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Sökning: swepub > Karlstads universitet > Germgård Ulf

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  • Deshpande, Raghu, 1979-, et al. (författare)
  • The influence of different types of bisulfite cooking liquors on pine wood components
  • 2016
  • Ingår i: BioResources. - Raleigh : North Carolina State University. - 1930-2126 .- 1930-2126. ; 11:3, s. 5961-5973
  • Tidskriftsartikel (refereegranskat)abstract
    • In this laboratory study, the initial phase of a single-stage sodium bisulfite cook was observed and analyzed. The experiments were carried out using either a lab- or a mill-prepared cooking acid, and the cooking temperature used in these experiments was 154 °C. Investigated parameters were the chemical consumption, the pH profile, and the pulp yield with respect to cellulose, lignin, glucomannan, xylan, and finally extractives. Cooking was extended down to approximately 60% pulp yield and the pulp composition during the cook, with respect to carbohydrates and lignin, was summarized in a kinetic model. The mill-prepared cooking acid had a higher COD (Chemical Oxygen Demand) and TOC (Total Organic Carbon) content than the lab-prepared cooking acid and this influenced the pH and the formation of thiosulfate during the cook. It was found that the presence of dissolved carbohydrates and lignin in the bisulfite cooking liquor affected the extractives removal and the thiosulfate formation.
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  • Germgård, Ulf, 1950-, et al. (författare)
  • Screening of chemical pulp, revisiting technology options, and the state-of-the-art equipment—A critical review
  • 2023
  • Ingår i: Canadian Journal of Chemical Engineering. - : John Wiley & Sons. - 0008-4034 .- 1939-019X. ; 101:10, s. 5643-5655
  • Tidskriftsartikel (refereegranskat)abstract
    • Screening of pulp can be expressed as a process where solid contaminants are removed from a pulp slurry without an excessive loss of fibres of acceptable quality. The impurities originate from the feedstock, or they are generated during the transport, handling, storage, or pulping process. The most typical impurities include bark, fibre bundles or shives, knots, plastic, rubber, and sand. Moreover, there are also other objectives for screening, such as the improvement of the pulp quality, savings in bleaching chemical consumption, and protection of process equipment. In industrial applications, pulp screening is typically carried out with more than one screen for a more beneficial screening result. The pulp screening equipment can be divided into different types by the separation technique employed, such as atmospheric or pressurized screens, centrifugal screens, vibrating screens, etc. In addition, there are other types of related equipment that are common in the pulp screening process, such as knotters, refiners, and hydrocyclones. The main objective of this review is to discuss the advantages and disadvantages of modern screening equipment as well as introduce contemporary screening strategies for chemical pulp mills.
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  • Heijnesson-Hulten, Anette, et al. (författare)
  • Impact of Drying on the Quality of Bamboo Kraft Pulps
  • 2013
  • Ingår i: BioResources. - : NORTH CAROLINA STATE UNIV DEPT WOOD & PAPER SCI, CAMPUS BOX 8005, RALEIGH, NC 27695-8005 USA. - 1930-2126 .- 1930-2126. ; 8:1, s. 1245-1257
  • Tidskriftsartikel (refereegranskat)abstract
    • This study investigates how drying affects the quality of bamboo kraft pulps. Two bamboo pulps, cooked to different kappa numbers (i.e. 10 and 26) and D(EOP)D bleached to approximately the same brightness, were used to examine the relationship between cooking, drying, refining, and pulp/fiber properties. Drying of the two pulps caused, as expected, a loss in tensile and burst strength while the tear index was improved. The bleached high kappa pulp required less energy to reach a certain Schopper Riegler value and exhibited greater strength properties than the low kappa number pulp. These differences were also maintained after drying. Results showed that the properties of the pulp before drying determined the final strength potential of the pulp after drying. Thus, kraft cooking of bamboo to high kappa number prior to bleaching gave pulps with improved response to refining and pulp strength properties, which in turn influenced the properties of the dried pulps.
