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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
481

As yet uncertain: a portrait in procession

Helmers, Thomas Richard 01 May 2016 (has links)
As Yet Uncertain: A Portrait in Procession is an installation of prints featuring a combination of image and text. Drawing inspiration from various depictions of the grotesque in art and literature, the project examines the grotesque form, both in body and mind. As Yet Uncertain: A Portrait in Procession observes how the grotesque—a body that is always in the act of becoming—relates to uncertainties and ambivalence in identity and humanity.
482

中國鈔票之總檢討

DENG, Gan Sheng 20 June 1936 (has links)
No description available.
483

Production and application of fine fractions made of chemical pulp for enhanced paperboard strength

Björk, Elisabeth January 2020 (has links)
For all kinds of paperboard packages, the bending stiffness of the paperboard is a crucial property. In multi-ply folding boxboard (FBB) grades, this is obtained by placing different stocks in the outer and centre plies of the board. In the outer plies, a stock with a high tensile stiffness is used, typically made from refined kraft pulp fibres. In the middle ply/plies a stock with more bulky properties is placed, typically comprising of a high proportion of CTMP (chemi-thermomechanical pulp). CTMP fibres are stiffer and more inflexible with poor bonding abilities resulting in low strength properties. To increase the bonding strength in the middle ply, broke, containing chemical pulp is added, and sometimes refined chemical kraft pulp as well. Both fibres and fines, i.e. smaller fibre fragments, in a pulp have a significant contribution to the properties of the product. Fines produced during refining of chemical pulp are especially beneficial for increasing the strength. To achieve pulp fraction with higher fines content the pulp can be fractionated with a micro-perforated screen basket; a fine fraction produced from a screen with very small holes will contain a large proportion of fines. By adding such a fine fraction to a middle ply stock, the bulk properties of the main pulp, for example a CTMP, can be conserved as less refining of this pulp is required to achieve the targeted strength properties. However, a drawback is that the fine fraction usually has a very low mass concentration after the screening process as a lot of water pass through the screen together with the fines and fibre fragments. The excess water must be removed to maintain the water balance of the papermaking process. Further, the larger volumes require extra pumping capacity. A resource-efficient production of a fine fraction must target a high fine fraction mass concentration and a high content of fines and short fibre fragments in order to be implemented industrially. The focus of the present work was on separation efficiency (i.e. the difference in fibre length distribution caused by screening) and process efficiency (i.e. the concentration of the fine fraction) for production of a fine fraction of chemical pulp by screening, and the utilisation of the fine fraction as strength agent. Pilot-scale fractionation trials with a pressure screen with different microperforated screen baskets were performed in order to evaluate how the separation efficiency and process efficiency were affected by parameters such as feed concentration, pulp type (hardwood or softwood kraft pulp), hole size of the screen, and refining treatment prior to screening. The trials were evaluated using fibre length distributions, flow rates and concentrations of viii the feed flow and the fractions. Here, two complementary quantitative measures, Proportion in fine fraction (for process efficiency) and Fine fraction enrichment (for separation efficiency), were developed. To evaluate the strength enhancing effect of the obtained fine fraction, a lab scale study was performed where the fine fraction of a highly refined pulp was compared with the highly refined pulp as strength agent for a CTMP. The results of this study were verified in a pilot paper machine trial. In a second pilot paper machine trial, sheets with different CTMP proportions in the middle ply were studied in order to find out if the bulk could be increased while maintaining strength, by using a fine fraction made from refined chemical pulp. Regarding process efficiency, it was found that the most important parameter to obtain a high fine fraction concentration was a high feed concentration. Further, a higher fine fraction concentration for a given screening process was also obtained when using hardwood pulp and refining the pulp prior to the screening process. A higher feed concentration also had a positive effect on the separation efficiency. Small holes and a smooth surface of the screen basket were also important to improve the separation efficiency. It was shown