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  • 1.
    Högberg, Ida
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för tillämpad naturvetenskap och design.
    Zasadowski, Dariusz
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för tillämpad naturvetenskap och design.
    Karlsson, Anette
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för tillämpad naturvetenskap och design.
    Wikman, Bengt
    SCA Rand D Centre, Box 716, SE-851 21 Sundsvall, Sweden.
    Andersson, Fredrik
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för tillämpad naturvetenskap och design.
    Hedenström, Erik
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för tillämpad naturvetenskap och design.
    Edlund, Håkan
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för tillämpad naturvetenskap och design.
    Norgren, Magnus
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för tillämpad naturvetenskap och design.
    Brightness development of a hydrogen peroxide bleached spruce TMP. Comparisons of pre-treatments with DTPA and a separable chelating surfactant2012Inngår i: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 27, nr 1, s. 50-55Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this investigation a new type of recoverable complexing agent (chelating surfactant) has been compared with a conventional complexing agent; diethylenetriamine pentaacetic acid (DTPA), in the metal ion sequestering of thermomechanical pulps (TMP) to be hydrogen peroxide bleached. After different degrees of washing of the pulps, bleaching experiments at different total alkali charges were performed with and without sodium silicate additions, and the ISO brightness of hand-made sheets was measured. The residual hydrogen peroxide in the bleaching liquor was also determined. No significant difference in either the brightness development or the residual hydrogen peroxide content could be detected between the pulps treated with equivalent molar ratios of the different complexing agents. Furthermore, the recovery of the chelating surfactant-manganese complexes from laboratory made white water by froth flotation was also studied. Two different foaming agents; sodium dodecyl sulphonate (SDS) and dimethyldodecylamine oxide (DDAO), were tested in the froth generation. After an addition of 160 ppm of DDAO, more than 80% of the manganese chelates could be recovered in the foam, containing 3% of the initial water mass.

  • 2.
    Högberg, Ida
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap, teknik och matematik.
    Zasadowski, Dariusz
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap, teknik och matematik.
    Karlsson, Anette
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap, teknik och matematik.
    Wikman, Bengt
    SCA R&D, Sundsvall, Sweden.
    Andersson, Fredrik
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap, teknik och matematik.
    Hedenström, Erik
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap, teknik och matematik.
    Edlund, Håkan
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap, teknik och matematik.
    Norgren, Magnus
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap, teknik och matematik.
    Use of chelating surfactants as complexing agents for removal of manganese from mechanical pulp fibres prior to hydrogen peroxide bleaching.2011Inngår i: 16th International Symposium on Wood, Fiber and Pulping Chemistry - Proceedings, ISWFPC / [ed] Wang, L.; Kuang, S.; Hou, Q.; Cao, C.;Si, C.; Zhang, H., Tianjin: China Light Industry Press , 2011, s. 682-686Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this investigation a new type of recoverable complexing agent (chelating surfactant) has been compared with a conventional complexing agent (DTPA) in the metal ion management of thermomechanical pulps (TMP) to be hydrogen peroxide bleached. After different degrees of washing of the pulps, bleaching experiments at different total alkali charges were performed with and without sodium silicate additions, and the ISO brightness of hand-made sheets was measured. The residual hydrogen peroxide in the bleaching liquor was also determined. No significant difference in either the brightness development or the residual hydrogen peroxide content could be detected between the pulps treated with equivalent molar ratios of the different complexing agents. Furthermore, the recovery of the surfactant-manganese complexes from laboratory made white water by foam flotation was also studied. Two different foaming agents, SDS and DDAO, were tested. After an addition of 160 ppm of the latter surfactant, about 80% of the manganese chelates could be recovered in the foam, containing 3% of the initial water mass.

  • 3.
    Karlsson, Anette
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap, teknik och matematik.
    High consistency hydrogen peroxide bleaching of a Norway spruce stone groundwood pulp: Influence of heat treatment and iron content2011Inngår i: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 26, nr 2, s. 186-196Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The objective of this work was to improve the understanding on how thermal treatments of mechanical pulps containing iron influence the unbleached brightness and hydrogen peroxide bleachability at high brightness levels. An unbleached Norway spruce stone groundwood (SGW) pulp was subjected to heat and iron (Fe3+) treatments followed by a chelating stage and a high consistency hydrogen peroxide bleaching stage. The hydrogen peroxide bleachability was studied on pulps as a function of pre-treatment at elevated temperatures and strongly bound iron content prior to bleaching and the alkali charge during bleaching. The evaluation was done using an experimental design based on the MODDE software (Umetrics AB).

    Heat treatment of the unbleached SGW pulp at 110 or 140 degrees C did not induce a significant increase in light absorption coefficient. Increasing the heat treatment temperature to 170 degrees C did, however, result in an increased light absorption coefficient corresponding to a brightness loss of 3.5% ISO. The light scattering coefficient was found to be essentially unchanged regardless of the heat-treatment conditions applied. The brightness loss resulting from the heat treatment could only partly be regained by hydrogen peroxide bleaching.

    An increased amount of strongly bound iron in the unbleached SGW pulp increased the light absorption coefficient. This increase was slightly higher when heat pre-treatment was performed at 140 and 170 degrees C compared to when heating at 110 degrees C. Hydrogen peroxide bleaching was found to reduce the iron content of the pulps and thus regain some of the brightness that was lost. This effect was most pronounced at the higher alkali charge levels. It is thus important to minimise the processing temperature, the time at high temperature and the iron content of the pulp in order to improve the unbleached brightness and bleachability of mechanical pulps.

  • 4.
    Karlsson, Anette
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap, teknik och matematik.
    High consistency hydrogen peroxide bleaching of Norway spruce mechanical pulps2010Licentiatavhandling, med artikler (Annet vitenskapelig)
  • 5.
    Karlsson, Anette
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för kemiteknik.
    Improved hydrogene peroxide bleaching of mechanical pulps through fundamental understanding of the influence of heat, iron, fines and chemical treatment on chromophore content2013Doktoravhandling, med artikler (Annet vitenskapelig)
  • 6.
    Karlsson, Anette
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap, teknik och matematik.
    Agnemo, Roland
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap, teknik och matematik.
    High consistency hydrogen peroxide bleaching of mechanical pulps with varying amounts of fines2010Inngår i: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 25, nr 3, s. 256-268Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Hydrogen peroxide is a widely used bleaching chemical for mechanical pulps and is particularly useful when high brightness levels are required. The objective of this work was to study fines as a limiting factor for reaching higher brightness levels in high consistency hydrogen peroxide bleaching of Norway spruce (Picea abies) thermomechanical (TMP) and stone groundwood (SGW) pulps. The hydrogen peroxide bleaching efficiency (i.e. light absorption coefficient reduction) was studied as a function of temperature, alkali charge and fines content using an experimental design based on MODDE software (Umetrics AB).It is known that all types of fines contain more lignin, hemicelluloses, pectins, metals and less cellulose than long fibres. The light absorption coefficient was greater for unbleached TMP than for unbleached SGW pulp and an increased quantity of fines increased the light absorption coefficient for both pulp types. The increase was, however, most pronounced for the TMP. Furthermore, the data suggests that both the fibre fraction and the fines fraction are more coloured in the thermomechanical pulp. In most cases, increased amounts of fines in the pulp had a negative impact on the bleached pulp brightness in spite of the improved light scattering ability accompanying the addition of fines. A level of fines exceeding 50% was especially detrimental resulting in lower pulp brightness due to a higher light absorption coefficient.Increasing the bleaching temperature did not improve the bleaching efficiency. The optimal bleaching temperature at a hydrogen peroxide charge of 4.5% was found to be 70°C within the tested interval of 70-110°C. For a fines content of 25%, the stone groundwood pulp displayed a brightness of 83% whereas the thermomechanical pulp achieved a brightness of 79%.

