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  • 1.
    Almlöf Ambjörnsson, Heléne
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Mercerization and Enzymatic Pretreatment of Cellulose in Dissolving Pulps2013Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis deals with the preparation of chemically and/or enzymatically modified cellulose. This modification can be either irreversible or reversible. Irreversible modification is used to prepare cellulose derivatives as end products, whereas reversible modification is used to enhance solubility in the preparation of regenerated cellulose.

    The irreversible modification studied here was the preparation of carboxymethyl cellulose (CMC) using extended mercerization of a spruce dissolving pulp. More specifically the parameters studied were the effect of mercerization at different proportions of cellulose I and II in the dissolving pulp, the concentration of alkali, the temperature and the reaction time. The parameters evaluated were the degree of substitution, the filterability and the amount of gel obtained when the resulting CMC was dissolved in water. Molecular structures of CMC and its gel fractions were analysed by using NIR FT Raman spectroscopy. It was found that the alkali concentration in the mercerization stage had an extensive influence on the subsequent etherification reaction. FT Raman spectra of CMC samples and their gel fractions prepared with low NaOH concentrations (9%) in the mercerization stage indicated an incomplete transformation of cellulose to Na-cellulose before carboxymethylation to CMC. Low average DS values of the CMC, i.e. between 0.42 and 0.50 were obtained. Such CMC dissolved in water resulted in very thick and semi solid gum-like gels, probably due to an uneven distribution of substituents along the cellulose backbone. FT Raman spectra of CMC samples and their gel fractions mercerized at higher alkaline concentration, i.e. 18.25 and 27.5% in the mercerization stage, indicated on the other hand a complete transformation of cellulose to Na-cellulose before carboxymethylation to CMC. Higher average DS values of the CMC, i.e. between 0.88 and 1.05 were therefore obtained. When dissolved in water such CMC caused gel formation especially when prepared from dissolving pulp with a high fraction of cellulose II.

    The reversible modification studied was the dissolution of cellulose in NaOH/ZnO. Here the effect of enzyme pretreatment was investigated by using two mono-component enzymes; namely xylanase and endoglucanase, used in consecutive stages. It was found that although the crystallinity and the specific surface area of the dissolving pulp sustained minimal change during the enzymatic treatment; the solubility of pulp increased in a NaOH/ZnO solution from 29% for untreated pulp up to 81% for enzymatic pretreated pulp.

  • 2.
    Almlöf Ambjörnsson, Heléne
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Germgård, Ulf
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Extended Mercerization Prior to Carboxymethyl Cellulose Preparation2011Conference paper (Other (popular science, discussion, etc.))
  • 3.
    Almlöf Ambjörnsson, Heléne
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Germgård, Ulf
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Jardeby, Kristina
    Borregaard Chemcell, Sarpsborg, Norge.
    Kreutz, Björn
    Borregaard Chemcell, Sarpsborg, Norge.
    The influence of mercerization on the degree of substitution in carboxymethyl cellulose2009Conference paper (Other (popular science, discussion, etc.))
  • 4.
    Almlöf Ambjörnsson, Heléne
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Schenzel, Karla
    Marthin-Luther University Halle-Wittenberg.
    Germgård, Ulf
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Characterization of CMC by NIR FT Raman spectroscopy2012Conference paper (Other (popular science, discussion, etc.))
  • 5.
    Almlöf, Heléne
    Karlstad University, Faculty of Technology and Science, Avdelningen för kemiteknik.
    Extended Mercerization Prior to Carboxymethyl Cellulose Preparation2010Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Carboxymethyl cellulose (CMC) is produced commercially in a two-stage process consisting of a mercerization stage, where the pulp is treated with alkali in a water alcohol solution, followed by an etherification stage in which monochloroacetic acid is added to the pulp slurry. In this thesis an extended mercerization stage of a spruce ether pulp was investigated where the parameters studied were the ratio of cellulose I and II, concentration of alkali, temperature and retention time. The influence of the mercerization stage conditions on the etherification stage, were evaluated as the degree of substitution (DS) of the resulting CMC and the filterability of CMC dissolved in water at a concentration of 1%. The DS results suggested that the NaOH concentration in the mercerization stage was the most important of the parameters studied. When the NaOH concentration in the mercerization step was low (9%), a high cellulose II content in the pulp used was found to have no negative impact on the DS of the resulting CMC compared with pulps with only cellulose I. However, when the NaOH concentration was high (27.5%), pulps with high content of cellulose II showed a lower reactivity than those with only cellulose I with respect to the DS of the CMC obtained after a given charge of NaMCA.

