaving approximately the same median separation in the spaces that remain. At dryness, the pore volume remaining in the wall is negligible.
During drying,the first pores to close do not reopen when the fibres are treated with water,whereas the pores that close during the later stages of drying do so. The lamellae separation after drying at 25°C and reswelling remains at a median value of about 35 Å, but it drops after drying at 105°C and reswelling to 25 Å, owing to a greater permanency of pore closure in the pores of larger size. It is tentatively suggested that a fibre dries radially inwards towards the lumen and that the pores that tend to remain closed after drying are located towards the outside of the fibre, whereas the pores that reopen easily upon rewetting after drying are located towards the lumen.
Fibres of very different composition, chemical treatment and morphology, as well as native and regenerated cellulose fibres, possess a wide range of pore volumes, yet are shown to have very similar pore size distributions and it is suggested that this distribution is not therefore of biological origin, but is based on a property of the cellulose molecule. No obvious correlation was found between the fractional extent of irreversible pore closure upon drying and the composition of the fibres.
In the swollen cell wall of spruce sulphite pulp fibres, which contain almost 1 cm3 water per gram of dry material, about 20 percent of the water is present in macro reticular pores (spaces between lamellae) and 80 per cent in micro reticular pores(spaces within lamellae). This ratio persists throughout the drying cycle.
The relationship between cell wall porosity and the papermaking properties of fibres is discussed briefly in terms of the loss of porosity during drying and its regain during beating.
Organic polymers have always been useful for the making of fibres, films, rubbers, plastics, adhesives and coatings and cover a wide range of properties. For several years, systematic efforts have been made to explore the use of fully synthetic fibres on a paper machine either alone or together with cellulose materials. Several sheet properties can be substantially improved by this approach. More recently, the preparation of polymer systems has been studied that occupy an intermediate position between a uniform fibre and a homogeneous film. They have been called `fibrids’ and permit one to prepare two-dimensional sheet-like entities without the use of a liquid vehicle (such as water on a papermachine) that range in their properties from paper to textiles.
A classification of the wide variety of solids according to physical, structural and chemical characteristics shows the category of heterophase solids to be the largest group of natural and artificial substances. Most manufacturing and manufactured materials fall in this category.
The structure of such materials can be described by the shape, size, concentration, orientation and topology of the constituent phases. Statistical methods in particular, geometric probability sometimes supplemented by certain physical ortopological restrictions, provide adequate tools for the description of naturally grown or artificially mixed systems.
Mechanical modulus properties as well as thermal and electrical properties can be treated in a fairly general manner,based either on field distortion of one phase by the presence of another phase or by means of phase models that give upper and lower limits for the property.
The problem of strength properties can be seen in terms of fracture mechanisms or as a statistical one, in which case extreme value theory provides a suitable method.
Cambridgepp 90-115Measurement and Significance of the Water Retention Properties of Papermaking FibresAbstractPDF
Equilibrium water retention isotherms have been determined for papermaking fibres through the range of moisture contents that is of greatest papermaking interest.
The experimental method provides not only a measure of the swelling of the fibres and the equilibrium water retention at any force of water removal, but, conversely, the method measures the force with which the water is held and the force with which fibres or fibre elements are held together by residual water.
Factors affecting the mechanism of water retention and the amount of water held by fibres are demonstrated by the isotherms of model and papermaking fibres of widely varying properties and treatments. The part played by the mechanism and extent of water retention on the development of wet web properties during drying is discussed and the need is demonstrated for more information than is provided by the isotherm.
Finally, consideration is given to the role of swelling and water retention in pulp evaluation and some general principles are suggested by which the running and papermaking properties of a pulp might be predicted.
This paper is a condensed survey of the interactions between water and cellulose materials. It is introduced by some general remarks about the interaction of water with solids, with special attention to hydrogen bonds, solutions and gels, then about the chemical and physical properties of cellulose fibres. The main discussion is devoted to the interaction of water below and above the saturation point, dimensional changes and restricted swelling, drying and hysteresis and, finally, the quantitative measurements of the absorbed water.
When elongated particles such as fibres are dispersed in water, they form a continuous network, provided the fibre concentration is above a certain level. A measuring technique utilising a concentric cylinder elasto-viscometer has been developed and used for studies of the mechanical properties of such networks.
Networks generally exhibited the same characteristic properties as solid visco-elastic bodies, hence should be characterised by methods used for such materials rather than by hydrodynamic methods. Nevertheless, a close connection was found between the mechanical properties of fibre networks as measured by quasi-static methods and the hydrodynamic behaviour of the same material, then considered as a fibre suspension.
A mechanism for the formation of fibre networks is proposed, in which the network is considered to derive its strength from the energy stored in the fibres when, after being bent in a turbulent shear field-such as is produced during agitation of the fibre suspension-they are prevented from straightening out by their interaction.
A mathematical model of random three-dimensional fibre networks of low concentration has been evolved. The fibre concentration, the length-to-radius ratio and the modulus of elasticity on bending are shown to be the most significant of the parameters determining the rigidity of the network. Experimental study of the shear modulus of model fibre networks substantiated the qualitative validity of the fibre network model.
