Dissertations / Theses on the topic 'Softwood kraft pulp'

The objective of this work was to explore fundamental aspects of utilizing (DZ) and (ZD) bleaching stages in the prebleaching of oxygen delignified Scandinavian softwood kraft pulp, and compare paper properties of fully bleached pulps with a DEoD₁ED₂ bleached EDF reference pulp. According to the literature, the use of chlorine dioxide and ozone in combination in (DZ) and (ZD) bleaching stages seems advantageous from both environmental and economical points of view. A significant reduction in the formation of chloro-organic compounds and efficient delignification relative to chemical consumption is obtained.

Abstract Washing during kraft pulping can be divided into two separate areas each with its own distinct features: namely brownstock washing and washing in bleaching. Research interest has so far concentrated mostly on investigating brownstock washing and factors affecting its efficiency. Pulp washing in bleaching, however, has been practically neglected. The basic phenomena are the same as in brownstock washing, but there are differences which have not been taken into consideration to a sufficient extent. This less explored area is the focus of this research. In this thesis, it is shown that brownstock washing and pulp washing between bleaching stages are distinct areas with their own specific features. They differ for example in terms of the composition and molecular size of the impurities in the pulp suspension. Various process conditions, pH, temperature and so on cause further differences between washing in bleaching and brownstock washing. The removal of specific compounds can be clearly affected by the appropriate selection of wash liquor. It is shown that the dynamic behaviour during washing is different for different compounds and depends on the properties of the wash water. The key element is to find the most harmful compounds in specific positions in bleaching and on the basis of that finding, to determine the most suitable wash liquor system. Chemical oxygen demand (COD) is a widely used method for evaluating the washing result, but as a collective measurement variable it does not describe the actual compounds that cause the "loss" of bleaching chemicals. Studies have shown that many compounds contribute to COD load but ultimately most of them have no real effect on the bleaching result. A suggestion for more precise definition of wash loss is offered than COD.

For paper producers, an understanding of the development of strength properties in the paper is of uttermost importance. Strong papers are important operators both in the traditional paper industry as well as in new fields of application, such as fibre-based packaging, furniture and light-weight building material. In the work reported in this thesis, three approaches to increasing paper strength were addressed: mixing different pulps, multilayering and reinforcement with man-made fibres. In specific: The effects of mixing Swedish softwood kraft pulp with southern pine or with abaca (Musa Textilis) were investigated. Handsheets of a softwood kraft pulp with the addition of abaca fibres were made in a conventional sheet former. It was seen that the addition of abaca fibres increased the tearing resistance, fracture toughness, folding endurance and air permeance. Tensile strength, tensile stiffness and tensile energy absorption, however, decreased somewhat. Still it was possible to add up to about 60% abaca without any great loss in tensile strength. As an example, with the addition of 30% abaca, the tear index was increased by 36%, while the tensile index was decreased by 8%. To study the effect of stratification, a handsheet former for the production of stratified sheets, the LB Multilayer Handsheet Former was evaluated. The advantage of this sheet former is that it forms a stratified sheet at low consistency giving a good ply bond. It was shown to produce sheets with good formation and the uniformity, evaluated as the variation of paper properties, 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 is generally at the same level as of those produced in conventional sheet formers. The effects of placing southern pine and abaca in separate layers, rather than mixing them homogeneously with softwood pulp were studied. Homogeneous and stratified sheets composed of softwood and southern pine or softwood and abaca were produced in the LB Multilayer Handsheet Former. It was found that by stratifying a sheet, so that a pulp with a high tear index and a 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%. Further, by mixing a pulp with less conformable fibres and no fines with a pulp with more flexible fibres and fines, a synergy in tensile strength (greater strength than that predicted by linear mass fraction additivity) was obtained. The effects of stratifying sheets composed of softwood and abaca were compared to the effects of refining the softwood pulp. Homogeneous and stratified sheets composed of softwood with three different dewatering resistances and abaca were also produced in the LB Multilayer Handsheet Former. It was found that by stratifying the sheets the tear index was retained while the tensile index was increased by the refining. The effects of reinforcing softwood pulp of different dewatering resistances with man-made fibres with low bonding ability were also investigated. Man-made fibres (i.e. regenerated cellulose, polyester and glass fibres) were added in the amounts 1, 3, or 5 wt% to softwood pulp of three different dewatering resistances. It was found that with refining of a softwood pulp and subsequent addition of long fibres with low bonding ability the tensile-tear relationship can be shifted towards higher strength values. The bonding ability of the man-made fibres was evaluated by pull-out tests and the results indicated that, in relation to the fibre strength, regenerated cellulose (lyocell) was most firmly attached to the softwood network while the glass fibres were most loosely attached.