    The results obtained from the filtration ability study of CMC water solutions suggested that both the amount of cellulose II in the original pulp and the temperature had a negative influence on the filtration ability whereas the NaOH concentration in the mercerization stage had a positive influence. The filtration ability was assumed to be influenced highly by the presence of poorly reacted cellulose segments. A retention time between 1-48 h in the mercerization stage had no effect on either the DS or the filtration ability of the CMC.

    Using NIR FT Raman spectroscopy molecular structures of CMC and its gel fraction were analyzed with respect to the conditions used in the extended mercerization stage. Here it was found that the alkaline concentration had a very strong influence on the following etherification reaction. FT Raman spectra of CMC samples and their gel fractions prepared with low NaOH concentrations (9%) in the mercerization stage indicated an incomplete transformation of cellulose to Na-cellulose before carboxymethylation to CMC. Low average DS values of the CMC, i.e. between 0.42 and 0.50, were yielded. Such CMC dissolved in water caused very thick and semi solid gum-like gels, probably due to an uneven distribution of substituting groups along the cellulose backbone. FT Raman spectra of CMC mercerized with alkaline concentrations at 18.25 and 27.5% in the mercerization stage indicated, however, that all of the cellulose molecules were totally transferred to CMC of high DS, i.e. between 0.88 and 1.05. When dissolved in water such CMC caused gels when they were prepared from ether pulp with a high fraction of cellulose II.

  • 6.
    Almlöf, Heléne
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Basta, Jiri
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Germgård, Ulf
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Guo, Sanchuan
    Heijnesson-Hulten, Anette
    The Effect of Stock Storage on The Quality of Bamboo Kraft Pulp2010In: O PAPEL, ISSN 0031-1057, Vol. 72, no 6, 43-53 p.Article in journal (Refereed)
  • 7.
    Almlöf, Heléne
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Kreutz, Bjørn
    Borregaard Chemcell, Norway.
    Jardeby, Kristina
    Borregaard Chemcell, Norway.
    Germgård, Ulf
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    The influence of extended mercerization on some properties of carboxymethyl cellulose (CMC)2012In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 66, 21-27 p.Article in journal (Refereed)
    Abstract [en]

    Carboxymethyl cellulose (CMC) is produced commercially in a two stage process consisting of a mercerization stage in which the pulp is treated with alkali in a water alcohol solution and a second etherification stage whereby monochloro-acetic acid is added to the pulp slurry. In this study, the influence of the conditions of an extended mercerization stage was evaluated on the etherification stage concerning the degree of substitution (DS) and the filterability of the resulting CMC. The parameters studied were: (1) the ratio of cellulose I and cellulose II in the original pulp, (2) the concentration of alkali, (3) the temperature and (4) the retention time in the mercerization stage. The DS results indicate that the NaOH concentration in the mercerization stage is the most important among the parameters studied. When the NaOH concentration in the mercerization stage was high (27.5%), cellulose II showed a lower reactivity than cellulose I with respect to the DS obtained in the resulting CMC. The results from the filtration ability of CMC water solutions are interpreted that the amount of cellulose II in the original pulp and the temperature has a negative influence, while the NaOH concentration in the mercerization stage has a positive influence on the filtration ability. Retention time between 1 h–48 h in the mercerization stage had no effect on the DS or the filtration value. The filtration ability was assumed to be highly influenced by the presence of poorly reacted cellulose segments. The CMC samples with the lowest filtration ability at a given DS can be assumed to have the highest degree of unevenly substituted segments.

