| 1. |
- Berthold, F, et al.
(författare)
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Dissolution of softwood kraft pulps by direct derivatization in lithium chloride/N,N-dimethylacetamide
- 2004
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Ingår i: Journal of Applied Polymer Science. - : Wiley. - 0021-8995 .- 1097-4628. ; 94:2, s. 424-431
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Tidskriftsartikel (refereegranskat)abstract
- A method for the characterization of the molar mass distributions (MMDs) of softwood kraft pulps dissolved in 0.5% lithium chloride (LiCl)/N,N-dimethylacetamide (DMAc) by size exclusion chromatography is presented. The method is based on derivatization with ethyl isocyanate and the dissolution of samples in 8% LiCl/DMAc. In this study, the derivatization of hardwood kraft pulps did not influence the MMD. In the case of softwood pulps, however, the derivatization decreased the proportion of the high-molecular-mass material and increased the proportion of the low-molecular-mass material, which resulted in a distribution similar to the MMD of a hardwood kraft pulp. The results suggest that associations between hemicellulose and cellulose in the softwood kraft pulp were ruptured during derivatization. This led to a more correct estimation of the MMD of derivatized softwood kraft pulps than obtained by the dissolution of nonderivatized samples. This new method offers several advantages over derivatization with phenyl isocyanate: a precipitation step is not necessary, it is possible to follow the lignin distribution in the samples, and the method allows very high levels of dissolution of softwood kraft pulps up to a kappa number of around 50.
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| 2. |
- Keyoumu, Ayiguli, et al.
(författare)
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Continuous Nano- and Ultrafiltration of Kraft Pulping Black Liquor with Ceramic Filters : A method for lowering the load on the recovery boiler while generating valuable side-products
- 2004
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Ingår i: Industrial crops and products (Print). - : Elsevier BV. - 0926-6690 .- 1872-633X. ; 20:2, s. 143-150
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Tidskriftsartikel (refereegranskat)abstract
- Ceramic membranes coated with ZrO2 were used for the continuous separation of a well-defined low molecular weight lignin from softwood and hardwood kraft black liquors on a pilot scale. The membranes used had M-w cut-offs of 1000, 5000, and 15,000 Da, respectively. The flux (permeate flow) through the different membranes measured as L/(m(2 .)h) was studied by varying the inlet pressure and temperature. The black liquor lignins in the permeate from the filters were isolated and studied with GPC and UV spectroscopy. The low molecular weight lignin fraction was highly phenolic and could be polymerised by one-electron oxidation.
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| 3. |
- Lundquist, L., et al.
(författare)
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Alkali-methanol-anthraquinone pulping of Miscanthus x giganteus for thermoplastic composite reinforcement
- 2004
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Ingår i: Journal of Applied Polymer Science. - : Wiley. - 0021-8995 .- 1097-4628. ; 92:4, s. 2132-2143
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Tidskriftsartikel (refereegranskat)abstract
- The potential of pulp fiber-reinforced thermoplastics is currently not fully explored in composites. One of the main reasons is that pulp fibers are extracted for the use in papermaking and are thus not optimized for use as reinforcements in thermoplastics. Furthermore, currently used processing methods constitute several severe thermomechanical steps inducing premature degradation of the fibers. A systematic development of these composite materials requires the study of both these aspects. The goal of this work was to optimize fiber extraction against properties relevant to the reinforcement of thermoplastics. To this end, thick-walled Miscanthus x giganteus pulp fibers were selected. The fibers were pulped by the alkaline-methanol-anthraquinone process. An unreplicated factorial design was applied to determine the effect of key operating variables on fiber thermal stability and mechanical properties. The thermomechanical properties of pulp fibers depend primarily on the morphology and chemical composition of the fiber resource in terms of the respective amounts of lignin, hemicellulose, and cellulose, all strongly influenced by the choice of pulping conditions. Optimal pulping parameters were identified, allowing production of fibers thermally stable up to 255 degreesC with an aspect ratio of 40, a straightness of 95%, and tensile strength as high as 890 MPa. Specific stiffness and strength values with respect to density and material cost of 56 GPa m(-3) $(-1) and 820 MPa m(-3) $(-1) were highly competitive with glass fibers, with corresponding values of 15 GPa m(-3) $(-1) and 270-490 MPa m(-3) $(-1), respectively.
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| 4. |
- Pettersson, E. A. K., et al.
(författare)
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Kraft cooking characteristics and hexenuronic acid concentration of pulps from Eucalypt and other hardwood species
- 2002
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Ingår i: Nordic Pulp & Paper Research Journal. - : Walter de Gruyter GmbH. - 0283-2631 .- 2000-0669. ; 17:3, s. 222-227
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Tidskriftsartikel (refereegranskat)abstract
- Fifteen different hardwood species have been investigated with regard to their kraft cooking characteristics. Firstly, all the species were cooked to a reference kappa number of 16.4+/-1.0. The evaluation of the results includes cooking yield, viscosity, xylan content and hexenuronic acid concentration. The difference between the different species is very large in many respects. In a second part of the study, ten Eucalypt species were cooked under identical conditions. Interestingly, the species yielding pulps with the highest kappa numbers also showed the lowest cooking yield, which emphasizes the importance of the choice of Eucalypt species when a forest is planted for pulping purposes. In a third part of the investigation, the mechanisms determining the concentration of hexenuronic acid in a pulp are discussed and exemplified with trials on Oak and Birch.
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| 5. |
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| 6. |
- Ragnar, M., et al.
(författare)
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Trithiocarbonate boosted kraft cooking for improved yield
- 2002
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Ingår i: Nordic Pulp & Paper Research Journal. - : Walter de Gruyter GmbH. - 0283-2631 .- 2000-0669. ; 17:2, s. 159-163
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Tidskriftsartikel (refereegranskat)abstract
- The effect of adding of carbon disulphide to a kraft cook has been investigated. Among the results obtained, ail increased yield has been recorded. In sulphide-containing alkaline liquors, carbon disulphide forms trithiocarbonate ions and the effects seen in the present study are attributed to this species. The increased yield is presumably an effect of end-group stabilisation of the carbohydrates.
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| 7. |
- 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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| 8. |
- Sjödahl, Ragnar, et al.
(författare)
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The Effect of Sodium Ion Concentration and Dissolved Wood Components in the Kraft Cook of Softwood
- 2004
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Ingår i: Nordic Pulp & Paper Research Journal. - : Walter de Gruyter GmbH. - 0283-2631 .- 2000-0669. ; 19:3, s. 325-329
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Tidskriftsartikel (refereegranskat)abstract
- The effect of ionic strength and dissolved wood components (DWC) in form of industrial black liquor on the delignification rate and the brightness of the unbleached softwood kraft pulp has been investigated. A technique with a high liquor-to-wood ratio (75 L/kg) a so-called constant composition cook was used to separate the effects of the different parameters. The study showed that an increase in the ionic strength led to a decrease in the rate of delignification and gave a more coloured pulp, where as the presence of DWC gave a more coloured pulp and an increase in the delignification rate.The influence of the ionic strength and DWC on the bleachability of the softwood kraft pulp in an ECF-sequence (D(EOP)DD) was also investigated. The results show that the bleachability i.e. consumption of bleaching chemicals to reach a certain brightness, was not affected by the ionic strength during the cook. The addition of DWC, on the other hand, increased the consumption of bleaching chemicals to reach ISO brightness 89%.
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