Dissertations / Theses on the topic 'Mechanical pulping process Tasmania'

The stability of hydrogen peroxide (H2O2) is a critical factor for the brightening of mechanical pulps. Inorganic ions, including Fe, Mn and Cu catalytically decompose H2O2. These troublesome metals promote the rapid transformation of H2O2 to nonselective hydroxyl radicals that degrade the cellulose fibres and decrease yields.
The interaction of aqueous metal•complexes with magnesium metal (Mg°) or bimetallic mixtures of magnesium with either palladium (Pd°/Mg°) or silver (Ag°/Mg°) were optimized to remove metals (Mn, Cu and Fe) from solution with concomitant release of the complexing reagent. The analyte metals were removed by both cementation on the surfaces of the excess Mg° and by precipitation as hydroxides. Overall, the reactions were rapid (3 or 10 min) and very efficient. The accelerators (Ag or Pd) were deposited on the surfaces of the Mg°. In a separate study, the excess of Mg° could be reused to mediate more metals removal without apparent loss of reactivity. Among the other iminodiacetate analogs (CDTA, MEDTA, EGTA, HEDTA, DPTA and MTBE), the EGTA and HEDTA proved to be possible substitutes for both efficient metal removal of Mn, Cu and Fe from solution and efficient release of chelating reagent. The measurement of particle size, performed by laser granulometry, demonstrated that smaller particles of precipitate were generated from metal-EDTA complexes by reaction with NaOH than by reaction with Pd°/Mg° bimetallic mixture. If the suspensions of particles were analyzed in the absence of ultrasound, the particles became aggregated into large flocs (up to 150 mum3 ). The reactivity of the bimetallic mixtures was exploited to remove Cu, Mn, Fe, Zn and Al that had been initially chelated with EDTA or DTPA from a thermomechanical pulp (TMP). After 15 min, the metals had been removed efficiently with the bimetallic mixtures. The EDTA released from the TMP filtrate could be recycled efficiently for a total of three cycles. On the other hand, the DTPA was not released as efficiently. Measurements of turbidity and chemical oxygen demand (COD) indicated no appreciable difference between the pulp samples with either chelating reagent. Residual H2O2 and ISO brightness measurements indicated no apparent differences among pulps that had been treated wi

The catalysed organosolv process is a novel method of pulping that has many advantages over other chemical pulping processes. One of the most important advantages is its 6-12 percentage point higher yield of pulp in comparison to other chemical pulping processes. Short cooking time, low disintegration and refining energy requirements, ease of pulp washing and simplified method of by-product recovery are some of the other advantages. However, due to differences in the chemical nature of the cooking liquor, the basic properties of the fibers differ considerably. In this thesis a detailed study has been carried out on some of the unique phenomena i.e., fiber liberation at a high yield, topochemical preference of delignification and their manifestation on morphology and strength properties of fibers. Pulping results show that softwoods can be pulped easily to a high pulp yield (60%) with a high viscosity of cellulose of 50 mPas. The observed delignification pattern indicates two distinct stages both having first order kinetics. By this process, fast delignification occurs in the bulk delignification stage within which about 70% of the lignin is removed. Loss of residual lignin occurs at a slower rate in the residual delignification stage. The ease of penetration of the cooking liquor and preferential removal of lignin from the middle lamella result in complete fiber liberation at a pulp yield of 57.3% and a Kappa number of 72 (7% residual lignin). The loss of lignin to carbohydrate ratio at 57.3%pulp yield is 1.21:1. The topochemistry of delignification in organosolv pulping is limited to a preferential removal of lignin from the cell corner and middle lamella regions rather than from the secondary wall. In the initial stages of pulping, lignin removal is mostly from the cell corner and middle lamella region. Secondary wall lignin was removed quite slowly and a substantial amount of lignin remained in the secondary wall even after extended delignification. This can be accounted for by the slow hemicellulose removal (loss) from the secondary wall. The relatively high residual lignin retained in the cell corner in comparison to the complete delignification in the middle lamella raises questions about chemical differences and solubility characteristics of the cell corner lignin. The fibers of high-yield pulps are found to be stiffer and form a low density paper with high tear, and average burst and tensile strength. These factors can be correlated with the higher amount of residual lignin material in the fiber secondary wall and the low bonding properties of the fibers. High residual lignin content decreases the internal fibrillation and ability of the fibers to conform with each other during sheet formation. On the other hand, the low-yield fibers (49.8%) were found to be quite flexible and showed higher strength than obtainable with high yield pulps. Organosolv handsheets contain 20 to 30% fewer fibers than kraft papers of the same basis weight. However, the apparent difference in strength properties between organosolv and kraft papers is not disproportionately large. Organosolv lignins isolated from the spent liquor have low molecular weight (1400-2400) and low polydispersity (1.95) when recovered from extended pulping liquors. This indicates that most of the lignin is degraded to a fairly uniform low molecular weight polymer without substantially affecting the reactivity of the natural lignin as it occurs in the native fibers. The simplicity of the pulping process together with the comparable strength properties of the fibers even at higher yields, reveals large potentials of this method as a new pulping process. With some refinements and closer optimization, pulp fully acceptable commercially could be produced by this process.
Forestry, Faculty of
Graduate

