| 1. |
- Andersson, Stefan, et al.
(författare)
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Comparison of mechanical pulps from two stage HC single disc and HC double disc - LC refining
- 2012
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Ingår i: Appita journal. - 1038-6807. ; 65:1, s. 57-62
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Tidskriftsartikel (refereegranskat)abstract
- A mechanical pulping line consisting of high consistency (HC) double disc (DD) and low consistency (LC) refining was compared with a two stage single disc (SD) high consistency twin refiner line. The purpose of this study was to evaluate specific energy consumption and pulp properties. The two different process solutions were tested running similar Norway spruce wood supply. At similar tensile index and freeness, the DD-LC concept reduced the electric energy consumption by 400 kWh/adt compared with the traditional two-stage SD-SD system. Pulp characteristics of the two refining concepts were compared at tensile index 47 Nm/g. Fibre length was reduced more after DD-LC refining than after SD-SD refining. Specific light scattering coefficient was higher after DD-LC refining than SD-SD refining, while the development in second stage refining was better for SD-SD pulp than for DD-LC pulp. Shive level was significantly lower for DD-LC pulp than for SD-SD pulp.
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| 2. |
- Annergren, Goran, et al.
(författare)
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Process aspects for sulfite pulping
- 2014
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Ingår i: Appita journal. - 1038-6807. ; 67:4, s. 270-276
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Tidskriftsartikel (refereegranskat)abstract
- Sulfite pulping of wood, with the aim of producing a paper product, can be carried out under acidic, neutral or alkaline conditions. However, if a dissolving pulp is required to be achieved, only acidic conditions may be employed. The main reason for this specific requirement for dissolving pulps is the high level of cellulose purity required. The hemicellulose content should therefore be low and hemicellulose molecules are best removed at low pH. Another difference is that in paper pulps it is the fibre properties that are of a dominant interest, while in a dissolving pulp the cellulose properties are of significant interest. However, one similarity for both paper and dissolving sulfite pulps is the risk of uncontrolled side-reactions, which can lead to severe lignin condensation reactions, and in extreme cases even to a totally black pulp. Thus, sulfite pulping is a relatively complex chemical process and an overview of the most important parameters is thus presented.
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| 3. |
- Antonsson, Stefan, et al.
(författare)
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Adding lignin derivatives to decrease the effect of mechano-sorptive creep in linerboard
- 2008
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Ingår i: Appita journal. - 1038-6807. ; 61:6, s. 468-471
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Tidskriftsartikel (refereegranskat)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.
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| 4. |
- Antonsson, Stefan, et al.
(författare)
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The relationship between hygroexpansion, tensile stiffness, and mechano–sorptive creep in bleached hardwood kraft pulps
- 2010
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Ingår i: Appita journal. - 1038-6807. ; 63:1, s. 231-
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Tidskriftsartikel (refereegranskat)abstract
- Hygroexpansion coefficient and tensile stiffness are important parameters in many paper applications. This study compares several bleached industrial hardwood kraft pulps, comprising five eucalypt pulps from South America, Europe, and Africa as well as an acacia pulp from Asia and a birch pulp from Scandinavia. Refined and unrefined pulps are compared. The results indicate significant differences in hygroexpansion but smaller differences in tensile stiffness index at comparable densities. No single factor offering a reasonable explanation of these differences in hygroexpansion coefficient, such as carbohydrate composition, fibre dimensions, or fibre form, was found. However, correlation between hygroexpansion coefficient and the mechano-sorptive creep stiffness was observed. We suggest that the hygroexpansion coefficient at a given tensile stiffness level can be used to rank pulps in terms of their mechano-sorptive creep properties.
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| 5. |
- Brännvall, Elisabet, et al.
(författare)
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The impact of ionic strength during kraft cooking on the strength properties of softwood kraft pulp
- 2007
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Ingår i: Appita journal. - 1038-6807. ; 60:1, s. 60-64
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Tidskriftsartikel (refereegranskat)abstract
- A study was undertaken in order to investigate the influence of ionic strength during pulping (measured as sodium ion concentration) on pulp strength (evaluated as tear index vs. tensile index) and on the pulps ability to resist mechanical damage. Sodium chloride was added to the cooking liquor in order to control the ionic strength during the laboratory kraft cooking of soft-wood. The strength properties were compared to a conventional laboratory pulp, pulped at an ionic strength equal to that originating solely from the cooking chemicals added.It was shown that the ionic strength of the cooking liquor had an impact on pulp strength. Tear index at a certain tensile index decreased at higher ionic strength. The fibre strength, measured as rewetted zero-span tensile index, also decreased. Furthermore, high ionic strength during cooking rendered the fibres more vulnerable to mechanical damage.
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| 6. |
- Enberg, Sofia, et al.
