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- Axelsson, Patrik, et al.
(författare)
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Bleachability of Alkaline Birch Pulps.
- 2000
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Ingår i: Proceedings 6<sup>th</sup> European Workshop on Lignocellulosics and Pulp..
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Konferensbidrag (refereegranskat)
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| 4. |
- Esperk, Toomas, et al.
(författare)
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Distinguishing between anticipatory and responsive plasticity in a seasonally polyphenic butterfly
- 2013
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Ingår i: Evolutionary Ecology. - : Springer Science and Business Media LLC. - 0269-7653 .- 1573-8477. ; 27:2, s. 315-332
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Tidskriftsartikel (refereegranskat)abstract
- Seasonal generations of short-lived organisms often differ in their morphological, behavioural and life history traits, including body size. These differences may be either due to immediate effects of seasonally variable environment on organisms (responsive plasticity) or rely on presumably adaptive responses of organisms to cues signalizing forthcoming seasonal changes (anticipatory plasticity). When directly developing individuals of insects are larger than their overwintering conspecifics, the between-generation differences are typically ascribed to responsive plasticity in larval growth. We tested this hypothesis using the papilionid butterly Iphiclides podalirius as a model species. In laboratory experiments, we demonstrated that seasonal differences in food quality could not explain the observed size difference. Similarly, the size differences are not likely to be explained by the immediate effects of ambient temperature and photoperiod on larval growth. The qualitative pattern of natural size differences between the directly developing and diapausing butterflies could be reproduced in the laboratory as a response to photoperiod, indicating anticipatory character of the response. Directly developing and diapausing individuals followed an identical growth trajectory until the end of the last larval instar, with size differences appearing just a few days before pupation. Taken together, various lines of evidence suggest that between-generation size differences in I. podalirius are not caused by immediate effects of environmental factors on larval growth. Instead, these differences rather represent anticipatory plasticity and are thus likely to have an adaptive explanation. It remains currently unclear, whether the seasonal differences in adult size per se are adaptive, or if they constitute co-product of processes related to the diapause. Our study shows that it may be feasible to distinguish between different types of plasticity on the basis of empirical data even if fitness cannot be directly measured, and contributes to the emerging view about the predominantly adaptive nature of seasonal polyphenisms in insects.
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| 5. |
- Gustafsson, Roland, et al.
(författare)
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Influence of the alkalinity in polysulphide pretreatment on results of cooking with normal liquor-to-wood ratios
- 2004
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Ingår i: Paperi ja puu. - 0031-1243. ; 86:3, s. 169-173
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Tidskriftsartikel (refereegranskat)abstract
- The effect of alkalinity in a polysulphide pretreatment on the delignification rate, pulp yield and the pulp viscosity in the following kraft cook was investigated. The results were compared to those with reference pretreatments with a corresponding concentrations of hydroxide and hydrogen sulphide ions. The experiments were carried out at liquor-to-wood ratio of 4:1, and the alkalinity in the pretreatments was varied from 0 to 2.5 mole hydroxide/litre. It was found that when the polysulphide preteatment is performed at very high initial hydroxide concentrations, > 1.5 mole/litre, the delignification rate in the cook is increased. The pulp viscosity was higher than that achieved with the sulphide reference when the pulping was extended to low kappa numbers and when the initial hydroxide ion concentration in the pretreatment was high.
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| 6. |
- Gustafsson, Roland, et al.
(författare)
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Polysulphide pretreatment of softwood for increased delignification and higher pulp viscosity
- 2004
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Ingår i: Journal of Pulp and Paper Science (JPPS). - 0826-6220. ; 30:5, s. 129-135
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Tidskriftsartikel (refereegranskat)abstract
- The effect of polysulphide pretreatment under various conditions prior to a kraft cook was investigated for spruce (Picea abies) chips using a technique with a liquor:wood ratio of 67:1 to keep the liquor composition as constant as possible during the pretreatment and cooking phases. If the polysulphidepretreatment is carried out at a very high hydroxide concentration, 1.5 mol OH-/L, three independent positive effects (compared with a corresponding sulphide pretreatment without polysulphide) can be observed: more extensive delignification; higher pulp, viscosity; and higher carbohydrate yield. When the alkali change was changed in the subsequent kraft cook (in the range 0.15-0.60 mol/L), the increase in delignification extent as a result of polysulphide pretreatment was not affected but the relative carbohydrate yield increase was favoured by a higher alkali charge during cooking. On the other hand, the absolute carbohydrate yield is favoured by a intermediate alkali charge.
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| 9. |
- Sjöstrom, Karin, et al.
(författare)
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Changes in light absorption coefficient spectra as a result of TCF bleaching
- 1999
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Ingår i: Paperi ja puu. - 0031-1243. ; 81:2, s. 130-137
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Tidskriftsartikel (refereegranskat)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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| 10. |
- Sjöstrom, Karin, et al.
(författare)
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Changes within the modified kraft process aiming to improve TCF bleachability
- 1999
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Ingår i: Journal of Pulp and Paper Science (JPPS). - 0826-6220. ; 25:5, s. 176-182
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Tidskriftsartikel (refereegranskat)abstract
- the investigated process modifications were: presulphonation, postsulphonation, polysulphide pretreatment and polysulphide pretreatment combined with a postsulphonation. The influence of the degree of delignification in the cook, on the selectivity and bleachability, was also investigated. The pulps were produced from softwood chips and were oxygen delignified before bleaching according to an AZQP sequence. All the investigated process variants had better process selectivity (pulp viscosity at a given brightness) and the pulps produced with a postsulphonation showed better bleachability, than the reference pulp. The bleachability and the process selectivity was improved by interrupting the cook at a higher kappa number and instead extending the delignification in the oxygen stage.
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