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  • Hellström, Pia, 1960-, et al. (författare)
  • A comparative study of enzymatic and Fenton pretreatment applied to a birch kraft pulp used for MFC production in a pilot scale high-pressure homogenizer
  • 2016
  • Ingår i: TAPPI Journal. - : TAPPI Press. - 0734-1415. ; 15:6, s. 375-381
  • Tidskriftsartikel (refereegranskat)abstract
    • Microfibrillated cellulose (MFC) was produced in pilot scale from a bleached birch (Betula verrucosa) kraft pulp that was pretreated with either Fenton's reagent or with a combined mechanical and enzymatic method used at the Centre Technique du Papier (CTP; Grenoble, France). The change in fiber fibrillation during the homogenization treatment was monitored by analyzing the fiber and the fines content, size fractionation, rheological properties and visualization by light-and scanning electron microscopy (SEM). The Fenton pretreatment resulted in MFC suspensions that contained a high amount of small sized elements. After five passes through the high-pressure homogenizer, the amount of particles smaller than 20 mu m was 37% for the Fenton pretreated MFC compared to 13% for the enzymatically (endoglucanase) pretreated MFC. Altogether, the Fenton pretreatment enabled preparation of MFC with a higher degree of fibrillation after the same number of passes through the high-pressure homogenizer. Another option is to produce MFC of the same amount of fibrillation as after an enzymatic stage, but at significantly lower energy consumption.
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  • Hellström, Pia, 1960-, et al. (författare)
  • Fenton pre-treated microfibrillated cellulose evaluated as a strength enhancer in the middle ply of paperboard
  • 2014
  • Ingår i: Nordic Pulp & Paper Research Journal. - 0283-2631 .- 2000-0669. ; 29:4, s. 732-740
  • Tidskriftsartikel (refereegranskat)abstract
    • Microfibrillated celluloses (MFCs), produced by various pre-treatments of a fully bleached birch kraft pulp, were evaluated as strength enhancers in test sheets representing the middle ply of paperboard. The furnish consisted of hydrogen peroxide bleached high temperature spruce chemithermomechanical pulp (HT-CTMP), MFC and a retention system containing cationic starch and an anionic silica sol. The MFC was prepared via a mechanical treatment in a colloid mill after pretreatment with Fenton's reagent, monocomponent endoglucanase or acidic hydrogen peroxide. Addition of 5% MFC, produced with Fenton pre-treatment, resulted in improved HT-CTMP properties with respect to increased tensile index (similar to 35%), z-directional strength (similar to 50%), tensile stiffness index (similar to 25%) compared to HT-CTMP test sheets prepared without MFC addition. The strength improvement was linearly correlated to the density of the tests sheet, to the surface area (BET) and to the surface charge of the enzymatic or chemically pre-treated MFCs.
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  • Hellström, Pia, 1960-, et al. (författare)
  • The effect of Fenton chemistry on the properties of microfibrillated cellulose
  • 2014
  • Ingår i: Cellulose. - : Springer. - 0969-0239 .- 1572-882X. ; 21:3, s. 1489-1503
  • Tidskriftsartikel (refereegranskat)abstract
    • A fully bleached birch kraft pulp was treated with acidic hydrogen peroxide in the presence of ferrous ions (Fenton's reagent) and thereafter treated mechanically in a colloid mill to produce a product containing microfibrillated cellulose (MFC). The produced MFC products were chemically and morphologically characterized and compared with MFC products produced without pretreatment as well as with enzymatic hydrolysis. Fenton treatment resulted in an increase in total charge and number of carbonyl groups while the intrinsic viscosity decreased. The Fenton treated pulps were easier to process mechanically i.e. they reached a higher specific surface area at a given mechanical treatment time and the MFC produced had a stable water-fibre suspension for at least 8 weeks compared to enzymatic pretreated pulps and pulps not subjected to any pretreatment.
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