  • 8.
    Almlöf, Heléne
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Schenzel, Karla
    Department of Natural Science III, Institute of Agriculture and Nutritional Science, Martin Luther University, Germany.
    Germgård, Ulf
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Carboxymethyl cellulose produced at different mercerization conditions and characterized by NIR FT Raman spectroscopy and chemometric methods2013In: BioResources, ISSN 1930-2126, E-ISSN 1930-2126, Vol. 8, no 2, 1918-1932 p.Article in journal (Refereed)
  • 9.
    Aman, Zaeem
    Karlstad University, Faculty of Technology and Science.
    Efficiency of Fluorescent Whitening Agents in Pigment Coatings2012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The objective of this work was to study the addition of fluorescent whitening agents (FWAs) for efficient use on pigment coating of paper substrates with low grammage and the goal was to achieve high optical response by using low amount of FWAs. A commercial light-weight coated (LWC) paper grade was provided by Stora Enso Corbehem Mill and isotropic laboratory sheets were produced at Stora Enso Research Centre using PFI sheet former. Optical properties such as brightness, whiteness and L, a* and b* colour space values were evaluated using Minolta spectrophotometer with D65 illuminant for both types of substrate using different types and amounts of FWA while the effect of the addition of dye was evaluated in both isotropic sheets and as well as in the coating. The results showed that brightness and whiteness of double-coated paper increased by increasing the amount of fluorescent whitening agent in the coating layer. Also, higher brightness and whiteness was achieved by introducing a higher amount of fluorescent whitening agent in the top coating rather than in a pre-coating. The addition of a shading colorant in the paper substrate had a positive influence not only on the brightness but also on the whiteness of coated paper.

  • 10. Andersson, Caisa
    et al.
    Järnström, Lars
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Paper Surface Centre. Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering. Karlstad University, Faculty of Technology and Science, Materials Science.
    Water-vapour permeability of barrier dispersion coating2001Conference paper (Other (popular science, discussion, etc.))
  • 11.
    Andersson, Elin
    Karlstad University, Faculty of Health, Science and Technology (starting 2013).
    Starch and Hemicellulose as Barrier Materials in Food Packaging: - A study of the materials permeability and structure with polyvinyl alcohol as a reference2015Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    To prevent permeation through food packages, the packaging are often combined with barrier coatings. Many of these coatings are petroleum based and wished to be replaced with renewable materials.

    The aim with this study was to produce laboratory barrier films of starch, hemicellulose and polyvinyl alcohol (PVA) and to examine the structures of these films and investigate how these barriers are affected by plasticizer additions. In this thesis PVA was mostly used as a reference material. In this way more knowledge can be obtained how the structures of the barrier affect the barrier performance. Different amounts of plasticizer, sorbitol, was added to the polymer solutions, different temperatures was used to dry the barriers and the barriers was coated with different thickness. The structure of the barrier was examined by several different analyses; oscillatory tests, scanning electron microscope (SEM), differential scanning calorimetry (DSC), permeability with oxygen transmission rate (OTR) and ambient oxygen transmission rate (AOIR).

    The results showed that sorbitol will be needed when making a barrier of starch and hemicellulose. This depends on the increasing entanglements in the polymers solutions when the sorbitol concentration is increasing; these entanglements decrease the glass transition temperature. Although, when the films are sticking together an increasing concentration of sorbitol seems to increase the permeability.

