| 1. |
- Gellerstedt, Göran, et al.
(författare)
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On the structure of lignin in kraft pulping
- 2004
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Ingår i: 2nd International Symposium on Technologies Of Pulping, Papermaking and Biotechnology on Fiber Plants, Proceedings. - NANJING : NANJING FORESTRY UNIV. - 9889788772 ; , s. 1-5
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Konferensbidrag (refereegranskat)abstract
- Lignin present in the residual delignification phase is difficult to dissolve and any further pulping leads to an increased loss of pulp strength and yield. In this work, a radical coupling mechanism during kraft pulping is suggested to contribute to the observed incomplete delignification. In such an electron transfer reaction, elemental sulfur may act as an initiator between the residual lignin in the pulp and phenolic structures present in the black liquor. To find support for such a mechanism, lignins from kraft cooks with kappa number of approximate to 30 prepared with and without a reactive phenol, 2,6-xylenol in the cook, were studied. GPC, GS-MS and NMR were the techniques used for analyses of isolated lignins and lignin samples obtained by thioacidolysis to support the suggested mechanism. The analytical data showed that the added phenol was incorporated into the polymeric lignin with a preferential formation of biphenyl structures.
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| 2. |
- Li, Jiebing, et al.
(författare)
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Acid soluble lignin content in kraft pulps, an artifact
- 2004
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Ingår i: 2nd International Symposium on Technologies Of Pulping, Papermaking and Biotechnology on Fiber Plants, Proceedings. - NANJING : NANJING FORESTRY UNIV. - 9889788772 ; , s. 53-57
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Konferensbidrag (refereegranskat)abstract
- Acid-soluble lignin (ASL) has been regarded as that part of the lignin in wood or pulp that dissolves in the acidic solution during Klason lignin determination. However, the absorption at 205 nm of the filtrate for the standard ASL determination cannot be considered as originating exclusively from lignin. Moreover, the standard method has been constructed only based on lignin models from woods, plants and semichemical bisulfite pulps, while is claimed to be universally applicable. In the present work, Kraft pulps from different wood species bleached using different sequences were subjected for the ASL determination and quantifications of different furan structures in the filtrate. It has been found that during the sulfuric acid hydrolysis, 20-30% and 70-80% of the hexenuronic acid in the pulp converts into 5-formyl-2-furancarboxylic acid and 2-furancarboxylic acid respectively. Both structures absorb substantially at 205 nm and account for up to 41% of the total absorption of the filtrate. On the other hand, furfural and hydroxymethyl furfural, decomposed from hemicellulose and cellulose respectively, account for a further up to 8.7% of the total absorption. Considering also other non-lignin structures in the filtrate which absorb 205 nm, we conclude that the existence of native and modified carbohydrates makes the ASL determination meaningless for Kraft pulps.
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| 3. |
- Sjödahl, Ragnar G., et al.
(författare)
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Addition of dissolved wood components for improvement of delignification rate and pulp yield in hardwood Kraft pulping
- 2004
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Ingår i: 2nd International Symposium on Technologies Of Pulping, Papermaking and Biotechnology on Fiber Plants, Proceedings. - NANJING : NANJING FORESTRY UNIV. - 9889788772 ; , s. 123-126
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Konferensbidrag (refereegranskat)abstract
- This study have investigated the effects of dissolved wood components (DWC) in the cooking liquor on the rate of delignification, pulp yield and HexA content during kraft pulping of Eucalyptus Urograndis. The cooking was carried out with and without the addition of DWC, in form of black liquor, as well as with and without the addition of a lignin-like model compound using a,. so-called constant composition cooking technique. The results show that the presence of DWC causes a rate increase in the delignification which makes it possible to reach kappa number 18 with around 40% less H-factor compared to a cook performed with a very low amount of DWC. The presence of DWC also results in a yield increase of up to two percentage units measured as lignin free yield.
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| 4. |
- Zhang, Liming, et al.
(författare)
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Qualitative and quantitative study of lignin structure by applying highresolution 2D HSQC NMR technique
- 2004
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Ingår i: 2nd International Symposium on Technologies Of Pulping, Papermaking and Biotechnology on Fiber Plants, Proceedings. - NANJING : NANJING FORESTRY UNIV. - 9889788772 ; , s. 88-92
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Konferensbidrag (refereegranskat)abstract
- High-resolution 2D HSQC NMR technique was found to be a powerful analytical tool for studies on lignin structure. High resolution in the F1 dimension of an HSQC spectrum can be obtained by proper sample purification and optimized shimming as well as by acquiring large enough increments. By combining the results from 2D HSQC, HSQC-TOCSY and HMBC NMR experiments, novel lignin structures, including spiro-dienone, secoisolariciresinol and neo-olivil have been observed and identified. The concept of quantitative structure determination by applying 2D HSQC NMR technique was investigated. The influence of T-2 relaxation decays, coupling constant, off-resonance effect and homonuclear couplings on NMR signal quantification have been discussed. beta-5 Structure in a lignin sample was accurately determined by using the HSQC NMR analysis through a unique way of selecting the proper internal standard reference signal(s).
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