Experiments with synthetic fibres and a special flow apparatus, yielding data for the water permeation of fibre mats in the viscous-turbulent flow regime are briefly described. It is found that, within the range of the variables concerned,the results conform well to a recently established empirical equation relating the flow resistance of a pad to the flow speed, pad porosity and fibre specific surface. This empirical expression is then used, along with an equation representing wet mat compression characteristics, to construct a theoretical model of high-speed filtration. The result is a system of non-linear partial differential equations for the suspension kinematics and the flow rate/density distributions within the forming mat. Examples of numerical solutions are presented and discussed.
When a constant pressure is applied to a fibre slurry initially at rest, it under goes a continuously decreasing acceleration, reaching a maximum filtration speed, after which the speed decreases uniformly, corresponding to a constant pressure drop filtration process. The peak speed may be as much as eight times greater than the speed characterising the final constant pressure zone. Theoretical results for the density distribution in a forming mat illustrate the effect of relative compressibility, for which the more compressible material exhibits a rapidly changing density profile near the supporting septum. It is also found that the rat eat which the mat builds up after peak slurry speed decreases with increasing time to an extent depending on the mat compressibility. Filtration experiments with a bleached sulphite pulp yield results that agree satisfactorily with the calculations, confirming predicted formation times to within less than 10 percent. The experiments thus further corroborate the predicted inverse relationship of formation time with applied pressure, as well as an approximate proportionality of formation time and sheet substance.
A method is described of determining the distribution of fibres in the thickness of a sheet of paper. It relies on observing the disposition of a small proportion of dyed fibres in a transparentised sheet. All the samples examined show a highly layered structure.
Density profiles of the boundary of a sheet being formed in a drainage apparatus have been measured and the movement of single fibres was observed in approaching the forming zone in a model of the wire part of a paper machine. Both experiments show that a diffuse zone exists at the boundary of the forming mat, in which thickening of the stock takes place. The length of this zone is only a few millimetres and most of the formation takes place by filtration rather than by thickening. This finding is confirmed by computations based on a theory of formation, which includes both thickening and filtration. An argument is advanced that the layered structure of paper is the inevitable result of this mechanism of formation, which takes place at the usual papermaking consistencies. Much higher consistencies would be needed in order to produce a more felted structure of the sheet.
Cambridgepp 269-298Dependence of Sheet Properties on Formation and Forming VariablesAbstractPDF
An investigation of the effect of forming variables on handsheet strength properties showed that stock dilution, shear gradients and controlled initial drainage are factors that have major effects on sheet structure and properties. A better understanding of the causes of changes in paper strength properties resulted from the introduction of a new concept of basic sheet properties.
One basic property is the specific tensile strength. This represents the average tensile strength throughout a sheet,in contrast with the standard tensile strength, which is generally a measure of strength in the weakest part of the test samples. The well-known loss of tensile strength that occurs when handsheets are formed from stock at higher concentrations is shown to be caused mainly by small-scale substance variability, since the specific tensile strength is essentially constant over the same range of concentrations.
The effect of substance variability on other strength properties was examined by means of uniform base layer sheets with superimposed substance spots. The spots were used to obtain a known and reproducible pattern of substance variability. Notwithstanding the increased substance of the spotted sheets, they were found to be physically weaker in all properties except tearing strength. Substance variability was found also to be responsible for the reciprocal dependence of tearing strength on bursting and tensile strengths.
As a test of the practical importance of dilution and shear gradients, Fourdrinier machine trials were run in which the water removal capacity was increased considerably by the application of fan-produced vacuum under the forming zone. Sheet properties were found to be still improving up to the maximum flow box dilution or speed set by other machine limits such as drying and stock pumping.
Cambridgepp 119-144Transverse Shrinkage of Individual Fibres by Micro-radiographyAbstractPDF
Micro-radiography has been used to determine the width and moisture content of individual pulp fibres during their drying from the swollen state. The method, which employs soft X-rays to produce contact radiographs of the fibres, is described and results are given for a spruce sulphite wood pulp. An assessment of changes in the thickness of the fibres while drying is also given.
Cambridgepp 242-267Visco-elasticity and Consolidation of the Fibre Network during Free Water DrainageAbstractPDF
Measurements of specific permeability and compressibility of pads of synthetic and wood pulp fibres have been made in an apparatus in which rate of flow of water through the pad, pressure drop across the pad, external applied load and pad thickness can be controlled and measured. For non-swelling fibres at high porosity, with no applied load, the Emersleben-lberall drag treatment was found to provide estimates of permeability in reasonable agreement with observed values. The relationships between solids concentration C and applied stress P and between C and pressure drop p have been studied separately in terms of the empirical compressibility equations C= MPN with p=0 and C=m(p)n with P=O. The connections between mean compacting pressure during flow and the total pressure drop, between the exponents N, n and between the coefficients M, m, are discussed. Factors influencing the compressibility and consolidation of the fibre network include the flexibility and lateral conformability of the wet fibres, which apparently affect not only their capacity to deform elastically, but also the extent to which irreversible relative movement can take place. These effects are illustrated by the properties of pads from two series of pulps, each covering a range of lignin content-Pinus radiata sulphate pulps at various stages of bleaching and Eucalyptus regnans NSSC pulps cooked to different degrees. When compacting pressures that are due to flow and external loads are applied simultaneously, the compressibility equations in Pand Ophold, within limits, for constant values of p and P,respectively.
