Showing papers in "Appita Journal in 1998"

Developing a method for the rapid assessment of pulp yield of plantation eucalypt trees beyond the year 2000

Abstract: This paper reviews work in the CRC for Hardwood Fibre and Paper Science directed towards the development of a methodology for assessing the potential pulp yields of temperate plantation eucalypts, especially Eucalyptus globulus and E.nitens. Sampling was by the withdrawal of cores using motorized equipment. The cores were then converted to wood meals which were analysed by near-infrared spectroscopy. Values of pulp yield for calibration were obtained by minipulping wood chips; the calibrations were developed using Partial Least Squares Regression. Where plentiful numbers of woods having known pulp yields were available, standard errors of calibration were as low as 0.7. Matching of new samples with existing calibrations was done by Principal Components Analysis and either Soft Independent Modelling of Class Analogy or Discriminant Analysis. Correlations between pulp yields predicted for cores at 10% tree height and whole-tree values indicated that useful predictions of whole-tree pulp yields might be obtained from measurements on cores.

Within tree variation and genetic control of basic density, fibre length and coarseness in Eucalyptus regnans in Tasmania

Abstract: The degree of genetic control over basic density, fibre length and fibre coarseness was examined using a ten year old Eucalyptus regnans progeny trial established with 200 families collected from the Moogara, Tasmania provenance. The trial had previously been assessed for tree growth and susceptibility to defoliation by the leaf eating beetle, Chrysophtharta bimaculata. Ten trees were destructively sampled to determine longitudinal (lengthwise) patterns of within-tree variation for each wood property. Data from this sampling were used to develop a representative non-destructive sampling strategy which required bark-to-bark cores. The top 50 families, based on growth, were then sampled, with cores being collected from 6 trees in each family. Estimates of heritability for wood properties were low to moderate, ranging from 0.15 for fibre coarseness and 0.17 for basic density to 0.36 for fibre length. Relationships between wood properties and tree height and diameter were generally not strong. However rate of tree growth appears to influence fibre length. Increasing levels of insect defoliation were associated with slower tree growth and shorter fibres but did not appear to influence basic density or fibre coarseness.

The use of a laccase mediator stage in bleaching eucalypt kraft pulps

Abstract: An oxygen-bleached eucalypt kraft pulp (Kappa number 10.5) was used in a study of oxidative delignification with laccase and the mediator 1-hydroxybenzotriazole. The laccase treatment, followed by alkali extraction, lowered the Kappa number to 6.6. Addition of xylanase to the reaction liquor resulted in a further reduction to 5.9. Spent liquor from the laccase treatment was not effective when used a second time. The hexenuronic acid groups in the treated pulps contributed to more than half of the measured Kappa numbers. The pulp was bleached with an L(EO)LQ(PO) sequence (where L is a laccase-mediator stage, (EO) an oxygen reinforced alkali extraction, Q a chelation stage and (PO) a pressurized hydrogen peroxide stage). Brightness of 89% ISO was attained and the tearing resistance was the same as that of pulp bleached with a D(EO)DD sequence. An extended delignification pulp (ITC procedure) was bleached to 90% brightness with this sequence, but the tearing resistance was about 15% lower than when the pulp was bleached with an ECF sequence.

Measuring the fibril angle of bleached fibres using micro-Raman spectroscopy

Abstract: A new technique for measuring the fibril angle of bleached pulp fibres is presented. It uses micro-Raman spectroscopy and involves measuring the ratio of the 1094 to 1120 cm -1 peak intensities as a function of angle. It is compared with a direct method of measuring of the fibril angle (cell wall striation method) and with two indirect methods (polarized light microscopy and pit aperture angle methods). A good correlation was obtained with the direct method indicating that the Raman method can accurately determine fibril angles in pine fibres. Poor correlations with the indirect methods suggest that these methods are inherently inaccurate.