that, when used as a strength agent in a CTMP pulp, the fine fraction of highly refined kraft pulp was twice as efficient as the highly refined kraft pulp, when added at equal mass proportion. However, both in the lab and pilot trial the strength increase was accompanied by a decreased bulk. This was expected, and to avoid this the proportion of the bulky CTMP had to be increased. The pilot paper machine trial with an increased CTMP proportion in the middle ply and a fine fraction of refined kraft pulp as strength agent demonstrated that it was possible to produce sheets with an increased bulk and maintained z-strength. / Böjstyvheten är en viktig egenskap för alla sorters hårda förpackningar. I flerskiktskartong får man böjstyvhet genom att ha ytterskikt med hög dragstyvhet tillverkade av fibrer från kemisk massa och ett mittskikt med hög bulk från styva fibrer, ofta med en stor andel CTMP (kemitermomekanisk massa). CTMP-fibrer är styva men ger lägre styrka i arket. För att öka styrkan i mittskiktet tillsätter man utskott (kasserad kartong) som delvis innehåller kemisk massa, och ibland även ren högmald kemisk massa. Både fibrer och finmaterial (fines) har stor betydelse för slutproduktens egenskaper. Fines som skapas vid malning av kemisk massa är särskilt effektiva för att öka styrkan. Genom att fraktionera massa med en mikroperforerad sil kan man få en finfraktion med högt finesinnehåll. Mikroperforerade silar är effektiva för längdfraktionering av massa; fines anrikas i den fraktionen som passerar silen medan långa fibrer stannar i den andra fraktionen. Genom att använda en sådan finfraktion i mittskiktet kan man få tillräcklig styrka och samtidigt behålla mer av bulken från CTMP:n genom att man inte behöver mala den för att få styrka. En nackdel är att finfraktionen vanligtvis har väldigt låg masskoncentration eftersom mycket vatten passerar silen tillsammans med fines och fiberfragment. Detta extra vatten måste tas bort för att vattenbalansen i papperstillverkningsprocessen ska bibehållas. Dessutom kräver den större volymen ökad pumpkapacitet. För att kunna använda en finfraktion industriellt behövs en effektiv produktion med hög koncentration och högt finesinnehåll. Fokus i det här arbetet lades på separationseffektivitet (skillnaden i fiberlängdsfördelning som resultat av silningen) och processeffektivitet (koncentrationen i finfraktionen) för tillverkning av en finfraktion av kemisk massa genom silning samt dess utnyttjande som styrkehöjande tillsats i ett mittskikt av kartong. För att utvärdera hur separationseffektiviteten och processeffektiviteten påverkas av parametrar som koncentrationen i flödet in till silen, typ av kemisk massa (gjord av lövved eller barrved), hålstorlek i silen samt malningen av massan, gjordes fraktioneringsförsök i pilotskala med en trycksil med olika mikroperforerade silkorgar. Resultatet av fraktioneringen utvärderades med hjälp av fiberlängdsfördelningar, flöden och koncentrationer i flödet till silen och de två fraktionerna efter silen. För utvärderingen togs två olika utvärderingsmetoder fram: Proportion i finfraktionen (för processeffektivitet) och Finfraktionsanrikning (för x separationseffektivitet). För att utvärdera hur effektiv en finfraktion av kemisk massa var som styrkeadditiv i ett CTMP-ark gjordes labbförsök där tillsats av högmald kemisk massa jämfördes med tillsats av enbart en finfraktion av den högmalda kemiska massan. Resultaten verifierades med ett försök på en pilotpappersmaskin. I ett följande försök på pilotpappersmaskinen tillverkades ark med ökat CTMP-innehåll för att öka bulken, och med en tillsats av en finfraktion av kemisk massa som styrkeadditiv. När det gäller processeffektivitet var hög koncentration i flödet till silen den viktigaste parametern för att få hög koncentration på finfraktionen. Detta var också positivt för separationseffektiviteten, färre av de längre partiklarna hamnade i finfraktionen. Vidare blev finfraktionens koncentration högre för lövvedsmassa. En finfraktion som ska användas som styrkeadditiv ska vara tillverkad av mald massa, malning av massan var också fördelaktigt för finfraktionens koncentration. Små hål och en slät yta på silkorgen var också positivt för separationseffektiviteten. Som styrkeadditiv i CTMP var finfraktionen av högmald kemisk massa dubbelt så effektiv som den högmalda kemiska massan vid lika stor tillsats. Men i både labbförsök och pilotförsök minskade bulken när styrkan ökade. Det var väntat eftersom att ersätta en del av originalmassan som har hög bulk, med en finfraktion eller högmald massa, som båda har mycket lägre bulk, alltid minskar bulken på arket. För att undvika en bulkförlust måste massasammansättningen i arket ändras. Försöket på pilotpappersmaskinen med ökat CTMP innehåll och en finfraktion av mald kemisk massa som styrkeadditiv visade att det är möjligt att tillverka ett ark med högre bulk och bibehållen styrka.
484