  • 12. Andersson, Niclas
    et al.
    Germgård, Ulf
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Johansson, Kristina
    Ljungqvist, Carl-Henrik
    Thuvander, Fredrik
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Paper Surface Centre. Karlstad University, Faculty of Technology and Science, Materials Science. Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
    Determining the strain to failure for constrained pulp fibres by means of single-fibre2002In: Appita Journal, Vol. vol 55 no 3Article in journal (Refereed)
  • 13. Andersson, Niclas
    et al.
    Germgård, Ulf
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Johansson, Kristina
    Ljungqvist, Carl-Henrik
    Thuvander, Fredrik
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Paper Surface Centre. Karlstad University, Faculty of Technology and Science, Materials Science. Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
    Determining the strain to failure for constrained pulp fibres by means of single-fibre fragmentation2002In: Appita Journal 55(2002)3, 224-229Article in journal (Refereed)
  • 14.
    Andersson, Niclas
    et al.
    BTG Process Solutions, Sweden.
    Wilke, Caroline
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences. BTG Process Solutions, Sweden.
    Akhlesh, Mathur
    BTG Process Solutions, Singapore.
    Smith, Dan
    BTG Process Solutions, USA.
    Germgård, Ulf
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Measurement of Dissolved Lignin, and its Impact in Fiberline Unit Operations.2017Conference paper (Refereed)
  • 15.
    Andersson, Niclas
    et al.
    BTG Instruments.
    Wilke, Caroline
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences. BTG Instruments.
    Biazzo, Tom
    BTG Americas Inc.
    Van Fleet, Rick
    BTG Americas Inc..
    Germgård, Ulf
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Beder-Miller, Sandra
    BTG Americas Inc..
    Is Conductivity the Best Measurement of Bleach Plant Carryover?2015In: Pulp & paper Canada, ISSN 0316-4004, 1-6 p.Article in journal (Refereed)
  • 16. Andersson, Niclas
    et al.
    Wilson, David
    Germgård, Ulf
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    An improved kinetic model structure for softwood kraft cooking2003In: Nordic Pulp and Paper Research Journal, Vol. vol 18 no 2Article in journal (Refereed)
  • 17. Andersson, Niclas
    et al.
    Wilson, David
    Germgård, Ulf
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Model based kraft cooking optimisation2003In: Nordic Pulp and Paper Research Journal, Vol. vol 18 no 4Article in journal (Refereed)
  • 18. Andersson, Niclas
    et al.
    Wilson, David
    Germgård, Ulf
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Using validated continuous kraft digester models for profile optimisation2002Conference paper (Refereed)
  • 19. Andersson, Niclas
    et al.
    Wilson, David
    Germgård, Ulf
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Validating continuous kraft digester kinetic models with online NIR measurements2002Conference paper (Refereed)
  • 20. Andersson, Niclas
    et al.
    Wilson, David
    Germgård, Ulf
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Lindström, Tomas
    Organic matter content in black liquor inside and outside chips during kraft cooking2001In: Paperi ja Puu, Vol. vol 83 no 7Article in journal (Refereed)
  • 21. Annergren, Göran
    et al.
    Germgård, Ulf
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Sulfate cooking - a commercially dominating and continously improving pulping process2014Report (Other academic)
    Abstract [en]

    Sulfite cooking was earlier the dominating pulping process but sulfate (kraft) cooking is today the most important process for the production of chemical pulps and high-yield pulps. One important reason for this development of the sulfate process is its ability to efficiently use different wood species, in particular different hardwood species. Another reason is that bleached hardwood sulfate pulps have become a strong competitor to bleached softwood sulfite pulps. The pros and cons of sulfate cooking are discussed in this report and compared with sulfite cooking.

     

  • 22. Ariño, I.
    et al.
    Kleist, U.
    Barros, Gustavo Gil
    Johansson, P.-Å.
    Rigdahl, M.
    Surface texture characterization of injection-molded pigmented plastics2004In: Polymer Engineering and Science, 44(9), 1615-1626 (2004)Article in journal (Refereed)
  • 23. Backfolk, K.
    et al.
    Johansson, Caisa
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering. Karlstad University, Faculty of Health, Science and Technology (starting 2013), Paper Surface Centre.
    Peltonen, J.
    Association between a sodium salt of a linear dodecylbenzene sulphonate and a non-ionic fatty alcohol ethoxylate surfactant during film formation of styrene/butadiene latex2006In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2006, 291 (1-3), 38-44Article in journal (Refereed)
  • 24. Balderud, Jonas
    Modelling validation and control of the wet-end of a five-layer board machine2003Report (Other academic)
  • 25.
    Barbier, Christophe
    et al.
    Karlstad University, Faculty of Technology and Science, Materials Science. Karlstad University, Faculty of Health, Science and Technology (starting 2013), Paper Surface Centre. Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering. Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
    Beghello, L
    Magnetic printing for packaging industry: methods and feasibility2006Conference paper (Refereed)
  • 26.
    Barbier, Christophe
    et al.
    Karlstad University, Faculty of Technology and Science, Materials Science. Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences, Paper Surface Centre. Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering. Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
    Larsson, Per-Lennart
    Östlund, Sören
    Hallbäck, Nils
    Karlstad University, Faculty of Technology and Science, Materials Science. Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
    Karathanasis, Michael
    On material characterization of paper coating materials by microindentation testing2005In: JCT: Journal of Coatings Technology, ISSN 0361-8773, Vol. 2, no 6, 463-471 p.Article in journal (Refereed)
    Abstract [en]

