During kraft cooking a significant part of the wood material, especially lignin and hemicelluloses, is degraded and dissolved in the cooking liquor, rendering a broad range of degradation products with different molecular mass and functional groups. The main part of this thesis has been devoted to clarify the role of these dissolved wood components (DWC) during kraft cooking. The investigations have covered their influence on e.g. the delignification rate, pulp yield, point of defibration, unbleached pulp c olour and pulp bleachability, i.e. the amount of bleaching chemicals consumed per kappa number or lignin unit to reach a certain brightness. Both softwood (Picea Abies) and hardwood (Eucalyptus urograndis) have been studied. During kraft cooking, many reactions occur simultaneously. Therefore emphasis has been put on separating the effects of hydroxide ions, hydrogen sulphide ions, sodium ions and DWC. This has been enabled by the use of a so called constant-composition-cooking technique, which enables the use of almost constant concentrations of the cooking chemicals during the cook and also results in a very low concentration of DWC in the cooking liquor. The presence of DWC has been controlled by the addition of industrial black liquor. To further scrutinise the role of DWC, the effect of different molecular mass fractions were studied and representative model substances were used to clarify the origin of the observed effects. A kinetic study showed that the delignification rate was significantly affected by the presence of DWC in the cooking liquor and resulted in a rate increase in the part of the cook where the bulk phase dominates and a decreased delignification rate when the residual phase dominates. The increase in delignification rate was dependent on the concentration of DWC and was observed in softwood as well as hardwood kraft cooks. The rate increasing effect was investigated further by the use of ultra- and nanofiltra tion. This way the DWC was divided into fractions with different molecular mass distributions. The results showed that the increase in delignification rate related more strongly to the content of free phenolic groups in the DWC than on the total amount of DWC. By cooking in the presence of representative model substances the effect was further clarified. Aromatic structures with free phenolic groups gave a rate increasing effect while no visible effect could be seen from other structures. This supports the finding that the delignification rate relates to the amount of free phenols in the cooking liquor and shows that the phenolic functionality take active part in the delignification reactions. Free phenolic groups in the degraded lignin may explain a large part of the rate increasing effect seen from the presence of DWC. Further, the presence of DWC increased the point of defibration in a eucalyptus kraft cook and made it possible to terminate the cook at a higher kappa number with the same amount of reject. By terminating the cook at a higher kappa number it was possible to noticeably increase the fully bleached pulp yield. The content of hexenuronic acids (HexA) in the eucalyptus pulp depends on the H-factor and increases with delignification, providing that the bulk phase still dominates. Therefore, by increasing the rat e of delignification and terminating the cook at a higher kappa number it was possible to significantly decrease the amount of HexA in the pulp. The presence of DWC causes a darkening of the unbleached pulp. Bleachability in a D(EOP)DD sequence was negatively affected by the presence of DWC during pulping of softwood, while no effect was seen on the bleachability of hardwood / QC 20100920

Fluffmassa är, i ordets rätta bemärkelse, ett fluffigt material som i de allra flesta fall tillverkas av fibrer ifrån trä, den utgör en viktig del i blöjor, hygienprodukter, näsdukar och ett flertal andra produkter. Syftet med fluffmassa i absorptionsprodukter är framförallt att sprida vätskan, öka absorbtionshastigheten och behålla superabsorberande polymerer på plats i nätverket. Två viktiga kvalitetsparametrar hos fluffmassan är defibreringsenergi och knuthalt. Dessa är korrelerade till hur enkelt fibrerna kan separeras ifrån varandra i torr eller fuktad luft. Denna separation av fibrer är ett högst avgörande steg för att skapa den fluffiga massan ifrån torkade massaark.  