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| 2. |
- Bravo, L, et al.
(författare)
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- 2021
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swepub:Mat__t
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| 3. |
- Tabiri, S, et al.
(författare)
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- 2021
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swepub:Mat__t
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| 4. |
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| 5. |
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| 6. |
- Al-Dajani, W. W., et al.
(författare)
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On the isolation and structure of softwood residual lignins
- 2002
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Ingår i: Nordic Pulp & Paper Research Journal. - : Walter de Gruyter GmbH. - 0283-2631 .- 2000-0669. ; 17:2, s. 193-198
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Tidskriftsartikel (refereegranskat)abstract
- Different softwood residual lignins were isolated by acid hydrolysis of kraft and soda Pulps. Complete isolation of lignin Could not be achieved in one hydrolysis step. The yield of lignin varied between 35 and 55%. A more acidic, second hydrolysis step was therefore necessary to isolate almost all the lignin remaining in the Pulp residue, giving a total lipin yield of 91%. Alkaline extraction of the pulp was almost as efficient as acid hydrolysis in isolating residual lignins. However, alkaline extraction gave less pure lignin fractions and there was a clear indication of the existence of lignin-carbohydrate bonds. Pine wood meal was acid-hydrolyzed in the same way as the pulps. After two-stage acid hydrolysis, the combined lignin yield was only 45% of the Klason lignin content, which means that native lignin is more difficult to isolate front wood than residual lignin front a chemical pulp. It is Concluded that the difficulty encountered in isolating residual lignin by acid hydrolysis is a problem of limited accessibility due to a complex carbohydrate network surrounding the lignin.
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| 7. |
- Al-Dajani, W. W., et al.
(författare)
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The effect of polysulphide pre-treatment and cooking parameters on the chemical properties and TCF bleachability of alkaline pulps
- 2001
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Ingår i: Pulp & paper Canada. - 0316-4004. ; 102:8, s. 44-48
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Tidskriftsartikel (refereegranskat)abstract
- The effect of pre-treating softwood chips with polysulphide on the chemical properties of the resulting pulp has been investigated. During subsequent pulping after such pre-treatment, high alkali content is maintained in the cooking liquor and, consequently, an unbleached pulp with a decreased amount of hexenuronic acid is obtained. As compared to other kraft pulps in this study, a polysulphide pre-treatment gives high cooking field, a high viscosity and brightness for the unbleached pulp and a pulp of good bleachability.
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| 8. |
- Gellerstedt, Göran, et al.
(författare)
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Bleachability of alkaline pulps - Part 1. The importance of beta-aryl ether linkages in lignin
- 2000
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Ingår i: Holzforschung. - 0018-3830 .- 1437-434X. ; 54:6, s. 609-617
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Tidskriftsartikel (refereegranskat)abstract
- Analytical and structural studies were done on different types of alkaline pulps and their isolated residual lignins. Although having the same degree of delignification after cooking, some pulps were easier to bleach than others. All isolated residual lignins were found to contain beta -aryl ether (beta -O-4) structures in reasonable amounts when analysed by thioacidolysis (greater than or equal to 10% of the native lignin value). At decreasing kappa numbers, there was also a corresponding decrease in the amount of beta -aryl ether structures in the residual lignin. Moreover, a high beta -aryl ether content in the unbleached residual lignin after cooking was found to contribute to a better bleachability of the pulp, especially when hydrogen peroxide stages were involved. At the same degree of delignification, the superior bleachability of alkaline sulfite pulps over kraft pulps was shown to be attributable to a higher content of beta -aryl ether linkages in the further type of pulps.
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| 9. |
- Gellerstedt, Göran, et al.
(författare)
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Some factors affecting the brightness and TCF-bleachability of kraft pulp
- 2003
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Ingår i: Nordic Pulp & Paper Research Journal. - : Walter de Gruyter GmbH. - 0283-2631 .- 2000-0669. ; 18:1, s. 56-62
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Tidskriftsartikel (refereegranskat)abstract
- By varying the cooking conditions, several series of kraft pulps having different brightness levels, i.e. different light absorption coefficients (k), were prepared. A clear correlation between the residual alkali concentration in the black liquor and the k-value was found. The darkening of the pulp (increasing k) was shown to be, in part, due to a higher content of calcium ions that increased lignin redeposition onto the fibers during the cook. Moreover, the production of a bright unbleached pulp (with low k-value) appeared to be beneficial for subsequent TCF-bleaching with hydrogen peroxide.
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