The aim of this Master thesis was to investigate if the xylan content had any influence on the physical properties of softwood kraft pulps. To achieve pulps with different xylan content different kraft cooking conditions were used; two different temperatures and two different effective alkali levels. The cooking conditions used were 160°C with 30% effective alkali (EA) referred to as reference cook and 145°C with 17% effective alkali (EA) referred to as the mild cook. The first step in this study was to determine the cooking time needed for reaching a certain kappa number, i.e.30. It was also determined whether the difference in xylan content between the pulp samples was sufficient when these cooking conditions were used. When the correct cooking time and cooking conditions had been found new cooks were made using these conditions. All cooks were made at a liqour to wood ratio of 4:1.   The difference in xylan content between the corresponding pulp samples was found to be 3%. The physical testing showed no significant difference in the tensile strength between the two pulps after beating. There was a difference in tear index however and the pulp with the highest content of xylan had the lowest tear index. Zero-span index was the same for the two pulps when unbeaten. After beating the zero-span index decreased for the pulp with highest xylan content but stayed unchanged for the pulp with the lower amount of xylan. These results can be explained by the results from the fibre analysis which showed that the fibres with high xylan content were longer, thicker and had a higher coarseness. Thicker fibres are probably stiffer than thinner fibres which gives the paper fewer bonding points and a lower strength. The result from the zero-span test indicated that the fibres with higher xylan content are affected more by beating than fibres with the lower xylan content.
Målet med examensarbetet var att undersöka om och hur mycket xylaneti pappersmassan påverkar fiberns och därmed papperets fysikaliska egenskaper. Egenskaperna som undersöktes var drag- och rivstyrka samt zero-spanstyrka. Xylaninnehållet skulle varieras genom att kokförhållandena förändrades dels genom olika koktemperaturer dels olika satsningar av effektivt alkali vid given sulfiditet. Dessa var 160ºC med 30% effektivt alkali(EA) hädanefter benämnd referenskoket och 145ºC med 17% effektivt alkali(EA) som benämns det milda koket i fortsättningen.En bestämning av koktiden gjordes för att nå 30 i kappatal och två provkok, ett vid varje temperatur behövde göras.Skillnaden i xylanhalt mellan de slutliga massaproverna låg på c:a 3% enheter.   Styrkeproverna gav inga entydiga svar på om skillnaden i xylanhalt gav någon effekt på massastyrkan. Dragproverna visade att för omald massa var massan från referenskoket starkast men att massan från det mildare koket reagerade kraftigare på malningen. Redan vid 1000 varv hade den i princip samma dragindex som referensmassan vid samma malgrad. Zero-span mätningarna visade att fibrerna hade samma styrka när de var omalda.   Resultaten från fiberanalysenverifierade resultaten från styrketesterna eftersom en tjockare fiber bör ge en styvare fiber och därmed erhålls färre bindningspunkter.  Färre bindningspunkter ger en lägre dragstyrka och det krävs mindre energi för att bryta bindningarna. Efter malningen kan man se att zero-span styrkan har minskat betydligt för massan med högre xylanhalt medan referensmassan behöll styrkan. Dessutom har dragstyrkan ökat för båda massorna men mest för massan med högre xylanhalt. Det kan förklaras med att malningen ger små fibriller på ytan av fibern och en mjukare och böjligare fiber. Därmed ökar bindningsstyrkan då bindningsarean ökar och fibern blir mjukare och böjligare. Den ökade bindningsgraden samt den minskade fiberstyrkan kan förklara varför rivindex fortfarande var lägre för massan med högre xylanhalt trots att dragindex ökade med ökad malning.En annan förklaring kan vara att vid ett långt kok med låg temperatur är det troligt att lignin adsorberas på fibrerna.Ligninet på ytan ger en sämre bindningsförmåga vilket leder till att de är lättare att dra ur nätverket med lägre energiåtgång som följd.

