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This paper uses a two-regime vector error-correction with a single cointegrating vector and a threshold in the error-correction term introduced by Hansen and Seo(2002). We propose a SupLM test for the presence of a threshold. We derive the asymptotic distribution and show how to simulate asymptotic critical region. Applying our methods to the 90-days and 180-days Commercial Paper rate, we find that there are an apparent threshold effect and inconsistent behaviors in the long-run equilibrium process.

<p>Xylan is the main hemicellulose in birch, eucalyptus, and most other hardwood species. During kraft pulping a series of chemical reactions and physical processes involving xylan take place. The processes studied in this thesis are the following: dissolution, degradation, redeposition onto the fibres, side group conversion, and cleavage of side groups off the xylan back bone. The side group in native xylan consists of methylglucuronic acid, which is mainly converted into hexenuronic acid during kraft cooking. Hexenuronic acid affect the pulp in terms of increased brightness reversion and deteriorated bleachability. The kinetics of the side group cleavage and conversion reactions were analysed using various analytical tools. The study revealed that the most commonly used methods for methylglucuronic acid measurements are not as accurate as has been claimed in the literature. A modification of two of the methods was suggested and evaluated.</p><p>A common practice used to minimise the hexenuronic acid content involves use of a high cooking temperature. The kinetic study showed that the degree of substitution of pulp xylan is only slightly affected by temperature, and that the observed effects are likely to be more associated with the xylan content of the pulp than with the hexenuronic acid content of the xylan. For the dissolved xylan, however, the degree of substitution showed a high temperature dependency and moreover it was always higher than in the pulp.</p><p>Xylan itself is known to have the capacity to increase the strength of the manufactured pulp. This knowledge was applied by exchanging cooking liquors between birch kraft cooks, in which a high amount of xylan is dissolved, and spruce cooks, which contain very small amounts of native xylan. This seems like an attractive alternative for softwood kraft cooking, since both the tensile strength and stiffness increased significantly. The magnitude of the strength increase was correlated with the molecular weight of the added xylan and with the increased surface charge of the fibres.</p>

<p>This thesis reports on an investigation of the mechanisms of edge wicking in retortable paperboard. Retortable board is used for packaging preserved food, a process which requires that the package and its contents be sterilised by exposure to high temperature steam for up to three hours. The board used must thus have higher water repellence than traditional liquid packaging. Water vapour that condenses on the cut edges on the outside of the board causes particular concern.</p><p>The paperboards studied were made from refined and unrefined bleached softwood kraft pulp and from refined unbleached softwood kraft pulp in one or two plies with different sizing levels and structures. Samples of each of the boards were immersed in a water bath at 95 °C. Other samples from the same boards were exposed to a combination of saturated steam at 130 °C and condensed steam in a special apparatus developed for this purpose. The board samples were placed on a cooling plate to simulate the temperature gradient when a container of cold food is sterilised with heated steam. Still other samples were exposed to heated steam in the absence of condensation by hanging them freely in the apparatus.</p><p>The extent of edge wicking in the boards was determined by gravimetric measurements and also by near-infrared (NIR) spectroscopy, a technique that yields more information about the moisture content profiles and the mechanisms of liquid sorption. The moisture content profiles of boards exposed to saturated steam in the absence of condensation show more uniform water uptake. This phenomenon can be explained by rapid vapour phase transport throughout the pore structure, followed by slower water uptake in the fibres. By contrast, in samples exposed to both heated steam and condensed steam, there was both liquid sorption in the fibre network and rapid vapour phase transport of the steam. The moisture content in those samples was much higher close to the edge and lower behind the liquid frontier.