Cambridgepp 299-304Dependence of Sheet Properties on Formation and Forming Variables – Prepared ContributionAbstractPDF
A description is given of experiments designed to substantiate some facets of the authors’ comprehensive theory of paper shrinkage and structure that was presented at the Oxford symposium. In particular, considerable evidence is presented in support of the basic concept in the theory-that is, the hypothesis of `adhesion before shrinkage’ of the constituent fibres. Examples are shown of a phenomenon that is the direct result of the latter process, termed necking of the fibres. Other factors important in the drying and shrinkage process are discussed.
The scanning electron microscope has been used to observe changes in the structure of paper at different stages of pressing and drying.
In the first experiments, beaten kraft pulp handsheets were subjected to various pressing and drying treatments. The structure at the solids content achieved was stabilised by freezing and drying by sublimation under vacuum. Photo micrographs show the collapse of the fibres and consolidation of the paper structure during processing.
Samples of the web were obtained at positions from the wet end to the reel of operating kraft, bond and newsprint paper machines. As soon as the specimens were sampled, they were quickly frozen and later dried under vacuum in the laboratory.
The influence of water removal on the web and fibre structure by pressing and drying is illustrated. The relative importance of fibre conformity and fine material differs for the three paper grades. Under pressure, fibres are deformed plastically, particularly at crossing points and asperities. Collapse of fibres on removal of water from the lumen and the fibre walls by drying can usually be distinguished from that produced by mechanical pressure.
Previous work on the sectioning of paper has not fully utilised the power of the light microscope. This paper describes techniques developed to enable the structure of paper to be seen in considerable detail in cross-section. The techniques are illustrated by sections of a wide range of types of paper. The consolidation of the structure of paper during manufacture is revealed by micrographs of the effects of beating, pressing, drying with and without restraint, super calendering and creping.
After a review of the development of extensible papers, a description of the double-roll compacting process and its variables is given. Its principal feature is the venturi section formed in the nip between a rubber and a steel roll, between which the paper web passes in a semi-dry state. On running the rubber roll more slowly than the steel roll, the web will shrink in the machine-direction. Experiments on a pilot machine showed an increase in the compacting effect with increasing nip pressure and speed difference, though with certain limitations. When considering nip width and peripheral speed difference as primary variables, however, linear relationships with the paper properties were found. The nip width will vary with the nip pressure and rubber thickness and hardness.
The mechanism of double-roll compacting is considered to involve tangential forces, which move the rubber towards the back side of the nip, where it contracts, thereby shrinking the web. The structure of the resulting extensible paper was examined by photo micrographs of surface and cross-sections, by measuring the thickness changes on stretching and by load elongation measurements. The fibres appear curved after the compacting operation. This will result in the breaking of bonds when stretching the paper and in an ultimate breaking load lower than for flat kraft. The total rupture energy, however, is considerably higher.
An apparent increase in the rubber roll diameter on increasing nip pressure was observed. This will cause a decrease in the mean speed difference at the nip. At a limited set speed difference, the rubber roll was found to change from being driven to be driving on increasing the nip pressure. In an appendix, the nip width and the slip have been treated theoretically as well as experimentally.
The studies upon which this contribution is based were made to investigate the structure and properties of high stretch papers. Webs produced by compaction and by creping, the two main commercial processes, were examined by light microscopy and physical testing.
The micro photography shows a variety of web configurations found in crepe papers, including examples of wave formations, internal delamination and two sidedness. The characteristic fibre orientation and densification are illustrated by photo micrographs of webs taken before and after the compacting process.
The mechanical behaviour of high stretch papers is illustrated by typical stress/strain curves and a discussion of their behaviour during the process of straining.
Cambridgepp 445-472Ultrasonic Impedometric Studies in the Cellulose Pulp/ water SystemAbstractPDF
The high frequency shear mechanical behaviour of cellulose pulp/ watersystems during theprocess of drying from 3 percent solids to total dryness has been non-destructively and continuously monitored by the technique of ultrasonic impedometry. Unusual fibre/water interactions have been detected at both extremes of the concentration range studied. These interactions are given interpretation in molecular terms.
Cambridgepp 473-474Ultrasonic Impedometric Studies in the Cellulose Pulp/water System – Prepared ContributionAbstractPDF
Cambridgepp 576-626Dynamic Consolidation of Paper during Calendering: Dynamic Compressibility of PaperAbstractPDF
Two dynamic compressibility testers are described and the accuracy of one of them is examined by means of an energy balance and found to be within 5 per cent. The relationship of dynamic and static compressibility is discussed, the effects of moisture and temperature briefly examined and the results of testing a number of papers on the dynamic tester are presented. The changes in compressibility through the calender stack of two papers are given as examples and the dwell time/pressure relationship for caliper reduction is given for three different papers. Printability is examined as a function of compressibility and the relative compression of press packing and various papers is examined. A graphical method for determining the specific pressure distribution in a calender nip is given and the implications of the results are discussed. Two extreme cases of materials in a calender nip, one completely elastic, the other completely plastic are briefly discussed and a rheological model for the calender action is presented in an appendix.