Modification of softwood kraft pulp by the addition of either polysulfide (PS) or sodium borohydride (NaBH4) has been shown to increase the pulp yield due to a higher retention of glucomannan.  The pulps with higher yield gave a paper with higher tensile index than reference pulp, especially at lower degrees of refining. The higher yield pulps also showed a greater porosity of the fibre wall, indicating an increase in the swelling potential of the fibres. This can lead to increased fibre flexibility and increased joint strength between the fibres and to the higher handsheet tensile index. However, the swelling increase associated with the higher hemicellulose content could also make dewatering more challenging because of the higher water retention of the pulp. The results of this study show however that the positive influence of the increase in yield (fewer fibres and a more open sheet structure) dominates over the negative influence of the higher hemicellulose content on the dewatering properties, especially at lower refining energy levels. Studies simulating full-scale tissue machine dewatering conditions showed that pulps with a higher yield and a higher hemicellulose content had a higher tensile index at the same dryness. Moreover, the same dryness level was achieved in a shorter dwell-time. A given tensile index was also achieved with less refining energy. Increasing the yield and hemicellulose content by the addition of either an oxidizing or a reducing agent in the softwood kraft pulping process thus has a potential for giving high quality fibres for tissue paper production with less refining energy and lower drying energy costs.

Vid tidpunkten för framläggningen av avhandlingen var följande delarbeten opublicerade: delarbete 2 inskickat.

At the time of the defence the following papers were unpublished: paper 2 submitted.

The purpose of this bachelor thesis was to investigate how charged groups within the pulp fibre affect the beatability and the strength of the papers. To obtain different levels of charges on the pulp it was carboxymethylated. The different pulp samples were beaten to different degrees to investigate how charges interact with the beating. A PFI-mill was used for the beating because of the relatively homogenous effect on the fibres and the low demand for pulp fibres for each beating. The influence of the amount of charged groups on the surface and bulk swelling, as a result of the beating process, was evaluated.   The fibres were then analysed in a Fibre tester and using a microscope to see what had happened to the fibre structure.  The results showed that the PFI-mill mainly affects the surface of the fibres. The beatability, defined as the swelling obtain for a specific energy input, was greatly increased by the introduction of charges. It was also shown that there is a possibility to replace some of the energy input in the mill with the introduction of charges to obtain the same swelling and strength.   Paper sheets were formed from the different samples and some mechanical properties were analyzed. It was shown that the strength was initially improved by the introduction of charges but the improvement was partially lost during the beating. At the highest rate of beating the difference in strength between the samples had disappeared. This can be explained by the fact that the fibres, from the sample with highest number of charges, were destroyed. Microscopic images showed that the fibre was delaminated and at some sites there were extreme balloon-like swellings
Syftet med detta examensarbete var att undersöka hur laddade grupper hos massafibrer påverkar malbarheten och styrkan hos de papper som tillverkats av dessa fibrer. För att skapa olika laddningsnivåer karboxymetylerades viss del av massan för att introducera laddade grupper, två delar av ursprungsmassan karboxymetylerades och en del användes som referensmassa.  De olika massaproverna maldes i olika nivåer för att undersöka hur laddningarna och malningen interagerade. En PFI-kvarn användes för att mala fibrerna då det endast krävs små mängder fibrer och denna typ av kvarn påverkar fibrerna relativt homogent. Fibrerna analyserades sedan i en Fibre tester och med ett mikroskop för att se vad som hade hänt med fiberstrukturen. Resultaten visade att en PFI-kvarn till största delen påverkar fibrernas yta.  Malbarheten, som definierades som den svällning som åstadkoms vid en viss energiinsats i form av malvarv i kvarnen, ökades markant då ytterligare laddningar fanns närvarande i fibrerna. Det visades också att det går att ersätta en del av malningen med introduktion av laddningar till fibrerna för att uppnå samma svällning och styrka. Pappersark tillverkades därefter av de olika massatyperna och några mekaniska egenskaper testades. Det visades att styrkan ökades initialt av introduktionen av laddningar men denna förbättring minskade vid malningen. Vid den högsta malgraden hade skillnaden mellan de olika massorna försvunnit. Det kan förklaras av att fibrerna, från den massatyp med mest laddningar, hade förstörts. På vissa ställen hade fibern helt delaminerats och extrema ballonglika svällningar fanns.

