Showing papers in "Appita Journal in 2008"

Non-wood pulping possibilities - A challenge for the chemical pulping industry

Abstract: Chemical pulping processes that are currently used for pulping non-woods are mainly based on those adapted from the pulping of wood. Several newer methods, still at the laboratory or pilot scale, have also been announced. This paper reviews the current status of chemical and chemi-mechanical non-wood pulping processes, and describes their advantages and disadvantages. The review is based on claims made in the literature and is aimed at assisting researchers in their preparation for the development of a small scale, competitive process that could be a part of a complete utilisation chain for annual plants. Overall it can be concluded that the chemical composition and/or the special features of the non-wood raw materials have so far not been fully exploited.

Inkjet Print Quality on Model Paper Coatings

Abstract: Laboratory paper coatings of simple composition, comprising only a single spherical plastic pigment and binder type, were analysed in terms of water-based inkjet print quality. Optical density and gamut of dye colours decreased with increasing pigment size, and followed the binder hierarchy from polyvinyl alcohol (best) to carboxymethyl cellulose to styrene-butadiene latex (worst). For the larger pigment size, density and gamut also decreased with decreasing binder content and increasing coat weight. Colour-colour sharpness was evaluated using four measures of line bleeding, of which mean line width and blurriness were found to be the most useful and well correlated. Both bleeding measures, while following the same binder chemistry hierarchy mentioned above, now worsened with decreasing pigment particle size. This tallies with expectations from capillarity and light scattering, e.g. Increasing particle size (in the range studied) increases both liquid penetration rate and opacity, thus resulting in decreased colour richness but increased sharpness.

Energy Varieties of Sugar Cane as a Novel Source of Fibre for the Cellulose and Paper Industry

Abstract: Several recently developed high-yield varieties of sugar cane (Saccharum spp.) with fibre content 20% higher than that of conventional cane and juice content 10% lower, have been studied. This new class (named 'energy cane') has been shown to grow well and to yield more than 100 tonnes dry matter per hectare, under a wide range of soil and climatic conditions. The average fibre length of the energy-cane bagasse was 1.5 to 1.7 mm, about 65% longer than that of conventional-cane bagasse. The fibre and lumen diameters as well as the chemical components were also analysed and found to be similar to those of conventional-cane fibre. A series of soda cooks were made using representative samples of energy-cane bagasse and conventional-cane bagasse. Preliminary test results indicated that energy-cane bagasse pulp had significantly higher burst tear and tensile strengths than those of conventional-cane bagasse pulp.

Grit Segments in TMP Refining

Abstract: An energy efficient technique to produce pulp fibres in thermomechanical pulp (TMP) refining was developed. Grit material applied to refiner segments was found to increase the disruption and opening of the fibre cell walls, promoting the development of fibres and reducing the energy consumption. The grits were made from self-fluxing tungsten-carbide powder and a Ni-base alloy powder, which were laser-cladded on the bar surfaces of refiner segments. The trial of grit segments was carried out on a Sunds Defibrator RGP 44 single-disc refiner. The results showed that there is potential for reducing the energy consumption at least 10% with minimal negative impacts on pulp and paper properties. Grit segments can disrupt fibre cell walls efficiently and allow a lower of energy consumption, depending on the operating conditions. The grit segments performed on the refiner showed no effects on the motor load and the feeding capacity.

Refractive Index Measurements for Brown Stock Washing Loss - Laboratory Investigations

Abstract: The latest studies have shown that the most effective wash loss indicator compound is lignin - not COD Based on these studies, it could be possible to develop an on-line measurement method of wash loss using lignin Because lignin has a high molecular size and refractive index, it is reasonable to investigate a refractive index measurement device to control the wash loss level The effect of process conditions, such as temperature, consistency and flow rate as well as different lignin fractions and other chemicals on the measurement of refractive index were studied under laboratory conditions The results indicated that process conditions did not affect the measuring device operation negatively, and that the measurement was dependent on the dissolved solids content of the filtrate The measurement was virtually independent of the concentration of methanol, thus the measuring of the real wash loss was better than the traditional COD measurement The results of this study also support the investigation of mill scale refractive index measurement

A Kinetic Study of Softwood Kraft Cooking : Carbohydrate Dissolution as a Function of the Cooking Conditions

Abstract: A softwood kraft pulp has three major carbohydrate components viz. cellulose, O-acetyl-galactoglucomannan and arabinoglucuronoxylan, and these give rise to different pulp properties. These components are partly degraded and dissolved during kraft cooking, but they react differently to the cooking conditions and this makes it possible to vary the carbohydrate composition in the final pulp. A model, based on a large kinetic study, has therefore been developed to make it possible to control the carbohydrate composition in the pulp leaving the digester.

