Showing papers in "Appita Journal in 1997"

Near-infrared spectra and chemical compositions of E. globulus and E. nitens plantation woods

Abstract: Near-infrared (NIR) spectroscopy has been examined as a rapid means of determining the chemical composition of plantation eucalypt woods. Faster analyses of the chemical composition, an important determinant of pulpwood quality, have been developed but the procedures are still too lengthy for scanning the numerous samples arising from tree improvement programs. A more rapid, albeit less precise methodology is needed. Correlations have been found between bands in NIR spectra and the chemical compositions of eleven E.globulus and twenty-one E.nitens wood samples. A partial least squares (PLS) method has been used to develop models for determining the chemical contents of the woods from the NIR spectral measurements with acceptable errors. Kraft pulp yields were also modelled in terms of the woods' glucan and xylan contents by using PLS regression.

Intra- and inter-fibre pore closure in wet pressing

Abstract: Three analytical techniques were used to measure the effect of wet pressing on fibre and web pore structure : nuclear magnetic resonance (NMR), solute exclusion and centrifugation. NMR showed that pores are closed in wet pressing and that some of the pores are reopened if the pressed sheet is dispersed in water. It is postulated that the reversible pore closure proceeds by a hydrodynamic mechanism, while the permanent pore closure indicates fibre hornification. Pore closure in pressing and drying was also measured with solute exclusion. The average pore size from NMR was somewhat larger than from solute exclusion. This is thought to be related to fundamental differences in the measurement methods. The centrifugal method showed that wet pressing also caused interfibre pore closure. Refining and fines content were seen to be important variables.

Characterization of mechanical pulp fines by image analysis

Abstract: An image analysis method was developed and tested for characterizing mechanical pulp fines. The work was focused on finding a set of parameters to describe relevant properties of the fines and to test the functionality of the image analysis. In the method fines particles were classified into fibrillar and non-fibrillar material. Laboratory handsheets were prepared from the same fines and standard measurements of the sheets were used as a reference to evaluate the parameters provided by image analysis. Of the image-based parameters, the mass proportion of fibrillar material was found to be the most important factor for indicating the properties of fines. An increase in the proportion of fibrillar material resulted in improved strength properties and sheet smoothness. An increase in the proportion of fibrillar material is associated with a decrease in the light scattering coefficient.

Measuring the fibril angle of fibres using confocal microscopy

Abstract: A new technique for measuring the S2 fibril angle in wood fibres using a confocal microscope in reflectance mode is presented. Polarized laser light is reflected from the fibre and passed through an analyser polaroid crossed with the polarization of the illuminating laser beam. The measured intensity goes through a minimum whenever the orientation of the fibrils matches the polarization of either the incoming laser light or the analyser. As the confocal optics of the microscope allows detection of only light scattered from on or around the focal plane of the microscope, optical interference from the second fibre wall is eliminated. Thus the fibril angle can be measured without extensive sample preparation. A number of examples of the new method are presented.

Inheritance of tracheid transverse dimensions and wood density in radiata pine

Abstract: An automated wood microstructure analyser, SilviScan, was employed to measure tracheid transverse cross-section dimensions from breast height increment cores of 60 25 year old radiata pine parent trees, whose open-pollinated offspring were planted in a progeny test. Twenty-five of the 60 parent trees were selected for extremes of both tracheid cell wall perimeter and wall thickness and eight open-pollinated offspring, aged 13, were core-sampled by 10 mm increment cores at breast height and the cores analysed similarly by SilviScan. Analysis of variance of the progeny data for weighted breast height mean tracheid dimensions and basic density was used to estimate narrow-sense heritabilities of these traits which ranged from 0.5 to 1.0. Narrow-sense heritabilities were also estimated by the regression of offspring mean on parental values for the same traits and ranged from 0.37 to 0.67 with similar relative ranking as for sib-analysis. Genetic gains from phenotypic selection, of 10 trees out of 100 for tracheid cross-sectional dimension traits, were mostly from 8 to 12%.