</p><p>The edge wicking of high temperature water was greatest in board that was not fully sized, in low density board, and in board made from unrefined pulp. The greater edge wicking in board made from unbleached pulp can be accounted for in terms of its greater swelling potential. In the low density board and the board made from unrefined pulp, the lumens at the unsized edge and the weaker bonding strength are suggested to affect the results. Capillary sorption takes place in lumens and delaminated bonds at the edge and then any further propagation takes place entirely by fibre diffusion. Capillary sorption may also be important in damaged areas where broken fibre-fibre bonds are exposed to liquid. The weaker bonded area in low density board therefore also contributes to water sorption.</p><p>Edge wicking in the boards placed on the cooling plate and exposed to a combination of saturated and condensed steam was of a different nature. For these samples, density was not an important factor. The difference is due to the different mechanism at work in this case, where the relative area of the edge exposed to condensed steam was larger in the high density boards than in the low density boards. In the high density boards, condensed steam was sorbed in the structure by diffusion in the fibre structure, whereas in low density boards, the dominant effect was vapour phase transport in the void spaces followed by water uptake in the fibres.</p>

<p>The degradation of cellulose found in wood is one of the most important degradation processes for the carbon flux on earth. The degradation is performed by microorganisms that typically use enzymes. Since the cellulose in wood is crystalline and embedded in other polymers, making it inaccessible and durable, the enzymatic methods of cellulose degradation is also complex.</p><p>In this thesis, the action of some of these enzymes, called cellulases, have been studied both fundamentally and for industrial purposes. By using model cellulose films and a quartz crystal microbalance it was found that endoglucanases not only depolymerize but also swell model cellulose films. Most probably, this contributes to the synergy seen between endoglucanases and exoglucanases.</p><p>When an pulp fibers were pre--treated with endoglucanases and beaten subsequently, the fibers became more swollen than reference fibers. The effects of beating enzyme pre--treated fibers were investigated, indicating that endoglucanases improves the fiber/fiber interaction but also alters the behavior of the fibers in the beating process to become more susceptible to the beating.</p><p>The second part of the thesis has been focused on the use of an albino fungi in order to decrease the amount of wood extractives in wood chips prior to thermo mechanical pulp production. The fungus decreased the most troublesome component, the triglycerides, by more than 90 percent in two weeks without any detrimental effects on pulp properties. On the contrary, pulp strength and optical properties were improved.</p>

<p>The interdependency between filler retention and paper formation is well-known, where a high retention is accompanied by impaired formation. A challenge for today’s papermakers is to increase the competitiveness for uncoated and coated fine paper, by improving the formation at the same level of retention.</p><p>Over the years, the use and the demands of retention aids have increased as a consequence of a higher system closure, increased machine speeds and increased filler content. The knowledge of whether some retention aid systems are more or less detrimental to paper formation than other systems, is very limited. The insuffiency of knowledge is, however, also true for other chemical, mechanical and interacting factors, which influence the retention/formation relationship in a complex manner.</p><p>In order to investigate the retention/formation relationship (features, retention aids, dosage points, etc.), a pilot-scale fourdrinier former (R/F-machine) has been developed. The R/F-machine provides a short circulation of the white water and controlled experimental conditions and is appropriate for cost-effective investigations. Moreover, the R/F-machine has been designed to have a short residence time to chemical equilibrium and the machine has also shown high reproducibility in the results.</p><p>This licentiate thesis presents the R/F-machine and examines, during constant experimental conditions, the retention/formation relationships for some different retention aid systems. Three single-component cationic polyacrylamides with varying molecular weights and two polyacrylamide-based microparticulate systems with varying microparticles were examined. The retention aid systems were investigated on the R/F-machine, for a fine paper stock (90 % bleached hardwood and 10 % bleached softwood) with addition of 25 % filler (based on total solids content).</p><p>The results showed that the retention/formation relationship was not dependent on the retention aid system used. All systems showed the same relationship between retention and formation. On the other hand, the various retention aid systems provided different effects considering their retention performance.</p>