Papír / Paper

Plášil, Ondřej Unknown Date (has links)
The aim of this thesis is to create a portfolio of paper products with respect to established ethical principles. The resulting products must have a suitable design optimized for the manufacturing process. Based on the changes in sales over the past two decades, this work revises the current market position of paper. In addition, it generally examines the unethical communication of paper entities towards the end user. The result of this thesis is a range of products of two selected basic types - notebook and photo album. The overall results of my efforts, including this work, are likely to result in the creation of a new, own brand.
485

Pulp compositions and their influence on the production of dialcohol cellulose / Olika sammansättningar av pappersmassa och deras påverkan på produktionen av dialkoholcellulosa

Carlsson, Viktoria January 2020 (has links)
The characteristics of products made from pulp can be modified through different methods. If the pulp is refined either laboratory or industrially, the fibres in the pulp become more flexible and therefore creates stronger bonds to each other, which results in a final product with a higher strength. The refining process also causes the formation of small fibre pieces that are called fines, which also contribute to the increased strength. The major component in pulp is cellulose, which can be chemically modified to materials with changed properties. Periodate oxidation of cellulose results in dialdehyde cellulose that can be further reduced with sodium borohydride to obtain dialcohol cellulose, which is a material with a higher ductility compared to regular cellulose. In this thesis, different pulp compositions and their influence on the production of dialcohol cellulose (DALC) were investigated. The aim of the study was to find out how the ductility of paper sheets made from DALC were affected by the presence of fines in the pulp. Nine different pulp compositions were prepared for the modification: unrefined pulp, unrefined pulp with added fines, industrially refined pulp, dewatered industrially refined pulp, and pulp refined 1000, 3000, 5000, 10 000 and 15 000 revolutions with a PFI Mill. Paper sheets were made with a Rapid Köthen sheet former and the mechanical properties of the sheets were tested with a Zwick Roell tensile tester. The surface of the sheets were analyzed using a scanning electron microscope (SEM). The results obtained from the tensile tests showed that DALC made from unrefined pulp and DALC made from pulp highly refined with a PFI Mill, resulted in sheets with a high strain-at-break. For each increased degree of refining with the PFI Mill, the resulting DALC sheets showed an improved elongation and tensile strength. When DALC was produced from industrially refined pulp and from unrefined pulp with added fines, the resulting sheets had a lower strain-at-break. These findings indicate that the presence of fines in the pulp do have a negative effect on the ductility of the resulting DALC sheets.
486

Xylan reactions in kraft cooking and their influence on paper sheet properties

Danielsson, Sverker January 2006 (has links)
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. 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. 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. / QC 20101111
487

Polyelectrolyte multilayers of cationic and anionic starch and their use for improving the strength of papers made from mechanical pulps

