Efficient dewatering is necessary to achieve an economically sustainable large-scale production of microfibrillated cellulose (MFC) because the low solids content of the final product (< 3 wt.%) results in high costs related to transportation and storage, and problems for products with water incompatibility. Mechanical dewatering is preferred to thermal drying due to its lower energy demand, but MFC has a very high filtration resistance, which implies that an excessive filter area is necessary. Thus, to improve the dewatering, electro-assisted filtration may be used. In this study a bench-scale dead-end filter press was modified and the electro-assisted filtration of MFC, with two degrees of fibrillation, was investigated. The impact of the degree of fibrillation was clear when either pressure or electric field were applied separately. It was more challenging to dewater MFC with a higher degree of fibrillation using conventional filtration due to a greater surface area being subjected to the liquid flow. The opposite was found when using an electric field alone: the more fibrillated material has a higher surface charge and thereby is impacted more by the electric field. A combination of pressure and electric field resulted in a greatly improved dewatering rate, but no significant difference could be observed between the two qualities. After dewatering, the water retention value was slightly decreased, but the material still showed a gel-like behaviour, although the network strength was slightly reduced, as seen by a reduction in yield stress, storage and loss moduli. This was plausibly due to a decrease in the surface area and/or deformed network.

Microfibrillated cellulose (MFC) is a biobased material with unique properties that can be used in a multitude of applications. Water removal from the dilute product streams is, however, challenging and hinders its commercial attractiveness. One possible method of improving dewatering is the use of electroassisted filtration, in which an electric field is applied across part of the filter chamber. In this work, a bench-scale dead-end filter press, modified to allow for electroassisted filtration, was used to dewater a suspension of MFC produced via 2,2,6,6-tetramethylpiperidinyl-1-oxyl (TEMPO)-mediated oxidation. A filter cake was produced with a channeled structure related to the design of the anode mesh, indicating that the cellulose microfibrils were aligned in the direction of the electric field. This was investigated, qualitatively and quantitively, using scanning electron microscopy and wide-angle X-ray scattering, which showed a preferred orientation on a microscopic level but only a partial orientation on a molecular level (fc between 0.49 and 0.57). The influence of the density of the anode mesh, in terms of the structure/permeability of the filter cake and dewatering rate, was also evaluated using two different anode mesh densities (5 x 5 and 10 x 10 mm). It was not, however, found to have any major impact on the dewatering rate.

This study investigates the influence of the ionic strength on the dead-end filtration of microcrystalline cellulose (MCC) suspensions in the range of 0.1–1 g/L NaCl, in altering the electrostatic interactions between particles. The formation of larger agglomerates of increasing ionic concentration was observed using Focused Beam Reflectance Measurement (FBRM®). Local filtration properties were investigated as the experimental set-up allowed for measurements of local hydrostatic pressure and solidosity to be made. The results show that the addition of ions decreases both the average and local filtration resistance. The formation of a resistant skin layer was observed for the suspension without the addition of NaCl but was counteracted when ions were added. Furthermore, the ionic strength did not seem to have any notable effect on the structure of the cake in the range 0.15–1.0 g/L NaCl. However, the pressure dependency of the solidosity at lower ionic concentration was higher. The local filtration properties were fitted to semi-empirical relations, which indicated the formation of moderately to highly compressible cakes when NaCl was added.

Autohydrolysis-based pretreatments enable extraction of hemicellulose from wood tissue prior to the paper pulp cooking processes enabling their further use as platform chemicals and in material applications. In this study, hot water extraction of birch meal was conducted in a small flow-through system. The combination of high surface area of the milled material with increased driving force induced by constant flow of freshwater, together with fast evacuation of extract, enabled a detailed study of the dissolution process. Based on the findings, deeper insight into acidification and autohydrolysis progress was obtained.

An electroassisted filtration technique has been employed to improve dewatering of a suspension of micro-fibrillated cellulose (MFC) produced via 2,2,6,6-tetramethylpiperidinyl-1-oxyl (TEMPO)-mediated oxidation. In addition, all-atom molecular dynamic (MD) simulations were performed to deepen the understanding of the complicated dewatering mechanism on a molecular level. Both the experimental and the simulation results implied that the dewatering rate was not only improved when electroassisted filtration was used but also found to be proportional to the strength of the electric field. A channeled dewatered structure was observed for these experiments and may have contributed to enhanced dewatering by providing high overall permeability. The MD simulations revealed that the electric field had a significant impact on the fibril movement, whereas the impact of pressure was limited. The simulations also suggested that the increased filtrate flow upon the application of an electric field was not only due to electroosmotic flow but also due to electrophoretic movement of the fibrils toward the anode that led to the release of water that had been trapped between the fibrils, allowing it to be pressed out together with the rest of the bulk water. This study shows that electroassisted filtration has the potential to improve the dewatering of TEMPO-MFC, and the MD simulations provide further insights into the dewatering mechanism.

