Thesis (Ph. D.)--Institute of Paper Chemistry, 1968.

Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniversitet, 2004. / Härtill 4 uppsatser.

Thesis (M.S.)--Oregon State University, 2005. / Printout. Includes bibliographical references (leaves 66-72). Also available on the World Wide Web.

Xylan dissolved during kraft cooking and later redeposited on fibre surfaces has been shown to give higher pulp yield and better strength properties. This is economically interesting from an industrial point of view. Many studies have been done to investigate xylan behaviour during kraft cooking, to discover the xylan-cellulose attachment mechanism, to find the optimal xylan retention or adsorption process, and to discover relations between xylan structure and strength enhancement. Most of them have concentrated on hardwood xylan. However, softwoods are the major raw materials for the pulp industries in the northern hemisphere. Earlier studies have shown that the xylan characteristics, rather than simply the amount of xylan, influence the strength-enhancing effect of xylan. To obtain optimal utilization of spruce xylan as a strength enhancer, it is essential to know what the beneficial xylan characteristics are and how cooking conditions affect the characteristics. In this study, kraft cooking of spruce chips was performed under varied cooking conditions and the xylan in the black liquor was precipitated and characterized. It was found that dissolved spruce xylan had a much higher amount of bound lignin compared to previous studies on xylan dissolved from hardwoods. Increased cooking temperature increased the dissolution rate of xylan. The lower alkali charge and higher ionic strength of the cooking liquor resulted in a lower amount of dissolved xylan. Apart from the effect of the amount, cooking conditions also affected substitution of dissolved xylan. Higher temperature and higher ionic strength led to a lower amount of MeGlcA, while the MeGlcA amount of dissolved xylan was preserved during lower alkali cooking. By distinguishing how different cooking conditions affect the characteristics of the xylan dissolved in the black liquor, xylans with different structures were designed to study their effects on pulp strength, that is, the addition of black liquors with certain known xylan characteristics in the kraft cooking process. It was found that the best effect of xylan on tensile strength occurred when the xylan penetrated some distance into the subsurface of the fibre wall. Both low molecular weight and high degree of substitution lowered the tendency of xylan to aggregate, which enabled the dissolved xylan to penetrate some distance into the exposed fibre surface. Upon beating, this xylan was exposed, thus facilitating improvement of fibre-fibre joint formation, which led to increased tensile strength. / <p>QC 20130326</p>

<p>For papermakers, an understanding of the development of strength properties in the paper is of uttermost importance. Strong papers are desirable both in the traditional paper industry as well as in new fields of application, such as fibre-based packaging and light-weight building material. In this study, the effects of adding abaca (Musa textilis) as a reinforcement fibre for softwood pulp was investigated. Moreover, the LB Multilayer Handsheet Former for the production of stratified sheets was evaluated and used to study the effects of placing selected fibres in separate layers, rather than by making homogeneous sheets from a mixture of the pulps.</p><p>Handsheets of a softwood sulphate pulp with the addition of abaca fibres were made in a conventional sheet former. It was seen that the addition of abaca fibres can increase the tearing resistance, fracture toughness, folding endurance and air permeance. Tensile strength, tensile stiffness and tensile energy absorption, however, decreased somewhat.</p><p>It was shown that the LB Multilayer Handsheet Former is suitable for studying the effects of stratification of paper. The sheet former produces sheets with good formation and the variation of paper properties of the sheets is retained at a fairly constant level when the number of layers in the stratified sheets is increased. The uniformity of the sheets produced in the LB Multilayer Handsheet Former are generally at the same level as of those produced in conventional sheet formers.</p><p>Homogeneous and stratified sheets were produced in the LB Multilayer Handsheet Former and it was found that by stratifying a sheet, so that pulp with a high tear index and pulp with a high tensile index are placed in separate layers, it was possible to increase the tear index by approximately 25%, while the tensile index was decreased by 10-20%.</p>