(författare)
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Mapping and modelling of optical properties from pulp to super calendered paper
- 2015
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Ingår i: Appita journal. - 1038-6807. ; 68:2, s. 128-138-
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Forskningsöversikt (refereegranskat)abstract
- During production of mechanical pulp based paper, the pulp darkenswithin the process which represents a significant cost for the mill. Amapping of the optical properties of the pulp was conducted along theprocess, from pulp mill to paper machine, at a mill producing supercalendered (SC) paper on three paper machines. The focus was to evaluateat which positions in the mill the discolouration occurs and also whichfraction of the pulp darkens the most.The fine fraction of the pulp darkened more than the long fibrefraction. Bleached pulp diluted with white water from the paper machinedarkened more during storage than pulp diluted with clear filtrate. Thewhite water contains a considerable amount of suspended solids, i.e.pulp fines and clay. There was a tendency for a shoulder in absorptionspectra of the pulp stored in white water from the paper machine in theregion 550 to 650 nm, both for fibres and for fines. This is in the sameregion where the added dyes have their absorption maxima and also somecomplexes between iron and some of the components among lignin and theextractives. Simulation of retention times of different fractions showedthat, although the main part of the fine material is retained in thepaper within a few hours, a small part might circulate for considerablylonger time.
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| 7. |
- Girlanda, O., et al.
(författare)
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Delamination position in multiply paperboard achieved by different testing methods
- 2008
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Ingår i: Appita journal. - 1038-6807. ; 61:2, s. 107-112
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Tidskriftsartikel (refereegranskat)abstract
- The determination 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.
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| 8. |
- Girlanda, O., et al.
(författare)
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Modelling of delamination in paperboard during sheet offset printing
- 2008
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Ingår i: Appita journal. - 1038-6807. ; 61:2, s. 113-119
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Tidskriftsartikel (refereegranskat)abstract
- Delamination of multiply paperboard during offset printing is caused by the ink tack induced forces applied on the surface of the board. The purpose of this investigation was to analyze the influence of mechanical properties of the plies and interface resistance on the delamination behaviour of the paperboard. Paperboard was modelled as a four-ply sandwich structure. A user-defined interface model described the mechanical behaviour of the interfaces between the plies. The results in terms of critical ink tack length and stress conditions in the interfaces at delamination initiation were defined for different ply structures. The delamination process in multiply paperboard was highly dependent on the stress concentration caused by the ink tack. The delamination always occurred in the interface between top and middle ply. The main stress component causing delamination was tensile stress in the thickness direction, whereas the interlaminar shear was less relevant. Bending stiffness and in-plane tensile stiffness influenced the critical ink tack length, but did not affect the stress situation at the delamination point.
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| 9. |
- Gorski, Dmitri, et al.
(författare)
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Mg(OH)(2)-based hydrogen peroxide refiner bleaching: influence of extractives content in dilution water on pulp properties and energy efficiency
- 2010
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Ingår i: Appita journal. - 1038-6807. ; 63:3, s. 218-225
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Tidskriftsartikel (refereegranskat)abstract
- Two refiner bleaching trials on TMP and SGW rejects using magnesium hydroxide and hydrogen peroxide were conducted in a reject refiner. Clear filtrate from a disc filter was used as dilution water during the first trial (normal mill operation) and fresh water was used during the second trial. Refiner bleached pulp had approximately nine %ISO higher brightness than reference pulps in both trials using a peroxide charge of 25 kg/t pulp. The brightness gain increased to 12 %ISO after high consistency storage at 755 degrees C for 30 minutes. The bleached pulp from the first trial had 10% lower tensile index compared to reference at similar refining energy. The extractives content on the surfaces of the bleached fibres (surface coverage measured by ESCA) was 20% higher compared to the unbleached reference pulp when clear filtrate was used as dilution water. Within this surface extractives content increase, the increase of triglycerides and steryl esters was largest, almost doubling in value. Acetone extraction of the pulps led to higher apparent sheet strength. The increase was equal for both the reference and the bleached samples but the bleached pulp still had inferior strength properties compared to the reference pulp. When a second trial was carried out with fresh water as dilution, much less difference in the strength properties of bleached and unbleached pulp was observed.It is suggested that addition of alkali to the refiner caused extractives in the clear filtrate to destabilise and re-deposit onto fibre surfaces. The fact that removal of extractives with acetone did not bring the strength of bleached pulp up to the level of the reference pulp suggests that extractives may have influenced the fibre development process of the bleached pulp fibres in the refiner.
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| 10. |
- Hammar, Lars-Åke, et al.
(författare)
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The effect of process conditions on pulp quality development in low consistency refining of mechanical pulp - TMP
- 2010
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Ingår i: Appita journal. - 1038-6807. ; 63:5, s. 377-380
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Tidskriftsartikel (refereegranskat)abstract
- High consistency (HC) defibration followed by secondary stage low consistency refining (LC) is an energy efficient process in mechanical pulping that has been explored for some time. In this study the effects of temperature, pH, specific edge load and specific energy on pulp quality have been investigated for LC refining using a mobile LC refiner rig placed after a primary stage HC refiner In the Braviken Paper mill. The trials showed that the specific energy consumption in production of mechanical pulp can be reduced with at least 15% with preserved pulp properties. High temperature, pH over 7 and low specific edge load were advantageous both for tensile index development and for preserving the fibre length of the pulp. The development of other pulp properties such as shives content and light scattering coefficient, as a function of freeness, were comparable for the second stage LC- and HC-refining.
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