Cambridgepp 544-549Effect of Drying on the Flexural Rigidity of Single Fibres – Prepared ContributionsAbstractPDF
Changes in the axial dimension of chemical pulp fibres were studied, using various combinations of drying and wetting. It was found that the commonly experienced elongation, brought about as a result of wetting, was exchanged for a shrinkage when the applied load before wetting was considerably lower than that applied before the preceding drying. Dimensional stabilisation was found for certain combinations of drying and wetting loads.
In addition, fibre stiffness was studied. During drying, the stiffness increased sharply within a dry solids content range of 15-35 percent. Upon further drying, the stiffness of the latewood fibres did not change, whereas that of the earlywood fibres was decreased. The former effect is most likely associated with an increased modulus of elasticity, whereas the latter is probably a result of changes in the fibre cross-section involving collapse.
Following a review of the effects of machine- and cross-direction forces in the web during drying on the stress/strain properties of the finished paper,the nature of the axial forces in the individual fibres during tension drying is discussed in the light of the theory of the structure. The effects on the mechanical properties and structure of individual holocellulose pulp fibres of tension drying have been carefully investigated. An unusual extensional behaviour was observed at the onset of drying. It was found that tension during drying promoted substantial increments in tensile strength, Young’s modulus and crystallite orientation; generally, the spring wood fibres under went larger changes than the summer wood ultimate elongation was reduced and crystallinity remained unchanged.
Partial removal of the hemicelluloses resulted in large decrements in tensile strength and Young’s modulus, a phenomenon not attributable to degradation of the fibre or to such side effects as swelling; the levels of these mechanical properties were reduced to those of ordinary pulp and cotton fibres. The relative enhancement of tensile strength and Young’s modulus in the extracted fibres caused by tension drying was much greater than that observed in the holocellulose pulp fibres, the latter property rising almost to that of the holocellulose fibres dried under load as the drying load was increased. The crystallinity of the extracted fibres (as determined by the method of half-width of a diffraction peak) was higher than that of the original holocellulose pulp, suggesting enhanced cellulose/cellulose bonding within the fibre, which, in turn, seems to account for the tension drying behaviour.
Theory and experimental data relating to the possible effects of tension drying on the zero-span tensile strength of machine-made paper are presented. It is indicated that more work needs to be done in this area and, more generally, on the effect of tension drying of individual fibres on all the mechanical properties of paper.
The goal of this study was to gain a greater understanding of the changes in the mechanical properties of spring wood fibres during the consolidation of the web. It was found that the elastic modulus of freely dried fibres E is essentially tripled by any axial load applied during drying. Their tensile strength t is increased and their stretch of is decreased in proportion to the loads applied during drying up a twofold change. The elastic modulus measured at 90°to the fibre axis E1, was found to be about 0.1E. These fibre properties are of paramount importance to the stress/strain properties of paper, which are described quantitatively in terms of the fibre properties and sheet structure in our second contribution to this symposium.
Cambridgepp 555-568Thermal Softening, Adhesive Properties and Glass Transitions in Lignin, Hemicellulose and CelluloseAbstractPDF
The thermal softening of isolated samples of lignin, hemicellulose and cellulose has been investigated by observation of the thermally induced collapse of a column of powder under constant gravitational load. Softening temperatures of lignins ranged from 127-193°C. Birch xylan and pine glucomannan softened at 167° and 181’C, respectively. Sorption of water by lignin and hemicellulose caused pronounced decrease of the softening temperature-in some cases,to as low as 54°C. Softening points of both dry and moist lignins or hemicelluloses have been shown to correlate with the temperature at which the sample develops adhesive properties. The softening and adhesive behaviour has been explained in terms of the concept of the glass transition for amorphous polymers. Sorbed water is considered to act as a low molecular weight diluent in plasticising the polymer chains and lowering the glass transition temperature.
Celluloses were found to soften at temperatures greater than 230°C. In contrast to lignin and hemicellulose, sorption of water by the cellulose had negligible effect on the softening temperature. This difference was probably due to the crystalline nature of cellulose and indicated that water did not plasticise individual cellulose chains at the molecular level.
Cambridgepp 569-572Thermal Softening, Adhesive Properties and Glass Transitions in Lignin, Hemicellulose and Cellulose – Prepared ContributionsAbstractPDF
The new theory of the load/elongation properties of paper, in essence, sums the loads developed in the fibres intersecting a line at right angles to the direction of straining. Fibre nonlinearity and the intermittent bond failure that occurs before the final gross rupture of the sheet are taken into account. The hypothesis is proposed that gross rupture is triggered by one of two mechanisms bond failure in sheets of strong fibres and fibre failure in sheets of weak fibres. The theory does not consider the phenomena occurring during gross rupture. Measured stress/strain curves of many handsheets of five pulps of springwood fibres were found to be in good agreement with calculated curves.