Converting wood into paper is a complex process involving many different stages, one of which is pulping. Pulping involves liberating the wood fibres from each other, which can be done either chemically or mechanically. This thesis focuses on the most common chemical pulping method, the kraft cooking process, and especially on a recently developed improvement of the impregnation phase, which is the first part of a kraft cook.

Extended impregnation kraft cooking (EIC) technique is demonstrated to be an improvement of the kraft pulping process and provides a way to utilize softwood to a higher degree, at higher pulp yield. We demonstrate that it is possible to produce softwood (Picea abies) kraft pulp using a new cooking technique, resulting in a pulp that can be defibrated without inline refining at as high lignin content as 8% on wood, measured as kappa numbers above 90. Lignin is the wood constituent that holds the wood fibres together in the wood matrix. The new cooking technique uses the differences in reaction rate between the diffusion and consumption of hydroxide ions; it is used to ensure a homogenous impregnation of wood chips at lower impregnation temperatures and longer impregnation times than are generally used in the industry. The applied cooking temperatures are also substantially lower than those used in conventional kraft pulping systems, promoting uniform delignification. This results in a narrower kappa number distribution than in lab-cooked conventional kraft pulp.

High-kappa-number pulps were investigated for pulp sheet properties such as tensile strength, tensile stiffness, and compression strength. It was demonstrated that an EIC pulp of kappa number 95 has strength properties comparable to those of a conventional pulp of kappa number 82. Comparing the effects of starch multilayers on conventional and EIC pulps reveals similar effects. The use of the starch multilayer treatment increased the tensile index and decreased the tensile stiffness and short-span compression test (SCT) indices.

The EIC technique has also been used to produce a series of bleachable-grade pulps. The results indicate the possibility of increasing the lignin content of the pulp entering the oxygen delignification stage, since the reject content of gently defibered pulp is lower than 0.1% at kappa number 49.

In this thesis, we recommend that wood chips be impregnated for 2 h at 110 °C to neutralize acidic compounds in the wood and impregnate the chips with cooking chemicals, and that the ensuing cook be performed at 135–140 °C, depending on the target kappa number. We also recommend increasing the available amounts of cooking chemicals in the impregnation stage by using a higher liquor-to-wood ratio and keeping the alkali profile fairly high in the ensuing cook. This concept will reduce the amount of reject material, increase the pulping uniformity, and increase the selectivity towards lignin degradation in the kraft cook.

Omvandling av ved till papper är en komplicerad process som består av många olika steg där ett är massaframställningen (eng. pulping). Massaframställning medför att vedfibrerna frigörs från varandra på kemisk eller mekanisk väg. Denna avhandling fokuserar på den vanligaste kemiska metoden, sulfatkokning och speciellt den nyligen utvecklade förbättringen av impregnerings fasen, som är den första delen av ett sulfatkok.

Här visas att Extended Impregnation kraft Cooking (EIC) innebär en förbättring av sulfatkokningen och ett sätt att uppnå högre vedutnyttjande vid högre utbyte för barrved. Vi visar att det är möjligt att producera barrvedsmassa med en ny kokningsprincip som resulterar i en massa som är defibrerbar utan inline-raffinering vid så högt lignin innehåll som 8% (på ved), mätt som kappatal över 90. Lignin är den vedkomponent som håller ihop vedfibrerna i vedmatrisen. Kokningsprincipen utnyttjar skillnaderna i reaktionshastighet mellan diffusion och konsumtion av hydroxidjoner och nyttjas till att skapa en homogen impregnering av vedflisen vid lägre impregneringstemperatur och under längre tid än vad som vanligen används i industrin. De använda koktemperaturerna är också betydligt lägre än vid konventionell sulfatkokning vilket gynnar jämn delignifiering. Detta resulterar i en smalare kappatalsfördelning jämfört med laboratoriekokade konventionella massor.

Massor med höga kappatal undersöktes med avseende på egenskaper hos handark, såsom dragstyrka, dragstyvhet och kompressionsstyrka Det visades att handark från EIC massa vid kappatal 95 hade jämförbara styrkeegenskaper med konventionell massa vid kappatal 82. Vid jämförelse av effekten av stärkelse multilager på konventionella och EIC massor avslöjar liknande effekter. Användningen av stärkelsemultilager ökade dragindex och minskade dragstyvhets- och kompressions index (SCT, short-compression test).