    Microindentation as a method for determining important material properties of paper coating materials is studied experimentally and numerically. The bulk of the investigation is concentrated upon the short-lived elastic part of a spherical indentation test, but determination of the failure stress of the coating is also discussed. The results indicate that microindentation can be a powerful tool for material characterization of these materials, but only if careful efforts are made to account for the influence from plasticity as well as from boundary effects

  • 27.
    Barbier, Christophe
    et al.
    Karlstad University, Faculty of Technology and Science, Materials Science. Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences, Paper Surface Centre. Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering. Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
    Larsson, PL
    KTH Stockholm.
    Östlund, S
    Experimental investigation of damage at folding of coated papers2002In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 17, no 1, 34- p.Article in journal (Refereed)
    Abstract [en]

    To achieve a better understanding of the folding properties of coated papers pertinent to the mechanical behaviour, a microscopic investigation was performed. The influence on the damage levels in the coating from such features as delamination, humidity and paper thickness have been studied

  • 28.
    Barbier, Christophe
    et al.
    Karlstad University, Faculty of Technology and Science, Materials Science. Karlstad University, Faculty of Health, Science and Technology (starting 2013), Paper Surface Centre. Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering. Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
    Larsson, PL
    Östlund, S
    Numerical investigation of folding of coated papers2005In: Composite StructuresArticle in journal (Refereed)
    Abstract [en]

    Folding of coated paper is examined numerically using the finite element method. Particular emphasis is put on the behaviour of field variables relevant for cracking of the coating layers. In the numerical analysis, the basepaper is modelled as an anisotropic elasticplastic material (both elastic and plastic anisotropy is accounted for) while the constitutive behaviour of the coating layers are approximated by classical (Mises) elastoplasticity. The numerical results suggest, among other things, that particular forms of plastic anisotropy can substantially reduce the maximum strain levels in the coating. It is also shown that delamination buckling, in the present circumstances, will have a very small influence on the strain levels in the coating layer subjected to high tensile loading

  • 29.
    Barbier, Christophe
    et al.
    Karlstad University, Faculty of Technology and Science, Materials Science. Karlstad University, Faculty of Health, Science and Technology (starting 2013), Paper Surface Centre. Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering. Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
    Larsson, PL
    Östlund, S
    On dynamic effects at folding of coated papers2005In: Composite StructuresArticle in journal (Refereed)
  • 30.
    Barbier, Christophe
    et al.
    Karlstad University, Faculty of Technology and Science, Materials Science. Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences, Paper Surface Centre. Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering. Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
    Larsson, PL
    KTH Stockholm.
    Östlund, S
    On the effect of high anisotropy at folding of coated papers2007In: Composite structures, ISSN 0263-8223, E-ISSN 1879-1085, Vol. 72, no 3, 330-338 p.Article in journal (Refereed)
    Abstract [en]

    A finite element procedure, developed in order to account for the effect of high anisotropy at folding of coated papers, is presented. The anisotropic behaviour (with very low stiffness in the thickness direction) is modelled using stiff structural elements (trusses and beams). The numerical results indicate that high elastic anisotropy leads to lower strain levels at folding than reported in previous analyses where this effect was not accounted for. High plastic anisotropy, on the other hand, will contradict this result

  • 31.
    Barbier, Christophe
    et al.
    Karlstad University, Faculty of Technology and Science, Materials Science. Karlstad University, Faculty of Health, Science and Technology (starting 2013), Paper Surface Centre. Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering. Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
    Larsson, PL
    Östlund, S
    Eklund, J
    Folding of printed papers: experiments and numerical analysis2003Conference paper (Other (popular science, discussion, etc.))
    Abstract [en]

