Stromrichtertransformatoren der Hochspannungsgleichstromübertragung bilden das Bindeglied zwischen Gleichspannungs- und Drehstromsystem. Um den ausfallsicheren Betrieb über die gesamte Lebensdauer zu gewährleisten, muss deren Öl-Papier-Isoliersystem entsprechend dimensioniert werden. Eine optimale Dimensionierung setzt ein detailliertes Verständnis über die Beanspruchung des Isoliersystems sowie deren zuverlässige Modellierung sowohl unter Betriebsspannung als auch bei den überlagerten, transienten Überspannungen voraus. Im Rahmen dieser Arbeit wird daher das dielektrische Verhalten des Öl-Papier-Isoliersystems in Anlehnung an dielektrische Prüfungen sowohl unter Gleichspannungsbelastung als auch einer zusammengesetzten Spannungsbelastung aus einer Gleich- und einer Blitzstoßspannung (einer sog. Mischspannungsbelastung) untersucht. Der Vergleich von numerischen Berechnungen auf Grundlage eines ladungsträgerbasierten Ansatzes nach Poisson-Nernst-Planck (PNP) mit Durchschlagexperimenten gibt dabei Aufschluss über die Beanspruchung des Öl-Papier-Isoliersystems. Weiterhin wird gezeigt, dass der in den etablierten, resistiv-kapazitiven Berechnungsmodellen vernachlässigte Ladungsträgereinfluss in Bezug auf die Beanspruchung des Isoliersystems unzureichende Ergebnisse zur Folge hat und demnach zwingend zu berücksichtigen ist. Die an realitätsnahen, Öl-Papier-isolierten Anordnungen erzielten Ergebnisse zeigen nicht nur den Einfluss der an Grenzflächen oder im Papier akkumulierten Ladungsträger auf die Beanspruchung des Isoliersystems. Ebenso werden die Annahmen des ladungsträgerbasierten Ansatzes und die Berechnungsergebnisse des PNP-Modells qualitativ bestätigt. