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  • 1.
    Sevastyanova, Olena
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Helander, Mikaela
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Chowdhury, Sudip
    Wedin, Helena
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Ek, Monica
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Kadla, John F.
    Lindström, Mikael E.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Evaluation of physico-chemical properties and prediction of spinning parameters for high-quality lignins produced by ultra-filtration of industrial Kraft liquor2013In: Abstract of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 245Article in journal (Other academic)
  • 2.
    Sevasyanova, Olena
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Helander, Mikaela
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Chowdhury, Sudip
    Lange, Heiko
    Wedin, Helena
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Zhang, Liming
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Ek, Monica
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Kadla, John F.
    Crestini, Claudia
    Lindström, Mikael F.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Tailoring the Molecular and Thermo-Mechanical Properties of Kraft Lignin by Ultrafiltration2014In: Journal of Applied Polymer Science, ISSN 0021-8995, E-ISSN 1097-4628, Vol. 131, no 18, p. 9505-9515Article in journal (Refereed)
    Abstract [en]

    This study has shown that ultrafiltration allows the selective extraction from industrial black liquors of lignin fraction with specific thermo-mechanical properties, which can be matched to the intended end uses. Ultrafiltration resulted in the efficient fractionation of kraft lignin according to its molecular weight, with an accumulation of sulfur-containing compounds in the low-molecular weight fractions. The obtained lignin samples had a varying quantities of functional groups, which correlated with their molecular weight with decreased molecular size, the lignin fractions had a higher amount of phenolic hydroxyl groups and fewer aliphatic hydroxyl groups. Depending on the molecular weight, glass-transition temperatures (T-g) between 70 and 170 degrees C were obtained for lignin samples isolated from the same batch of black liquor, a tendency confirmed by two independent methods, DSC, and dynamic rheology (DMA). The Fox-Flory equation adequately described the relationship between the number average molecular masses (M-n) and T-g's-irrespective of the method applied. DMA showed that low-molecular-weight lignin exhibits a good flow behavior as well as high-temperature crosslinking capability. Unfractionated and high molecular weight lignin (M-w > 5 kDa), on the other hand, do not soften sufficiently and may require additional modifications for use in thermal processings where melt-flow is required as the first step.

  • 3.
    Wedin, Helena
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Aspects of extended impregnation kraft cooking for high-yield pulping of hardwood2012Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The long-term trend regarding wood is an increase in price. Because wood contributes to a large part of production costs, the efficient utilisation of wood is greatly desired to reduce production costs for kraft pulp producers. During the 1990s, the development of improved modified kraft cooking began, which led to higher yields. There was also a trend of terminating kraft cooking at a higher kappa number to maximise the overall yield. For hardwood, the defibration point became a critical setback in allowing this termination at a high kappa number. This thesis discusses how this issue has been tackled in the laboratory by using improved modified kraft cooking combined with extended impregnation to enable a decrease in reject content and shift the defibration point towards a higher kappa number for hardwood. This lab concept is referred to as extended impregnation kraft cooking (EIC), and this thesis reveals that EIC cooking efficiently reduces the reject content for both birch and eucalypt. By using EIC cooking, the defibration point was shifted to a kappa number of ca. 30 from ca. 20 using conventional kraft cooking. This study demonstrates the great potential for achieving a higher overall yield for eucalypt by terminating the EIC cooking at a high kappa number, but with the conditions used in this thesis, no improvement in yield was observed for birch.

     

    An important issue is that the termination of kraft cooking at high kappa number increases the demand for extended oxygen delignification to reach a similar kappa number into bleaching, i.e., due to cost and environmental reasons. Extended oxygen delignification was shown to be possible for both birch and eucalypt EIC pulps (i.e., from kappa number 27 to 10) with an acceptable pulp viscosity number.

     

    The other part of this thesis addresses aspects regarding the limitations in oxygen delignification. It has previously been shown in the literature that a high xylan yield of kraft cooking could negatively affect the efficiency of subsequent oxygen delignification. In this work, the increased xylan content in eucalypt kraft pulp within the range of 8–18% had only a marginally negative impact on the oxygen delignification efficiency after correcting for the HexA contribution to the kappa number. It is also desired to extend the oxygen delignification towards lower kappa number, i.e., below kappa number 10 to decrease the bleaching chemical requirement. In this study, the hypothesis that the reduced efficiency of oxygen delignification at low kappa numbers could partly be due to the formation of oxidisable carbohydrate-related structures (i.e., HexA and/or other non-lignin structures) was also tested. No formation was established. On the other hand, a final oxygen delignification stage in the bleaching could be an attractive alternative for reducing yellowing and enhancing brightness; in fact, this has led to the development of a patent (SE 528066).

  • 4.
    Wedin, Helena
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Antonsson, Stefan
    Ragnar, Martin
    Lindström, Mikael E.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Influence Of Xylan Content On The Oxygen Delignification Performance Of Eucalypt Kraft Pulps As Studied Using Prehydrolysis And Xylanase Treatments2012In: BioResources, ISSN 1930-2126, E-ISSN 1930-2126, Vol. 7, no 4, p. 5527-5541Article in journal (Refereed)
    Abstract [en]

    Common metrics for evaluating the efficiency of oxygen delignification include the kappa number and Klason lignin content. As a change in xylan content often leads to a change in HexA content, the kappa number must be corrected for the HexA contribution before evaluating the degree of oxygen delignification when trying to understand the process in detail. Questions could also be raised about the accuracy of the Klason lignin method for oxygen-delignified hardwood kraft pulps, since the amount of residual lignin is small in such pulp. This study investigates the influence of xylan content on oxygen delignification efficiency in Eucalyptus urograndis kraft pulps. Xylan content was varied using two methods: treatment with xylanase and with acid prehydrolysis for various times before kraft cooking. The degree of oxygen delignification, expressed as the HexA-corrected kappa number, indicated no significant trend with xylan removal, and no significant trend was evident when expressed as Klason lignin content.

  • 5.
    Wedin, Helena
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Fiskari, Juha
    Kovasin, Kari
    Ragnar, Martin
    Lindström, Mikael E.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Further insights into extended-impregnation kraft cooking of birch2012In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 27, no 5, p. 890-899Article in journal (Refereed)
    Abstract [en]

    Extended-impregnation kraft cooking (EIC) is a cooking concept that combines prolonged impregnation with modern improved modified kraft cooking. In the current investigation, the EIC cooking of birch was studied in relation to conventional kraft cooking. Specifically, the reject content and carbohydrate yield retention when terminating at a high cooking kappa number were examined. It was demonstrated that EIC cooking reduced the reject content. Unexpectedly, a high cooking kappa number led to no increase in carbohydrate yield, possibly due to the chemical composition of birch wood and the EIC cook lab procedure. A large amount of liquor was withdrawn after the impregnation, resulting in a loss of dissolved xylan that otherwise could have redeposited on the fibres and contributed to the carbohydrate yield. The effects of EIC cooking on extended oxygen delignification, bleaching chemical requirement in a D(OP)DP sequence, and strength properties were also examined. Compared with conventional lab cooking, EIC cooking resulted in a lower bleaching chemical requirement and similar strength properties.

  • 6.
    Wedin, Helena
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Lindström, Mikael E.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Ragnar, Martin
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    From simple theory to industrial application: extended impregnation kraft cooking2011Conference paper (Other academic)
  • 7.
    Wedin, Helena
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Lindström, Mikael E.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Ragnar, Martin
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Inorganic chemistry in oxygen delignification: the effect of counter ion and ionic strength2007Conference paper (Refereed)
  • 8.
    Wedin, Helena
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Lindström, Mikael E.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Ragnar, Martin
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    On the role of Xylan in Oxygen Delignification2007Conference paper (Other academic)
  • 9.
    Wedin, Helena
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Lindström, Mikael
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Ragnar, M.
    On the role of carbohydrates in oxygen delignification2005In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 20, no 4, p. 448-452Article in journal (Refereed)
    Abstract [en]

    The decrease in efficiency of the oxygen delignification of chemical pulps at low kappa numbers has been investigated. In order to study the role of the carbohydrates, five different fully bleached pulps were oxygen delignified and carefully analysed. The results show that no permanganate-consuming structures were formed in the carbohydrates during oxygen delignification, but that small amounts of lignin are slowly degraded. Unexpectedly, the ISO brightness was significantly increased, while the yellowing tendency was reduced, in some cases dramatically, making a final oxygen delignification treatment after a bleaching sequence an interesting option for market pulp producers with yellowing problems.

  • 10.
    Wedin, Helena
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Lindström, Mikael
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Ragnar, Martin
    Extended impregnation in the kraft cook: an approach to improve the overall yield in eucalypt kraft pulping2010In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 25, no 1, p. 7-14Article in journal (Refereed)
    Abstract [en]

    A potential way to improve the overall yield is to terminate the kraft cook at higher kappa number. This method was investigated using Extended Impregnation kraft Cook (EIC). As a reference, kraft pulp manufactured by conventional kraft cooking was used. By utilising the EIC concept, the defibration point in the kraft cook is shifted towards higher kappa numbers, resulting in a lower reject content at a given kappa number. This enables a termination of the ETC cook at higher kappa number. The results show that an overall yield gain of 2.6 percentage units could be achieved using ETC with higher cooking kappa number followed by extended oxygen delignification and bleaching with a D*(OP)D sequence to full brightness. However, the EIC concept at higher cooking kappa number resulted in somewhat higher bleaching chemical requirement. Extended oxygen delignification was shown to be possible to reach as low a kappa number as 10, but a high cooking kappa number is clearly a disadvantage if a high limiting viscosity number after oxygen delignification is required.

  • 11.
    Wedin, Helena
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Sevastyanova, Olena
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Evtuguin, Dmitry
    Ragnar, Martin
    Lindström, Mikael E.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Impact of extended-impregnation cooking on the xylan structure in Eucalyptus urograndis kraft pulps2013In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 28, no 4, p. 498-505Article in journal (Refereed)
    Abstract [en]

    Compared to conventional kraft cooking, (CK), extended-impregnation kraft cooking (EIC) gives higher yield of cellulose and xylan. In the present study, the amount of xylan and its degree of substitution (DS) with 4-O-methyl glucuronic acid (MeGlcA) and hexenuronic acid groups (HexA) in unbleached and OD*(OP)D-bleached E. urograndis EIC and CK has been compared. Additionally, the molecular weight distributions of the EIC and CK pulps after oxygen delignification and of xylan isolated from these pulps were investigated. The EIC cooking resulted in pulps with xylan with higher degree of substitution with both 4-O-methyl glucuronic acid and hexenuronic acid groups. The DS of xylan with hexenuronic acid groups increased progressively when the kappa number of the pulps decreased from 34 to 16. Also after oxygen delignification and D*(OP)D bleaching, the xylan in the EIC pulps possessed up to 50% more MeGlcA groups than the xylan in the CK pulp. Almost all the HexA groups were removed from the pulps during bleaching. The weight average molecular weight of cellulose in unbleached EIC pulps was higher than for cellulose in CK pulps. Xylan in EIC pulps had a wider molecular weight distribution than xylan in CK pulps.

  • 12.
    Wedin, Helena
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Sevastyanova, Olena
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Evtuguin, Dmitry
    Ragnar, Martin
    Lindström, Mikael E.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Influence of extended-impregnation kraft cooking on the xylan structure of Eucalyptus urograndisManuscript (preprint) (Other academic)
  • 13.
    Wedin, Helena
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Sevastyanova, Olena
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Evtuguin, itry
    University of Aveiro, Portugal.
    Ragnar, Martin
    Lindström, Mikael
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    The effect of extended impregnation kraft cooking and oxygen delignification on xylan structure2010In: 11th European Workshop on Lignocelluloses and Pulp (EWLP), 2010, p. 113-117Conference paper (Other academic)
1 - 13 of 13
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