    Folding of digital prints has been investigated experimentally in order to determine the influence from different features on the residual strength of the folded paper. In particular, the effect of toner-layer, paper-fibre orientation and pre-creasing is investigated and the experimental results are supplemented with numerical ones based on the finite element method. The results indicate that creasing, and to a less extend also fibre orientation, is the most important factor influencing the residual tensile strength after folding

  • 32. Barros, Gustavo Gil
    Influence of Substrate Topography on Ink Distribution in Flexography2006Doctoral thesis, monograph (Other academic)
  • 33.
    Barros, Gustavo Gil
    Karlstad University, Faculty of Technology and Science.
    Influence of Substrate Topography on Ink Distribution in Flexography2006Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    The printability of paper in flexography is largely dependent on the topographical characteristics of the substrate. Topography imaging instruments make it possible to obtain three-dimensional scans of paper surfaces that can be further used to calculate valuable quality parameters. The primary aim of the work described in this thesis has been to identify and isolate structural properties of the paper surface which significantly influence the ink distribution during printing and limit the subsequently attainable print quality.

    OptiTopo is an optical imaging technique which provides precise and fast topographic scans of both printed and unprinted paper surfaces. The potential and limitations of the technique have been evaluated. The optical requirements on the substrate for an accurate and precise topographic scan were determined. Detail-rendering was substantially improved using a custom-designed restoring filter, and a new enhanced spatial resolution range was established. A combination of further algorithm improvements made it possible also to obtain reflectance-factor-calibrated intensity images of scanned printed surfaces.

    Serious deficiencies affecting the quality of flexographic prints may appear in the form of local unprinted areas (UCA) in a full-tone print, generally caused by incomplete ink transfer. An algorithm detecting and quantifying local uncovered area was developed, tested and successfully integrated with the OptiTopo instrument. A UCA occurrence frequency distribution, indicating the percentage of the uncovered area at a certain topographical elevation, was calculated for different prints. The topographic characteristics of the uncovered areas clearly indicate that surface depressions are the primary cause of uncovered areas in flexographic printing.

    Four different predictive models based on topography thresholding were proposed and tested using two independent quality judgement criteria. These quality indices took into account both the amount and location of the predictions. A deeper understanding of the topographical features governing UCA occurrence was established with a proposed ink bridging effect. The total risk of non-ink-covered areas in flexography printing due to topographical features was estimated.

    The overall influence of paper topography on the flexography printability of full-tone areas was studied and its importance for the ink distribution assessed. The impacts of printing plate hardness, printing pressure, anilox cylinder volume and substrate roughness were quantified. Two typical flexography patterns were identified and their origin discussed: sub-millimetre elongated structures and millimetre-scale blotches.

  • 34. Barros, Gustavo Gil
    Optical Topographical Characterisation for Flexographic Printability2004Licentiate thesis, monograph (Other academic)
    Abstract [en]

    The flexographic printability is largely dependent on the topographical characteristics of the substrate. OptiTopo is a recently developed optical imaging technique, which provides precise and fast topographic scans of both printed and unprinted paper surfaces. The potential and limitations of the technique have been evaluated by comparing OptiTopo scans from a wide variety of commercial paper grades with those of other imaging techniques. The optical requirements on the substrate for an accurate and precise topographic scan were determined. Detail rendering was substantially improved using a custom-designed restoring filter, and a new enhanced spatial resolution range was established.