Non-destructive sampling for basic density in Eucalyptus globulus and E. nitens

Abstract: The feasibility and efficiency of predicting whole tree basic density using either a pilodyn or bark-to-bark core samples is examined for plantation grown Eucalyptus globulus and E.nitens. Each species was sampled from a range of sites and ages across southern Australia. For each tree discs were cut from a combination of percentage heights (0, 10, 20...70%) and fixed heights (0.5m, 0.7m...1.5m), heights easily accessible from the ground. In the first part of this study the efficiency of evaluating basic density using a pilodyn was examined with single readings taken from each of four aspects at each of the fixed heights. The second part covered the examination of the feasibility of using bark-to-bark cores. Both species showed an initial drop in density between the ground level and 0.5m, followed by a linear increase in density between 10 and 70% of tree height. Density at all fixed heights was highly correlated with whole tree values for E.globulus, but results were variable across sites for E.nitens. For E.globulus optimal sampling height was 1.1m above ground, while, for E.nitens, optimum sampling height was below 1.1m. The costs and accuracies of collecting samples in the field via the two non-destructive sampling methods are compared to destructive sampling. A bark-to-bark core sample is recommended as the most cost effective method.

Kraft fibre and pulp qualities of 29 trees of New Zealand grown Eucalyptus nitens

Abstract: There is a need to determine the between tree variation in the wood properties and kraft fibre and pulp qualities of softwoods and hardwoods that grow well in New Zealand. This information will be used in the planning and management of end-product directed plantation forests and tree-breeding programs. Variation among 29 individual trees of E. nitens is extremely high; for the individual tree chip samples the basic density range is 390-556kg/m 3 , total lignin content 25.1-29.7%, and kraft pulp yield 54-59%. Between tree variation in some important kraft pulp properties are: fibre length (0.780.95mm), fibre perimeter (19.0-21.6mm), wall area (coarseness) (53-70mm 2 ), and handsheet bulk at 500 PFI mill rev (1.59-1.37cm 3 /g).The fibre width:thickness ratio and length combination (r 2 = 0.67), and the chip density and length combination (r 2 = 0.64) are the best predictors of handsheet bulk. Fibres are curled and consequently 'shortened' by pulp bleaching.

Comparison of methods to measure fibril angle in wood fibres

Abstract: Fibril angle is a key determinant of fibre mechanical properties. Two of the most useful techniques for measuring fibril angle are X-ray diffractometry (XRD), for solid wood, and confocal microscopy, for individual fibres or small groups of fibres. This paper compares fibril angles determined using XRD and confocal microscopy for one spruce and two radiata pine samples. Good agreement was obtained between the fibril angles given by the two methods.

Eucalyptus grandis fertilizer trials : growth, wood properties and kraft pulp yield

Abstract: A fertilizer experiment was established with Eucalyptus grandis near Gympie, Queensland in 1987. Treatments included nitrogen (N) and phosphorus (P) fertilizer in factorial combination (five levels of each at rates of up to 1600 kg/ha N and 480 kg/ha P). Application of fertilizer substantially improved tree growth with optimum response at 800 kg/ha N and 60 kg/ha P (N 3 P 1 ). Volume production at age 5.6 years almost doubled from 76 m 3 /ha in unfertilized control plots to 145 m 3 /ha in the optimum treatment (N 3 P 1 ). Trees from the five 'diagonal' treatments of the factorial experiment (N 0 P 0 , N 1 P 1 , N 2 P 2 , N 3 P 3 , N 4 P 4 ) were harvested at 5 years of age for testing of wood and pulp properties. Compared with values for unfertilized trees, basic density and pulp yield of wood from trees in treatment N 3 P 3 both increased by 5 to 6% (basic density 412 kg/m 3 compared with 436 kg/m 3 and pulp yield of 47% compared with 50%). The combined effect of these changes increased the quantity of screened pulp per unit volume of wood (pulpwood productivity) by about 12% from 194 to 217 kilograms pulp per cubic metre of wood. Production of screened pulp on a plantation area basis doubled from 16 t/ha/a untreated to 32 t/ha/a for N 3 P 3 .

Flexographic printability of packaging grade papers

Abstract: Laboratory printer requirements for simulating pre-printing linerboard and post-printing corrugated board are identified. One of the major problems of flexographic printability research has been the lack of a high quality laboratory research press to reproduce commercial press performance on small paper samples. A selection of available presses is examined. PAPRO have recently received an IGT F1 flexographic printability tester for the study of linerboard and corrugated board printability. Initial evaluation of the IGT F1 shows it to be suitable for linerboard research and with some modification, suitable for corrugated board.