The thesis comprises three parts: Existing methods for characterisation of fibre crosssections have been improved, and new methods have been developed. These methods have then been applied to study the effects of wood characteristics and the pulping process on mechanical pulp fibres. Links have been established between fibre structure and paper properties such as surface smoothness and light scattering coefficient.

New methods, based on SEM-images and image analysis, are described for providing cross-sectional fibre dimensions for large fibre populations, for wood tracheids (app. 60 000 tracheids in a wood trunk) and for processed pulp fibres (app. 1000 fibres per sample). The methods are suited e.g. for evaluation of changes in the fibre cross-sections from wood to the finished paper, or for mapping of fibre parameters within and between growth rings in a wood trunk. The treatment of data is discussed, showing how one may examine the changes in different groups of fibres (earlywood fibres, latewood fibres, split fibres) throughout a process.

It is known from the literature that groundwood-based paper is superior to TMP-based paper with respect to printability. Fibres from SGW and PGW-pulp were found to be much more split in the longitudinal direction than TMP-fibres at comparable freeness. Intact groundwood fibres had thicker walls than intact TMP-fibres, but nevertheless super calendered hand sheets made from groundwood fibres were less roughened by moistening than were TMP-based sheets. Both for groundwood pulps and for TMPpulps, it was shown that reduced fibre wall thickness and increased fibre splitting was beneficial for improved surface smoothness and opacity.

Latewood defibrate easier than earlywood during refining. In the case of grinding, there was no particular preference for earlywood or latewood to be defibrated. Reject refining of groundwood reject was, however, found to be very important for defibration of latewood-containing shives. Pulps made from a raw material with more compact fibres (high wall area to lumen area ratio) were found to defibrate easier, and contain less shives. It was found that refining tends to reduce wall thickness most on thickwalled parts of the fibre, thus causing a reduction of the wall thickness variation around the perimeter.

Earlywood fibres were found to be preferentially split during refining. Most fibre splitting occurs during the primary stage, while the fibres are firmly attached to chips or fibre bundles. Latewood fibre wall thickness decreases considerably more than earlywood fibre wall thickness during refining. It seems that choosing an appropriate raw material is more effective than using excessive energy on reducing the wall thickness of thickwalled fibres. Earlywood fibres became more flattened during refining compared to latewood fibres, possibly due to repeated compressions and relaxations in the refiner.

The energy consumption to a given freeness was found to be considerably larger for Scots Pine than for Norway Spruce. However, the fibre transverse dimensions did not differ much between Norway Spruce and Scots Pine. Pine pulps were far less developed than spruce pulps at similar energy level. A possible explanation for the large energy consumption may be that redistribution of extractives at the fibre surface could reduce friction in the refiner. This hypothesis should be further explored.