Kraft pulp fibre property prediction from wood properties in eleven radiata pine clones

Abstract: Patterns of variation in density, tracheid cross-section dimensions and kraft pulp fibre dimensions have been estimated in a series of eleven 16-year old radiata pine (Pinus radiata) clones. The aims were to compare wood and pulp fibre measurements and to estimate the efficiency of sampling at breast height (BH: 1.4 metre) for prediction of whole tree wood and kraft pulp fibre properties. Radial sections were examined from six heights in twenty-four trees, representing the eleven clones. Density and tracheid cross-section dimensions were measured at a radial resolution of 50 μm using SilviScan-1, a combined image analyser and scanning microdensitometer. Fibre length distributions of the kraft pulps were measured using the Kajaani FS200, and the cross-section dimensions of dried, unrefined fibres were obtained by image analysis of thin sections. Correlations between BH wood properties and whole-tree estimates were very strong, but there was no significant correlation between tracheid perimeter and wall thickness. It is concluded that tracheid cross-section dimensions may be independently selected in tree improvement programs and that BH sampling is reliable for radiata pine clones.

Mechanisms of xylanase-aided bleaching of kraft pulps. Part I: Process parameters

Abstract: The ability of xylanase to enhance the bleaching of kraft pulp has been successfully implemented at the industrial scale to provide an economically competitive option for the reduction of chlorine use. It is not clear how this enzymic process works because the carbohydrate-degrading enzyme is not expected to act directly on the residual lignin in pulp. The elucidation of the mechanisms of xylanase aided bleaching has been difficult due to the variable responses of different pulping and bleaching parameters. Two patterns have nevertheless been demonstrated, bleach boosting where there are substantial savings in bleaching chemicals after xylanase pretreatment and direct brightening where there is a small but significant increase in pulp brightness immediately after a xylanase treatment. The former is commonly observed in chlorine based bleaching while the latter seems to occur in partially bleached pulps. To determine the target substrates responsible for these apparently different phenomena, carefully designed experiments will be required so that the effects dependent on pulping and bleaching conditions, pulp washing, and the type of wood and enzyme are taken into account.

Growth and wood properties of provenances and trees of nine Eucalypt species

Abstract: Trees and provenances of nine eucalypt species in a trial in South Africa were evaluated at half rotation age for growth (diameter, height, utilizable volume and wood properties (chemical composition, dimensions of anatomical elements, density, and percentage heart-wood). Highly significant differences were found between species for growth and most wood properties. Eucalyptus oreades had the largest underbark volume followed by E.fraxinoides and E.smithii, E.macarthurii the lowest. E.smithii had the best chemical composition while E.macarthurii and E.fastigata had the poorest. E.macarthurii and E.smithii had highest density and E.grandis the lowest. Between tree variation was largest for growth properties followed by some wood properties (density and heartwood) ; it was least for chemical composition and dimensions of anatomical elements. Although species differed significantly in dimensions of most anatomical elements, there was more variation in vessels than fibres.

Time trends in the genetic control of wood microstructure traits in Pinus radiata

Abstract: Age-related changes in the genetic and environmental components of ring width, density and fibre traits (diameter, wall thickness, coarseness and specific surface area) were studied. Fibre diameter and coarseness both came under strong genetic control by age 4-5 years. The other traits first exhibited stable genetic control at around age 8-9 years (crown-closure). Selection efficiencies of all traits become optimal after crown-closure. 80055 progeny, which is renowned for producing bright newsprint requiring low refining energy has the widest growth rings, largest fibre perimeter, highest fibre coarseness and the lowest density. This family has a density range that was half that of family 12197, which has the densest wood in the experiment,. However, the fibre perimeter range of 80055 progeny is three times that of 12197 progeny, indicating more variability across the stem in this trait. The study shows that strengths of correlations between pairs of traits change with time and genotype.

