| 1. |
- Berg, Jan-Erik, 1957-
(författare)
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Wood and fibre mechanics related to the thermomechanical pulping process
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The main objective of this thesis was to improve the understanding of some aspects on wood and fibre mechanics related to conditions in the thermomechanical pulping process. Another objective was to measure the power distribution between the rotating plates in a refiner. The thesis comprises the following parts: –A literature review aimed at describing fracture in wood and fibres as related to the thermomechanical pulping process –An experimental study of fracture in wood under compression, at conditions similar to those in feeding of chips into preheaters and chip refiners –An experimental study of the effect of impact velocity on the fracture of wood, related to conditions of fibre separation in the breaker bar zone in a chip refiner –A micromechanical model of the deterioration of wood fibres, related to the development of fibre properties during the intense treatment in the small gap in the refining zone –Measurements of the power distribution in a refiner. The fracture in wood under compression was investigated by use of acoustic emission monitoring. The wood was compressed in both lateral and longitudinal directions to predict preferred modes of deformation in order to achieve desired irreversible changes in the wood structure. It was concluded that the most efficient compression direction in this respect is longitudinal. Preferable temperature at which the compression should be carried out and specific energy input needed in order to achieve substantial changes in the wood structure were also given. The fibre separation step and specifically the effect of impact velocity on the fracture energy were studied by use of a falling weight impact tester. The fracture surfaces were also examined under a microscope. An increase in impact velocity resulted in an increase in fracture energy. In the thermomechanical pulping process the fibres are subjected to lateral compression, tension and shear which causes the creation of microcracks in the fibre wall. This damage reduces the fibre wall stiffness. A simplified analytical model is presented for the prediction of the stiffness degradation due to the damage state in a wood fibre, loaded in uni-axial tension or shear. The model was based on an assumed displacement field together with the minimum total potential energy theorem. For the damage development an energy criterion was employed. The model was applied to calculate the relevant stiffness coefficients as a function of the damage state. The energy consumption in order to achieve a certain damage state in a softwood fibre by uniaxial tension or shear load was also calculated. The energy consumption was found to be dependent on the microfibril angle in the middle secondary wall, the loading case, the thicknesses of the fibre cell wall layers, and conditions such as moisture content and temperature. At conditions, prevailing at the entrance of the gap between the plates in a refiner and at relative high damage states, more energy was needed to create cracks at higher microfibril angles. The energy consumption was lower for earlywood compared to latewood fibres. For low microfibril angles, the energy consumption was lower for loading in shear compared to tension for both earlywood and latewood fibres. Material parameters, such as initial damage state and specific fracture energy, were determined by fitting of input parameters to experimental data. Only a part of the electrical energy demand in the thermomechanical pulping process is considered to be effective in fibre separation and developing fibre properties. Therefore it is important to improve the understanding of how this energy is distributed along the refining zone. Investigations have been carried out in a laboratory single-disc refiner. It was found that a new developed force sensor is an effective way of measuring the power distribution within the refining zone. The collected data show that the tangential force per area and consequently also the power per unit area increased with radial position. The results in this thesis improve the understanding of the influence of some process parameters in thermomechanical pulping related wood and fibre mechanics such as loading rate, loading direction, moisture content and temperature to separate the fibres from the wood and to achieve desired irreversible changes in the fibre structure. Further, the thesis gives an insight of the spatial energy distribution in a refiner during thermomechanical pulping.