Cambridgepp 801-803A New Theory for the Load/elongation Properties of Paper – Prepared ContributionsAbstractPDF
Cambridgepp 852-872Anisotropic Elasticity of Paper from Sonic Velocity MeasurementsAbstractPDF
The theory of anisotropic elasticity for paper is reviewed. Sonic pulse velocity measurements were used to evaluate Young’s modulus, shear modulus and Poisson’s ratio of paper. The effects of fibre orientation and drying stresses on paper elasticity are readily measured by sonic velocity. A previously proposed relationship between the fourin-plane elastic constants is approximately true for well-bonded paper. Local modulus variations in a single specimen can be detected by sonic velocity measurements. Any dependence of sonic velocity on substance is due to real differences in mechanical properties of the sheet.
Cambridgepp 627-630Dynamic Consolidation of Paper during Calendering: Dynamic Compressibility of Paper – Prepared ContributionsAbstractPDF
Recent literature relating to the structure of paper and its load/ elongation behaviour is reviewed.
Following an outline of the more important load/elongation features and the effects on them of testing conditions and sheet variables, paper structure is considered in terms of the fibre (its strength, conformability and response to drying tension), the interfibre bond (its structure, area, frequency, strength and energy) and the sheet geometry. The structural changes that occur in the sheet as a whole and in its various elements during elongation and rupture are also described.
Theories relating mechanical properties to sheet structure are summarised in three categories-general theories, quantitative theories for the prediction of sheet elasticity and the application of the Griffith crack theory to paper. Some concluding remarks are offered about the significance, particularly in sheet elasticity theories, of the ability of a paper to distribute load evenly over all its structural elements.
Cambridgepp 875-895Effects of High Consistency Refining on the Properties of the Consolidated WebAbstractPDF
The treatment of pulps at low consistencies in conventional beaters or refiners is partially a destructive process that severely damages and shortens the fibres. These disadvantages are over come in high consistency refining (HCR), a technique developed commercially in the USA, which treats a pulp at consistencies of 20-40 per cent by transmitting mechanical energy to a semi-solid fibre pad between the plates of a discrefiner. The refining action is brought about by strong inter fibres hearing actions, by rubbing and sliding of fibres on each other and by the intensive internal friction forces that result. This mechanism gives the fibres a unique appearance that makes it possible readily to detect the HCR pulp in a furnish.
The preservation of the average fibre length while developing extensive fibrillation is the most important feature of the HCR process. The properties of webs formed from an HCR pulp and a jordan refined stock differ noticeably in every phase of sheet consolidation. HCR fibres lurries frequently have a poorer formation, but seem to drain better-at least, in the higher freeness range. The tensile strength of wet HCR fibre mats is not much different from that of conventionally refined pulps, but they have a higher stretch. This was confirmed incommercial newsprint runs. HCR results also in a lower water retention after wet pressing and a greater web shrinkage in the dryer section.
Papers produced from HCR pulps show a very high tearing strength, a higher stretch and a somewhat lower tensile strength than papers obtained from a jordan refined stock. This is largely a result of the much lower fines content of HCR pulps.
Cambridgepp 639-686Effects of Hydrophilic Colloids and Other Non-fibrous Materials on Fibre Flocculation and Network ConsolidationAbstractPDF
Non-fibrous materials used in papermaking are considered under the headings of colloids (positive or negative, hydrophilic or hydrophobic), surfactants (cationic, anionic or non-ionic), electrolytes and other non-polymeric materials. Their effects on flocculation of fibres are discussed in terms of entanglement, bridging and electrokinetic theories of fibre interaction. Various methods of measuring the heterogeneity of pulp suspensions and papersheets are reviewed and it is concluded that the beta-ray scanning method offers several advantages for paper studies. In this work, the heterogeneity of handsheets made from short-fibred and long-fibred pulps has been determined with a beta-ray scanner (Pm14’7 source). The experimental results showed that flocculation was more pronounced in the long-fibred pulps, but that the reduction in paper strength with increasing heterogeneity is greater in the short-fibred paper. Scanning across the handsheet diameter revealed that in some sheets the observed heterogeneity is partly due to systematic variation. In the study of electrokinetic properties of fibre/water interfaces, two parameters-zeta-potential and ionic charge density in the double layer-have been evaluated for alum-treated and polyamide-treated pulps. The results indicate that the variation in zeta-potential with additive concentration is primarily related to charge on the fibre surface for the polyamide-treated pulps and to electrolyte concentration for the alum-treated pulps. The effect of nonfibrous materials on consolidation is considered in terms of surface tension, fibre collapse and hydrogen bonding. Preliminary work on the erect of cationic starch on fibre strength is reported and a method of obtaining lateral load/compression curves of single fibres is described. The curves can be compared to those observed with tubes of differing wall thickness and elastic modulus. Experiments on the effect of modified starches and starch fractions on inter fibre bonding are also described; these lead to the conclusion that the bonding efficiency depends on the state of dispersion of the colloid, the internal cohesion of the dried colloid film and the adhesion at the colloid/fibre interface.