Gaining insight into the oxidation of hardwood kraft fibres using hydrogen peroxide at mildly acidic conditions was the main aim of this study. The oxidized hardwood pulp had an increased number of carbonyl groups and, when formed into sheets, an enhanced durability in water was seen due to the formation of cross-links, known as hemiacetals. The carbonyl groups formed were found to be mainly ketones with the exception of the case with longer reaction times (60-90 minutes) at 85 degrees C, where aldehydes were detected. Through compositional analysis it was found that mainly xylan was oxidized, likely due to the higher amount of xylan close to the surface of the fibre wall. The influence of xylan on the oxidation process was investigated using cold caustic extraction (CCE) performed prior to oxidation. When the CCE pulp was oxidized, there was an increased rate of introduced carbonyl groups and degradation was more pronounced. This is likely due to the accessible surface area being increased, caused by the formation of pores when the lower molecular weight xylan was being extracted during CCE.

Hypothesis: Interfacial tensions play an important role in dewatering of hydrophilic materials like nanofibrillated cellulose, and are affected by the molecular organization of water at the interface. Application of an electric field influences the orientation of water molecules along the field direction. Hence, it should be possible to alter the interfacial free energies to tune the wettability of cellulose sur face through application of an external electric field thus, aiding the dewatering process. Simulations: Molecular dynamics simulations of cellulose surface in contact with water under the influence of an external electric field have been conducted with GLYCAM-06 forcefield. The effect of variation in electric field intensity and directions on the spreading coefficient has been addressed via orientational preference of water molecules and interfacial free energy analyses. Findings: The application of electric field influences the interfacial free energy difference at the cellulosewater interface. The spreading coefficient increases with the electric field directed parallel to the cellulose-water interface while it decreases in the perpendicular electric field. Variation in interfacial free energies seems to explain the change in contact angle adequately in presence of an electric field. The wettability of cellulose surface can be tuned by the application of an external electric field.

The aim of this work was to provide softwood kraft pulp fibres with new functionalities by the introduction of carbonyl groups. Carbonyl groups are known to affect properties such as wet strength through the formation of covalent bonds, i.e. hemiacetals. The method developed involves oxidation using hydrogen peroxide at mildly acidic conditions. It was found that the carbonyl group content increased with both increasing temperature and residence time when oxidized at acidic conditions. The number of carboxylic groups, however, remained approximately constant. There was virtually no increase in carbonyl groups when oxidation was performed at alkaline conditions. The maximum increase in carbonyl groups was found at a residence time of 90 min, a reaction temperature of 85 degrees C and a pH of 4. These conditions resulted in an increase in carbonyl groups from 30 to 122 mu mol/g. When formed into a sheet, the pulp oxidized at acidic conditions proved to maintain its structural integrity at aqueous conditions. This indicates the formation of hemiacetal bonds between the introduced carbonyl groups and the hydroxyl groups on the carbohydrate chains. Thus, a possible application for the method could be fibre modification during the final bleaching stage of softwood kraft pulp, where the wet strength of the pulp could be increased.

In this study, the formation of particles and evolution of the particle size distribution in the micron range were monitored in situ during acid precipitation of kraft lignin. The objective of this work was to study the influence of anionic specificity and the ion concentration level. The concentrations of ions in the solution were altered both in terms of the concentration of Na+ and the type of anion in the salt added (SO42- and Cl-). The results indicate that a salting-out phenomenon occurred as NaCl was added (Na+ >= 2 mol kg(-1) water) to the kraft lignin solution at high pH, but not when Na2SO4 was added. However, the onset pH of the formation of particles (>= 1 mu m), triggered by acidification, showed to be virtually non-specific to the anion but strongly dependent on the Na+ concentration. As the pH decreased further to below the onset pH of the formation of particles >= 1 mu m, the chord length distributions (particle-size related) indicated that most of the volume of the precipitated kraft lignin (and thus possibly also the mass) may be found among the micron-sized particles, despite the fact that a relatively large number of submicron particles may also be present. The volumebased distributions tended to be wide at relatively low pH and high Na' concentrations (e.g. pH 9.4 and 2.0 mol kg(-1) water).

In this study, the manners in which temperature (45-77 degrees C) and the addition of xylan (5 g/95 g lignin) influence the onset of precipitation and evolution of the particle size distribution during acid precipitation of softwood kraft lignin were investigated in situ. No systematic trend between the onset pH of precipitation and the temperature or the addition of xylan could be observed at these conditions: the average onset pH was found to be 9.3. However, the size of the agglomerates increased as the temperature was increased, but added xylan rendered a decrease in agglomerate size. A higher onset pH was measured at increased Na ion concentration. The results indicate that the ionization degree of the phenolic groups influences the precipitation at 1 M Na ions but it is also probable that the degree of ionization of the carboxylic groups (on kraft lignin and xylan) influences precipitation (particle numbers and sizes).