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| 2. |
- Enberg, Sofia
(författare)
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Storage of Hydrogen Peroxide Bleached Mechanical Pulp : Reduction in Reflectance over the Visible Spectrum
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The objective of this thesis is to determine possible causes of the darkening of hydrogen peroxide bleached mechanical pulp over the visible spectrum and their relative contributions. It focuses on both process conditions and the composition of the pulp and the dilution water, including additions or losses of material along the process line from the bleach tower to the paper machine.A mapping of the optical properties of the pulp along the process showed that the fine fraction of the pulp darkened more than the long fibre fraction. Simulation of retention times of different fractions showed that the main part of the fine material is retained in the paper within a few hours, a small part might circulate for considerably longer time and may therefore be strongly coloured.Storage trials were mainly performed using a hydrogen peroxide bleached mechanical pulp intended for SC paper made of Norway spruce (Picea abies), sampled on one occasion and stored in a freezer. Unwashed or well-washed pulp was stored in distilled water or in different process waters. Some complementary trials were included, e.g. unbleached pulp.Time and temperature were the process variables that gave the strongest darkening of the pulp, as expected, both in a clean and a more process-like system, whereas pH only had an effect in the presence of process waters; the highest brightness stability was seen at a pH around 5.5–6.0.The darkening was due to an increase in the light absorption coefficient (k) beginning at short wavelengths, but after longer storage times the increase in kλ also became noticeable at longer wavelengths. The colour (CIE L*, a*, b*) of the pulp changed towards red and yellow, initially more towards red and then more towards yellow. These changes were clearly visible.Washing of the bleached pulp made it less sensitive to storage; possibly due to the removal of extractives, lignin-like substances, metals and pulp fines. This washing had little effect before storage and the amount of material removed was small.The pulp darkened more when stored in process waters compared to distilled water. Apart from fibres, most of the colour was associated with pulp fines or filler but some colour was also found in the dissolved and colloidal fractions. At an increased pulp consistency, the increase in k460 was smaller.Storage in white water from the paper machine gave extensive discolouration with a shoulder in the absorption spectrum around 550–650 nm, which increased with time. The addition of ferric ions increased the light absorption coefficient during storage, but could not explain the increased absorption at 550–650 nm nor could it be the only cause of the darkening in the mill system. A cationic basic violet dye gave a shoulder in the absorption spectrum similar to that of the mill system, but the absorption of the dye did not increase during storage. Model calculations indicate, but do not prove, that ferric ions together with violet and red dyes could have played a major, but not exclusive role in the colour observed in the mill system after storage. The darkening not accounted for, at longer wavelengths and around 550–650 nm, is suggested to be related to fines and fillers including dissolved and colloidal substances associated with these particles.A method to produce representative sheets for determination of optical properties of mechanical pulps was developed. The new method makes it possible to follow changes in light absorption and light scattering coefficients over the visible range of wavelengths. It is approximately six times faster than standard methods, reduces the risk of additional darkening of the sample and can be used with small pulp quantities.The deviation from the expected linear behaviour of the light scattering coefficient, s, at wavelengths corresponding to strong light absorption has been studied using the Kubelka-Munk model and the angular resolved DORT2002 radiative transfer solution method. The decrease in s could not be explained by errors introduced in the Kubelka-Munk modelling by anisotropic scattering.
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| 3. |
- Ferritsius, Olof
(författare)
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Beyond averages – some aspects of how to describe a heterogeneous material, mechanical pulp, on particle level
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- For a more profound understanding of how a process works, it is essential to have a relevant description of the material being processed. With this description, it will be easier to evaluate and control processes to produce more uniform products with the right properties. The focus of this thesis is on how to describe mechanical pulps in ways that reflect its character.Mechanical pulps are made from wood, a highly heterogeneous material. Common practice within the pulping industry and academy is to describe mechanical pulps and its wide variety of particles in terms of averages. The energy efficiency of the mechanical pulping process is usually calculated without taking into account the characteristics of the wood fed to the process. The main objective of the thesis is to explore ways to make more detailed descriptions of mechanical pulps. A second objective is to propose useful ways to visualise these descriptions.The studies were carried out in full-scale mill operations for TMP of publication grades and CTMP for board grades with Norwegian spruce as raw material. The particles in the pulps were analysed in an optical particle analyser for several properties such as length, curl, wall thickness, diameter,and external fibrillation for 10,000 to 60,000 particles per sample to cover their wide property variation. The data was analysed by factor analysis, a method to reduce the multidimensional data space, and also compared with data simulations.Several examples were identified where averages based on wide and skewed distributions may hide useful information and therefore result in misleading conclusions regarding the fibrous material and process performance. A method was developed to calculate the distribution of a common bonding factor, BIND (bonding indicator) for individual particles. This factor is calculated from external fibrillation, wall thickness and diameter measured in an optical particle analyser. Distributions of BIND is one way to characterize and visualise the heterogeneity of mechanical pulp. A characteristic