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  • 1.
    Ekbåge, Daniel
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Nilsson, Lars
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Håkansson, Helena
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Time series analysis of refining conditions and estimated pulp properties in a chemi-thermomechanical pulp process2019In: BioResources, ISSN 1930-2126, E-ISSN 1930-2126, Vol. 14, no 3, p. 5451-5466Article in journal (Refereed)
    Abstract [en]

    Frequently sampled process data from a conical disc refiner and infrequently sampled pulp data from a full scale chemi-thermomechanical pulp (CTMP) mill were evaluated to study autocovariance with aspects of potential dynamic modelling applicability. Two trial measurements with an online pulp analyzer at decreased sampling intervals were performed. For variability analysis, time-series containing up to one day of operational data were used. At the chip refiner, the clearest significant autocovariance was identified for the specific electricity consumption, based on the longer sequences. Most of the estimated pulp properties indicated low or non-significant autocovariance, limiting applicability of a specific dynamic model. A mill trial was conducted to investigate the impact from an increase in the conical disc gap on the specific electricity consumption and the resulting freeness. The response time from the gap change in the refiner to measured change in freeness was estimated at 19 min, which was approximately the hydraulic residence time in the latency chest. The relevance of this study lies in applicability of mill-data-driven modelling to capture the dynamics of a specific refining process. Through mill trials the sampling speed of pulp properties was more than doubled to gain insights into short term systematic variations by applying time-series-analysis.

  • 2.
    Ekbåge, Daniel
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Nilsson, Lars
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Håkansson, Helena
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Trial measurements in a CTMP-process to perform time-series analysis of refining conditions and estimated pulp properties2017Conference paper (Other academic)
  • 3.
    Ekbåge, Daniel
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Nilsson, Lars
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Håkansson, Helena
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Lin, Ping-I
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Health Sciences (from 2013).
    Multiple linear regression modelling of pulp and handsheet properties based on fiber morphology measurements and process data2020In: BioResources, ISSN 1930-2126, E-ISSN 1930-2126, Vol. 15, no 1, p. 654-676Article in journal (Refereed)
    Abstract [en]

    A multiple regression model was evaluated to predict pulp and handsheet properties including z-directional tensile strength (z-strength) and Scott bond values. One hypothesis that was central for the model evaluation was that the crill content, as measured with ultraviolet and infrared lights, would improve the statistical models. A chemi-thermomechanical pulp (CTMP) mill designed with two parallel primary refining lines and a reject refiner was the basis for this study, and all process data and pulp samples were gathered from the specific process. Pulp was extracted from the process for an extended period from a position after the latency chest (primary refined pulp) and from the pulp-stream exiting the mill to the board machine (accept pulp). The crill content was positively correlated to the z-strength of the accept pulp, explaining 55% of the variance with a linear regression model with the drill content as the sole predictor. The estimation model of the z-strength of accept pulp was based on a combination of the crill content, freeness, fibril perimeter for longer fibers, and mean kink angle, and resulted in an R-2 of 0.79. When applying cross-validation to determine the predictive model performance, the highest R-2 obtained was 0.67. This latter model included the crill content, fibril perimeter, and mean kink angle as predictors.

  • 4.
    Germgård, Ulf
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Håkansson, Helena
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Acid Hydrolysis of pulps2003Conference paper (Other (popular science, discussion, etc.))
  • 5.
    Germgård, Ulf
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Håkansson, Helena
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering. Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Östberg, Linda
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Activation of Dissolving Pulp with Enzymes Prior to Preparation of High Viscosity Viscose2009Conference paper (Other (popular science, discussion, etc.))
  • 6.
    Germgård, Ulf
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Östberg, Linda
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Håkansson, Helena
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering. Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Enzyme Activation of Pulp and its Influence on the Gamma Number of Viscose2011Conference paper (Other (popular science, discussion, etc.))
  • 7.
    Germgård, Ulf
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Östberg, Linda
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Håkansson, Helena
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering. Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Lab Scale Preparation of High Viscosity Viscose at Karlstad University2011Conference paper (Other (popular science, discussion, etc.))
  • 8.
    Hellström, Pia
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences. AkzoNobel.
    Heijnesson- Hultén, Anette
    AkzoNobel.
    Paulsson, Magnus
    AkzoNobel, Mid Sweden University.
    Håkansson, Helena
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Germgård, Ulf
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    The effect of Fenton chemistry on the properties of microfibrillated cellulose (MFC)2013Other (Other academic)
  • 9.
    Hellström, Pia
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013). AkzoNobel Pulp & Performance Chem, S-44580 Bohus, Sweden..
    Heijnesson-Hulten, Anette
    AkzoNobel Pulp & Performance Chem, S-44580 Bohus, Sweden..
    Paulsson, Magnus
    AkzoNobel Pulp & Performance Chem, S-44580 Bohus, Sweden.;Mid Sweden Univ, FSCN, S-85170 Sundsvall, Sweden..
    Hakansson, Helena
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Germgård, Ulf
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    The effect of Fenton chemistry on the properties of microfibrillated cellulose2014In: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 21, no 3, p. 1489-1503Article in journal (Refereed)
    Abstract [en]

    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.

