Research concerning lignin has increased during the last years due to its renewability and ready availability in black liquor at pulp mills. Today, the kraft lignin found in black liquor is used as a fuel to gain energy in the recovery boiler at the mill. However, a new isolation concept, LignoBoost®, has enabled isolation of part of the lignin while allowing the use of black liquor as a fuel. This isolated lignin can be utilised as a fuel in, for example, thermal power stations or further upgraded to more value-added products. In this context, the most interesting value-added product is carbon fibre. The demand for carbon fibre has increased, but the biggest obstacle for a more extended use is the high production cost. About half of the production cost is related to the raw material. In this work, the possibility of using kraft lignin as a precursor for carbon fibre production has been investigated through fundamental studies. Kraft lignins originating from birch, Eucalyptus globulus, softwoods and softwoods from liner production have been studied. By separating the lignin while still in solution in the black liquor, unwanted large particles such as carbohydrates can easily be removed. After isolation according to the LignoBoost process and purification with the use of an ion-exchanger, the lignins have been both chemically and thermally characterised. Identification of the released compounds at different temperatures has been performed because only 40% of carbon relative to original lignin remains, down from theoretical 60% after thermal treatment up to 1000°C. The main released compounds were phenols, as revealed by pyrolysis-GC/MS. Additionally, a pre-oxidation was done in order to try to stabilise the lignins. It was shown that an oxidation prior to the thermal treatment increases the yield by more than 10% and that the main release of compounds takes place between 400°C and 600°C. Fractionated lignin is better qualified as raw material for carbon fibre production because it is purer and its softening temperature can be detected. Fractionated kraft lignins from all investigated wood sources have high possibilities to act as precursors for the manufacture of carbon fibre.

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Sewage sludge is an inevitable by-product from waste water treatment plants. Sludgemanagement is a difficult task since sludge has a high moisture content, poordewaterability and generally contain heavy metals, pharmaceutical residues,polyfluorinated alkyl substances (PFAS) and organic pollutants. Recentlyhydrothermal carbonization (HTC) has been getting attention for its suitability to treatsewage sludge. HTC is a flexible process which can handle feedstocks with highmoisture content. The process stabilizes the organic content in a solid residue calledhydrochar which has an increased energy content and decreased moisture contentcompared to the starting material. Hydrochar can be used as soil amendment materialsince it has a good nutrient content and can prevent leaching of fertilizers. However,there is a concern for the risk of high levels of poly aromatic hydrocarbons (PAHs) inthe hydrochar which might limit its applicability in soil applications. PAHs are acomplex group of organic pollutants that can be toxic and even cancerogenic tohumans. 16 PAHs have been described as priority pollutants by the US EnvironmentalProtection Agency due to their toxicity and risk for human exposure. In this studyHTC was performed, with municipal sewage sludge as feedstock, at different processconditions to investigate its influence on the PAH content in the produced hydrocharsand aqueous residues. Ten experiments were performed with varying reactiontemperature (ranging from 180 °C to 260 °C fixed at 1 h residence time) and varyingresidence time (ranging from 1 h to 5 h fixed at 200 °C and 260 °C). The PAH contentof the products was analysed using GC/MS. The hydrochars suitability for soil amendment was investigated. At a 1.7wt.%amendment level (approximately 60 tons/hectare) the results showed that the PAHcontribution from the hydrochars to the soil was well below the SwedishEnvironmental Protection Agency (SEPA) contamination guidelines. No significantPAH content in the products, that might limit the hydrochars applicability for landusages, was observed. The content of the 16 priority PAHs (PAH 16) in thehydrochars were below the international biochar (IBI) limit (6mg/kg TS) and theEuropean Biochar Certificate (EBC) EBC-Agro limit (6mg/kg TS). The PAH contentof the filtrates where below the Swedish Petroleum institute (SPI) irrigationguidelines, except for the filtrate produced at 260 °C, 5 h. In the raw material no PAHspecies was found, however, the reporting limit was higher compared to thehydrochars. Overall, the content of PAH was lower in the filtrates compared to thehydrochar, e.g. at 200 °C, 1 h the content PAH M were 0.05 and 0.85 mg/kg sludgeTS for the filtrate and hydrochar respectively. This was expected since PAHsgenerally has a low solubility in water. To assess the toxicity of the hydrochars thetoxic equivalent quantity (TEQ) was used. The TEQ for the hydrochars wereapproximately ~0.0 to 0.68 mg/kg TS which is below the IBI limit level at 3.0 mg/kgTS. Temperatures around 200 °C to 220° C were found to be favourable in terms ofPAH content in the hydrochar, at 220 °C and 1 h the sum of PAH16 is lower than forall other samples, for both the hydrochar and the filtrate (<R.L and 0.01mg/kg sludgeTS for the hydrochar and filtrate respectively). No significant correlation betweenresidence time and PAH content was observed, except at 260 °C where the PAH16content increased significantly in the filtrates between 1 h and 5 h residence time(0.05 to 0.85 mg/kg sludge TS). In conclusion, HTC was found to be a promisingprocess for utilizing sewage sludge and the results indicates that the risk of high levelsof PAH content of the hydrochars are relatively low.

Microfibrillated cellulose (MFC) films have gained a lot of industrial interest lately dueto their good barrier properties and good mechanical strength. In this study it wasinvestigated whether rheological characteristics and conductivity of MFC dispersionscomprised of different MFC grades could be correlated to tensile properties of the MFCfilms produced from the corresponding MFC dispersion. A rheological characterizationmethod was developed for MFC dispersions with 3 wt% MFC and a secret additiveusing a dynamic rotational rheometer and a smooth “plate to plate” geometry. Themethod consisted of an amplitude sweep, a frequency sweep, and a controlled shearrate measurement. Two predicting OPLS models were created in SIMCA: model 1correlated values from rheological measurements and ionic conductivity to tensileproperties and model 2 correlated MFC grades to tensile properties. A slight correlationbetween MFC rheology and tensile properties could be observed, but due to the lowpredictive ability of model 1 (Q2=0.47) it was deemed that the model was insufficientas a tool for facilitated predictions of new samples. It was concluded that tensileproperties are more correlated to the composition of MFC dispersions than whatrheological characteristics and ionic conductivity the dispersions display, based on thegood predictive ability of model 2 (Q2=0.59).