<p>Papper uppvisar betydande tidsberoende mekaniska egenskaper som krypning och spänningsrelaxation. Det är känt att krypningen hos pappret påverkar till exempel en wellpapplådas förmåga att bära last under lång tid. En möjlighet att tillverka papper som kryper långsammare är därför önskvärd. Polyelektrolyter används ofta för att öka styrkan hos papper, och skulle kanske också kunna användas till att minska papprets krypning. Inverkan av polymera additiv på pappers krypegenskaper är emellertid knapphändigt beskrivet i litteraturen. Existerande studier har visat att polymera additiv inte påverkar krypningen hos starka papper och att fiberväggarna och fiber/fiber fogarna har fundamentalt olika betydelse för krypegenskaperna.</p><p>Avsikten med denna avhandling var att undersöka hur adsorberade polyelektrolyter påverkar krypegenskaperna hos pappret. Ett av huvudsyftena var att studera om adsorptionen av en katjonisk polyelektrolyt – polyallylamin – endast till fiberytan eller tvärs hela fiberväggen ger olika effekt på krypningen hos papper tillverkade av dessa fibrer.</p><p>En ny teknik där polyelektrolyten märks med en fluorescerande markör gör det möjligt att visualisera var i fibern de adsorberade molekylerna befinner sig. Resultaten visar att adsorption vid låg jonstyrka under kort tid bara ger adsorption till de yttre delarna av fiberväggen. Hög jonstyrka och lång adsorptions tid resulterar å andra sidan i adsorption tvärs hela fiberväggen. Med hjälp av denna teknik blev det också möjligt att klarlägga vilken inverkan polyelektrolytens läge i fiberväggen har på de slutgiltiga arkens mekaniska egenskaper.</p><p>Krypprovning av de tillverkade arken visade tydligt att polyallylamin som endast adsorberat till fibrernas yttre delar minskade krypningen vid både 50 % och 90 % relativ luftfuktighet. Den uppnådda effekten visade sig dock bero på vilken typ av fibrer arken tillverkades av. Adsorption av katjoniserad stärkelse till fibrernas yta gav ingen nämnvärd effekt på arkens krypegenskaper, detta trots att stärkelse gav lika hög arkstyrka som polyallylamin.</p><p>När polyallylamin adsorberades tvärs igenom fibrerväggen ökade krypningen vid 90 % relativ luftfuktighet väsentligt. Detta föreslås bero på att den adsorberade polyelektrolyten avsväller fibrerna vilket ger färre fiber/fiber kontakter och därmed en sämre fördelning av mekanisk last i arken. Det var emellertid inte möjligt att dra några definitiva slutsatser angående mekanismerna bakom de observerade skillnaderna i krypegenskaper.</p> / <p>Paper materials exhibit a significant time-dependent mechanical behaviour, such as creep and stress-relaxation. It is known that the creep of the paper affects the performance of corrugated boxes. The production of a paper having a lower creep rate is therefore desirable. Polyelectrolytes commonly used to increase the strength of paper could be an alternative for improving the creep properties. The influence of polymeric additives on the creep properties of paper is, however, poorly described in the literature. Published studies have shown that polymeric additives do not affect the creep behaviour of fully efficiently loaded paper sheets and that the fibre cell walls and the fibre/fibre joints have fundamentally different effects on the creep behaviour.</p><p>The aim of the present thesis was to examine the influence of adsorbed polyelectrolytes on the creep behaviour of paper sheets made from the modified fibres. One of the main objectives was to establish whether there is a difference in effect on creep properties between adsorbing a cationic polyelectrolyte – polyallylamine – to the fibre surfaces or throughout the fibre cell walls.</p><p>A technique which includes the labelling of polyelectrolytes with a fluorescent dye and microscopy of single fibres provided a visual record of the localisation of the adsorbed polyelectrolyte. This method showed that a low ionic strength and a short adsorption time resulted in adsorption of the polyelectrolyte only to the external parts of the fibres. A high ionic strength and a long adsorption time on the other hand, resulted in adsorption throughout the fibre walls. This made it possible to study the relationship between the mechanical properties of the sheets and the localisation of the adsorbed polyelectrolyte.</p><p>Creep testing of the sheets showed that the adsorption of polyallylamine to the exterior parts of fibres decreased the creep at both 50% and 90% RH. The effect depended, however, on the type of fibre used. Adsorption of cationic starch to the fibres gave no significant reduction in creep rate, despite the fact that starch and polyallylamine had similar effect on the paper strength.</p><p>When polyallylamine was adsorbed into the fibre cell walls, the creep at 90% RH increased. It is suggested that this was due to a deswelling of the fibres by the adsorbed polyelectrolyte, which resulted in fewer fibre/fibre contact points and hence a less efficient distribution of stresses in the sheet. It was not, however, possible to draw any definitive conclusions about the mechanisms behind the observed differences in creep behaviour.</p>

