| 1. |
- Axegard, Peter, et al.
(författare)
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Bleaching of softwood kraft pulps with H2O2, O3, and ClO2
- 1996
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Ingår i: TAPPI Journal. - 0734-1415. ; 79:1, s. 113-119
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Tidskriftsartikel (refereegranskat)abstract
- Ozone or chlorine dioxide bleaching prior to hydrogen peroxide bleaching greatly improves the performance of the hydrogen peroxide stage. The efficiency is further improved by a chelating treatment immediately after the ozone or chlorine dioxide stage. With an optimal metal ion profile, laboratory bleached (OAZQP) softwood kraft pulps can reach brightness levels above 90% ISO, with 5-10% lower pulp strength properties and bleaching costs comparable to ECF bleaching. It also is possible to obtain full brightness with only hydrogen peroxide provided the metal ion profile is optimal, e.g., by using multiple QP treatments. The chemical consumptions, expressed as oxidation equivalents per decreased kappa number are the same as for sequences including ozone or chlorine dioxide. Ozone and chlorine dioxide are comparable as far as delignification and brightness efficiency go.
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| 2. |
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| 3. |
- Bergnor, Elisabeth, et al.
(författare)
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The role of metal ions in TCF-bleaching.
- 1994
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Ingår i: Proceedings 3<sup>rd</sup> European Workshop on Lignocellulosics and Pulp. ; , s. 284-289
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Konferensbidrag (refereegranskat)
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| 4. |
- Buchert, Johanna, et al.
(författare)
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Significance of xylan and glucomannan in the brightness reversion of kraft pulps
- 1997
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Ingår i: TAPPI Journal. - 0734-1415. ; 80:6, s. 165-171
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Tidskriftsartikel (refereegranskat)abstract
- The brightness reversion of kraft pulps is caused by the presence of residual lignin, chlorinated extractives, or oxidized carbohydrates. The effect of hemicellulose content, i.e., xylan (I) and glucomannan (II), on the thermal stability of modern bleached kraft pulps was investigated. Different O-delignified hard- and softwood kraft pulps were bleached with different bleaching sequences contg. ClO2, H2O2, or O3. Hemicellulose-degrading enzymes, i.e., xylanase or mannanase, were used for selective removal of the resp. hemicellulose from the pulps, and the role of partially removed I and II on the brightness stability of these pulps was studied. Because of the structure of kraft I, enzymic removal of I also resulted in a decreased carboxyl group content in the pulps, whereas II removal did not affect the carboxyl group content. By decreasing the carboxyl groups in the pulps in conjunction with I removal, the thermal aging of the pulps was significantly decreased. The role of II was less significant. Thus, the uronic acids present in the pulp participate in the brightness reversion of kraft pulps.
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| 5. |
- Buchert, Johanna, et al.
(författare)
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The role of xylan and glucomannan in yellowing of kraft pulps.
- 1995
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Ingår i: Proceedings 8<sup>th</sup> Int. Symp. Wood Pulp. Chem.. ; , s. 43-48
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Konferensbidrag (refereegranskat)abstract
- The effects of xylan and glucomannan on the thermal stability of unbleached, partially bleached, and fully bleached pine and birch kraft pulps were studied. The choice of bleaching chems. strongly affected the brightness reversion. Compared with hydrogen peroxide or chlorine dioxide, bleaching with ozone reduced the amt. of carboxyl groups and subsequently the pc-nos. of oxygen-delignified pulps. Xylan removal reduced also the amt. of carboxyl groups in the pulps and this was reflected in improved brightness stability whereas glucomannan removal had no effect. Thus, the uronic acids bound to pulp xylan were found to participate in the brightness reversion of kraft pulps.
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| 6. |
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| 7. |
- Salmen, Lennart, et al.
(författare)
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Extrusion of Softwood Kraft Lignins as Precursors for Carbon Fibres
- 2015
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Ingår i: BioResources. - 1930-2126. ; 10:4
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Tidskriftsartikel (refereegranskat)abstract
- There is much interest in using less expensive raw materials as precursors for carbon fibre manufacture to increase the utilisation of strong, light-weight composite materials in the transportation sector. One such potential raw material is lignin. Most studies exploring melt spinning of lignin have used lignins from organosolv or hardwood kraft delignification processes. There has been little success reported in utilisation of the more commercially available softwood kraft lignins. In this study, lignins from different softwood kraft cooking processes were investigated with respect to their melt spinning performance and conversion to carbon fibres. The isolated lignins differed mainly in molecular weight, glass transition temperature, and softening temperature. All of the lignins produced from the laboratory cooks could be extruded without any plasticizer addition. However, the lignins contained volatiles that resulted in bubbles being formed along the length of the fibres. After vacuum drying, at elevated temperatures to remove volatiles, only the lignin originating from conventional kraft cooking was able to be melt extruded without plasticiser addition; this lignin had the lowest molecular weight amongst the samples. The stabilisation and carbonisation of these fibres gave carbon fibres with strengths comparable to those produced from lignins of other origins.
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