Over the past 10 years, growing concerns over the modification of fibers have led researchers to focus on enriching the carboxyl group content of fibers by chemical oxidation and topochemical grafting. The current series of experiments continues this line of research by investigating the carboxyl group content of fibers during kraft pulping, alkaline peroxide bleaching, and 2,2,6,6-tetrametyl-1-piperidinyloxy radical (TEMPO)-KBr-NaClO oxidation system. The first experiment characterizes changes in the carboxyl group content of fibers for two sets of kraft pulps: 1) conventional laboratory cooked loblolly pine kraft pulps, and 2) conventional pulping (CK) versus Lo-Solids pulping (LS) pulps. The results indicate that effective alkali (EA), temperature, and H-factor are the primary factors controlling fiber charge during kraft pulping. Another set of kraft pulps distinguished by conventional pulping and Lo-Solids pulping were investigated to determine the effect of H-factor and pulping protocol on fiber charge. The second experiment examines the influence of alkaline peroxide treatment on elementally chlorine-free (ECF) bleached softwood kraft pulp. The effect of increased fiber charge on refining, cationic starch adsorption, and hornification was examined. The final experiment investigates the effect of TEMPO-mediated oxidation of an ECF bleached softwood kraft pulp on carboxyl group content, carbonyl group contents, degree of polymerization, and water retention value of fibers. The results show that TEMPO-mediated oxidation is useful in enriching the carboxyl and carbonyl groups to fibers, as well as enhancing the property of water adsorption of fibers. These findings suggest that: (1) kraft pulping process can be modified to obtain the target carboxyl group content, (2) terminal peroxide bleaching provides higher fiber charge which can save energy and chemical charge of subsequent refining and wet-end processes, respectively, as well as reduce hornification during drying, (3) TEMPO-mediated oxidation of fibers is capable of improving the properties of fibers, including fiber charge and water adsorption, and enhancing final paper strength.

På pappersmaskin 11 i Hallsta pappersbruk tillverkas högglansigt papper som bleks med väteperoxid. Om väteperoxiden som finns kvar efter blekningen, kallat restperoxid, kommer ut på pappersmaskinen sliter detta på termovalsarna, vilket påverkar slutprodukten. Det finns en bakteriekultur på bruket, bestående av släktet Tepidiphilus som bryter ner väteperoxiden med hjälp av katalas och hindrar den från att komma ut på maskinen. Om bakterierna slås ut, av exempelvis ogynnsamma förhållanden, märks detta genom att restperoxiden ökar. Målet med detta arbete är att försöka identifiera vilka faktorer som påverkar bakterierna och lägga fram ett förslag för hur man kan förhindra uppkomsten av restperoxid. För att utföra detta användes i första hand principalkomponentanalys, samt så studerades hur olika faktorer förändrades i förhållanden till uppkomsten av restperoxid. Ett antal parametrar kunde identifieras baserat på tillgängliga data. Dock kan inga absoluta slutsatser dras då det inte går att bekräfta några teorier med labbförsök eller genom att manipulera processen. De parametrar som tros ha störst påverkan är mek. renat färg, rest-aluminium, grumlighet, manganhalten i vatten, pH för kar K0203, returmälden samt inloppslådan och klorhalterna som uppmätts för mek. renat total klor, RVV1 fri klor, varmvatten total klor och mek. renat fri klor. Dessa parametrar bör därför övervakas framåt, och kan i det fall att restperoxid återigen uppkommer antingen bekräftas eller dementeras deras faktiska påverkan och samspel för bakteriernas välmående. / Paper machine 11 in Hallsta paper mill produces high-gloss paper that is bleached with hydrogen peroxide. If the hydrogen peroxide that remains after the bleaching, called residual peroxide, gets out on the paper machine, this wears down the thermal rollers, which affects the final product.  There is a bacterial culture at the mill, consisting of the genus Tepidiphilus, which breaks down the hydrogen peroxide with the help of catalase and prevents it from getting out to the machine. If the bacteria are killed, for example by unfavourable conditions, this is noticeable by an increase in residual peroxide. The goal of this project is to try to identify which factors affect the bacteria and put forward a proposal for how to prevent the occurrence of residual peroxide. To carry this out, principal component analysis was primarily used, and how different factors changed in relation to the appearance of residual peroxide was studied. Several parameters could be identified based on the available data. However, no conclusive conclusions could be drawn as it is not possible to confirm any theories with lab tests or by manipulating the process. The parameters believed to have the greatest influence are coloration of mechanically cleaned water (mech. water), residual aluminium, turbidity, manganese content of the water, pH for tank K0203, the returning pulp suspension as well as the headbox and the chlorine levels for mech. water total chlorine, RVV1 free chlorine, hot water total chlorine and mech. water free chlorine. These parameters should therefore be monitored going forward, and if residual peroxide occurs again, their possible interactions and actual impact on the well-being of the bacteria can either be confirmed or denied