    Serious deficiencies affecting the quality of flexographic prints may appear in the form of local unprinted areas in a full-tone print, generally caused by incomplete ink transfer. An OptiTopo instrument with an integrated algorithm for the detection of uncovered areas was developed and tested on a range of commercial board samples printed on a laboratory flexographic press. A frequency distribution of uncovered areas, indicating how large a percentage of the surface area with a certain topographical elevation was uncovered, was calculated for the different prints. The topographic characteristics of the uncovered areas clearly indicate that surface depressions are the primary cause of uncovered areas in flexographic printing. Different uncovered area predictability models based on spectral analysis and topographic thresholding are proposed

  • 35.
    Barros, Gustavo Gil
    et al.
    Karlstad University, Faculty of Technology and Science.
    Johansson, Per-Åke
    Mottle and Ink Distribution in Full-Tone Flexography Prints on Coated Linerboard2007In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 33, no 4, 217-226 p.Article in journal (Refereed)
  • 36.
    Barros, Gustavo Gil
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Johansson, Per-Åke
    STFI-Packforsk AB, Stockholm, Sweden .
    Prediction of UnCovered Area occurrence in flexography based on topography: A feasibility study2006In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 21, no 2, 172-179 p.Article in journal (Refereed)
    Abstract [en]

    This investigation concerns the development and prediction of uncovered areas (UCA) in flexographic full-tone prints based purely on substrate topographic information. Four different predictive models based on topography thresholding were proposed and tested using two independent quality judgement criteria. 

  • 37. Barros, Gustavo Gil
    et al.
    Johansson, P.Å.
    Distribution Of Uncovered Areas (UCA) In Full Tone Flexographic2005In: TAGA J., 2(1), 43-57 (2005)Article in journal (Refereed)
  • 38. Barros, Gustavo Gil
    et al.
    Johansson, P.-Å.
    Prediction of UnCovered Area Occurrence in Flexography Based on Topography ' A Feasibility Study2005In: Accepted for publication in Nordic Pulp Paper Res. Journal, 2005Article in journal (Refereed)
  • 39. Barros, Gustavo Gil
    et al.
    Johansson,, P.Å.
    The OptiTopo Technique for Fast Assessment of Paper Topography ' Limitations, Applications and Imporvements2005In: J. Imaging Sci. Technol., 49(2), 170-178 (2005)Article in journal (Refereed)
  • 40.
    Beghello, Luciano
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering. Karlstad University, Faculty of Health, Science and Technology (starting 2013), Paper Surface Centre.
    A New Generation of Durable Banknote Paper1999Conference paper (Other (popular science, discussion, etc.))
  • 41.
    Bergendahl, Rikard
    Karlstad University, Division for Chemistry.
    Felkällor och systematiska avvikelser i kvalitetsuppföljningen av tidnings- och journalpapper2008Independent thesis Basic level (professional degree), 20 points / 30 hpStudent thesis
    Abstract [en]

    In paper production demands are set not only on quality and quantity, but it is also required that samples from the production are taken out and handled in a correct way. From the moment when a sample is taken out and up to the point when it is examined in the laboratory of the mill, a number of factors may affect the sample and thus the test result. Such changes can arise from the handling of samples from the paper machine and the transport of the samples to the laboratory and also from the handling of the samples in the laboratory. Another factor that can influence the samples is the climate and the seasons spring and autumn is the times when the samples are influenced most. Samples are examined with even intervals from finished papers and is used for calibration of on-line measurement on the paper machine and some of the sample results are sent directly to the costumer in the form of an analysis certificate.

    The purpose of this project was to analyze certain error sources in the sample handling and the impact of the climate on the sample result. It was examined how varying climates on the paper machine could influence the sample results for samples that were examined directly and compared with samples that were conditioned for one hour on the laboratory in a permanent climate (23°C, 50% RH). Samples that were conditioned were either taken directly to the lab or left by the paper machine for an extended period of time. In the work, it was included that seasons would be simulated and it was carried out on Stora Enso Research centre in Falun in a climate room. The climates that papers were examined in then were extreme dry and extreme damp and these results were compared with results from normal climate for testing paper.

    The paper qualities that were examined where 45 g/m2 standard newspaper from papermachine 11 and 52 g/m2 SC-paper (uncoated journal papers) from the new papermachine 12 in Kvarnsveden. What were examined were the critical parameters were it exists risk to rejection of papers. The critical properties that have a limit when the papers are rejected are grammage, ISO-brightness and nuance and in certain cases also roughness and tear strength.