The use of molecular modelling in studying pitch deposition

Abstract: Molecular modelling is proving to be a useful tool in understanding the fundamental interactions between molecules and surfaces. With the use of the supercomputer at Australian National University (ANU) calculations on quite large molecules such as triglycerides and polymers can be made. The effect of the chemical structure of different fixatives on the interaction with the various components within pitch can be understood with the use of molecular modelling. Care is needed in choosing the most appropriate method to model the interactions. Geometry optimisation at the higher level of theory using quantum mechanics is needed. Comparison of different quantum mechanical methods yielded similar results indicating that the methods using the less computing power would be adequate in helping to gain a more fundamental understanding of the interactions that occur between various fixatives and pitch.

Shear/Compression of Chips for Lower Energy Consumption in TMP Refining

Abstract: Fundamental studies of the deformation behaviour of wood show that combining small amounts of shear along with compression within a roll press reduces the work required for cell wall deformation. This permanent deformation can be increased by: - increased number of passes through the nip - reduced roll speed - increased process temperature. Refining trials showed that the strength properties (except for the tear index), as well as the optical properties of TMP produced from these shear/compression pretreated chips are improved, with the potential of reducing electric energy by approx. 100 kWh/tonne, when compared to untreated chips.

Ink-fountain Solution Emulsion in Offset Printing Studied Using Confocal Microscopy

Abstract: Development of a new method for the visualization and measurement of fountain solution (FS) droplet size distributions in lithographic inks using confocal microscopy is described. The quantity and the state of FS droplets in offset inks are important as they significantly affect ink transfer and drying properties. The application of the confocal microscopy technique offers the possibility and versatility to study FS in ink emulsion through careful choice of fluorescent dyes and selection of suitable experimental conditions. This method has, for the first time, enabled the visual examination of the FS droplets in a 3D form. With the choice of suitable software, this method has the potential to provide quantitative information of the droplet size and size distribution. Some problems associated with the confocal method are also discussed. This method may have wide application in studying FS/ink, FS/plate and FS/paper interactions.

Delamination Position in Multiply Paperboard Achieved by Different Testing Methods

Abstract: The delamination properties of nine commercial multiply board grades, both coated and uncoated, were measured using four testing methods, the Z-Directional Tensile Strength test (ZDTS), the Scott Bond Test (SBT), the Wheel Delamination Test (WDT), and the IGT method. The positions of delamination failure in the thickness direction were then recorded and compared. For the IGT tests, failure profiles and the final failure positions were evaluated. The results showed that the failures in the ZDTS, WDT and SBT tests mainly occur in the middle ply, whereas failure in the IGT tests occurs in the top plies as well as in the middle ply. Some boards presented also more than one failure position for the same type of test. The correlations between the different delamination resistances were also investigated. The WDT and SBT method showed a good correlation, whereas no correlation could be found between the other methods.

Adding Lignin Derivatives to Decrease the Effect of Mechano-sorptive Creep in Linerboard

Abstract: When load is applied to any type of paper while varying the relative humidity, the paper will creep more than if the same load is applied at constant humidity. This behaviour is called mechano-sorptive creep or accelerated creep, and the reasons for its occurrence in paper are still not fully understood. However, wet strength and the addition of apolar (hydrophobic) compounds to sheets have previously been suggested as factors improving the mechano-sorptive creep performance. This work evaluates a method for improving wet strength and tests the addition of a hydrophobic compound, with particular reference to mechano-sorptive creep stiffness. Wet strength was improved by subjecting kraft liner pulp to low-molecular-weight lignin, obtained by cross-flow filtration, and to the radical initiator manganese( III). The hydrophobic compound added was a suberin-like lignin derivative. Adding the suberin-like lignin derivative significantly increased the mechano-sorptive creep stiffness, even though the stiffness at 90% rh decreased in the tested samples. This was probably because of the decrease in hygroexpansion caused by this hydrophobic additive. Even though it is possible significantly to increase the wet strength of kraft liner pulp by adding manganese(III) and cross-flow-filtered lignin, doing so has no significant effect on mechano-sorptive creep stiffness.

Black Liquor Impregnation of Scots Pine Sawdust and Chip Screenings

Abstract: Fine wood particles (sawdust and chip screenings) and wood chips made of Scots pine were impregnated with kraft pulping liquor and the results were compared. The effect of removing the smallest fractions from the fine wood particles was also studied. The fine wood particles differed significantly from the chips. Some differences were observed even between sawdust and chip screenings but the removal of the smallest fractions had only minor effects on the impregnation. Pine chip screenings generated residual liquors with lower EA than sawdust in the beginning of the impregnation but with higher EA sorption and consumption. In addition, pine chip screenings produced lower impregnation yields than sawdust, indicated by lower residual liquor dry solids and TOC contents. Pine chips again generated residual liquors with higher EA than fine wood particles and the EA sorption and consumption were substantially lower.