| 1. |
- Engstrand, Per, et al.
(author)
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The impact of chemical addition on refining parameters
- 1995
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In: International Mechanical Pulping Conference 1995, Ottawa/St Paul, Canada. - Ottawa, : Ontario Technical Section, CPPA. - 1895288843 ; , s. 281-286
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Conference paper (other academic/artistic)
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| 2. |
- Gustavsson, Catrin, et al.
(author)
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The influence of cooking conditions on the bleachability and chemical structure of kraft pulps
- 1999
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In: Nordic Pulp & Paper Research Journal. - : Walter de Gruyter GmbH. - 0283-2631 .- 2000-0669. ; 14:1, s. 71-81
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Journal article (peer-reviewed)abstract
- The purpose of this investigation was primarily td investigate how variations in cooking conditions in the kraft pulping of softwood influence the subsequent bleaching, and secondly to study the relationship between the bleaching response and the chemical structure of the pulp. The cooking variables studied were hydroxide ion concentration, hydrogen sulfide ion concentration and cooking temperature. The pulps had the same kappa number after the cook, about 20, and were oxygen delignified to about kappa number 8 before bleaching. The influence of the cooking variables on the TCF-bleachability was studied in an AZQP*- and in a QPQP*-sequence (A=acid treatment, Z=ozone stage, Q=chelating agent stage, P*=peroxide stage with the addition of magnesium ions). All three cooking variables studied influenced the TCF-bleachability, but to different extents. The bleachability was improved by increased temperature for low chemical charges, but not at higher chemical charges. When [HS-] was increased the QPQP*-bleachability was improved but the AZQP*-bleachability was not affected. When [HO-] was varied a bleachability maximum was seen for the intermediate hydroxide ion concentration. The content of hexenuronic acid in the pulp after cooking could be reduced by using high initial [HO-], low initial [HS-] and a long cooking time. A high content of beta-O-4 structures in the unbleached residual lignin was found to contribute to a better bleachability of the pulp. However, the phenolic hydroxyl content could not be related to the bleaching response.
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| 3. |
- Sjöstrom, Karin, et al.
(author)
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Changes in light absorption coefficient spectra as a result of TCF bleaching
- 1999
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In: Paperi ja puu. - 0031-1243. ; 81:2, s. 130-137
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Journal article (peer-reviewed)abstract
- Light absorption coefficient, k, spectra in the wavelength range from 200 to 700 nm have been determined for a number of modified kraft and alkaline sulfite pulps after O, OAZ and OAZQP* bleaching (O=oxygen, A=acid treatment, Z=ozone, Q=complexing agent, P*=peroxide stage with Mg addition). The different pulp types have earlier shown differences in bleachability and selectivity when bleached in an OAZQP* sequence and also in other sequences. However, the reason for the differences in bleachability are not fully understood. In this paper, the changes in k spectra after the different bleaching stages for the different pulp types are shown, and the differences are discussed, The accuracy in the determination of k is also discussed and why it is preferable to measure k rather than brightness. There were no significant differences between the shape of the k spectra for the different pulp types that could explain the known differences in bleachability between the pulp types. However, the levels of the k spectra after the oxygen stage could be correlated to the known differences in bleachability between the pulps, The k spectra for the ASAM pulp, the pulp that has shown best bleachability, was significantly lower compared to the other investigated pulps. Ozone and peroxide bleached pulps showed k spectra of approximately the same shape as the oxygen-delignified pulps. In this study, k values as high as about 10 m(2)/kg were correctly measured. At higher k values, the light scattering coefficient (s) began to deviate due to too high a light absorption. Dilution, i.e. mixing the pulp with a brighter pulp of lower and known k value so that the k value of the mixture does not exceed 10 m2/kg is a way of circumventing the problem. However, there are also some limitations with the pulp mixing method, which are discussed.
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| 4. |
- Sjöstrom, Karin
(author)
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Influence of ionic strength on kraft cooking and subsequent TCF-bleaching
- 1999
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In: Nordic Pulp & Paper Research Journal. - : Walter de Gruyter GmbH. - 0283-2631 .- 2000-0669. ; 14:3, s. 226-235
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Journal article (peer-reviewed)abstract
- The TCF-bleachability of softwood kraft pulps produced with different ionic strength profiles has been investigated. In addition, the relationship between the bleaching response and some of the chemical structures in the pulp were studied. The ionic strength was changed by adding NaCl(s) at two alternative positions in the cook: after the pretreatment, or in the final part of the cook to give three different process variants. All cooks began with a standardized hydrogen sulfide ion pretreatment stage at low alkalinity. Pulps at two different kappa number levels, about 21 and 16, were investigated. After further delignification in an oxygen stage, the bleachability was studied with a QPQP*-sequence (Q=chelating agent stage, P=peroxide-stage, *=Mg ions addition). Pulping with a higher ionic strength led to a lower delignification cation rate and thus a greater hydroxide ion consumption to reach a given kappa number. The results also show an increasing light absorption coefficient/kappa number ratio for unbleached pulps with increasing ionic strength in the cook. The degree of delignification in the oxygen stage was higher with a higher ionic strength in the cook. The bleachability as well as the yield and the process selectivity were improved by a low ionic strength in the cook for all the three investigated process variants.