The results in this study improve the knowledge of which fibre parameters that matter for surface smoothness and opacity of wood-containing publication paper. Further, this study elucidates how important fibre parameters such as wall thickness and fibre splitting are altered during a refining process. The results may be utilized to identify possible ways of modifying the TMP-process in order to produce paper with improved surface smoothness and opacity.

The main abjectives of this work were to evaluate the extent to which extractives in wood chips for mechanical pulping are released into process water during compressive pre-treatment before refining and to develop a method to remove the released extractives from the process water. In thermomechanical pulping, pre-treatments based on a high compression ratio and high temperature, are used to reduce the amount of extractives in wood chips of different raw materials before refining. One objective of this study was to evaluate the removal of extractives from the wood chips during compressive pre-treatment, in an Impressafiner by determining mass balance of extractives around a mill scale Impressafiner installation. The mass balance showed that it was possible to remove up to 15% of extractives before the refining process. Thus one advantage of using an Impressafiner is that removal of dispersed extractives can be done with little loss of fibres, from a small concentrated water stream. Handling of this water is important in order to avoid that the extractives enter the effluent treatment or reach undesirable levels in the process water. Thus the solubility, colloidal stability and flocculation of the extractives in the pressate water was studied. The objective was to obtain a better understanding of the effects of cationic polyelectrolytes on the stability of colloidal extractives in the pressate water from Impressafiner. A high charge density and low molecular mass polymer (poly-DADMAC), a high molecular mass and low charge density polymer (C-PAM) and combination of the polymers (mass ratio 1:1) were used. It was found that these polymers efficiently flocculate colloidal extractives present in the process water via two different flocculation mechanisms: charge neutralization and bridging flocculation. Extractives which are removed from the process water have to be taken care of in an economical way. They have to be brought into a form making it possible to remove them from the process water before the water is sent to the effluent treatment or before the water is reused in the mill. In that respect, the extent to which the extractives are present in either dissolved, colloidal or bound to fibres is important. In this work, Dissolved Air Flotation (DAF) was used to remove the flocculated extractives from Impressafiner process water. For comparison, laboratory experiments were also conducted on water from chip washer. It was shown in both laboratory and pilot scale that by using DAF in combination with flocculation of the extractives with polyelectrolyte the colloidal and fibre bound extractives could be removed from the process water with a removal efficiency of 80-90%, with equal efficiency for the Impressafiner and chip washer waters. The results attained in the thesis strongly suggest that by using a compressive pretreatment method of the wood chips is possible to remove a substantial fraction of extractives before the refining process. A larger fraction of the more toxic extractive components, resin acids, than of fatty acids were removed. Further, this study emphasizes the importance of the polymer properties for their floccculation efficiency of colloidal extractives present in process water. The results also show that Dissolved Air Flotation is a convenient method to remove flocculated extractives from process water.