  • 10.
    Hellström, Pia
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013). Akzo Nobel Pulp & Paper Performance Chem AB, Bleaching Chem Applicat RD&I, Bohus, Sweden..
    Heijnesson-Hulten, Anette
    Akzo Nobel Pulp & Paper Performance Chem AB, Bleaching Chem Applicat RD&I, Bohus, Sweden..
    Paulsson, Magnus
    Akzo Nobel Pulp & Performance Chem AB, Bleaching Chem Applicat RD&I, Bohus, Sweden.;Mid Sweden Univ, Sundsvall, Sweden..
    Håkansson, Helena
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Germgård, Ulf
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    A comparative study of enzymatic and Fenton pretreatment applied to a birch kraft pulp used for MFC production in a pilot scale high-pressure homogenizer2016In: TAPPI Journal, ISSN 0734-1415, Vol. 15, no 6, p. 375-381Article in journal (Refereed)
    Abstract [en]

    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.

  • 11.
    Hellström, Pia
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013). AkzoNobel Pulp & Performance Chem, SE-44580 Bohus, Sweden.
    Heijnesson-Hulten, Anette
    AkzoNobel Pulp & Performance Chem, SE-44580 Bohus, Sweden..
    Paulsson, Magnus
    AkzoNobel Pulp & Performance Chem, SE-44580 Bohus, Sweden.;Mid Sweden Univ, FSCN, SE-85170 Sundsvall, Sweden..
    Håkansson, Helena
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Germgård, Ulf
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Fenton pre-treated microfibrillated cellulose evaluated as a strength enhancer in the middle ply of paperboard2014In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 29, no 4, p. 732-740Article in journal (Refereed)
    Abstract [en]

    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.

  • 12. Hellström, Pia
    et al.
    Heijnesson-Hultén, Anette
    Paulsson, Magnus
    3FSCN, Mid Sweden University, SE-851 70 Sundsvall, Sweden.
    Håkansson, Helena
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Germgård, Ulf
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    The effect of Fenton chemistry on the production of microfibrillated cellulose - characterization and paper board application2013Conference paper (Refereed)
    Abstract [en]

    A fully bleached birch (Betula verucosa) sulphate pulp was treated with acidic hydrogen peroxide in the presence of ferrous iron (i.e. Fenton's reagent) and thereafter treated mechanically in a colloid mill to produce microfibrillated cellulose (MFC). The produced MFCs were chemically and morphologically characterized and compared with MFCs produced with enzymatic (monocomponent endoglucanase) pre-treatment (Figure 1). As a reference MFC produced with only acid pre-treatment was also included in the study.

    The Fenton pre-treatment increased the total charge of the fibres, decreased the viscosity and introduced new carbonyl groups. Addition of 10 and 50 kg/t hydrogen peroxide resulted in a yield loss of 2 and 4%, respectively. The enzymatic hydrolysis did not substantially change the total charge or the carbonyl group content of the pulp and did not release any organic material. The Fenton pre-treated pulps were easier to process mechanically, i.e. they reached a higher specific surface (BET) area and thereby a higher surface charge at a given mechanical treatment time, indicating a potential to reduce the energy demand in the final mechanical processing stage. The Fenton pre-treatment produced microfibrillated cellulose that in a water suspension (0.5% consistency) was stable with respect to sedimentation for at least eight weeks (Figure 2). Further, the Fenton pre-treatment gave a MFC product that contained a higher amount of small well fibrillated particles, as indicated by fractionation and scanning electron microscopy, compared with the enzymatic and acid pre-treatment methods studied.

  • 13.
    Håkansson, Helena
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Ethanol Pulping of Reed Canary Grass1995Licentiate thesis, monograph (Other academic)
    Abstract [en]

    The aim of this study was to investigate the possibility of processing an agricultural crop grown in Sweden to usable pulp. A further purpose was to study ethanol pulping applied to a non-wood raw material.



    The first part of this thesis deals with the criteria for selecting a fibre crop for further studies. Based on the content of fibres and the harvested yield reed canary grass was found to be the most interesting crop. The effect on fibre content of the amount of leaves was investigated and it was found that leaves contain a very small amount of fibres. If the amount of leaves in the crop is 25 % or less they have a rather small influence, however.



    In the second part of the thesis the studies of ethanol-alkali pulping and autocatalysed acidic ethanol pulping of reed canary grass are reported. The effects of the pulping conditions in the two methods were investigated using a response surface methodology. In ethanol-alkali pulping, the results were compared at the point of fibre liberation, which occurred at a kappa number of about 13. The shortest cooking time (80 min) required to reach kappa number 13 was obtained at an ethanol concentration of about 32 %, a liquor-to-raw material ratio of 4 l/kg and an alkali charge of 25 %. The highest pulp yield at kappa number 13 was obtained at about 38 % ethanol, 15 % alkali and any of the investigated liquor-to-raw material ratios (4 to 10 l/kg). In autocatalysed ethanol pulping, the results were compared at the end of the bulk delignification. The lowest possible kappa number (about 35) was obtained using 60 % ethanol at a liquor-to-raw material ratio of 10 l/kg.