  • 7.
    Karlsson, Anette
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för tillämpad naturvetenskap och design.
    Enberg, Sofia
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för tillämpad naturvetenskap och design.
    Rundlöf, Mats
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för tillämpad naturvetenskap och design.
    Paulsson, Magnus
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för tillämpad naturvetenskap och design.
    Edström, Per
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för tillämpad naturvetenskap och design.
    Determining optical properties of mechanical pulps: Sheetmaking procedure and investigation of different ways to evaluate light absorption2012Inngår i: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 27, nr 3, s. 531-541Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A method to produce representative sheets for determination of optical properties of mechanical pulps has been developed. It reduces the risk of contamination and discoloration and can be used with small pulp quantities. The deviation from the expected linear behaviour of the light scattering coefficient, s, at wavelengths corresponding to strong light absorption, has been studied using the Kubelka-Munk model and the angular resolved DORT2002 radiative transfer solution method. This decrease in s could not be explained by errors introduced in the Kubelka-Munk modelling by anisotropic scattering. Linear extrapolation of s can therefore not be justified as a way to obtain a more correct light absorption coefficient, k. For thepulps studied, the decrease in s at short wavelengths had little effect on k at 457 nm.

  • 8.
    Karlsson, Anette
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för kemiteknik.
    Paulsson, Magnus
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för kemiteknik.
    Engstrand, Per
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för kemiteknik.
    Hedenström, Erik
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för kemiteknik.
    Reduced heat-induced darkening and enhanced bleachability of mechanical pulps studied using the UV-visible absorption spectraManuskript (preprint) (Annet vitenskapelig)
  • 9.
    Karlsson, Anette
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för kemiteknik. SCA R and D Centre AB, SE-851 21 Sundsvall, Sweden.
    Paulsson, Magnus
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för kemiteknik. AkzoNobel Pulp and Performance Chemicals, SE-445 80 Bohus, Sweden.
    Engstrand, Per
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för kemiteknik.
    Hedenström, Erik
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för kemiteknik.
    Strategies to reduce heat-induced darkening for enhanced bleachability of mechanical pulps2014Inngår i: Appita journal, ISSN 1038-6807, Vol. 67, nr 1, s. 50-57Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Under mechanical pulping conditions, elevated temperature initiates reactions in the wood constituents resulting in the formation of coloured structures. In an attempt to reduce the formation of colour, a number of additives have been examined to assess their ability to inhibit heat-induced darkening of a Norway spruce (Picea abies) stone groundwood (SGW) pulp. SGW pulp was used as a model pulp with the purpose of imitating a thermomechanical pulp (IMP). The heat-treated SGW pulp, both with and without additives present, was subsequently bleached with 4.5% hydrogen peroxide at high pulp consistency and with varying alkali charges in order to examine the hydrogen peroxide bleachability of such pulps. Heat treatment at 170 °C resulted in a loss of brightness of about 4% ISO after heating for 60 seconds. The reduction in brightness could only partly be regained through high consistency hydrogen peroxide bleaching; the SGW pulp displayed a brightness of 83.7% ISO whereas the heat-treated SGW pulp reached a brightness of 80.4% ISO. Heat treatment with a low addition rate (1 %) of alkaline hydrogen peroxide, sodium bisulfite or sodium sulfite, with a subsequent hydrogen peroxide bleaching stage, resulted in an improved bleached brightness of about 81.6% ISO, i.e. the loss of brightness due to heat was still approximately 2% ISO. Sodium borohydride (1 %) did not suppress the thermal darkening but improved the bleached brightness by approximately 2% ISO compared to the heat-treated SGW pulp and resulted in a brightness of 82.6% ISO. Addition of a chelating agent (DTPA, 0.11 and 0.45%) and the radical scavengers phthalic hydrazide (1 %) and 1 -hexanol (1 %) suppressed the heat-induced darkening somewhat but did not improve the hydrogen peroxide bleachability to any noticeable extent. Addition of citric acid (0.6%) did not suppress the thermal darkening and resulted in impaired bleachability.

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