Mechanisms of xylanase-aided bleaching of kraft pulps. Part II: Target substrates

Abstract: It has not been apparent how xylanase enhances the bleaching of kraft pulp because this carbohydrate degrading enzyme is not expected to act directly on residual lignin. There is, however, increasing evidence that modified carbohydrates can contribute to Kappa number, and perhaps pulp colour. Xylanase may therefore act by hydrolysing xylan that carries xylan derived chromophores, xylan in lignin-xylan complexes, xylan that physically entraps lignin or xylan that affects fibre swelling. The target substrate for xylanase in a chlorine bleaching sequence may differ from that in a peroxide bleaching sequence. The former presently seems to be either xylan that entraps lignin or lignin-xylan complexes, their removal leading to bleach boosting, while the latter may be either lignin-xylan complexes or xylan derived chromophores, their removal leading to direct brightening. More thorough analyses, that examine the light scattering and opacity properties of pulp as well, are required to determine whether a common target substrate could be responsible for the apparently different phenomena that are observed under different process conditions. Observations to-date also indicate that the distribution of xylan and lignin, across the fibre wall and among fibre types, plays an important role in xylanase aided bleaching.

Handsheet property prediction from kraft-fibre and wood-tracheid properties in eleven radiata pine clones

Abstract: There is a prevailing need for non destructive methods to measure wood tracheid properties in standing trees so that large numbers of trees can be screened for their tracheid and potential kraft pulp properties. This report describes handsheet property predictability using kraft fibre, and whole-tree and breast-height tracheid dimension data. The predictions of handsheet properties were evaluated using eleven 16 year old clones of radiata pine (Pinus radiata), two trees per clone. Handsheet apparent density, and tensile, tear and burst strength, are predictable from the kraft fibre or wood tracheid (both whole-tree and breast-height) wall thickness and perimeter, and kraft fibre length combination. Other useful handsheet property predictors are the fibre or tracheid perimeter/wall thickness ratio and fibre length combination, and the chip or wood basic density and fibre length combinations. The kraft fibre width/thickness ratio is by itself a good predictor of handsheet properties. Fibre coarseness is a poor predictor of handsheet properties.

Technique for determining the fibre distribution in the z-direction using confocal microscopy and image analysis

Abstract: Confocal microscopy provides a nondestructive method for sectioning a sheet into a large number of discrete layers. Fibres in each layer can be identified using image analysis, by devising a technique that separates them from air and artefacts. In this paper, the image collection process using a confocal microscope is first briefly described and then the methods used to find fibre area in an image are discussed. A dynamic thresholding method is suggested to measure fibre area accurately. As an example, the fibre distribution from the top surface to 50 micrometres deep within a 60 g/m 2 handsheet is examined. The result shows that the top 20 micrometres of the sheet has an open structure and the fibre percentage varies between 50 and 70% at a depth of 20-50 μm.

Effects of enzymatic modification on radiata pine kraft fibre wall chemistry and physical properties

Abstract: This paper examines the effects of treatments with six purified enzymes (two xylanases, one cellobiohydrolase and three endoglucanases from Trichoderma reesei) on a range of properties of kraft pulps from radiata pine. After initial dose response experiments, 20 individual treatments were performed involving combinations of the six enzymes and four pulp types, i.e. bleached and unbleached kraft pulps from radiata pine slabwood and thinnings. Slabwood and thinnings pulps responded similarly to the treatments. Bleached pulps showed increased carbohydrate removal after treatments with some enzymes, but not others. Cellulose depolymerization after endoglucanase treatments was strongly correlated with decreases in fibre strength, i.e. wet zero span tensile index. Decreases in fibre strength after endo-glucanase treatments were, in turn, strongly correlated with losses of handsheet strength. This suggests that the weakening of handsheet webs by endo-glucanase treatments was mainly due to weakening of individual fibres and not to effects on interfibre bonding potential or overall fibre length.

Vessel distribution at two percentage heights from pith to bark in a seven year old Eucalyptus globulus tree

Abstract: Pith to bark profiles of vessel area, distribution and shape are presented for a 5% height disc sample of one Eucalyptus globulus tree. Results of analyses show that vessel areas, distributions and shape are very ordered. Individual vessel areas increased and vessel numbers decreased from pith to bark Total vessel area increased slowly across the disc from pith to bark, but was influenced by position within annual rings; decreasing from latewood (LW) to first earlywood (EW), then increasing in midwood (MW). Within-ring analyses showed regions containing dramatically different numbers, areas and total areas of vessels. It is proposed that vessel distributions change in synchrony with EW, MW and LW segmentation shown for fibre dimensions in both E. globulus and E. nitens. These findings may have implications to pulp utilization, future genetic modification technologies and tree breeding.