Kokprincipen har även använts för att ta fram en serie blekbara massor. Resultaten visar på möjligheten att öka lignininnehållet i massan in till i syrgasdelignifierings-steget eftersom spetinnehållet för milt defibrerad massa var lägre än 0,1% vid kappatal 49.

I den här avhandlingen rekommenderar vi att vedflis impregneras i 2 timmar vid 110 °C för att neutralisera sura komponenter i veden och impregnera flisen med kokkemikalier, samt att utföra det efterföljande koket vid 135–140 °C beroende på önskat kappatal. Vi rekommenderar även att öka den tillgängliga mängden kokkemikalier i impregneringssteget genom att använda högre vätske-ved förhållande och att hålla alkali profilen relativt hög i det efterföljande koket. Detta koncept reducerar spetmängden, ger jämnare kokning och ökar selektiviteten för nedbrytning av lignin i sulfatkoket.

The aim of this work is to contribute to the process development of the ECF light bleaching sequence Q(OP)D(PO) by providing a better understanding of the bleaching of softwood kraft pulp. There are few published studies on this type of sequence, and more knowledge is needed on how to reduce environmental impact, improve cost-effectiveness and ensure a high pulp quality. Firstly, this research showed that using a pH buffer to stabilize the pH at a near-neutral level during bleaching with chlorine dioxide can lower the formation of adsorbable organically bound halogens (AOX) without altering the bleaching efficiency. A near-neutral pH decreases the formation of strongly chlorinating species so that the AOX content in the bleaching effluents is reduced by up to 30%. The increased pH in the near-neutral pH D stage compared with the reference lowered the chlorine dioxide consumption, resulting in a higher kappa number and viscosity. A lower degradation of hexenuronic acid correlated well with a lower AOX content in the effluents, affirming earlier theories that hexenuronic acid has an important impact on AOX formation. Secondly, this research aimed at studying bleachability in (OO)Q(OP)D(PO). The bleachability was defined as delignifying and brightness gain bleachability, which is suited to ECF light bleaching sequences. The delignifying and brightness gain bleachability were used to evaluate the stages in (OO)Q(OP)D(PO) in regard to the unbleached kappa number. When comparing different stages, it is possible to distinguish the bleaching efficiency in each stage. For this ECF light sequence, the bleachability depends on the purpose of the stage. It was found that in the stages that are mainly delignifying (OO and D), a higher unbleached kappa number is beneficial for the delignifying bleachability, although the brightness gain is not improved. However, in the stages that are mainly brightness increasing (OP and PO), the brightness gain bleachability is improved by a lower unbleached kappa number. Thirdly, the bleaching of the pulp samples in this study with the ECF light sequence was most effective with a kappa number around 32 after cooking. Although an even higher kappa number resulted in a higher yield after cooking, it seemed that this bleaching sequence cannot preserve the yield gain. Kappa number 32 also gave the best results in regard to brightness ceiling and viscosity. On the other hand, kappa number 27 was the most favourable with regard to yellowing and chemical charge.

Examinator: Helena Håkansson, lektor, Karlstads universitet

One of the problems encountered in paper converting is caused by the occurrence of "baggy webs", which essentially is when the tension profile of the paper web is uneven. In an area with low tension the paper is longer, which results in bagginess. The baggy parts can not usually be stretched to even out the tension of the paper web in a converting machine, with the result that runnability problems are likely to occur. The aim of the work described in this thesis was to investigate three particular stages in papermaking, namely drying, calendering and storage, and rank them according to their propensity for inducing baggy webs. The focus was placed on investigating the effects of uneven moisture and grammage profiles on the machine-direction strain difference profile. The largest strain difference occurred when there were systematic thick streaks throughout a reel that formed ridges. Stress relaxation during storage then gave rise to a difference in strain of 0.14% when the ridge height was around 2-3 mm. Thickness variations due to variations in grammage is also a source of moisture variation. A difference in moisture of 5% in the calendering stage resulted in strain differences of about 0.05-0.08%. These strain differences resulted in creases being formed as early on as in the calender nip when differences in both grammage and moisture content were present. Most creases appeared when the moisture difference was 2-8%. The difference in grammage could be large without creases being formed when no differences in moisture content were present. A moisture difference of about 5-6% during drying resulted in a strain difference of 0.1% measured on isotropic samples. The moist area turned into a tight streak when the moisture difference appeared at moisture contents higher than 25%. At moisture contents lower than 20%, on the contrary, the moist area turned into a slack streak. The conclusion drawn is that papermakers should concentrate first and foremost on eliminating variations in grammage, especially if these are systematic. This would also eliminate some variations in moisture content, which would solve more problems.