Cambridgepp 692-734Effects of Sizing, Adhesives and Fillers on the Formation and Consolidation of Paper WebsAbstractPDF
The effect of additives of industrial importance in modern high speed papermaking is reviewed. These sizes, adhesives and fillers will be detrimental to formation, consolidation, physical and optical properties of paper or board, if they exist in a tightly aggregated condition and are poorly distributed in the fibrous product. Data are presented to illustrate suitable dimensions of the solid particles to supply the desired property with the least amount of addition. The retention of the additives without sacrifice of their efficiency is a difficult problem.
Alumina precipitates can decrease paper strength to very low values, but can increase it again with additional aluminium sulphate. The absence of sulphate ions permits gain in strength above the starting value. Anionic polyacrylamide, carboxymethyl starch, urea-formaldehyde and cationic melamine-formaldehyde resins become considerably more effective with a closely controlled alumina compound. Recent studies on the degree of neutralisation of alum and the advantage of a moderate cationic charge in rosin sizing are reviewed, as well as an explanation for the improved efficiency of fortified rosin and synthetic sizes. Bridging by polyacrylamide molecules, the sorption and movement to fibre contact areas by molecules and macromolecular fragments from cationic starch are discussed.
Evidence is presented for the agglomerated state of pigments in paper and electron micrographs establish that titanium dioxide can be retained at about 0.25 u. Modern criteria for pigment evaluation are given. Debonding reduces pick resistance in offset printings,but helps in the ability to run letterpress paper.
Cambridgepp 735-736Effects of Sizing, Adhesives and Fillers on the Formation and Consolidation of Paper Webs – Prepared ContributionsAbstractPDF
Cambridgepp 741-772Effects of Soluble Non-fibrous Materials on Formation and Consolidation of Paper WebsAbstractPDF
The effects of soluble electrolytes and certain polyelectrolytes on fibre swelling, beating rate, fibre flocculation, drainage and strength properties are discussed. Pulp fibres sorb electrolytes because of various acidic groups naturally present in hemicelluloses and lignin residues, also because of various oxidation reactions. Ion exchange reactions occur between the acidic groups and electrolytes on wood pulps, but purified pulps are much less acidic and sorb salts by means of surface reactions that are less well characterised. Dilute alkalis increase fibre swelling, beating rate and strength properties of pulps. The effects of cations vary with valency and concentration. Generally, rate of beating and strength properties are enhanced slightly by monovalent cations, retarded and reduced markedly by trivalent and quadrivalent cations, unaffected by divalent cations. Ion antagonism is observed. Electrolytes change the electrokinetic potential of fibres as expected and drainage rate of the pulp is a maximum at the isoelectric point, unless hydrous precipitates have formed by hydrolysis of the salt. The effects of surface-active agents are more complex.
Low molecular weight electrolytes have discernible effects on fibre flocculation at low consistencies (0.01-0.05 per cent) and low rates of shear, but these effects are negligible at papermaking consistencies, unless hydrolysis of the salt occurs. The effects of polyelectrolytes are pronounced under papermaking conditions and may possibly be explained by La Mer’s theory of polymer flocculation.
The factors that influence retention of wet strength polymers by fibres are discussed. The rate of retention appears to be governed by a diffusional transport process rather than a molecular segment adsorption step.
The mechanism of development of wet strength apparently involves partial diffusion of the resin into the fibrous structure followed by curing of the resin, which subsequently restricts swelling of the bond region in water. Little evidence exists for the formation of chemical bonds between pulp fibres and the wet strength polymer. Very pure pulps may be an exception.
Soluble gases become insoluble during papermaking and have profound effects upon stock preparation, drainage and formation on the machine and final sheet properties. Foam is discussed as a competition between two rate processes-the rate of introduction of gases and the rate of foam collapse. The rate of foam collapse may be increased substantially by anti-foams. A theory of anti-foam action is discussed.
Cambridgepp 773Effects of Soluble Non-fibrous Materials on Formation and Consolidation of Paper Webs – Prepared ContributionAbstractPDF
Cambridgepp 959-976Effects of Dry Pressing on Printing Properties of Uncoated Paper WebsAbstractPDF
Uncoated paper webs containing ground wood were pressed between surfaces of various hardnesses, using different combinations of pressure and moisture content. The physical and printing properties of the pressed webs were measured. For a given web, the properties that affect print-through such as opacity, scattering power and bulk were determined by the combination of moisture content and pressure that was used. In addition, roughness was influenced by the hardness of the surface used to press the paper. Some treatments gave results similar to super calendered paper in all respects but for gloss, even though no shear was used during pressing. It was concluded that an optimum degree of compacting existed for paper intended to be printed on both sides.
Cambridgepp 896Effects of High Consistency Refining on the Properties of the Consolidated Web – Prepared ContributionsAbstractPDF
A theory is presented to describe the relationship between the structure ofasheetofpaperandtheflowoffluidsthroughit.Basedonthemultiplanarconcept of paper, it defines a pore through the sheet in terms of structural and hydrodynamic variables. The effective pore size distribution thus depends on the type of flow,as well as on the structure of the sheet. It is in all cases approximately lognormal, with a standard deviation proportional to the mean.
The theory is applied to the problem of the maximum pore size and to laminar flow, for which the connection with the Kozeny-Carman equation is established.
The theory correctly predicts relationships between physical and structural variables and fibre/sheet properties. Numerical agreement with experiments is still limited by the lack of an appropriate definition of a layer in the multi-planar model.