In order to gain insights into ultrastructural changes taking place during the conversion of hardwoods into mechanical pulps, refiner pulp fibres were studied in detail using several microscopical techniques. Aspen (Populus tremuloides Michx.) and white birch (Betula papyrifera Marsh.) wood chips were used to produce thermomechanical (TMP), chemithermomechanical (CTMP) and chemimechanical (CMP) pulps. Following the hypothesis that there are fundamental differences in the surface and state of the fibres due to species and processing conditions, four pulps for each species and process were analyzed. Trends in fibre characteristic development were obtained within each group, based on the detailed optical analysis of 300 fibre cross-sections for each pulp. Fibre surface quality was the most important aspect of this study. Retention of middle lamella and of the layer, as well as the extent of exposure of the S₂ layer were evaluated. It was found that TMP processing of wood chips produced fibres with more exposure of the S₂ layer. Chemical pretreatment did not improve the extent of S₂ layer exposure nor the extent of fibrillation. However, the TMP fibres remained stiff, producing pulp sheets of low density and strength. Birch fibres showed a marked tendency to produce separation at or near the S₁/S₂ boundary. This resulted in high exposure of S₂ layers in TMP fibres, but produced a sheath of S₁ and ML around fibres from chemically-treated chips. This sheath was sometimes rolled back, exposing the fibre S₂ layer. Aspen TMP pulps showed high proportions of fibres with partially exposed S₂ layer. The application of chemical pretreatments to aspen chips resulted in fibres of similar levels of S₂ exposure than those achieved by TMP processing of this species, but only after reaching freeness levels of about 100 mL CSF. Fibres that showed radial failure were frequent in TMP but not in CTMP nor CMP pulps. The breakdown pattern of tension wood fibres (G-fibres) was also studied. TMP processing showed preferential breakdown of G-fibres, from which the G-layers were freed. This was not the case in the G-fibres from chemically-treated chips, in which the G-layer generally remained inside the fibres. Other categories discussed in the analysis of fibre cross sections included fibres with delamination of the S₂ layer and proportion of fibres distorted due to chemical impregnation. The breakdown of vessel elements (VE) was studied by comparing VE size frequency distributions and the proportion of whole VE that survived refining. TMP reduced VE into small fragments showing virtually no whole VE, while wood softening due to chemical pretreatment was responsible for a high proportion of whole VE in CTMP and CMP pulps. The VE from birch tend to be destroyed more easily than those from aspen, due to the intervessel pitting arrangement of the former. It is concluded that despite superior bonding potential of TMP fibres due to: - large S₂ exposure in fibres on account of separation at or near the S₁/S₂ boundary, - increased fibrillation, - longer fibrils in fines, and - release and exposure of highly cellulosic G-layers from tension wood in the case of aspen, the lack of conformability of TMP fibres, which translates into low sheet density, negates the promising benefits that otherwise would be obtained.
Forestry, Faculty of
Graduate

The thesis is focussed on low consistency (LC) refining of mechanical pulp. Theresearch included evaluations of energy efficiency, development of pulpproperties, the influence of fibre concentration on LC refining and effects of rotorposition in a two-zoned LC refiner. Trials were made in mill scale in a modern TMP line equipped with an MSDImpressafiner for chip pre-treatment, double disc (DD) first stage refining and aprototype 72-inch TwinFlo LC refiner in the second stage. Tensile index increasedby 8 Nm/g and fibre length was reduced by 10 % in LC refining at 140 kWh/adtgross specific refining energy and specific edge load 1.0 J/m. Specific lightscattering coefficient did not develop significantly over the LC refiner. The above mentioned TMP line was compared with a two stage single disc highconsistency Twin 60 refiner line. The purpose was to evaluate specific energyconsumption and pulp properties. The two different process solutions were testedin mill scale, running similar Norway spruce wood supply. At the same tensileindex and freeness, the specific energy consumption was 400 kWh/adt lower in theDD-LC concept compared with the SD-SD system. Pulp characteristics of the tworefining concepts were compared at tensile index 47 Nm/g. Fibre length was lowerafter DD-LC refining than after SD-SD refining. Specific light scattering coefficientwas higher and shive content much lower for DD-LC pulp. The effects of sulphite chip pre-treatment on second stage LC refining were alsoevaluated. No apparent differences in fibre properties after LC refining werenoticed between treated and untreated pulps. Sulphite chip pre-treatment iniiicombination with LC refining in second stage, yielded a pulp without screeningand reject refining with tensile index and shives content that were similar to nonpre-treated final pulp after screening and reject refining. A pilot scale study was performed to investigate the influence of fibreconcentration on pulp properties in LC refining of mechanical pulps. MarketCTMP was utilised in all trials and fibre concentrations were controlled by meansof adjustments of the pulp consistency and by screen fractionation of the pulp. Inaddition, various refiner parameters were studied, such as no-load, gap and baredge length. Pulp with the highest fibre concentration supported a larger refinergap than pulp with low fibre concentration at a given gross power input. Fibreshortening was lower and tensile index increase was higher for long fibre enrichedpulp. The results from this study support the interesting concept of combiningmain line LC refining and screening, where screen reject is recycled to the LCrefiner inlet. It has been observed that the rotor in two-zoned refiners is not always centred,even though pulp flow rate is equal in both refining zones. This leads to unequalplate gaps, which renders unevenly refined pulp. Trials were performed in millscale, using the 72-inch TwinFlo, to investigate differences in pulp properties androtor positions by means of altering the pressure difference between the refiningzones. In order to produce homogenous pulp, it was found that uneven plate gapscan be compensated for in LC refiners with dual refining zones. Results from thedifferent flow rate adjustments indicated that the control setting with similar plategap gave the most homogenous pulp.