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| 5. |
- Sjöstrom, Karin
(author)
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Kraft cooking with varying alkali concentration : Influence on TCF-bleachability
- 1998
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In: Nordic Pulp & Paper Research Journal. - : Walter de Gruyter GmbH. - 0283-2631 .- 2000-0669. ; 13:1, s. 57-63
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Journal article (peer-reviewed)abstract
- The TCF-bleachability of softwood pulps produced by kraft pulping processes with varying alkali concentrations was investigated. The cooks began with a hydrogen sulfide ion pretreatment at low alkalinity, i.e. simulating a black liquor preimpregnation. The alkalinity in the cooks was varied in three different ways: already at the beginning of the cook, both at 40 % sulfidity and at a HS- concentration of 0.3 mol/l (2-stage cooks), and in the final part of a modified kraft cook (4-stage cooks) simulating an ITC (Isothermal cooking) cook. The pulps had the same kappa number after the cook, about 17, and were oxygen delignified before bleaching. The influence of the alkali concentration profile in the cook on the bleachability was studied with a QPQP*-sequence (Q=chelating agent stage, P*=peroxide-stage with the addition of 0.05 % Mg ions). The bleachability (pulp brightness achieved for a given consumption of bleaching agent per kappa number) was found to reach a maximum for pulps with a residual alkali concentration in the vicinity of 0.5 mol/l. The bleachability was however affected to only a minor extent by the alkali concentration during the cook. The hexeneuronic acid content was found to decrease with increasing alkali concentration and this was taken into consideration when calculating the chemical consumption per amount of lignin. The process selectivity (pulp viscosity at a given brightness) decreased with increasing residual alkali. The bleachability was not improved by conducting the cook with a levelled out active cooking chemical profile, when the comparison was made at the same residual alkali concentration, but the selectivity was improved.
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| 6. |
- Teder, Ants, et al.
(author)
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A comparison of bleachability in TCF sequences for alkaline sulphite and kraft pulps
- 1996
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In: Journal of Pulp and Paper Science (JPPS). - 0826-6220. ; 22:8, s. J296-J300
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Journal article (peer-reviewed)abstract
- The bleachability in different totally chlorine-free (TCF) bleaching sequences was investigated for two types of alkaline sulphite pulps, ASAM and MSSAQ, and compared with that of pulps produced by different new and industrially applied modified kraft pulping processes. The TCF sequences included oxygen, ozone, peroxide and complexing agent stages. The alkaline sulphite pulps were found to be easier to bleach in terms of the consumption of oxidative agents required to reach a given brightness than the pulps produced by the different modified kraft pulping processes. The relationship between pulp brightness and pulp viscosity was also much better for the sulphite pulps, although the new types of kraft pulps are gradually approaching the level of the alkaline sulphite pulps in this respect. There was no significant difference between the ASAM (alkaline sulphite anthraquinone methanol) and the two-stage MSSAQ (minisulphide sulphite anthraquinone) processes.
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| 7. |
- Zhang, L, et al.
(author)
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Effects of molecular weight of nitrocellulose on structure and properties of polyurethane nitrocellulose IPNs
- 1999
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In: Journal of Polymer Science Part B-Polymer Physics. ; 37:14, s. 1623-1631
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Journal article (peer-reviewed)abstract
- Semi-interpenetrating polymer network (semi-IPN) coatings were prepared by using castor oil-based polyurethane (PU) and nitrocellulose (NC) with various viscosity-average molecular weights (Mη) from 6 × 104 to 42 × 104, and coated on a regenerated cellulose (RC) film to obtain water-resistant film. The PU/NC coatings and coated films, which were cured at 80°C for 5 min and 2 min, respectively, were investigated by infrared (IR) and ultraviolet (UV) spectroscopy, X-ray diffraction, swelling test, strength test, dynamic mechanical thermal analysis (DMTA), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). The results show that the crosslink densities of the PU/NC semi-IPNs were smaller than that of pure PU, and decreased with the decrease of Mη of nitrocellulose (NC Mη), indicating NC molecules cohered intimately with PU, and hindered the PU network formation. The physical and mechanical properties of the films coated with PU/NC coatings were significantly improved. With the increase of NC Mη, the strength and thermal stability of the coated films increased, but the pliability, water resistivity, and optical transmission decreased slowly. The PU/NC coating with low NC Mη more readily penetrated into the RC film, and reacted with cellulose, resulting in a strong interfacial bonding and dense surface caused by intimate blend of PU/NC in the coated films.
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| 8. |
- Zhang, L, et al.
(author)
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Water-resistant film from polyurethane/nitrocellulose coating to regenerated cellulose
- 1997
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In: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 0888-5885 .- 1520-5045. ; 36:7, s. 2651-2656
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Journal article (peer-reviewed)abstract
- Water-resistant films were obtained from polyurethane (PU)/nitrocellulose coating to regenerated cellulose films, which were prepared by coagulating cellulose cuoxam solution. The PU/nitrocellulose coating layer was cured at 80 degrees C for 2 min and formed semi-interpenetrating polymer networks (semi-IPNs) structure. The tensile strength (sigma(b)), water resistivity (R), water vapor permeability (P), and light transmittance of the coated films changed with nitrocellulose content in the coating, and the best values (such as sigma(b), 679 kg.cm(-2); R, 53%; P, 0.004 g.cm(-2).day(-1)) were attained at 33 wt % nitrocellulose. The TEM, EPMA, DTA, IRI and UV results-showed that the coated films have strong interfacial bonding, which is caused by covalent and hydrogen bonds between the cellulose film and the semi-IPNs coating. The biodegradation half-life t(1/2) of the coated films in soil at 20-30 degrees C was given to be 58 days, and after about 6 months the coated films were almost completely decomposed by microorganisms. SEM and the kinetics of decay studied on the biodegradability were discussed. The water-resistant films coated with PU/nitrocellulose have promising application where biodegradation is important.
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| 9. |
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| 10. |
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