BIND-distribution is set in the primary refiner stage, depending on both wood and process conditions and remains mostly intact through the process.It was demonstrated that both BIND-distributions and 4D maps of the measured property distributions could be used to assess the tails of the distributions (extreme values), energy efficiency, and fractionation efficiency in a new way. It was even possible to get a measure for energy efficiency for a primary stage refiner, since a method was developed where the wood raw material was evaluated in the same way as the pulp discharged from the refiner.It was demonstrated that the average length-length-weighted fibre length, commonly referred to as the average weight-weighted fibre length, is a relevant way to express the amount of long fibres, i.e. “length factor”. The commonly used average length-weighted fibre length may lead to erroneous conclusions. Through data simulations of curl and fibre length on particle level it was found that today’s analysers may underestimate the true length of the particles, especially if they are prone to be curled. As a result, theranking of pulps may be altered.It was concluded that although there is an ISO standard, or long-time used property, it does not necessarily imply that it is a relevant method. Misleading conclusions may be drawn based on current methods; here, modifications of these methods are suggested.The main contribution of this study is the finding that that a highly heterogeneous material such as mechanical pulps could be described in new ways through visualisation of data in 4D maps. These maps reveal casualconnections and more pertinent questions may be raised in thecommunication along the chain product-pulp-wood.Going beyond averages may reveal discrepancies in the process and material that were previously unknown, and lead to a more profound understanding. It seems that the mechanical pulping process can be even further simplified than previously expected. It has been concluded that to operate the process more efficiently, and for make products with just the right quality, the main focus should be on the raw material and the primary refiner stage from a heterogeneity point of view.
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| 4. |
- Gorski, Dmitri
(författare)
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ATMP Process : Improved Energy Efficiency in TMP Refining Utilizing Selective Wood Disintegration and Targeted Application of Chemicals
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis is focused on the novel wood chip refining process called AdvancedThermomechanical Pulp (ATMP) refining. ATMP consists of mechanical pretreatmentof chips in Impressafiner and Fiberizer prior to first stage refining atincreased intensity. Process chemicals (this study was concentrated on hydrogenperoxide and magnesium hydroxide) are introduced into the first stage refiner.It is known that the use of chemicals in TMP process and first stage refining atelevated intensity can reduce the energy demands of refining. The downside is thatthey also alter the character of the produced pulp. Reductions in fibre length andtear index are usually the consequences of refining at elevated intensity. Additionof chemicals usually leads to reduction of the light scattering coefficient. Usingstatistical methods it was shown that it is possible to maintain the TMP character ofthe pulp using the ATMP process. This is explained by a separation of thedefibration and the fibre development phases in refining. This separation allowsdefibration of chips to fibres and fibre bundles without addition of chemicals orincrease in refining intensity. Chemicals are applied in the fibre developmentphase only (first stage refiner). The energy demand in refining to reach tensileindex of 25 Nm/g was reduced by up to 1.1 MWh/odt (42 %) using the ATMPprocess on Loblolly pine. The energy demand in refining of White spruce, requiredto reach tensile index of 30 Nm/g, was reduced by 0.65 MWh/odt (37%).Characterizations of individual fibre properties, properties of sheets made fromlong fibre fractions and model fibre sheets with different fines fractions werecarried out. It was established that both the process equipment configuration (i.e.the mechanical pre‐treatment and the elevated refining intensity) and the additionof process chemicals in the ATMP process influence fibre properties such as external and internal fibrillation as well as the amount of split fibres. Improvementof these properties translated into improved properties of sheets, made from thelong fibre fractions of the studied pulps. The quality of the fines fraction alsoimproved. However, the mechanisms of improvement in the fines quality seem tobe different for fines, generated using improved process configuration andaddition of process chemicals. The first type of fines contributed to better bondingof model long fibre sheets through the densification of the structure. Fines whichhave been influenced by the addition of the process chemicals seemed in additionto improve bonding between long fibres by enhancing the specific bond strength.The improved fibre and fines properties also translated into better airpermeability and surface roughness of paper sheets, properties which areespecially important for supercalendered (SC) printing paper. The magnitude offibre roughening after moistening was mainly influenced by the processequipment configuration while the addition of process chemicals yielded lowestfinal surface roughness due to the lowest initial surface roughness. There was nodifference in how fines fractions from the studied processes influenced the fibreroughening. However, fines with better bonding yielded model fibre sheets withhigher PPS, probably due to their consolidation around fibre joints. Hence, thedecrease in PPS can probably be attributed to the improvements in the long fibrefraction properties while the improvement of fines quality contributed to thereduction of air permeability.The process chemicals, utilized in the ATMP process (Mg(OH)2 and H2O2) alsoproved to be an effective bleaching system. Comparable increases in brightnesscould be reached using the ATMP process and conventional tower bleaching.Maximum brightness of the pulp was reached after approximately 10 minutes ofhigh‐consistency storage after refining or 40 minutes of conventional bleaching.This study was conducted using a pilot scale refiner system operated as a batchprocess. Most of the experiments were performed using White spruce (Piceaglauca). In Paper I, Loblolly pine (Pinus taeda) was used. It is believed that theresults presented in this thesis are valid for other softwood raw materials as well,but this limitation should be considered.