Dynamic (or 2D) FT-IR spectroscopy in combination withpolarized IR irradiation has been used in this work to studywood polymer orientation and interactions on theultrastructural level in wood fibers in the native state aswell as the effects of different pulping processes. The woodpolymer interactions were studied under both dry and humidconditions.

The matrix of lignin and hemicelluloses located between thewell-ordered cellulose fibrils in the wood cell wall of sprucewas here shown to be more highly ordered than has earlier beenrevealed. It was confirmed that glucomannan is orientedparallel to the cellulose fibrils and is highly coupled to it.The lignin was also shown to have a main orientation in thestructure although this is probably not as strong as that ofglucomannan. The orientation of the lignin may derive from thefact that the polysaccharides act as templates during thelignification of the cell wall. This organization implies thatnot only the cellulose but also the lignin and thehemicelluloses have different mechanical properties in thelongitudinal and cross-fiber directions.

The ability to gain molecular information on the stresstransfer in polymers with dynamic FT-IR spectroscopy made itpossible to verify experimentally earlier molecularcalculations on the stress transfer within the cellulose chain.It was also possible to show, on the molecular level, thedominant importance of the cellulose fibrils for the stresstransfer in the longitudinal direction of pulp fibers,including lignin-rich mechanical pulp fibers. The glucomannanof softwood fibers was also shown to participate in the stresstransfer in the fiber direction indicating a close associationwith the cellulose, whereas the xylan showed no dynamicresponse. Already under dry conditions, the lignin was shown tohave a more viscoelastic response than the polysaccharidesduring the loading of pulp fibers and it was thus able to moveindependently of the cellulose.

The enhanced spectral resolution obtained with dynamic FT-IRspectroscopy made it possible to study the crystalstructure/chain order of cellulose in pulp fibers. Thepossibility of following changes in the relative cellulose Iallomorph composition of pulp fibers was demonstrated for somechemical pulps.

Dynamic FT-IR experiments under humid conditions and ofelevated temperatures made it possible to study the softeningof the biopolymers in their native environment. This was alsodemonstrated for some different pulps, and this may be apromising tool for obtaining viscoelastic information on themolecular level in composite systems such as wood fibers.

Keywords:cellulose, cooperation, crystallinity, dynamictest, glucomannan, hardwood, holocellulose, humidity, infraredspectroscopy, kraft pulp, lignin, mechanical pulp, orientation,polarised light, softwood, strain, sulphite pulp,viscoelasticity, xylan

This study first examined the kinetic changes of fiber carboxyl group content in bulk fiber, polysaccharide, and residual lignin of oxygen delignified pulps during one-stage oxygen delignification of a low kappa (32.5) kraft pulp. The carboxyl group contents determined in different chemical components of oxygen delignified pulps was used to establish the distribution of carboxyl groups in lignin and pulp polysaccharide and decouple the responses from residual lignin and polysaccharide. Following this study, two high kappa (~ 49.0) SW kraft pulps prepared were delignified through two-stage oxygen delignification. Fiber carboxyl group profiles of these pulps were elucidated to investigate the effect of lignin content of incoming unbleached kraft pulps on fiber carboxyl group formation. Due to a limitation to enhance fiber carboxyl groups only by parameter optimization during one- and two- stage oxygen delignification, a catalytic oxidation program was developed to enhance fiber carboxyl groups by 52.2 116.0 % employing 0.10 - 0.18% of a bismuth ruthenium pyrochlore oxide catalyst during oxygen delignification. The mechanism of fiber carboxyl group formation through the catalytic oxidation was proposed. The main factor on carboxyl group formation in pulp carbohydrate was identified to follow the order: NaOH > oxygen pressure> reaction temperature through a 3-factor at 3-level (L933) orthogonal experimental design and the optimal conditions were found at 2.5% NaOH, 85-100 oC, and 800-960 kPa O2 during the catalytic oxidation. ECF bleaching study was also conducted on these pulps with higher amount of fiber carboxyl group enhanced at early pulping and oxygen delignification processes. The bleaching results demonstrated that the early-stage enhanced fiber carboxyl groups were partially retained through ECF bleaching. Additionally, fiber carboxyl groups of fully bleached kraft pulps were ~ 20% different from typical bleaching protocols, depending on bleaching chemicals used and the bleaching sequences such as DEDED, (D+C)EDED, ODEDD, and OQPZP. This study finally demonstrated that an increase of fiber carboxyl groups by 17.4-62.1% through chemical oxidation resulted in reduced fiber curl, increased fiber WRVs, 4.3-25.5 % increase in paper tensile index at comparable pulp viscosity; and 4.4 -30.1% increase in paper dry tensile stiffness.