    The results showed that at extreme climate relations from the studies on Stora Enso Research centre samples had been influenced to that degree that many of the samples had to be rejected. For SC-paper roughness was the property that was most critical at extremely dry climate and at damp climate the grammage was the most sensitive property. Standard newspaper was very sensitive at both extremely damp and dry climates for grammage and tearing strength.

    The study on Kvarnsveden showed that the moisture content in the paper was influenced more than the other properties but its changes were only marginal and within the respective limit for rejection. Nuance and the other optic properties had only marginal changes for both varying and extreme climates and the changes can in most cases be considered negligible for the production.

    In those cases when there are extreme climates, like during certain seasons, it is very important that the operator handles the samples correctly. Then, it is important that the samples are sent down to the laboratory as fast as possible where the impact is smaller than if the samples stay in the machine room.

  • 42.
    Berghel, Jonas
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Energy, Environmental and Building Technology.
    Nilsson, Lars
    Karlstad University, Faculty of Technology and Science, Department of Energy, Environmental and Building Technology.
    Renström, Roger
    Karlstad University, Faculty of Technology and Science, Department of Energy, Environmental and Building Technology.
    Particle mixing and residence time when drying sawdust in a continuous spouted bed2008In: Chemical Engineering and Processing, ISSN 0255-2701, E-ISSN 1873-3204, Vol. 47, no 8, 1252-1257 p.Article in journal (Refereed)
  • 43.
    Bergman, Helene
    et al.
    Karlstad University, Division for Chemistry.
    Gillstedt, Anna
    Karlstad University, Division for Chemistry.
    Tungmetallbalans över Gruvöns bruk2002Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
  • 44.
    Bergström, Jens
    et al.
    Karlstad University, Faculty of Technology and Science, Materials Science. Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
    Fredriksson, Gunnel
    Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering. Karlstad University, Faculty of Technology and Science, Materials Science.
    Johansson, M
    Kotik, Ouliana
    Thuvander, Fredrik
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Paper Surface Centre. Karlstad University, Faculty of Technology and Science, Materials Science. Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
    The Use of Tool Steels: Experience and Research2002Book (Refereed)
  • 45. Bergström, L.
    et al.
    Sjöberg, M.
    Järnström, Lars
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Paper Surface Centre. Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering. Karlstad University, Faculty of Technology and Science, Materials Science.
    Concentrated Kaolinite Suspensions - Polymer Adsorption and Rheological Properties1996In: in "Science of Whitewares", ed. by V.E. Henkes, G.Y. Onoda and W.M. Carty, American Ceramic Society, Westerville, OH, 1996, pp. 65-77 / [ed] V.E. Henkes, G.Y. Onoda and W.M. Carty, 1996Chapter in book (Refereed)
  • 46. Bjorklund, R.B.
    et al.
    Arwin, H.
    Järnström, Lars
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Paper Surface Centre. Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering. Karlstad University, Faculty of Technology and Science, Materials Science.
    Adsorption of Anionic and Cationic Polymers on Porous and Non-Porous Calcium Carbonate Surfaces1994In: Appl.Surf.Sci.,75,197(1994)Article in journal (Refereed)
  • 47. Björklund, Magnus
    et al.
    Germgård, Ulf
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Basta, Jiri
    Effect of cooking conditions on ECF bleaching and brightness reversion of birch kraft pulp2005In: Tappi JournalArticle in journal (Refereed)
  • 48. Björklund, Magnus
    et al.
    Germgård, Ulf
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Basta, Jiri
    Formation of AOX and OCI in ECF-bleaching of birch pulp2004In: Tappi Journal 3(2004)8, 7-11Article in journal (Refereed)
  • 49. Björklund, Magnus
    et al.
    Germgård, Ulf
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Basta, Jiri
    Formation of AOX and OCl in ECF-bleaching of birch pulp2004In: Tappi Journal, Vol. vol 3 no 8Article in journal (Refereed)
  • 50. Björklund, Magnus
    et al.
    Germgård, Ulf
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Basta, Jiri
    The influence of softwood kraft cooking conditions on the brightness development in ECF- bleaching2004In: Appita Journal, Vol. vol 57 no 3Article in journal (Refereed)
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