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| 5. |
- Hellström, Lisbeth
(författare)
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On the wood chipping process : a study on basic mechanisms in order to optimize chip properties for pulping
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In both the chemical and mechanical pulping process, the logs are cut into wood chips by a disc chipper before fibre separation. To make the wood chipping process more efficient, one have to investigate in detail the coupling between process parameters and the quality of the chips. One objective of this thesis was to obtain an understanding of the fundamental mechanisms behind the creation of wood chips. Another objective with the thesis was to investigate whether it was possible to, in a way tailor the chipping process so as to reduce the energy consumption in a following mechanical refining process.Both experimental and analytical/numerical approaches have been taken in this work. The first part of the experimental investigations, were performed with an in-house developed chipping device and a digital speckle photography equipment.The results from the experimental investigation showed that the friction between the log and chipping tool is probably one crucial factor for the chip formation. Further more it was found that the indentation process is approximately self-similar, and that the stress field over the entire crack-plane is critical for chip creation.The developed analytical model predicts the normal and shear strain distribution and to be more specific, the model can predict the compressive stresses parallel to the fibre direction for an assumed linear elastic and orthotropic material. The analytical distributions were found to be in reasonable agreement with the corresponding distributions obtained from a finite element analysis.To be able to study the chipping process under realistic conditions, which for example means to use chipping rates representative for a real wood chipper, a laboratory chipper was developed. Details regarding the chipper and how to evaluate the force measurements are given together with an example of how the force on the cutting tool (the knife) varies with time during cutting.To investigate the influence of a certain chipping process parameter, the chips were after production in the laboratory chipper, refined in a pilot refiner during conditions optimized for TMP (thermomechanical pulp) and CTMP (chemithermomechanical pulp) processes. It was concluded that the details concerning the chip process had a large impact on e.g. the energy consumption in both first stage and second stage refining. Results showing this are given in this thesis.
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| 6. |
- Joelsson, Tove
(författare)
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The influence of Pulp Type and Hot-pressing Conditions on Paper Strength Development
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The hot-pressing technology has proven to have the potential for manufacturing of strong, wet stable materials based on eco-friendly renewable and recyclable lignocellulose. The purpose of this work was to study how the pulp characteristics and the hot-pressing conditions affect the dry and wet strength properties of paper. Two different devices for hot-pressing were used. One using felted nip and a heated cylinder with a temperature limit at 200°C and one new design using a hard nip and an IR-heated steel belt with a temperature limit of 300°C.The results showed that dry strength can increase up to 150% for high yield pulp (HYP) based sheets at pressing temperatures well above the softening temperature of lignin. The maximum dry tensile strength obtained was 70 kNm/kg at 200°C pressing temperature and the corresponding value for a lignin-rich kraft pulp was about 130 kNm/kg, an increase of 30%. For all lignin-rich pulps the dry strength increased linearly with density up to 200°C whereafter it levelled off and was reduced.The wet tensile strength for paper based on HYP increase from 2 to 28 kNm/kg and for paper based on unbleached kraft pulp from 5 up to 60 kNm/kg in the temperature interval 20-270°C. The increase in wet strength independently of pulp grade seemed to be exponential to the pressing temperature with the steepest slope above 150°C. For unbleached kraft pulp a lignin content of minimum 7% seemed to be necessary for improved wet strength but 12% gave the highest value within the studied interval. In HYPs the lignin content is 25-28% depending on the pulping process but the level of wet strength was lower which is probably related to the lower density and lower dry strength compared to unbleached kraft pulps.Dry strength of lignin-rich paper is enhanced by improved fibre-fibre contact that can be improved by compression at high temperature, well above softening temperature (Tg) of moist lignin, native or chemically modified. It is known that sulfonation of lignin lowers the Tg in moist conditions. It