Cambridgepp 909-927Relationships between Mechanical and Optical Properties of Paper Affected by Web ConsolidationAbstractPDF
The relationships between bonding strength and web consolidation as affected by beating and wet pressing have been investigated. The effect of both the forces of external pressure and surface tension on the structure and on single fibre elements and crossings is discussed in the light of relevant publications. Wet pressing can exercise both direct effects and effects attributable to the induced liquid flow in the sheet. Various types of bonding strength measurement have been covered and attention has been devoted to the question whether data on the magnitude of the bonded area can be derived from scattering measurements. On introducing variations in the bonded area by means of variation in the wet pressure, investigations have shown that, for a given increase in bonded area, beating is more effective than wet pressing in increasing the rupture strength.
In the present investigation, use has been made of a method developed previously to relate irreversibly expended work to bond breakage with a view to assessing the effect of beating and wet pressing on the bonding strength value. These tests indicate that, for some pulp qualities with a high hemicellulose content, the bonding strength rises with increases in the degree of beating and falls on the application of higher wet pressure. For bleached and unbleached pulp with a low hemicellulose content, the bonding strength is (as has been found earlier) virtually independent of both beating and wet pressing. The possible reasons for the beating and wet pressing effects are discussed and some alternatives proposed. Although no satisfactory explanation can be found, it is believed that beating increases the possibilities of intimate contact between the surfaces and gives rise to a structure that has larger radii of curvature between the building elements. On the other hand, wet pressing may permanently damage the cell walls and result in less entangled contact zones and a structure of more angular configuration.
The Kubelka-Munk equations are presented and some consequences of these regarding the influence of brightness, formation and optical bleaching agents on opacity are discussed. The main part of the paper deals with the lights cattering properties of paper and the influence on the opacity of such different variables as fibre dimensions, pulping and bleaching processes, pulp drying,beating, fibre orientation, pressing and drying on the paper machine. It is shown how intimately opacity is affected by the degree of fibre-to-fibre bonding within the sheet.
Cambridgepp 943-947Some Optical Consequences of the Consolidation of Paper – Prepared ContributionsAbstractPDF
Oxfordpp 801-811Determination of Length and Width of Nanocelluloses from Their Dilute DispersionsAbstractPDFLength/width and their distribution of nanocelluloses, prepared from wood pulps with or without chemical pretreatment, are key factors in application to high-strength and light-weight composites, transparent optical films, gas-barrier films, electronic devices, etc. Although microscopy images provide some length/width information, the number of measurable nanocellulose elements is limited. In this paper, three methods to determine nanocellulose lengths and widths are presented. The field-flow-fractionation (FFF) method combined with static light scattering was applied to dilute aqueous TEMPO-oxidised cellulose nanofibril (TOCN) dispersions to obtain avarage lengths, length distributions, and widths of different TOCNs. Although TOCN elements with lengths > 300 nm coiuld not be separated properly according to their lengths by the FFF system, TOCNs with lengths < 300 nm were adequately separated, depending on the lengths by the FFF system, and provided length/length distributions and widths, well corresponding to those obtained from microscopy images. Intrinsic viscosities of TOCNs with different lengths and widths were obtained viscosities of TOCNs with different lengths and widths were obtained uusing shear viscosity measurement of dilute aqueous TOCN dispersions . When the obtained intrinsic viscosities of TOCN dispersions were compared with aspect ratios p of TOCNs measured from their microscopy images, these two factors had good relationship, when the constant value of TOCN density (), =0.15*p1.9 was used. Compared to length measurement from microscopy images, the viscosity methods provide average lengths og numerous amounts of TOCN elements present in the dispersions. Seven types of nanocelluloses with different average widths and width distributions as well as those with different network strictures were prepared via different mechanical and chemical/mechanical processes, and the turbidities of their dilute dispersions were measured. The widths of nanocelluloses were calculated from the respective turbidity plots based on the theory of light scattering for thin and long particles. The turbidity-derived widths of the seven nanocelluloses ranges from 2 to 10 nm, and showed good correlations with the thickness of nanocelluloses measured from their microscopy images.
Oxfordpp 823-836Investigating Silica Nanoparticle-polyelectrolyte Structures in Microﬁ Brillated Cellulose Flms by Scattering TechniquesAbstractPDF
We report the cationic polyelectrolyte (CPAM)-SiO2 nanoparticle (NP) interactions in suspension and in a sheet form, when mixed with microfibrillated (MFC), using dynamic light scattering (DLS) and small angle X-ray scattering (SAXS) techniques. The CPAM-SiO2 NP suspensions were prepared by adding NPs into CPAM drop wise and composites were prepared by adding CPAM-SiO2 suspension into MFC and through standard paper making procedure. DLS revealed that increase in CPAM dosage creates larger sized CPAM-NP aggragates because more NPs can be picked up by stretched CPAM chains. SAXS study revealed that CPAM-SiO2 NP assembly in the formed nanopaper fits well with a sperical core shell model (with SiO2 partially covered with CPAM) and sphere model (SiO2 alone) combined together. Understanding the interaction between polyelectrolyte-NP system through such scattering techniques enables us to engineer novel cellulose based composites for specific applications.