Characterization of resin in radiata pine woods, bisulfite pulps and mill pitch samples

Abstract: Methods for the chromatographic analysis of lipophilic extractives (resin) in radiata pine (Pinus radiata) wood, bisulfite pulp and mill pitch samples are described. The mass of substances extracted from fresh wood samples decreased as the polarity of solvents decreased, in the order methanol > acetone > dichloromethane > hexane. However the amounts of individual lipophilic extractives analysed were not as dependent on extraction solvent. High performance size exclusion chromatography (HPSEC) separated the extracts into four fractions namely triglycerides, steryl esters, sterols and fatty acids, and resin acids. Gas chromatography-mass spectrometry (GC-MS) of trimethylsilyl (TMS) derivatives of the extracts gave good separation of resin acids and fatty acids as their TMS esters, and of sterols as their TMS ethers The pitch sample consisted mainly of salts of fatty acids, with smaller amounts of resin acid salts, sterols and steryl esters, and only trace amounts of triglycerides. It is concluded that the combination of GC-MS and HPSEC is useful for the analysis of radiata pine extractives, allowing the estimation of individual resin and fatty acids and steroids, and total amounts of steryl esters and triglycerides.

Enhancement of strength and drainage of secondary fibres

Abstract: Several chemical additives including modified polyacrylamides, modified starches and a preparation of cellulase and hemicellulase enzyme were evaluated for their effectiveness to improve the strength and drainage of secondary fibres containing corrugated kraft cuttings and corrugated boxes. The effect of enzyme treatment was limited to improvement in drainage by 40% over the control without any appreciable change in pulp strength. However the treatment of pulp with various chemical additives resulted in substantial improvement of drainage as well as pulp strength. Best results were from an anionic polyacrylamide.

Polyoxometalate delignification : study of lignin model compounds

Abstract: The oxidation of four lignin model compounds (phenolic and non-phenolic, with or without an α-carbonyl group) with polyoxometalates was studied It was found that the reactivity of non-phenolic lignin structures towards polyoxometalates is negligible while the reaction with phenolic lignin structures takes place readily The kinetic study shows that the oxidation of vanillin with α-k 5 [SiV 5+ W 11 O 4() ] exhibits a first order reaction with respect to vanillin and a second order with respect to the polyoxometalates The effect of pH was also studied A reaction mechanism compatible to the observed experimental evidence was proposed Further study explored the use of polyoxometalates in a catalytic amount during oxygen delignification, however, the results were not successful because the re-oxidation of the reduced polyoxometalates under the present conditions was not feasible

Xylanase bleaching of eucalyptus kraft pulp : an economical ECF process : The use of xylanase in the bleaching of eucalyptus kraft pulp

Abstract: The use of xylanase in Eucalyptus globulus kraft pulp bleaching improves bleachability in subsequent stages. Sequences ODPD and XODPD were compared. At the same final brightness of 88% ISO enzyme treatment pulp can save 34% in chlorine dioxide or 47% in hydrogen peroxide consumption. Other optical and physical properties are similar for both sequences. Enzyme treatment produces an increase of COD in effluent due to the hydrolysis of hemicelluloses.

Prediction of fractionation efficiency for pressure screens

Abstract: The separation of pulp fibres into fractions with different properties by pressure screening allows the selective processing of these fractions. The optimization of screen configurations can be achieved more economically if the performance of the individual screens can be predicted for arbitrary furnishes and reject rates. Most modelling of screen fractionation efficiency has used Nelson's screening quotient, Q. However this is only valid for components that are small proportions of the feed, (for example shive contents), and it requires knowledge of the mass reject rate to predict the fractionation efficiency. An approach based on the volumetric reject rate is shown to be more versatile for the prediction of screen fibre length fractionation efficiencies.