Målet med arbetet har varit att reducera defibreringsenergin och knuthalten genom att behandla massa med oorganiska partiklar genom att använda den sk. lager-på-lager (LbL) – metoden där en konsekutiv behandling av fibrerna med motsatt laddade polyelektrolyter och nanopartilkar. Genom att belägga fiberytan med tunna skikt av ett oorganiskt material var avsikten att reducera fiber-fiber-interaktionerna för att slutligen minska defiberingsenergin och knuthalten. Studien visade att en viss effekt kunde uppnås med LbL-skikt av pDADMAC (diallyldimetylammonium klorid) och MMT (montmorillonit) vilket noterades som en minskning av knuthalten från 35% till ungefär 20%, medan defibreringsenergin däremot var oförändrad jämfört med ett obehandlat referensprov. De bildade lagren visade sig vara tunnare och jämnare än förväntat vilket sannolikt ledde till en relativt liten minskning av kontaktyta och molekylär adhesion mellan fibrerna vilket kan förklara den relativt sett låga effekten av tillsatserna. De tunna lagren kan också vara en förklaring till varför ingen nämnvärd skillnad detekteras för olika antal av bildade bilager. Eftersom enbart maximalt 3 bilager studerades kan det vara rimligt att anta att en ytterligare adsorption av bilager kan leda till en ytterligare minskning av knuthalten och defibreringsenergin.  Eftersom MMT-partiklarna inte var direkt synliga i SEM-analyserna är det svårt att säga exakt hur de är fördelade på fiberytan. Antingen är de jämnt fördelade eller så har vissa områden på fiberytan inte blivit täckta av MMT.  Resultaten indikerar också att det finns många intressanta sätt att förbättra lagren för att nå lägre defibrerinsergier och knuthalter. Genom att tex. adsorbera större partiklar istället för tunna MMT-partiklar skulle det vara möjligt att skapa en högre ytråhet och därmed en minskad kontaktyta mellan fibrerna vilket i sin tur skulle kunna minska knuthalten och defibreringsenergin. / Fluff pulp is indeed a fluffy material, it is most commonly composed of pulp fibers from wood and it serves as a vital constituent in diapers, feminine hygiene products, napkins and a variety of other products. The purpose of fluff pulp in absorbent products is mainly to distribute fluids, increase absorption speed and hold superabsorbent polymers within the network. Two important quality parameters of fluff pulp are the defibration energy and the knot content, which are related to the ease at which the fibers can be separated from each other under dry to moist conditions. This separation of fibers is an essential step in generating the fluffy material from sheets.   This project aims to reduce the defibration energy and the knot content by treating fibers with inorganic particles according to the Layer-by-Layer (LBL) technique. The main assumption was that by applying coatings to the fibers, the inter-fiber interactions can be reduced leading to a lowered defibration energy and knot content. The study showed that some effect was accomplished using layers of pDADMAC (diallydimethylammoinium chloride) and MMT (montmorillonite clay), the knot content was reduced from 35% to around 20%, but the defibration energy was unchanged compared to the untreated reference sample. The formed LBL layers appeared to be thinner and smoother than anticipated which likely lead to only a slight decrease in contact area between the fibers, hence, the reduction of knot content was detectable but not very large. Since the formed LBL layers were so thin it was difficult to find any distinguishable difference for the different numbers of bilayers, however, the maximum number of bilayers produced was only three and additional layers could lead to an amplified effect.  Since the MMT particles could not be clearly visualized from the SEM instruments, it is difficult to conclude exactly how the clay platelets were distributed on the fibers. Either the MMT was distributed rather evenly across the surface of the fibers, or some areas of the fibers were left free from LbLs.   The results from the present investigation show that there are many interesting ways to further improve the layers to reach lower defibration energies and knot contents. As an example the adsorption of larger particles instead of thin MMT platelets could be used allowing for a minimization of the contact area between the fibers due to an increased surface roughness of to the fiber surfaces.