Fibre deformation during medium consistency mixing : role of residence time and impeller geometry

Abstract: Mechanical treatment of pulp fibres during medium consistency (MC) mixing increases fibre deformation and affects pulp quality. A laboratory batch mixer was used to investigate pulp quality changes with residence time and impeller geometry and to compare the changes to those measured across an industrial MC mixer. Laboratory experiments illustrated impeller geometry (not residence time) was the main variable controlling fibre curl during MC mixing. Progressively increasing impeller blade thickness (6, 12, 24 mm) and rotor diameter (130, 154, 164 mm) reduced the tendency to curl pulp fibres. Pulps produced with the largest impeller (164 mm diam., 24 mm blade thickness) achieved curl indices most like those of the industrially mixed samples. The observed trends suggest a uniform shear gap between the impeller and stationary vessel wall, like many industrial MC mixers, would induce minimal curl during mixing. Fibre wall dislocations increased in proportion to residence time during laboratory mixing. Increasing residence time within industrial mixers, due to reduced pulp flow, could significantly increase the induced fibre wall damage.

Adsorption of cationic starch on eucalypt pulp fibres and fines

Abstract: Cationic starch is extensively used in papermaking to increase paper strength and improve first pass retention. Starch, a high molar mass polymer of glucose, is commercially extracted from a number of plant sources including corn, wheat, potato and tapioca. In their natural state, starch polymers are generally uncharged (i.e. electrically neutral) and are only weakly adsorbed by fibres. The cationization process, in which the starch polymers are chemically modified by substituting positively charged (i.e. cationic) chemical groups into the polymer, was developed during the 1950s. This led to a substantial improvement in the efficiency of starch utilization, as cationic starch is able to chemically bond through electrostatic attraction to fibres and fines which are negatively charged (i.e. anionic).

An evaluation of three formation testers using radiata pine and spruce kraft pulps

Abstract: Uniformity of sheet structure is important for the processing and performance of paper and paperboard. The measurement of mass distribution or formation is a fundamental way of assessing product uniformity. Three formation testers, namely, Toyo Seiki, PFI and Ambertec Beta, were used for comparison of handsheets from radiata pine and spruce bleached kraft pulps. A secondary aim was to study the variation of formation in handsheets made from a benchmarked single-fibre resource while decoupling the processing effects in industrial paper machine formers. Trends in the formation data with changing fibre class are similar although the results vary from instrument to instrument. The formation index values from all formation testers correlated well with selected fibre properties. Preliminary data are presented for some kraft-TMP composite handsheets.

Chromophore changes during oxygen delignification of a radiata pine kraft pulp

Abstract: Changes to the chromophores, or light-absorbing groups, during oxygen delignification were investigated using isolated spent liquor lignins. Radiata pine kraft and kraft-oxygen spent liquor lignins were isolated and their absorption spectra compared both before and after chemical treatments. The changes in the absorption spectra of kraft lignin after oxygen delignification were associated with removal and formation of chromophores. Removal of stilbenes accounted for a major portion of the change in the ultraviolet region on oxygen delignification. Evidence was also seen in the spectra for removal of phenolic guaiacyl units and formation of new phenolic α-carbonyl units. Elimination and formation of quinones and products derived from them may also occur during oxygen delignification and contribute to the changes in the absorption spectra. Much of the absorbance of the kraft and kraft-oxygen lignins in the visible region of the spectrum was removed by reduction with borohydride or dithionite, suggesting the colour of both these lignins was due to carbonyl-containing chromophores, including, but not restricted to quinones.

An improved peracetic acid bleaching process

Abstract: An improved peracetic acid pulp bleaching process, Pa (pH) has been developed and applied to both oxygen and ozone delignified softwood kraft pulps, as well as a spruce CTM pulp. The difference between the Pa (pH) stage and a conventional Pa stage is that the former has an initial pH of 7, after 20 minutes later increasing to pH 9.5 and a final pH of around a neutral range, while the latter has an initial pH of 7 and a final pH of 5-5.5. The Pa (pH) stage leads to a higher brightness than the Pa stage while the carbohydrate degradation during the treatment is not affected.