An experiment was designed to test the hypothesis that each softwood pulp is unique and requires a specific, well defined mechanical treatment to derive its maximum strength potential. Three bleached softwood Kraft pulps and respective wood samples were sourced from both the Northern and Southern Hemispheres. The raw fibre characteristics of P. patula (Southern Hemisphere), P. menziesii (Northern Hemisphere) and P. mariana (Northern Hemisphere) were measured and compared. The raw pulp sheets were refined at different energies and intensities under controlled laboratory conditions using a 12” single disc pilot refiner. Results were assessed to determine the raw fibre characteristics, optimum refining conditions and the relative refined strength potential for each of the three samples. Results from anatomy measurements on the three wood samples differed significantly. P. patula exhibited a relatively high proportion of springwood growth in the early growing years. As the P. patula aged and formed mature wood there was a significant increase in the frequency of latewood formation. This was characterized by an abrupt and significant increase in the wall thickness, beyond that of the two Northern softwood samples. When the cell wall thickness increased, the lumen width and fibre diameter of the P. patula decreased significantly, yielding extremely coarse, stiff fibres. The Northern P .mariana and P. menziesii samples were characterized by a relatively consistent transition between high and low densities from the pith to the bark of the tree. The Southern P. patula had a unique density trend with an increasing frequency of high density peaks indicative of an increased latewood formation from the pith to the bark. The slower growing Northern P. menziesii and P. mariana samples did not have as clear a differentiation in fibre characteristics between juvenile and mature wood formation. The Northern samples did however contain a significantly higher proportion of juvenile latewood growth than the P. patula. However, the difference in fibre characteristics between earlywood and latewood formation was not as significant as that noted with the Southern P. patula Fibre morphology measurements on the unrefined bleached Kraft pulps also revealed significant differences between the three samples. The average MORFI LAB01 results on the P. patula defined fibres with a high coarseness and relatively low number of fibres per gram of pulp. The extremely coarse latewood fibres formed during mature wood growth being the most likely source. However, P. patula was also characterized with a high fibre flexibility and large lumen, characteristics consistent with earlywood fibres. The Pulmac Z-Span 3000 was used to define the individual fibre strength, when due consideration was given to the number of fibres per gram, the corrected Pulmac results suggested P. patula had the strongest fibres. When refined, using a standard disc refining programme, P. patula exhibited a fast freeness development. Conventional thinking would suggest that this was an indication of a weaker fibre. However, this species had a robust morphology compared to the Northern Hemisphere woods. The theory developed in this dissertation suggests that the effect of coarseness and the concomitant number of fibres per gram plays a significant role. These two parameters are not included in the “traditional” refining calculations. The applied refining load and intensity was calculated on the flow of the pulp passing through the refiner. The calculation did not consider the actual number of fibres present in that specific volume. The implication is that when a fixed refining load is applied to a pulp with coarse fibres there may be a higher effective load on those fewer fibres (resulting in fibre cutting and fines generation). In this case, the Northern samples have a comparatively low coarseness and more fibres per gram with each receiving a smaller portion of the total load and intensity. In terms of refined pulp properties, P. patula developed a relatively high bulk and tear index consistent with coarse, rigid fibres. The Northern P. mariana and P. menziesii samples produced a pulp with good tensile properties, consistent with a greater number of finer, collapsible fibres with a higher relative bonding area. P. patula fibres were extremely heterogeneous in nature containing the smallest relative lumen width during latewood formation and the largest lumen width during earlywood growth. As a result, P. patula contains extremes of both fine and coarse fibres in the same blend. It may be more beneficial for this species than the others to improve both the tear and tensile properties through fibre fractionation with appropriate development of the separate accepts and rejects streams. In terms of fibre development, low intensity refining parameters maximized the tensile strength of the Southern P. patula. The Northern P. mariana and P. menziesii samples had a greater number of fibres per gram of pulp requiring both a higher refining energy and intensity to develop the pulp to its maximum potential. To develop optimum tear results, high intensity refining, with a relatively low specific energy provided optimum results for all 3 samples. Results confirmed that there were significant differences in the fibre morphology both between the three different species and between the two Hemispheres. There was strong evidence that the fibre characteristics dictate the manner in which a fibre responds to refining which in turn determines the relative contribution to specific refined pulp properties. It may be possible to use fibre characteristics to determine the appropriate refining parameters for optimal fibre development which will enhance the value of the end product. To derive the maximum strength potential from P. patula pulp samples, it is recommended that further studies investigate Hydracyclone fractionation and the concomitant benefits of refining the separate streams. Furthermore, a separate study on fibre morphology and refining characteristics of the same species grown in both the Northern and Southern Hemisphere would provide valuable insight.
Thesis (M.Sc.Eng)-University of KwaZulu-Natal, Durban, 2009.