was observed that at 150°C temperature the dry strength increased by 15% to a level of 71 kNm/kg for the high sulfonated pulp compared to the lower sulfonated pulp that had a dry strength of 60 kNm/kg at the same density. The level of wet strength was however not found to be affected by the sulfonation.Paper strength is to a large extent related to pulp fibre morphology and fines content. In this work studied these aspects where briefly studied with respect to hot-pressing and the results indicate that the relative influence of fibre morphology seems to be reduced with increasing pressing temperature. Hot-pressed sheets based on a coarse fines free fibre fraction showed 100% dry strength increase and wet strength increase up to 20 kNm/kg. The dry and wet strength were however also shown to be favoured by the presence of fines fraction.Wet strength development as a function of temperature was fitted to an Arrhenius type of equation and activation energies were found to be similar for very different pulp grades provided that the lignin content is above 7%. This could indicate that the process(es) giving wet strength were similar.It was found that the ratio wet:dry strength was about 35-60% for all lignin containing pulp grades. A rule of thumb for an efficient wet strength resin is that the wet: dry strength ratios are 15%. This means that it should be possible to manufacture wet-strong paper from lignin-rich pulps by means of hot-pressing without using wet strength chemicals. The concern regarding repulpability of such material led to an initial test to disintegrate this paper showing that re-pulping under vigorous mixing at room temperature is possible.The connection between dry and wet strength, high pressing temperature, and lignin content of pulp fibres is suggested to be related to some redistribution mechanisms of surface lignin between adjacent fibres. The improved wet strength and water resistance could be due to intermixing of lignin polymers across the interface between contacting fibre surfaces, or it could be lignin sufficient to cover the fibre-fibre bonds and/or chemical modifications, but these remain open questions.
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| 7. |
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| 8. |
- Nelsson, Erik, 1983-
(författare)
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Improved energy efficiency in mill scale production of mechanical pulp by increased wood softening and refining intensity
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis focuses on the electric energy efficiency of single stage double disc refining for production of printing grade mechanical pulp from Norway spruce wood chips. The thesis is based on the hypothesis, that more energy efficiency refining can be attained by balanced increases of wood softening and refining intensity. Five mill scale trials were performed where wood softening and refining intensity was varied by applying or changing the following process parameters and variables:Chip pretreatment/impregnation with waterLow dosages of sodium sulfite (Na2SO3) added to impregnationTemperature and retention time in the atmospheric preheater binRefining temperature (housing pressure)Feeding segment design combined with increased production rateBy combining suitable increases in wood softening and refining intensity, it was possible to reduce the specific electric energy consumption in refining by 15% (~290 kWh per bone dry ton (bdt)) while preserving important pulp properties within ±5%, compared to the standard double disc refining process. This was done by combining chip impregnation, using an addition of 0.36% (on bone dry basis) sodium sulfite, with a new feeding segment design which enabled 25% higher production rate.When using the new feeding segment design at an increased production rate at unchanged wood softening, it led to reduced fiber length and increased sheet light scattering coefficient at certain tensile index, compared with the standard segment design at normal production rate. This is consistent with the effects normally seen when the refining intensity is increasing. The specific electric energy consumption was 8% lower at a tensile index of 43.5 Nm/g (on Rapid Köthen laboratory sheets) compared to refining at lower intensity using the standard segment design at normal production rate.Mechanical chip pretreatment with subsequent water impregnation showed a reduction in specific electric energy consumption of 6% (~120 kWh/bdt). When chip impregnation was applied in a later trial with a milder chip compression, it led to increased wood softening seen as better preserved fiber length and reduced light scattering coefficient. This resulted in a reduction in tensile index at certain specific electric energy consumption when applied with the standard refining condition but to an increase in tensile index when applied with refining at higher intensity using the feeding segment design at higher production rate.An addition of 1.2% sodium sulfite