The main objective of this thesis was to improve the understanding of some aspects on wood and fibre mechanics related to conditions in the thermomechanical pulping process. Another objective was to measure the power distribution between the rotating plates in a refiner.   The thesis comprises the following parts: –A literature review aimed at describing fracture in wood and fibres as related to the thermomechanical pulping process –An experimental study of fracture in wood under compression, at conditions similar to those in feeding of chips into preheaters and chip refiners –An experimental study of the effect of impact velocity on the fracture of wood, related to conditions of fibre separation in the breaker bar zone in a chip refiner –A micromechanical model of the deterioration of wood fibres, related to the development of fibre properties during the intense treatment in the small gap in the refining zone –Measurements of the power distribution in a refiner.   The fracture in wood under compression was investigated by use of acoustic emission monitoring. The wood was compressed in both lateral and longitudinal directions to predict preferred modes of deformation in order to achieve desired irreversible changes in the wood structure. It was concluded that the most efficient compression direction in this respect is longitudinal. Preferable temperature at which the compression should be carried out and specific energy input needed in order to achieve substantial changes in the wood structure were also given.   The fibre separation step and specifically the effect of impact velocity on the fracture energy were studied by use of a falling weight impact tester. The fracture surfaces were also examined under a microscope. An increase in impact velocity resulted in an increase in fracture energy. In the thermomechanical pulping process the fibres are subjected to lateral compression, tension and shear which causes the creation of microcracks in the fibre wall. This damage reduces the fibre wall stiffness. A simplified analytical model is presented for the prediction of the stiffness degradation due to the damage state in a wood fibre, loaded in uni-axial tension or shear. The model was based on an assumed displacement field together with the minimum total potential energy theorem. For the damage development an energy criterion was employed. The model was applied to calculate the relevant stiffness coefficients as a function of the damage state. The energy consumption in order to achieve a certain damage state in a softwood fibre by uniaxial tension or shear load was also calculated. The energy consumption was found to be dependent on the microfibril angle in the middle secondary wall, the loading case, the thicknesses of the fibre cell wall layers, and conditions such as moisture content and temperature. At conditions, prevailing at the entrance of the gap between the plates in a refiner and at relative high damage states, more energy was needed to create cracks at higher microfibril angles. The energy consumption was lower for earlywood compared to latewood fibres. For low microfibril angles, the energy consumption was lower for loading in shear compared to tension for both earlywood and latewood fibres. Material parameters, such as initial damage state and specific fracture energy, were determined by fitting of input parameters to experimental data. Only a part of the electrical energy demand in the thermomechanical pulping process is considered to be effective in fibre separation and developing fibre properties. Therefore it is important to improve the understanding of how this energy is distributed along the refining zone. Investigations have been carried out in a laboratory single-disc refiner. It was found that a new developed force sensor is an effective way of measuring the power distribution within the refining zone. The collected data show that the tangential force per area and consequently also the power per unit area increased with radial position. The results in this thesis improve the understanding of the influence of some process parameters in thermomechanical pulping related wood and fibre mechanics such as loading rate, loading direction, moisture content and temperature to separate the fibres from the wood and to achieve desired irreversible changes in the fibre structure. Further, the thesis gives an insight of the spatial energy distribution in a refiner during thermomechanical pulping.

The purpose of this thesis was to develop an economical, sustainable, and environmentally friendly straw Medium Density Fibreboard (MDF) process, capable of full-scale manufacturing and to produce MDF of requested quality. The investigated straw was based on wheat (Triticum aestivum L.) and rice (Oryzae sativa L.). In this thesis three different methods were taken for manufacture of straw MDF; (A) wheat-straw fibre was blowline blended with melamine-modified urea-formaldehyde (MUF), (B) rice-straw fibre was mixed with methylene diphenyl diisocyanate (MDI) in a resin drum-blender, and (C) wheat-straw fibre was activated in the blowline by the addition of Fenton’s reagent (H2O2/Fe2+) for production of non-resin MDF panels.  