Determining fibre coarseness of small wood samples from Acacia mearnsii and Eucalyptus grandis by Kajaani FS 200 fibre analyser

Abstract: Within-tree variation of fibre coarseness was studied in an eight year old, plantation grown tree of each of Acacia mearnsii De Wild and Encalyptus grandis Hill ex Maiden. The trees were sampled at six height levels. A radial strip was prepared from each sample disc and pulped clamped between perforated plates. Fibre coarseness was measured with a Kajaani FS 200 fibre analyser. Oven dry mass of fibres in the dilute suspensions was determined using Millipore filters. A. mearnsii had finer fibres than E. grandis (4.2 compared with 6.2 mg/100m). Fibre coarseness increased with height in A. mearnsii but decreased with height in E. grandis. With distance from pith, coarseness increased in E. grandis, and was constant for A. mearnsii.

Use of dissolved air flotation to clean process water

Abstract: The pulp and paper industry has traditionally been a large user of water in its manufacturing operations but this situation has been changing over many years. New mills are often designed to use less than 10 m 3 of process water per tonne of paper produced. This reduction in water consumption has led to an increase in the circulating load of colloidal and dissolved material. In 1993, Australian Newsprint Mills Ltd started a 50 000 tonne per annum recycling and deinking plant to supply pulp to its newsprint machine at Albury. A dissolved air flotation (DAF) clarifier was installed to treat the effluent from the plant to reduce the solids load on the mill waste water treatment plant. In 1994/95 the deinking plant was expanded to 125 000 tonnes per annum A dissolved air flotation clarifier was installed to clarify all paper machine clear filtrate before use in other parts of the mill and another DAF unit was installed to clarify the clear white water from the second disc filter in the deinking plant.

Factors influencing paper friction and its reproducibility : is third test best ?

Abstract: This paper explores the suitability of the TAPPI standard (T816 om-92) for determining coefficient of friction of paper materials. Three assumptions of the TAPPI method are tested. Namely : more than one slide improves test to test variability ; third slide result represents given applications better than the first slide result ; different surface to surface materials can be treated in the same way. i.e., give the same relative results albeit of different magnitudes but retaining relative sample ranking. Tests on three different paper products suggest that test result variability is not improved after the second slide. The first slide result of a friction determination corresponds to the third slide result and different test surfaces impose different test conditions and cannot be directly compared. Testing time can be cut by two-thirds by only reporting the first slide result. The observation that the contact time before starting a slide increases the static coefficient is explained with a simple qualitative model.

FAS (thiourea dioxide) bleaching of recycled pulp

Abstract: The use of recycled fibre (RCF) for high brightness paper grades has increased the demand for bleaching chemicals. The move away from chlorine based bleaching agents has meant that FAS, sodium hydrosulfite and hydrogen peroxide have taken up most of this demand. Two case studies in which FAS is used for the bleaching of RCF pulp are discussed. The first study focuses on the optimum conditions for FAS bleaching of wood free waste (WFW). The effect of bleaching time, temperature and FAS on brightness development of WFW is examined. Study two considers the effect of post bleaching wood containing waste with FAS. In particular the effect of FAS dose is examined in relation to pulp treated at various levels of peroxide in the pulper. Finally a comparison is made between FAS and hydrosulfite as reducing agents for RCF pulp, focusing on bleaching performance, handling, safety, environmental concerns and economics.

Recycle paper mill trial using enzyme and polymer for upgrading recycled fibre

Abstract: Enzyme-polymer technology which improves the freeness of various types of pulps and the runnability of paper machines was developed. This technology was evaluated in various recycle paper mills. Improvements in machine speed and strength were found. Other advantages of the developed technology are discussed.

Calcium and magnesium balance in an unbleached fibre line : a mill case

Abstract: The occurrence of scale deposits on digesters is mainly dependent on calcium concentration in cooking liquor. The calcium balance in the unbleached fibre line of the Portucel Industrial Setubal mill, and also the calcium profile in the digesters, are presented. In addition, the same determinations were also performed for magnesium. The deposits build up were analysed, focusing on their dependence on wood species and also on the bark content, since wood is the main input of calcium to the system. The results presented in this work are for Eucalyptus globulus and are based on mill results.