The effect of humidity on packaging grade paper elastic modulus

Abstract: A large proportion of the corrugating components manufactured in New Zealand are used for the manufacture of corrugated cases for horticultural products. These products along with the packaging are stored at low temperature and high relative humidities. To model the performance of corrugated board under these storage conditions the elastic modulus and other stress-strain parameters of the board components are required. The vacuum compression apparatus is an ideal instrument to obtain these properties for both tension and compression modes at relative humidities from 35 to 95% rh. This study shows that at relative humidities higher than 50% the elastic modulus is not the same for tension and compression and that the compression elastic modulus is significantly higher than the tension elastic modulus.

Activator for peroxide bleaching of mechanical pulp

Abstract: In situ activation of peroxide by tetraacetylethylenediamine (TAED) to produce a strong oxidant is a safe and low cost (capital intensive) alternative to pre-formed peracids or other strong oxidizing agents. Unlike pre-formed peracids, the combination of TAED and peroxide can provide effective bleaching. In alkaline medium, one mole of TAED reacts with two moles of perhydroxyl ion (hydrogen peroxide) to produce two moles of peracetic anion. Generally peracids are considered to be better and more active bleaching agents than peroxide. Various aspects of peroxide reaction with a commercial thermomechanical softwood pulp have been investigated namely temperature, time, charge, peroxide/TAED ratio, alkalinity, and buffering to maximize brightness gain. Considering that bleaching processes vary from mill to mill, experiments were conducted to evaluate the impact of the sequence of addition of an activator in one- and two-stages using peroxide and TAED. The use of TAED in peroxide bleaching liquor offers a mean to significantly improve pulp brightness. Enhanced bleaching efficiency is achieved using a short time cycle implying lower energy requirement and reduction in production costs.

Further classification of eucalypt pulpwoods using principal components analysis of near-infrared spectra

Abstract: Models derived from principal components analysis (PCA) of the near infrared (NIR) spectra of eucalypt woods have been shown to be a good means of classifying the woods. However they do not give numerical measures of the distances between the classes. In this report the soft independent modelling of class analogy (SIMCA) approach is used to determine distances between the PCA models. The NIR spectra and pulp yields used in the models were derived from samples of woods from two provenances of each of E. globulus and E. nitens and one of E. grandis grown on four sites in the Esperance Valley in Tasmania. Some further E. globulus samples were a mixed age set from various Tasmanian provenances of native forest origin. The distances between models for species tended to be greater than the distances between models for provenances of the same species and age. The model for older aged native forest woods from E. globulus was a large distance from the model of the same species grown in plantation. The compliance of the data with the models was checked graphically and the discrimination and modelling powers of the NIR data determined across the whole range (1100 - 2500 nm).

Effect of lignin demethylation on oxygen delignification

Abstract: Treatment of radiata pine kraft and kraft-oxygen pulps with sodium ethanethiolate (NaSEt) in dimethylformamide (DMF) reduced the methoxyl content of the fibre lignin. Demethylation increased as the level of NaSEt applied was raised. Lignin removal in a subsequent oxygen stage increased as the extent of demethylation was raised. For example, after NaSEt pretreatment low pulp concentration oxygen delignification reduced the Kappa number of a kraft-oxygen pulp from 17.9 to 3.8, versus 7.9 for the nonpretreated pulp. The methoxyl content of lignin isolated from pretreated kraft or kraft-oxygen pulps was approximately linearly related to the Kappa number after oxygen delignification. Improved methods for demethylation of the fibre lignin are required if the enhanced reactivity to oxygen is to be exploited as treatment with NaSEt in DMF led to significant losses in both pulp viscosity and pulp yield.

Characterization of eucalypt fibre surface using inverse gas chromatography and X-ray photoelectron spectroscopy

Abstract: Inverse gas chromatography and X-ray photoelectron spectroscopy (XPS) were used to characterize the surface of bleached eucalypt kraft pulp fibres. The dispersive component of the surface energy and the work of adhesion due to specific (acid-base) interactions (W A AB ) with molecular probes were measured for both the whole pulp and the primary fines. The effect of extraction, sizing and recycling of the fibres on these characteristics were also studied. The W A AB values reveal that the bleached eucalypt pulp fibres are bipolar with a strong acidic character. The primary fines, however, have a strong basic character. XPS results suggest that the primary fines have a higher surface concentration of lignin and extractives. Extraction of the fibre seems to remove unattached material from the fibre surface (this material is most likely to be composed of residual extractives and lignin that reprecipitated on the fibre surface during washing) and, as a result, extraction increases the fibre surface energy and polarity. The surface of recycled fibres is more hydrophobic than virgin fibres. This is likely to be due to deposits of hydrophobic ink components and/or deinking chemicals. Most of the contaminants do not bond strongly to the fibre surface. The implications of some of these fibre surface properties for sheet properties are discussed.