<p>The chemical interactions between the main wood components i.e., cellulose, hemicelluloses and lignin are of fundamental importance for understanding the chemical aspects of wood formation and its reactivity during fibre processing e.g during chemical pulping of wood. Future progress in the development of new high value products from wood will greatly depend on a detailed knowledge of how the fibre elements interact with each other in the biological material. The existence of covalent bonds between lignin and carbohydrates (LCC) has been one of the most controversial issues in the field of wood chemistry. Only until recently, the existence of such bonds has in its entirety been shown by way of indirect analyses, normally suffering from low yields obtained at rather drastic conditions. Furthermore, previous studies on LCC have been targeted on studying the specific lignin carbohydrate linkage and less emphasis has been put on the whole LCC networks. Detailed structural studies of entire LCC are therefore of importance in understanding the chemistry involved in wood formation and wood reactivity.</p><p>The aim of this study was to isolate intact LCC from wood and corresponding chemical pulps made from it in quantitative yield and to clarify their detailed chemical structure. For the first time, a method for the quantitative analysis of lignin-carbohydrate complexes (LCCs) in softwood is presented and it could be concluded that no carbohydrate-free lignin was present in these wood fibres. From mildly ball-milled wood, all lignin was isolated as LCCs in a sequence involving a partial enzymatic hydrolysis of cellulose, subsequent swelling and quantitative dissolution, into 4 major fractions; a galactoglucomannan-lignin-pectin LCC (GalGlcMan-L-P) containing ~8% of the wood lignin, a glucane LCC (Glc-L) containing ~4% of the wood lignin, a xylan-lignin-glucomannan network LCC (Xyl-L-GlcMan) (with a predominance of xylan over glucomannan) containing ~40% of the wood and a glucomannan-lignin-xylan network LCC (GlcMan-L-Xyl) (with a predominance of glucomannan over xylan) containing ~48% of the wood lignin.</p><p>From unbleached kraft pulps, 85 - 90% of residual lignin was found to be chemically bonded to carbohydrates. The effect of the degree of delignification on the LCC types during kraft pulping and during subsequent oxygen stage was studied in order to understand the role of LCC for the stability of residual lignin. For both processes, high delignification rates were observed for the xylan-rich LCC and cellulose-rich LCC fractions, whereas the glucomannan-rich LCC was relatively stable. After a severe oxygen stage, almost all the residual lignin was isolated in the latter complex.</p><p>Thioacidolysis in combination with gas chromatography was used to determine the content of β-O-4 structures in the lignin. Periodate oxidation and methanol determinations were used to quantify the phenolic hydroxyl groups, whereas size exclusion chromatography (SEC) of the thioacidolysis fractions was used to monitor any differences between the original molecular size distribution and that after the delignification processes. Major differences between the various LCC fractions were observed, clearly indicating that two different forms of lignin are present in the wood fibre wall. These forms are linked to glucomannan and xylan respectively. The xylan linked lignin was found to consist largely of β-O-4 structures indicating a rather linear coupling mode, whereas the glucomannan linked lignin was more heterogeneous with respect to the known lignin inter-unit linkage types. Based on these findings, a modified arrangement of the fibre wall polymers is suggested. From acid sulfite pulp (Kappa number 11) residual lignin was isolated at ~80% yield on LCC basis. About 60% was linked to xylan, 30% to glucomannan and 10% to glucans. These values differ greatly from those obtained for softwood pulped to a similar kappa number by the Kraft method. Model compound studies indicated that the benzyl ether type of LC linkage were likely to survive cleavage at the acidic sulfite pulping conditions</p>