during impregnation led to a sulfonate content of pulps of ~0.28% (as Na2SO3 equivalents, including post sulfonation) and an average increase in tensile index of about 8.3 Nm/g, when compared to unsulfonated pulps at certain specific electric energy consumption. The increase in tensile index correlated with increased delamination and internal fibrillation of fibers (measured by Simon’s staining), which indicate that the increase in tensile index for sulfonated pulps was a result of improved fiber flexibility and collapsibility. The reduction in disc gap at certain specific electric energy consumption in refining due to an increased wood softening after sulfonation may explain the increase in delamination and internal fibrillation for sulfonated pulps. The smaller disc gap probably led to a more intense refining, i.e. loading at higher deformation rates due to a higher degree of deformation in bar crossings.Different temperatures (80 vs. 97°C) and retention times (6 vs. 9 min.) in the atmospheric preheater bin were studied. This showed that the lower temperature and shorter retention time was beneficial for the tensile strength and light scattering of pulp when applying low dosage sodium sulfite pretreatment. This was most likely a result of too high degree of wood softening prior to defibration in the breaker bar zone when combining low dosage sodium sulfite pretreatment with the higher preheating bin temperature at longer retention time.Different refining temperatures (4.6 and 6.4 bar(g) refiner housing pressure) were evaluated both without and with low additions (0.6% and 1.2%) of sodium sulfite. Raising the refining temperature increased tensile index by 3.2 Nm/g and the addition of 1.2% sodium sulfite by 8.6 Nm/g. The combined increase (~12 Nm/g) was similar to the effect of increasing the specific electric energy consumption by 380 kWh/bdt, when comparing pulps at equal tensile index. However, the pulps produced with increased refining temperature and sodium sulfite addition had lower light scattering coefficient at certain tensile index. The combination of increased refining temperature and addition of 0.6% sodium sulfite was interesting and resulted in pulp with higher tensile index, light scattering coefficient and brightness together with lower shives content at certain specific electric energy consumption, compared with pulp produced at the lower refining temperature without addition of sodium sulfite.Finally, an implementation of the technology presented here is discussed in relation to the Braviken mill (Holmen Paper AB, Norrköping, Sweden) concerning reduction in electric energy consumption and steam recovery. The technology has potential to reduce the electrical energy use by ~100 GWh/year at the Braviken paper mill, where this study was performed.
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| 9. |
- Osong, Sinke Henshaw
(författare)
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Mechanical Pulp-Based Nanocellulose : Processing and applications relating to paper and paperboard, composite films, and foams
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis deals with processing of nanocellulose originating from pulps, with focus on mechanical pulp fibres and fines fractions. The nanocellulose materials produced within this research project were tested for different purposes ranging from strength additives in paper and paperboard products, via composite films to foam materials. TAPPI (Technical Association of Pulp & Paper Industry) has recently suggested a standard terminology and nomenclature for nanocellulose materials (see paper I). In spite of that we have decided to use the terms nano-ligno-cellulose (NLC), microfibrillated cellulose (MFC), nanofibrillated cellulose (NFC) and nanocellulose (NC) in this thesis . It is well-known that mainly chemical pulps are used as starting material in nanocellulose production. However, chemical pulps as bleached sulphite and bleached kraft are quite expensive. One more cost-effective alternative can be to use fibres or fines fractions from thermo-mechanical pulp (TMP) and chemi-thermomechanical pulp (CTMP). In paper II-IV, fractionation has been used to obtain fines fractions that can easily be mechanically treated using homogenisation. The idea with this study was to investigate the possibility to use fractions of low quality materials from fines fractions for the production of nanocellulose. The integration of a nanocellulose unit process in a high-yield pulping production line has a potential to become a future way to improve the quality level of traditional products such as paper and paperboard grades. Paper III describes how to utilise the crill measurement technique as a tool for qualitative estimation of the amount of micro- and nano-material produced in a certain process. The crill values of TMP- and CTMP-based nanocelluloses were measured as a function of the homogenisation time. Results showed that the crill values of both TMP-NLC and CTMP-NLC correlated with the