Lundström, Lisa January 2009 (has links)
Graphic paper is experiencing severe competition from other materials and, most of all, from other media. This means there is a great need to improve paper quality while reducing raw material and production costs. Polyelectrolyte multilayer (PEM) treatment (i.e., consecutively adding cationic and anionic polyelectrolytes to the charged surface of wood fibres and fines, to form layers of these polyelectrolytes on the fibres/fines) has in recent years been found to offer great potential both to introduce new properties and to improve the mechanical properties of papers made of the treated fibres. The main objective of this thesis was to develop a strategy for the PEM treatment of cationic and anionic starch to improve the mechanical properties of paper made of thermomechanical pulp (TMP), since PEM treatment of fibres has displayed great potential to improve the mechanical properties of sheets made of chemical pulp. Mechanical pulp, however, has a large fine material content. Since the fine material is highly charged, polyelectrolyte consumption would be unacceptably high if the entire pulp were PEM treated, so we applied PEM treatment only to a fibre fraction of the pulps in most trials in the present work. The polyelectrolytes used for PEMs have so far mostly been well-defined, expensive ones unsuitable for use in standard paper grades; to develop a more economically realistic alternative, we used cationic and anionic starches. PEM formation on SiO2 surfaces from three differently charged cationic and anionic starches was first evaluated at three different salt levels using quartz crystal microbalance with dissipation (QCM-D) and stagnation point adsorption reflectometry (SPAR). The starch combinations displaying the highest potential for stable PEM formation at higher salt concentrations were then evaluated on an entire TMP pulp, as well as on a fraction of the pulp to reduce the amount of starch needed for PEM formation. The results indicate that it is possible to form PEMs from cationic and anionic starch on a SiO2 surface. The charge density, salt concentration, and combination of starches all influenced PEM formation. PEM formation on mechanical fibres produced large improvements in the mechanical properties of the sheets made of the treated fibres, and the tensile index, stretch-at-break, Z-strength, and Scott bond values all increased. Fractionating the pulp and PEM treating only a fraction of the pulp, the long fibre and middle fraction, produced large decreases in the amount of starch needed and large improvements in the mechanical properties of the sheets when no fine material was subsequently added. As untreated fine material was subsequently added, the improvement in mechanical properties decreased. PEM formation produced almost no reduction in formation and only a slight increase in sheet density. / Grafiskt papper är under hård konkurrens från andra material och, framför allt, andra media.  På grund av detta finns det ett stort behov av att förbättra papperskvalitén samtidigt som råmaterial- och produktionskostnader sänks. Polyelektrolyt-multiskikt (multiskikt) på massa (dvs. växelvis adsorption av katjoniska och anjoniska polyelektrolyter till träfibrer och finmaterial) har på senare år visat sig ha bra potential både för att ge nya egenskaper och för att förbättra de mekaniska egenskaperna hos papper gjorda av behandlad fiber. Huvudsyftet med denna avhandling var att utveckla en strategi för multiskiktsbehandling med katjonisk och anjonisk stärkelse för att förbättra de mekaniska egenskaperna hos papper gjort av behandlad termomekanisk massa (TMP). Multiskiktsbehandling av fiber har visat stor potential för att ge förbättrade mekaniska egenskaper till ark gjorda av behandlad kemisk massa. Mekanisk massa innehåller dock en stor andel högladdat finmaterial som kan öka mängden polyelektrolyt som krävs för multiskiktsbehandling, därför multiskiktsbehandlas bara en fraktion av massan i de flesta experiment i detta arbete. De polyelektrolyter som använts för multiskikt har hittills mest varit väldefinierade och dyra, och därmed opassande för användning i vanliga papperskvalitéer. För att utveckla ett mer realistiskt alternativ så användes katjonisk och anjonisk stärkelse i detta arbete. Multiskiktsuppbyggnad på SiO2-ytor av tre katjoniska och tre anjoniska stärkelser med olika laddningsdensitet utvärderades först vid tre olika saltnivåer genom att använda kvartskristal‑mikrogravimetri (QCM-D) och reflektometri (SPAR). Stärkelsekombinationerna som uppvisade störst potential för en stabil multiskiktsuppbyggnad på högre saltkoncentrationer blev sedan utvärderade på en hel TMP-massa, men även på en fraktion av massan för att minska mängden stärkelse som krävdes för multiskiktsuppbyggnad. Resultaten visar på att det är möjligt att bygga upp multiskikt av katjonisk och anjonisk stärkelse på en SiO2-yta. Laddningsdensiteten, saltkoncentrationen och kombinationen av stärkelser var faktorer som påverkade multiskiktsuppbyggnaden. Multiskiktsuppbyggnad på mekaniska fibrer gav stora förbättringar av de mekaniska egenskaperna hos ark gjorda av behandlad fiber, och dragindex, töjning, Z-styrka och Scott bond-värde ökade. Fraktionering av massan och multiskiktsbehandling av endast en del av massan, långfiber- och mellanfraktion, innebar att mycket mindre stärkelse behövdes och gav stora förbättringar av de mekaniska egenskaperna hos arken om inget obehandlat finmaterial tillsattes efteråt. Då obehandlat finmaterial tillsattes så blev förbättringarna hos de mekaniska egenskaperna mindre. Multiskitsuppbyggnad gav nästan ingen reduktion av formationen och endast en liten ökning i arkdensitet.
488