For over a decade, the kraft pulp and paper industry has been challenged to find bleaching sequences that produce bright, high quality pulp without causing detrimental effects on the receiving environment. Historically kraft pulp was bleached with elemental chlorine and other chlorine containing compounds. However, after the discovery of toxic chlorinated organics in bleached kraft mill effluents, industry has tried to limit the use of these chemicals. Pretreatment of kraft pulps with the enzyme xylanase, a hemicellulase that degrades the xylan component of hemicellulose, has been shown to enhance the efficiency of the subsequent bleaching stage. In this study the application of xylanase in a totally chlorine-free (TCF) bleaching sequence was examined using three commercial xylanase preparations and kraft pulps derived from Douglas-fir, western hemlock and cedar woods. The activity of the xylanases Pulpzyme HB, Pulpzyme HC and Irgazyme 40 was compared in order to determine the enzymatic loadings required for the bleaching trials. The kraft pulps were treated with these enzymes (X) in two types of multiple peroxide (P) bleaching sequences (XQPP or QPXP) which included one chelation (Q) stage. The same experiment was repeated with oxygen delignified kraft pulps (OXQPP or OQPXP). The enzyme activity on the pulp was verified by monitoring increases in carbohydrate and UV-absorbing material in the filtrates collected immediately following the xylanase treatment. It was apparent that neither oxygen delignification nor peroxide bleaching inhibited the solubilization of sugar and UV-absorbing materials by the enzymes. Although the xylanases caused a range of brightening effects, direct brightening could be achieved for all of the partially bleached pulps, but not for the kraft brownstocks. In most cases, xylanase treatment directly delignified the brownstock, oxygen delignified and partially bleached pulps. Of the three xylanases, pretreatment with Irgazyme 40 elicited the most consistent bleaching improvements. Kraft pulp derived from cedar reached the highest brightnesses after oxygen delignification for both bleaching sequences tested. After xylanase pretreatment there appeared to be no detrimental effect on fiber strength for any of the bleaching trials. The final component of this work examined the toxicity, as monitored by Daphnia magna and Microtox, of the filtrates derived from the pulps after xylanase treatments and peroxide bleaching. The filtrates collected immediately after the xylanase stage were predominantly non toxic, the exceptions being those collected following the OQPX sequence. The toxic response elicited by the combined filtrates was found to be caused primarily by residual peroxide. In modern mills the residual peroxide is neutralized and is therefore not usually a problem. In many cases, xylanase pretreatment, in conjunction with the TCF bleaching sequence used for this study, improved final pulp brightness by 1-1.5 % ISO. Although this improvement in final brightness was variable, optimization of enzyme conditions could further enhance the applicability of xylanase in industry.