Thesis (Ph. D.)--Institute of Paper Science and Technology, Georgia Institute of Technology, 2005.
Alan Rudie, Committee Member ; Derek Page, Committee Member ; Douglas Coffin, Committee Member ; Kari Ebeling, Committee Member ; Timothy Patterson, Committee Member. Includes bibliographical references (p. 222-231).

Dissolved and Colloidal substances (DSC) and metals are released from woodduring thermomechanical pulp (TMP) production. These components have atendency to accumulate in process waters, as the water circulation systems inintegrated paper mills are closed. Disturbances such as pitch depositions in thepaper machine (pitch problems), specks in the paper, decreased wet and drystrength, interference with cationic process chemicals, and impaired sheetbrightness and friction properties appear when DSC are present. Transition metalions such as manganese results in higher consumption of bleaching chemicals(hydrogen peroxide) and lowers the optical quality of the final product, andaddition of complexing agents, such as EDTA or DTPA, to prevent this is needed.The never ending trends to decrease water consumption and increase processefficiency in pulp and paper production emphasizes that it is very important bothto know the effects of wood substances on pulping and papermaking and to beable to remove them in an efficient way. From a biorefinery point of view, DSCcomponents can be promising renewable raw materials for biofuels, bio‐basedchemicals and materials.In this thesis, a new approach using induced air flotation (IAF) without a cationicpolyelectrolyte addition for the removal of pitch and metal ions from mechanicalpulp mill process waters is presented. The induced air flotation of different processwaters is facilitated by the addition of a chelating surfactant and different foamingagents. The influence of the pH value, temperature and foaming agentconcentration on the flotation efficiency has been investigated. The investigations presented show that the disturbing components can be removed from TMP presswater to a high extent. A 90% decrease in turbidity and a 91% removal of lipophilicextractives (i.e. resin and fatty acids, triglycerides, sterols and steryl esters) fromunbleached and bleached TMP process water can be obtained by addition of acationic surfactant as foaming agent during flotation. Lower amount of foamingagent is needed to purify efficiently bleached TMP process water, than unbleached.Additionally, fibres located in TMP press water are not removed with the foamfraction but purified. A retained concentration of hydrophilic extractives (i.e.hemicelluloses and lignans) in the process water indicates that the flotation isselective. Moreover, by introduction of a new recoverable surface activecomplexing agent, a chelating surfactant, manganese ions in the form of chelatescan be successfully removed from the pulp fibres and separated from the processwater in the same flotation process. Furthermore, from the purified unbleachedTMP process water a 90% recovery of dissolved hemicelluloses by anti‐solventprecipitation was obtained.The findings presented above indicate new possibilities for the internal watercleaning stage to decrease DSC emissions to recipient and for recovery of valuableraw materials from purified process water if flotation technology is applied in anintegrated mechanical pulp mill.
FORE

A piezo-ceramic sensor was developed to measure normal and tangential shear forces applied to a bar at one location in the refining zone of a Sunds Defibrator Conflo® JC-00 refiner. Testing was completed at the Pulp and Paper Research Institute of Canada in Vancouver. BC using CTMP pulp with a stock consistency of 3.15%. Distributions have been determined for peak normal and shear forces. peak coefficient of friction. shear work. and shear lead. These distributions were analysed to assess possible correlations with specific edge load. Force magnitudes were found to increase with an increase in specific edge load. The peak coefficient of friction was calculated that ranged from 0.13 to 0.16. Both the normal and shear force magnitudes varied by as much as a factor of 3, due to rotor out-of-tram of only 0.06 mm. These distributions could provide greater insight to the mechanisms responsible for fibre development in papermaking and thus "In Process" control of various refiner conditions.