    Some paper properties were investigated on an unbleached soda pulp from reed canary grass,

    an unbleached ethanol-alkali pulp from reed canary grass, an unbleached ethanol pulp from reed canary grass and a bleached (ODED) ethanol pulp from reed canary grass. For comparison, the properties of an unbleached and a bleached industrial birch kraft pulp were tested. The strength properties of the reed canary grass pulps are generally lower than those of the birch pulps.



    The investigated ethanol pulping techniques can be used for the pulping of reed canary grass. The pulps are not suitable in products where strength is important. They may be useful, however, as e.g. a component in printing paper.

  • 14.
    Håkansson, Helena
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Preparation and Characterization of Chemical Pulps from Wood and Reed Canary Grass2005Doctoral thesis, monograph (Other academic)
    Abstract [en]

    This thesis presents laboratory results from ethanol pulping of reed canary grass for the production of paper pulp. The focus was on the influence of cooking pa-rameters on the delignification. The strength of the grass pulps was found to be low and the use of such pulps will therefore be limited to a few products.



    The use of reed canary grass pulp for the preparation of microcrystalline cellulose by acid hydrolysis was also studied.



    The degradation of cellulose in different pulps during acid hydrolysis was investi-gated mainly through the levelling-off degree of polymerization (LODP) and the weight loss. The effect of hydrolysis conditions on the LODP and on the weight loss was studied, and a method for determining LODP was established.



    Pulps from birch, eucalyptus and reed canary grass with different hemicellulose contents were prepared. The hemicellulose content was reduced either by a prehy-drolysis step before kraft pulping or by alkali treatment of the bleached pulps. The crystallite size, as determined by LODP, of the pulps was strongly affected by the xylan content in the pulps after acid hydrolysis. A mechanism for the degradation of cellulose in pulps with different hemicellulose content was suggested.



    The size of the fiber fragments after acid hydrolysis was also influenced by the xy-lan content. At a given xylan content the fiber fragments from reed canary grass were smaller than those from the hardwoods.

  • 15.
    Håkansson, Helena
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Ahlgren, Per
    Acid Hydrolysis of Some Industrial Pulps: Effect of Hydrolysis Conditions and Raw Material2005In: Cellulose, vol 12, 2 (2005)Article in journal (Refereed)
  • 16.
    Håkansson, Helena
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Ahlgren, Per
    Germgård, Ulf
    The Degree of Disorder in Hardwood Kraft Pulps Studied by Means of LODP2005In: (accepted for publication in Cellulose, 2005)Article in journal (Refereed)
  • 17.
    Håkansson, Helena
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Ahlgren, Per
    Sjöberg, Lars-Arne
    Ethanol-Alkali Pulping of Reed Canary Grass1994In: Nordic Pulp & Paper Research Journal, vol. 9, 4 (1994)Article in journal (Refereed)
  • 18.
    Håkansson, Helena
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Sjöberg, Lars-Arne
    Ahlgren, P.
    Autocatalysed Ethanol Pulping of Reed Canary Grass1996In: Nordic Pulp and Paper ResearchJournal. 11, 2:100Article in journal (Refereed)
  • 19.
    Östberg, Linda
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Håkansson, Helena
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Germgård, Ulf
    Karlstad University, Faculty of Technology and Science.
    Some aspects of the reactivity of pulp intended for high-viscosity viscose2012In: BioResources, ISSN 1930-2126, E-ISSN 1930-2126, Vol. 7, no 1, p. 743-755Article in journal (Refereed)
    Abstract [en]

    The original objective of this study was to reduce the consumption of carbon disulphide in the preparation of high-viscosity viscose by pre-treating two softwood pulps with enzymes prior to the viscose stages. Reactivity can, however, be measured in different ways and the methods used in this study are Fock´s test of the pulp and the gamma number of the viscose solution prior to regeneration. It was found that whilst the reactivity of a pulp that had been subjected to enzyme pretreatment increased according to Fock´s test, it did not increase when the gamma number obtained in a standardized viscose preparation process was used. This unexpected difference that was discovered between the two reactivity tests made it difficult to analyze the impact of the enzyme stage on reactivity; the underlying reasons for the different reactivity results obtained were therefore investigated first. The conclusion that may be drawn from this investigation is that Fock´s test measures the extent to which carbon disulphide reacts with a pulp sample during a standardized test whereas the gamma number measures the resulting degree of xanthate substitution on the cellulose backbone. These two reactivity tests are thus not totally correlated. It was concluded that the gamma number was the more relevant of the two tests since it reflects the dissolution ability of a pulp in the viscose preparation, which is a very basic property of viscose. A higher gamma number also means that the coagulation time in the spinning process is prolonged; this is beneficial as it can be used to increase the tenacity of the viscose fibres. Measuring the reactivity according to Fock´s test, on the contrary, provides more dubious results as the test has no undisputed correlation to the viscose preparation process.

1 - 19 of 19
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