Interaction of mechanical and chemical treatments on pulp strength during kraft pulp bleaching

Abstract: The advent of less selective low- and non-chlorine bleach technologies has placed greater emphasis on maintaining pulp strength after bleaching, thus a more detailed understanding of the mechanism of strength loss during bleaching is required. Pulp bleach treatments can decrease fibre strength through unselective chemical degradation of the cellulose fraction. Recent work has shown that physical processes (pumping, mixing, pressing) during bleaching can also affect fibre properties, including those related to intrinsic fibre strength. The present work investigated the potential interaction between mechanical damage during processing and chemical damage during bleaching.

Refining intensity impact on slabwood and thinnings TMP

Abstract: Refining intensity affects on two morphologically different radiata pine wood types are presented in this study. Thermomechanical pulps from low density (340 kg/m 3 ) thinnings and high density (500 kg/m 3 ) slabwood were produced using three different sets of refiner plates with impact frequencies in the outer bar section of 23400, 15000 and 8700 Hz. Increasing the refining intensity caused fibre length, Bauer McNett R30 fraction, and tear, burst and tensile to decrease and stretch, light scattering coefficient and opacity to increase, for both wood types compared at a common specific energy input. The Bauer McNett -200 fraction was unchanged. During the primary and secondary refining stages the thicker-walled, longer slabwood fibres lost length more quickly than the thinner-walled shorter thinnings fibres. Increasing refining intensity caused fibre length loss to increase, with the slabwood being affected to a greater extent than the thinnings. For a given mass production rate, a refiner using thinnings has approximately 2.5 times the number of fibres within the refining zone as a refiner using slabwood. Thus each slabwood fibre was estimated to receive up to 2.5 times the energy applied to each thinnings fibre.

Correlation among growth, density, fibre diameter and heartwood in radiata pine

Abstract: Relationships were studied among growth traits (tree height, diameter and sapwood area), wood microstructure traits (density, fibre radial and tangential diameter) and heartwood formation traits (initial 5 year radius, heartwood area and number of heartwood rings) using simple correlations and principal component analysis. Traits were measured in a small radiata pine (Pinus radiata D. Don) diallel experiment involving a parent whose progeny require low energy and produce bright paper during thermomechanical pulping. Results indicate that some larger trees had much greater heartwood area than some smaller trees. There was a tendency for some trees of low density to form more heartwood than some trees of high density. Density was unrelated to growth traits but was inversely related to fibre tangential and radial diameters. This implies that phenotypic selection of trees on growth traits could result in trees of different density.

Differentiating timber to optimize the pulping process

Abstract: Large variations in important pulping properties have been demonstrated for wood from trees, not only of different genera, but also between species within a genus, and between their provenances, families and, even the individual clones within families. Tree breeders, who in general have been among the leaders in measuring this variation have shown that much of it is under genetic control but site and growth factors affect expression. Some of these properties such as pulp yield, rate of delignification, alkali consumption and residual unbleached pulp brightness have strong financial implications on the profitability of processing. The industry has been slow in becoming sufficiently flexible and adapting processes to take advantage of this variation to optimize financial retum from the furnish. A way needs to be found to compensate the wood grower for successfully grown, bred or genetically modified superior pulping material. The processor then needs to find a way to adjust the process to match the properties of these materials to best advantage. Both interests call for the development of a rapid evaluation technique at the mill gate or in loading the digester, and near infrared spectroscopy (NIRA) is suggested as a possible way forward. Harvest scheduling, woodyard management and ways of directing batches of timber with predictable properties to the digester in an ordered manner to minimize within-batch variability are lesser challenges that will surely follow.