For papermakers, an understanding of the development of strength properties in the paper is of uttermost importance. Strong papers are desirable both in the traditional paper industry as well as in new fields of application, such as fibre-based packaging and light-weight building material. In this study, the effects of adding abaca (Musa textilis) as a reinforcement fibre for softwood pulp was investigated. Moreover, the LB Multilayer Handsheet Former for the production of stratified sheets was evaluated and used to study the effects of placing selected fibres in separate layers, rather than by making homogeneous sheets from a mixture of the pulps. Handsheets of a softwood sulphate pulp with the addition of abaca fibres were made in a conventional sheet former. It was seen that the addition of abaca fibres can increase the tearing resistance, fracture toughness, folding endurance and air permeance. Tensile strength, tensile stiffness and tensile energy absorption, however, decreased somewhat. It was shown that the LB Multilayer Handsheet Former is suitable for studying the effects of stratification of paper. The sheet former produces sheets with good formation and the variation of paper properties of the sheets is retained at a fairly constant level when the number of layers in the stratified sheets is increased. The uniformity of the sheets produced in the LB Multilayer Handsheet Former are generally at the same level as of those produced in conventional sheet formers. Homogeneous and stratified sheets were produced in the LB Multilayer Handsheet Former and it was found that by stratifying a sheet, so that pulp with a high tear index and pulp with a high tensile index are placed in separate layers, it was possible to increase the tear index by approximately 25%, while the tensile index was decreased by 10-20%.

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 takes place. The processes studied here are the following: dissolution, degradation, redeposition onto the fibres, side-group conversion, and cleavage of side groups off the xylan backbone. The side group in native xylan consists of methylglucuronic acid, which is partly converted into hexenuronic acid during kraft cooking. Hexenuronic acid affects the pulp in terms of increased brightness reversion and reduced bleachability. The kinetics of the side-group cleavage and conversion reactions were studied using various analytical tools. The study revealed that the most common methods for methylglucuronic acid quantifcation can be signifcantly improved in terms of accuracy. A modifcation and combination of two of the methods was suggested and evaluated. In order to minimise the hexenuronic acid content, a common suggestion involves the use of a high cooking temperature. The kinetic study found 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 indicated a high temperature dependency for birch kraft cooking. By collecting black liquors at different stages in the cook, different molecular properties of the dissolved xylan was obtained. The liquors were charged at later parts of the cook, making the dissolved xylan to reattach to the fibres. Depending on the molecular properties of the added xylan, the tensile strength properties of the produced paper were improved. These improvements in paper properties were correlated to the molecular behaviour of the added xylan in solution. / QC 20100702

The paper industry utilizes fillers either to reduce the cost or to provide desired functional or end-use properties of paper products. However, there are disadvantages associated with higher filler loadings beyond a certain level, which reduces paper strength. The present study focused on improving the physical property of filled papers. Three methods of structuring fillers were designed; precipitation with starch, complexation with starch and fatty acid, and regeneration with cellulose. Because cellulose and starch have hydroxyl groups on the chemical structure, the hydrogen bonding between fillers and wood fibers is assumed to be occurred by structuring fillers. For starch application, we used two different approaches; salt precipitation and fatty acid complexation. The cooked starch can be precipitated by certain salt solutions such as (NH4)2SO4. Also, the cooked starch can be complexed with fatty acid to produce an insoluble crystalline structure. When starch composites with clay made by both methods were put into the furnish as fillers, dramatic strength improvement was achieved such as 100-200% gains in tensile strength. This is due to the strong bonding between clay fillers and wood fibers, which is determined by Z-directional tensile strength. One of advantages is that using the starch-fatty acid complex has an inherent water repellent property, sizing effect. For cellulose as a bonding material, N-methylmorpholine-N-oxide was used as a solvent to dissolve the cellulose. The advantage of using this method is that we can use the low grade cellulose. The physical properties of the cellulose coated clay handsheets were significantly improved, but optical properties such as brightness and opacity were inferior to the hadnsheets filled with starch-clay composites due to relatively large particle size. In order to model the strength improvement by the composite filler, BDT theory, which is a modified Pages Equation, was used. After calculating the factors such as surface area and specific bond strength, the model matched well with the experimental results. Using this model, the tensile strength improvement could be predicted in terms of the change of bond strength and composite size.

The aim with this master thesis was to investigate the potential of using non-wood fibers to enhance the paper strength. Abaca, sisal and banana fibers were added to conventional bleached chemical softwood pulp. The effect of refining was investigated, both as co-refining and as separate refining. The fiber properties were determined with a Fiber Tester and the drainage resistance was determined with Schopper-Riegler. Density, tensile index, tear index and burst index were determined on paper sheets made in a Rapid-Köthen sheet former. The results showed that abaca had longer fiber length than softwood, while sisal had slightly shorter fiber length compared with softwood. Sheet density was lowered with addition of all three fiber types, while the drainage resistance was increased for the same. It was also observed that the tensile index increased with additions of abaca, while additions of sisal and banana fibers gave lower tensile indexes. The same trend was observed for the tear index and burst index. Refining gave higher values of the drainage resistance, density, tensile index and burst index. However, the tear index was affected differently depending on the fiber type and fiber blend. For sisal and banana fibers, the tear index was first increased at lower refining degrees and were thereafter decreased with further refining. When studying abaca and softwood, a declining trend was observed over the entire refining interval. The conclusion was that addition of abaca fibers increased all investigated strength properties. Sisal and banana fibers gave higher values of the tear strength, when exposed to mild refining.