The MUF/wheat straw MDF panels were approved according to the requirements of the EN standard for MDF (EN 622-5, 2006). The MDI/rice-straw MDF panels were approved according to requirements of the standard for MDF of the American National Standard Institute (ANSI A208.2-2002). The non-resin wheat-straw panels showed mediocre MDF panel properties and were not approved according to the requirements in the MDF standard. The dry process for wood-based MDF was modified for production of straw MDF. The straw MDF process was divided into seven main process steps. 1.       Size-reduction (hammer-milling) and screening of straw 2.       Wetting and heating of straw 3.       Defibration 4.       Resination of straw fibre 5.       Mat forming 6.       Pre-pressing 7.       Hot-pressing       The primary results were that the straw MDF process was capable of providing satisfactory straw MDF panels based on different types of straw species and adhesives. Moreover, the straw MDF process was performed in pilot-plant scale and demonstrated as a suitable method for producing straw MDF from straw bales to finished straw MDF panels. In the environmental perspective the agricultural straw-waste is a suitable source for producing MDF to avoid open field burning and to capture carbon dioxide (CO2), the biological sink for extended time into MDF panels, instead of converting straw directly into bio energy or applying straw fibre a few times as recycled paper. Additionally, the straw MDF panels can be recycled or converted to energy after utilization. A relationship between water retention value (WRV) of resinated straw fibres, the thickness swelling of corresponding straw MDF panels, and the amount of applied adhesive was determined. WRV of the straw fibre increased and the TS of straw MDF declined as a function of the resin content. The empirical models developed were of acceptable significance and the R2 values were 0.69 (WRV) and 0.75 (TS), respectively. Reduced thickness swelling of MDF as the resin content is increased is well-known. The increase of WRV as a function of added polymers is not completely established within the science of fibre swelling. Fortunately, more fundamental research can be initiated and likely a simple method for prediction of thickness swelling of MDF by analysis of the dried and resinated MDF fibres is possible. / Syftet med denna avhandling var att lägga grunden för en ekonomisk, hållbar och miljövänlig MDF process för halmråvara, kapabel för fullskalig produktion av MDF och goda skivegenskaper. Framställningen av MDF skivor utgick från halm av vete (Triticum aestivum L.) och ris (Oryzae sativa L.). Tre olika metoder användes för att producera MDF av halm; (A) fibrer av vetehalm belimmades i blåsledning med ett melaminmodifierat urea-formaldehydlim (MUF), (B) fibrer av rishalm belimmades i en limblandare med metylen difenyl diisocyanate (MDI), (C) Limfria MDF skivor av vetehalm framställdes med aktivering av fibrer genom tillsats av Fenton´s reagens (H2O2/Fe2+) i blåsledning utan någon tillsats av syntetiskt lim. Sammanfattningsvis kan det understrykas att framställda MDF-skivor av MUF/vetehalm var godkända enligt standard för MDF (EN 622-5, 2006). Dessutom var framställda MDF skivor av MDI/rishalm också godkända enligt krav i standard för MDF ”American National Standard Institute” (ANSI A2008.2-2002). Limfria vetehalmskivor visade på måttliga skivegenskaper och klarade inte kraven i MDF standard.   Fiberframställningsprocessen för MDF modifierades till en produktion utgående från halm. MDF processen för halm delades upp i sju primära processoperationer.   (1)            Storleksreducering och sållning av halm (2)            Vätning och uppvärmning av halm (3)            Defibrering (4)            Belimning av halmfiber (5)            Mattformning (6)            Förpressning (7)            Pressning   De viktigaste resultaten från denna studie är att MDF av halm kunde produceras utgående från olika typer av halmsorter och lim. Dessutom utfördes MDF-processen i pilotskala och visade på en lämplig metod för framställning av MDF-skivor från halmbalar till färdiga halmfiberskivor. Det miljömässiga perspektivet på att använda jordbruksavfall till framställning av halmskivor är att undvika förbränning av halm ute på fältet, men det är även möjligt att binda koldioxid (CO2) i halmskivor under längre tid än att omsätta halmråvaran omedelbart som bioenergi eller använda halmfiber som returpapper några få gånger. Dessutom kan MDF återanvändas eller bli omsatt till energi efter användning.   Ett förhållande mellan ”water retention value” (WRV), av belimmade halmfiber, tjocklekssvällning för motsvarande MDF av halmskivor och mängden av tillsatt lim vid olika nivåer har undersökts. Med ökande limhalt tilltog WRV fibersvällning, vidare minskade tjocklekssvällning för motsvarande MDF skivor. De framtagna empiriska modellerna var godtagbara och beräknade R2 värden var 0.69 (WRV) och 0.75 (TS). Minskad tjocklekssvällning med ökad limhalt är dokumenterad sen tidigare. Ökad fibersvällning WRV vid tillsats av polymerer (limmer) är inte fullständigt etablerad inom vetenskapen för fibersvällning. Lyckligtvis kan grundläggande forskning initieras och sannolikt föreligger en enkel metod för att prediktera tjocklekssvällning av MDF genom analyser av torkade och belimmad MDF fiber.