Suberin based polyesters

Olsson, Ann January 2009 (has links)
In the wish to replace oil-based chemicals and materials with such based on biodegradable and renewable resources, this work has been performed. In a biorefinary concept, waste birch bark from paper pulp mills and timber production has been evaluated as a potential source for polyesters.  In the present thesis investigations are made on synthesis of epoxy-functionalized polyesters from the birch outer bark aliphatic suberin ω-hydroxy fatty acid, cis-9,10-epoxy-18-hydroxyoctadecanoic acid. Studies of accessibility and reactivity of cellulose have been performed as a first step to enable covalent attachment or grafting of the epoxy-functionalized polyesters to cellulose.  Candida antarctica lipase B (Novozym 435) is reported to be an efficient catalyst for condensation polymerization of cis-9,10-epoxy-18-hydroxyoctadecanoic acid to form poly(9,10-epoxy-18-hydroxyoctadecanoic acid) with high molecular weight (Mw). Performed in toluene in the presence of molecular sieves a Mw of 20000 (reaction time 68 h, Mw/Mn 2.2) was obtained. Performed in bulk without any drying agent a Mw of 15000  was obtained at a much shorter reaction time (reaction time 3h, Mw/Mn 2.2). Further the same lipase has been used for succesful co-polymerizations of cis-9,10-epoxy-18-hydroxyoctadecanoic acid with lactones. By combining condensation and ring-opening polymerization, epoxy-functionalized linear polyesters and cyclic oligomers have been synthesized. For example, co-polymerization of cis-9,10-epoxy-18-hydroxy-octadecanoic acid and ε-caprolactone performed in toluene in the presence of molecular sieves gave mainly cyclic oligomers, especially at shorter reaction times. Co-polymerization performed in bulk gave linear polyesters with a Mw of 35000 (reaction time 24 h, Mw/Mn 6), irrespective molecular sieves were added or not.  The epoxy-functionalized polyesters could be used for surface modification of pulp fibres and cellulose fibrils, which further can be used for production of new valuable composite materials with improved features. Knowledge of how different processing conditions affect the structure of cellulose is an important tool in the work to achieve successful grafting of produced polyesters to cellulose fibres/fibrils. CP/MAS 13C-NMR spectroscopy has been used to study structural changes caused by the dissolving pulp process. An irreversible increase in average fibril aggregate width from raw pulp to final pulp during the process is shown. This increase in aggregate width could negatively influence the reactivity of the cellulose.
489

Predicting failure distribution for varying load histories applied to paper materials

Rosdahl, Matilda January 2021 (has links)
Paper materials are renewable and recyclable and are often used for packaging applications, e.g., as in corrugated fiberboard boxes. From an engineering perspective, paper materials can be used to construct packaging with low weight but with high relative strength. However, compared to other packaging materials, it can be a challenge to design paper-based packaging for distribution chains with demanding conditions. Boxes made from paper can be sensitive to exposure of moisture, duration of load, and dynamic forces. Along the distribution chain, boxes can be exposed to forces that could potentially cause failure before the boxes intended service life is fulfilled. Therefore, it is important to know how to predict the failure distribution for a specific combination of packaging and distribution chain so that materials with the right properties can be chosen for a given purpose and the risk of failures can be minimized. In this project, we have investigated a statistical material model developed by Bernard D. Coleman. It is based on three material parameters that describe the cumulative distribution function (CDF) of a fiber-breaking behavior for an arbitrary load history. The model has been shown to work for fiber network systems subjected to constant load and constant load rate (CLR). Our purpose was to investigate if it is applicable for fiber network systems of higher structural hierarchy and for more complex load histories. To investigate this, we have performed compression tests with CLR on four different types of corrugated fiberboard and determined the material parameters. Afterward, we performed compression tests for a more complex load history. A periodic, triangular-shaped, load curve was chosen for cyclic testing. Finally, we used the material parameters from the CLR tests to determine the CDF for the periodic load cases. We compared the result with an empirical CDF. The CDFs showed to be in relatively good agreement, but there were some differences. We found that our measurements turned out to produce load history data that deviated from the intended load history. The material parameters were also shown to be less accurate than expected. Due to these deviations, we could not expect a perfect agreement between the CDFs. Therefore, we can not with certainty state that Coleman’s theory is applicable for varying load histories. However, despite the difficulties to experimentally achieve the intended load history, the results showed good agreement in several cases, and the deviations from the theory could possibly be explained by the load history deviations. To be certain, more accurate measurements with higher accuracy need to be done.
490

Paper spray mass spectrometry for rapid drug screening

Jett, Rachel 08 1900 (has links)
Indiana University-Purdue University Indianapolis (IUPUI) / Paper spray mass spectrometry is an alternative technique for toxicological screening that is able to quickly and adequately screen for compounds encountered in postmortem investigations with little sample handling and no sample preparation. For analysis of dried blood spots using a triple quadrupole mass spectrometer, detection criteria were defined to align with relevant regulatory guidelines while considering how fragment ion selection, method sensitivity, and fragment ion ratio tolerances are best utilized in paper spray mass spectrometry. For analysis, drugs and drug metabolites relevant to postmortem investigations were spiked into drug-free blood, and by monitoring two fragment ion channels in selected reaction monitoring mode, as well as the ratio between the two fragment ions, a method was developed capable of detecting over 120 drug and drug metabolites at concentrations relevant to postmortem drug screening. Total analysis time for the developed method is less than 8 minutes, and less than 50µL of sample and 5mL of solvent are consumed during analysis.

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