Oxfordpp 813-821Preparation and Utilization of Highly Transparent and Viscous Dispersion of Phosphorylated Cellulose NanoﬁbersAbstractPDF
Oxfordpp 839-863Fiber-ﬁber Bond Formation and Failure: Mechanisms and Analytical TechniquesAbstractPDF
In this paper we give a literature overview on three different aspects of pulp fiber-fiber bonding. First we are reviewing how the adhesion between the pulp fibers is created by the capillary pressure during drying of a sheet. Second we are discussing the individual mechanisms relevant for fiber-fiber bonding. They can be grouped in three different groups: (a) The area in molecular contact, which also includes interdiffusion; (b) the intermolecular bonding mechanisms hydrogen bonding, Van der waals forces and coulomb interaction; (c) the mechanical bonding mechanisms which are capillary bridges and mechanical interlocking. The third and last part of the review discusses the failure process of fiber-fiber bonds and related single fiber-fiber bond testing methods. The general emphasis of the paper is set on providing a general understanding of the processes responsible for how bonds between fibers are created, how they work and how they are failing.
A novel methodology is developed to visualize and quantify biomolecules adsorption at the cellulose film0liquid interface. Hydrogenated cellulose (HC) films were made from cellulose acetate and deuterated cellulose (DC) films produced using deuterated bacterial cellulose. Deuterated bacterial cellulose was obtained by growing the Gluconacetobacter xylinus strain ATCC 53524 in D2O media. Horse Radish Peroxidase (HRP), a robust and well knw enzyme, was selected as model functional biomacromolecule to adsorb at the cellulose interface. The film thickness and quantification of adsorbed HRP molecules were characterized by X-ray and neutron reflectivity (NR) measurements. Reflectivity data analysis reveals the cellulose films to be smooth (low roughness) and uniform. The HC and DC films are 206 A and 92 A thick, respectively, and both films swell in the aqueous buffer solution. In NR measurements, it is difficult to trace the adsorbed HRP layer on HC film due to the small scaterring length density (SLD) difference between HC and HRP providing no contrast. However, using deuterated cellulose (DC) film provides sufficient SLD difference (contrast) with respect to the SLD of HRP. The adsorbed HRP layer is 110A thick and occupies a volume fraction of 20%. Using deuterated cellulose films enabled the quantification of thin and partial layers of proteins at the liquid interface. Quantifying and controlling the morphology and functionality of biomolecules at the cellulose interface enables to efficiently develop and optimize low cost cellulose based diagnostics devices with superior functionalization.
Reactivity is an important quality parameter form some grades of pulp, but its estimation is usually complex and time demanding. The study verified the possibility to utilize an alternative rheological approach to investigate pulp reactivity rapidly and with limited effort. 12.5 mL of pulp at 1.5% consistency was dissolved in 12.5 mL bis(ethylenediamine) pulp copper (II) hydroxide solution (CED) 1M The reaction was monitored by a torque rheogram and its two indices: the optimal dissolution time (ODT) and the initial dissolution rate (IDR). The method used to assess pulps either hornified to different extents or subjected to enzymatic hydrolysis. ODT was shown to decrease with increasing pulp swelling, while IDR reported the opposite trend. Both the indices were shown to be sensitive to pulp treatments. However, the ODT showed larger differences between hardwood and softwood pulps. The method had reasonable statistical reliability and required only 1.5 h per measurement.
Oxfordpp 865-894Towards Wet Resilient Paper – Fiber Modiﬁcations and Test Method DevelopmentAbstractPDF
Wet paper that has been crumpled into a ball shows little tendency to recover to a planar shape when the applied pressure is released – a characteristic called poor wet resiliency. We report the results of an investigation into approaches to improve paper wet resiliency through the choice of fiber types and fiber treatments. Following the lead of the textile industry and the patent literature, wet recovery angle (WRA) was used as a measure of wet resiliency. In this technique, wet strips of paper are folded, without creasing, pressed, and then released. The WRA was measured after the paper relaxed – the greater the WRA, the more resilient the paper.
All of our sheets with a WRA > 0° contained PAE, a standard wet strength resin. Except for sheets based on Abaca fibers, standard PAE or PAE + CMC (carboxymethyl cellulose) applications gave very low WRA. Instead, conventional fibers had to undergo wither TEMPO oxidation or CMC grafting before PAE application. Both fiber treatments substantially increase fiber surface charge density, promoting PAE adsorption and, more importantly, giving covalent bonding sites on the fiber surfaces for grafting PAE.
When comparing the WRA values from treated fibers (TEMPO oxidation or CMC grafting), the ranking was Abaca >>Lyocell > bleached southern softwood kraft > bleached eucalyptus kraft. For pulp mixtures, treated fiber contents of 20-40% had a much bigger influence on WRA compared to wet tensile strength.
Wet-resiliency is due to the swelling of the “hinge region” in folded wet paper, in combination with a sufficiently strong fiber network that can translate the swelling forces into shape recovery. Limited data suggests that the extent of recovery from z-directional wet compression is directly correlated with WRA values. By contrast, wet tensile strength is weakly correlated with WRA.