Measurement of Wall Thickness of Fully Collapsed Fibres by Confocal Microscopy and Image Analysis

Abstract: Fibre wall thickness is usually determined by dividing the wall cross-section area by its centreline length. This method has been successfully used in the measurement of fibres with detectable lumens however some fibres collapse on drying or during pulping and refining. The extent of the collapse may be such that the two sides of the inner wall touch, completely closing the lumen. This degree of collapse usually leads to the failure of the above method for the measurement of wall thickness. In this paper, two approaches are proposed for measuring the wall thickness of such collapsed fibres. Image analysis macros have been constructed to process confocal images and to measure fibre wall thickness using different methods. The application of the macros to bleached eucalypt kraft pulp fibres is described and the results are compared with those from the existing method.

Eucalypt fibre size fractions : modelling and measuring their effect on sheet properties

Abstract: This paper presents theoretical and experimental studies on the effect of fibre geometrical property distributions on handsheet properties. Previous studies (on fines-free pulps) have concentrated on mean dimensions of fibres whereas this study examines the effect of spread and skewness of these dimensions. Recent mathematical models of fibre pullout have been extended to study the effects of broadening fibre length distribution on total pullout energy (debatably related to tearing resistance) and tensile strength. A selection of the theoretical predictions is presented in graphical form. In the second part of the study, commercial eucalypt kraft pulp (fines removed) was fractionated in a laboratory fibre classifier using a two stage screening process with altered screening intervals. Further treatment of individual length fractions through a hydrocyclone, then produced separate fibre cross-section fractions. Laboratory handsheets from these fibre fractions and mixtures thereof were then tested for comparison with model predictions. Results show an encouraging degree of agreement. We show clearly that mean fibre length alone is a poor predictor of sheet properties even when comparing different fractions taken from the same pulp.

Network Changes in Paper Under Compression in the Z-Direction: The Effect of Loading Rate and Fibre Wall Thickness

Abstract: This paper presents results for the z-direction compression characteristics of paper structures. Under load control, the results show a significant effect of rate of load application and release on the load-displacement characteristics of handsheets made from air dried, unbeaten, bleached, eucalypt kraft pulp. There are time-dependent effects which are manifest in the creep and anelastic recovery observed in the handsheets. Separate compressibility tests performed on handsheets of similar grammage but made from fibres of different cell wall thickness also indicate a difference in their load-displacement characteristics. Confocal microscopy is used with image processing to collect and present images of the surface and internal structure of the same area of sample. The mechanism of local deformation of sheets is discussed and a simple theory of paper deformation under load in the z-direction is presented.

Statistical theory of chemical pulp refining : an innovative combined approach

Abstract: The type and degree of treatment concept is an appropriate basis for describing the pulp refining as a fatigue process characterized by the number of impacts and their intensity. The aim of the proposed theory is to formulate equations from the fundamental investigations of Giertz and to quantitatively correlate the rate of fibre property development to the mechanical treatment severity. The statistical mechanics methods of Boltzman allow the impact intensity distribution to be established. The concept of rate of fibre property development and the concept of minimal level of impact intensity are introduced, by analogy with fatigue phenomena. This theory identifies optimum impact intensities, in terms of energy efficiency specific to each property and raw material. Energy optimization and process quality diagrams permit quantitative analysis of the potential of pulp blend and refining equipment.

Modelling of fluid transport in an anisotropic fibre network

Abstract: The numerical simulations of lattice Boltzmann (LB) are developed to predict the structure and transport properties of fluid-fibre systems in a massive parallel computer at the Pittsburgh Supercomputing Center by using work sharing technique. The algorithm of the LB simulation is parallel in nature due to the fact that particles collide at a node and move to their neighbours so that information is locally and independently transferred at each node. No-slip boundary conditions are easily imposed for irregular boundaries by using the bounce back collision rules. The effects of microstructure of fibre networks on permeability have been studied ; in-plane directional permeability decreases and z-directional permeability increases with increasing the z-directional polar angles offibres at a constant porosity. The ratio of permeability in MD to that in CD increases with decreasing fibre orientation in CD.