Syftet med arbetet var att undersöka hur olika reaktionsbetingelser skulle påverka syrgasdelignifieringen av en sur sulfitmassa. De betingelser som undersöktes var utbyte, slut-pH, viskositet och kappatal. Massan som användes kom från Nordic Paper Seffle och alkalit som användes var magnesiumoxid.  Syrgasdelignifiering av massan gjordes  i autoklaver i ett PEG bad där tid, temperatur och alkalisatser varierades. Resultaten visar att alla utbyten låg mellan 90-97% och att även de mest aggressiva betingelserna bara gav en viskositets reduktion på 260 enheter, motsvarande 19% av den totala viskositeten. Slut-pH för syrgasavluten hamnade mellan 6,5-9,4 beroende på alkalimängd och temperatur under delignifieringen. Slut-pH minskade när mängden alkali hölls konstant men temperaturen varierades mellan 110-140°C. Kappatalet för massan kunde effektivt reduceras från ett startvärde på 23,4 till ett slutvärde på under 5 med en temperatur på 140°C, alkalisats på 10 kg/ODT och en tid på två timmar utan större förluster av vare sig viskositet eller utbyte. En ovanligt resultat som upptäcktes under arbetet var att delignifieringen tappade i effektivitet med ökad alkalimängd och detta samband gällde vid alla betingelser. En teori om detta kan vara att jonstyrkan i lösningen gör att fibrerna i massan drar ihop sig och att syrgasen får svårare att reagera med ligninet. / The purpose of the study was to investigate how different reaction conditions would affect oxygendelignification of an acid sulfite pulp. The conditions being explored were yield, final-pH, viscosity and kappa number. The pulp used in the testing was collected from Nordic Paper Seffle and the active alkali during the delignification was magnesium oxide. The oxygendelignification of the pulp was done with autoclaves suspended in a PEG bath, where they were allowed to rotate, and time, temperature and alkali amount  was varied throughout the testing. Results show that the yield for all pulp samples were between 90-97% for all conditions used in this project while viscosity of the pulps were only decreased by about 260 units for the most severe of conditions. This accounts for a viscosity loss of 19%. Final-pH varied between 6,5-9,4 depedning on temperature and alkali amount chosen. Final-pH levels dropped when the alkali was kept constant but temperature was varied from 110-140°C. The pulps kappa number could effetively be lowered from its starting value of 23,4 to a final value of under 5 when an alkali amount of 10 kg/ODT and a temperature of 140°C was used during 2 hours. This lead to no substantial losses of either viscosity or yield. A strange result that the project also highlighted was that the delignification lost in efficiency when more alkali was added in at a set temperature. This phenomenom was found at all conditions investigated throughout the project. A theory about this is that it might be the increased ionic strength from the magnesium cations in the solution making the fibers shrink and by that lessening the reaction area of the fibres for the oxygen, which will then have a harder time reacting with the lignin.

This thesis forms part of a project with the objective of developing and implementing a novel, wood-based, process for the industrial production of cellulose textile fibres. This new process should not only be cost effective but also have far less environmental impact then current processes. Natural and man-made fibres are usually plagued with problems (e.g. economic and environmental) and are unsuitable in meeting growing demands. The focus of this thesis was therefore to investigate the dissolution of cellulose derived from various pulps in novel aqueous solvent systems.             It was shown that cellulose could be dissolved in a NaOH/H2O solvent at low temperatures (<0°C) and that such an alkaline solvent can be improved regarding the solubility, stability and rheological properties of the cellulose dopes formed if different additives (salts or amphiphilic molecules) are used. The effect of different kinds of pretreatment (individually and combined) and the influence of pulp properties on cellulose accessibility and dissolution were also evaluated. These pretreatments affected, as expected, some characteristic properties of the pulps mainly by reducing the DP but also, for example, changing the composition of the carbohydrates. Not only did the pretreatment affect the solubility it also increased the stability of the cellulose dopes, resembling the effect of chemical additives to the NaOH system. According to multivariate data analysis it was established that, of the pulp properties analyzed, only the composition of carbohydrates and the DP had a significant influence on the solubility of the pulps used in this study. Finally, it was emphasized that the dissolution of cellulose pulps seemed to be controlled by a very complex interaction between both kinetic and thermodynamic parameters. / CelluNova