The failure properties of interfibre bonds are the key for the build-up of strength in fibrous materials such as paper and paperboard. In order to tailor the properties of such materials by chemical or mechanical treatments and to learn how such modifications influence the properties at a microscopic level, direct measurement of individual fibre--fibre crosses are typically performed. However, the state of loading in the interfibre joint, in testing of individual fibre--fibre crosses, is in general very complex and a greater understanding for how to evaluate the mechanical properties of interfibre joints is desirable. In Paper A, a method for manufacturing multiple fibre--fibre cross specimens and a procedure for testing interfibre joints at different modes of loading is presented. The method is applied to investigate the strength of fibre-fibre crosses with different geometry and at two principally different modes of loading. Also, an investigation on the influence of drying pressure, the drying method as well as a comparison of pulp fibres from two different degrees of refining is presented. The force at rupture is scaled in terms of different geometric parameters; nominal overlap area, length and width of the joint region. It is shown that neither of the methods of scaling unambiguously reduced the coefficient of variation of the mean strength and that the force at rupture in a peeling type of loading was about 20% of the ones tested in the conventional shearing type of loading. In Paper B, a procedure for evaluating interfibre joint strength measurements in terms of resultant forces and moments at rupture is presented. The method is applied to investigate the state of loading in fibre-fibre crosses tested in two principally different modes of loading. It is shown that for a typical interfibre joint test, the modes of loading other than pure shear, cannot in general be neglected and is strongly dependent on the structural geometry of the fibre-fibre crosses. Also, the stress state in the interface centroid was estimated in order to quantify how the mode of loading influence the amount of normal stresses that develop in relation to the amount of shear stresses in the interfibre joint. / De brottmekaniska egenskaperna hos fiberfogar är nyckeln för uppbyggnaden av styrka hos fibrösa material såsom papper och kartong. För att effektivt skräddarsy sådana materials egenskaper genom kemisk eller mekanisk behandling och för att förstå hur sådana modifieringar påverkar egenskaperna på en mikroskopisk nivå är provning av individuella fiber-fiber-kors en allmänt använd metod. Belastningen i en fiberfog vid provning av individuella fiber-fiber kors är dock generellt mycket komplicerad och ytterligare kunskap om hur fiberfogars mekaniska egenskaper skall utvärderas är önskvärd. I Artikel A, presenteras en metod för samtidig tillverkning av flera fiber-fiber kors samt en metod för mekanisk provning av dessa med olika typer av belastning. Metoden tillämpades för att studera styrkan av fiber-fiber-kors med olika geometri och vid två olika lastfall. En undersökning av hur torktrycket, torkmetoden samt graden av malning inverkar på fogstyrkan presenteras. De uppmätta brottlasterna skalades med olika karakteristiska längder för fogen; nominell överlapparea samt fogens längd och bredd. Resultaten visade att ingendera av normaliseringsmetoderna reducerade variationskoefficienten (av medelvärdet av styrkan) samt att brottlasten för en globalt fläkande belastning var omkring 20 % av brottlasten för prov utförda med den konventionella skjuvande belastningen. I Artikel B, presenteras en metod för utvärdering av mätningar av styrkan hos fiberfogar med hänseende på kraft- och moment- resultanterna i gränsytan mellan fibrerna. Metoden används för att studera belastningsmoden hos fiber-fiber--kors provade i två principiellt olika lastfall. Resultaten visar att för ett typiskt fiberfogsprov av isolerade fiber-fiber-kors med långa fria fibersegment, så kan inte belastningsmoderna vid sidan av skjuvning försummas och att de är starkt beroende av fiber-fiber-korsets geometri. För att kunna jämföra fiberfogar av olika storlek och kvantifiera förhållandet mellan normal- och skjuvbelastningen i fogen skalades de resulterande krafterna och momenten med tvärsnittsstorheter baserade på en approximation av fogareans utformning. / <p>QC 20130125</p> / BiMaC Innovation