The shape of the ring crush curve

Abstract: Two experimental rigs have been developed for attachment to a universal tester for quick and accurate measurement of tensile and ring crush load displacement curves at various environmental conditions. The full load displacement curve of the ring crush test is available to examine the effect of testing conditions. Handsheets were formed from a randomized stock of never dried NSCC pulp. The ring crush load displacement curve exhibited an initial take up response then an almost linear region before a peak load at which the sample was not crushed and was visually undamaged. This contradicts traditional ideas that the ring crush failure mechanism is the crushing of the ring corresponding to the recorded peak load. The general shape of the ring crush curve was independent of loading rate and moisture content. The peak load was more sensitive to moisture than the stiffness of the specimen. The modulus of the ring crush sample was significantly lower than the modulus in tension with the shape of the stress strain ring crush curve significantly different from that of the tension curve.

Kinetics of chloride dioxide delignification

Abstract: The transformation function, developed for oxygen delignification of kraft pulps, can be also used to characterize chlorine dioxide delignification. The transformation function can be applied to different types of kraft pulp treated under well-mixed conditions at different pulp stock consistencies. Simulations of the obtained transformation functions show clearly the effect of stock consistency on the delignification rate. At low temperature there are marked differences in delignification rate between high and low consistencies. However these differences diminish when the temperature is increased to about 100°C.

! Peroxide bleaching using zeolites Part 1: peroxide decomposition

Abstract: Addition of certain levels of zeolite and sodium citrate to hydrogen peroxide solutions containing manganese decreased the rate of peroxide decomposition. There were differences in the ability of commercially available zeolites to reduce decomposition of peroxide. Addition of small amounts of sodium citrate to a particular zeolite system improved its ability to chelate metal ions. Sodium citrate appears to act as a transfer agent, facilitating the migration of metal ions to the zeolite. However addition of excess zeolite and citrate increase manganese induced peroxide decomposition. If the manganese-oxygen complex that decomposes peroxide under alkaline conditions was allowed to form prior to the addition of either the zeolite or citrate then the two chelating agents were unable to interact with the complex and prevent decomposition.

Instantaneous effectiveness of ozone bleaching at high consistency

Abstract: A laboratory scale flowthrough reactor with special features was used to study the effectiveness of ozone during the ozonation of an oxygen delignified kraft eucalypt pulp. The rate of ozone consumption depends on the initial Kappa number of the pulp and the inlet ozone concentration. The initial stage of delignification is fast and corresponds to a high rate of ozone consumption. Ozone is most effective in the bleaching of oxygen delignified kraft pulps when a high ozone concentration is used in conjunction with a low initial Kappa number.The effectiveness of ozone bleaching can be better than the average values previously reported if the appropriate conditions for bleaching are selected.

Characterization of volatile constituents in radiata pine high temperature mechanical pulp screw press effluent

Abstract: Results are presented arising from an investigation to characterize volatile constituents released from radiata pine in the manufacture of high temperature thermomechanical pulp, prior to refining, by analysis of the screw press effluent. Effluent samples were taken from commercial operations and pilot plant trials at the post presteaming and preheating stages. The volatile constituents in the effluents were determined after extraction by GCMS analysis. The main compounds identified were α-pinene, β-pinene, limonene, furfural, 1,4-terpineol, α-terpineol, pimarinal, and resin acid methyl esters. The total concentrations of extractable components were 200-1000 mg/kg for the post presteamer effluent and 60-130 mg/kg for the post preheater effluent. Concentrations of formaldehyde, acetic acid and methanol were also determined. Chemical oxygen demand values for the presteamer effluent were in the range 11-20 g/L and for biochemical oxygen demand 3.6-9.9 g/L.

Fibre passage through a single screen aperture

Abstract: Fibre passage was examined for the case of flow through a narrow aperture under conditions similar to pulp screening. An expression for fibre passage, quantified by passage ratio, was derived in terms of the upstream fibre concentration profile. Fibre concentration profiles were measured for nylon fibres with lengths, L, equal to 1, 2, and 3 mm, and shown to be zero at the wall, to increase linearly with distance from the wall to approximately U3, and to remain constant beyond U3. Assuming fibres follow the fluid streamlines, passage ratio was calculated and compared with experiment for a broad range of fibre lengths, slot widths, W, average slot fluid velocities, V s , and average cross-flow fluid velocities, V u . Short fibre passage (L/W ≤ 2), was governed by the fibre concentration profile alone. Long fibre passage (L/W > 2), was largely governed by the concentration profile; however, at low V s /V u the experimentally measured passage ratio was less than that predicted by the concentration profile, and at high V s /V u , the experimental measurements were greater than predicted.