homogenisation time. In Paper V pretreating methods, hydrogen peroxide and TEMPO are evaluated. Crill measurement showed that hydrogen peroxide pretreatment (1% and 4%) and mechanical treatment time did not improve fibrillation efficiency as much as expected. However, for TEMPO-oxidised nanocelluloses, the crill value significantly increased with both the TEMPO chemical treatment and mechanical treatment time. In paper V-VII TEMPO-mediated oxidation systems (TEMPO/NaBr/NaClO) are applied to these fibres (CTMP and Sulphite pulp) in order to swell them so that it becomes easy to disrupt the fibres into nanofibres with mechanical treatment. The demand for paperboard and other packaging materials are steadily increasing. Paper strength properties are crucial when the paperboard is to withstand high load. A solution that are investigated in papers IV and VI, is to use MFC as an alternative paper strength additive in papermaking. However, if one wish to target extremely higher strength improvement results, particularly for packaging paperboards, then it would be fair to use MFC or cationic starch (CS). In paper VI CS or TEMPO-based MFC was used to improve the strength properties of CTMP-based paperboard products. Results here indicate significant strength improvement with the use of different levels of CS (i.e., 20 and 10 kg t–1) and 5% MFC. The strengthening impact of 5% MFC was approximately equal to that of 10 kg t–1 of CS. In paper VII, NFC and nanographite (NG) was used when producing composite films with enhanced sheet-resistance and mechanical properties. The films produced being quite stable, flexible, and bendable. Realising this concept of NFC-NG composite film would create new possibilities for technological advancement in the area of high-yield pulp technology. Finally, in paper VIII, a new processing method for nanocellulose is introduced where an organic acid (i.e., formic acid) is used. This eco-friendly approach has shown to be successful, a nanocellulose with a uniform size distribution has been produced.
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| 10. |
- Rahman, Hafizur, Research Engineer, 1978-
(författare)
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Aspects of optimizing pulp fibre properties for tissue and packaging materials
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- To improve the competitive advantages of pulp fibre-based materials for tissue and packaging over fossil-based products, it is essential to increase knowledge of the selectivity of the cooking and the chemimechanical processes by optimizing the unit operations of impregnation, cooking and refining. A general goal in pulping processes is to achieve as efficient and even fibre separation as possible. A key to achieving this is to improve impregnation uniformity. In the case of chemical pulping, we need to study how a more even distribution of lignin at the fibre level via easily impregnated wood chips can be achieved using classic measures such as equalized hydroxide ion concentration, increased initial sulphide ion concentration, low sodium ion concentration and a low cooking temperature combined with an oxidative and reductive environment. In the case of chemithermomechanical pulp (CTMP) manufacturing, we need to achieve as even a degree of sulphonation as possible at the level of the individual fibres by means of improved sulphite ion distribution within the wood chips before they are pre-heated prior to entering the refiner. Firstly, we have studied selective cooking systems for sulphate pulp manufacturing in oxidative (polysulfide) and reductive (sodium borohydride) environments. The yield increased from 48% to a maximum of 53%, which resulted in faster dewatering when mimicking a tissue papermaking process. This could explain how the advantage of the increased yield (fewer fibres and a more open sheet structure) outweighs the negative effects of the higher hemicellulose content on the dewatering properties. Moreover, the increased proportion of hemicellulose in the fibre walls resulted in improved bonding and increased tensile index at a certain refining energy. Secondly, we have studied the uniformity of impregnation at the fibre level by developing an accurate way of measuring sulphur and sodium content in measuring points that are 5-10 µm in diameter with miniaturized X-ray-based technology. This technology is considered cheap and efficient enough to be introduced in industrial labs and/or in online equipment. Our newly built miniaturized energy dispersive X-ray fluorescence (ED-XRF) demonstrates the capability of imaging sulphur and possibly sodium distribution in wood chip fibres or individual fibres on a micro scale. In parallel, to the above research we have studied a new catalytic lignin-selective cooking method where a substantial portion of the dissolved lignin can be extracted as vanillin, creating significant value and opportunities for new cost-efficient wood biorefinery systems.
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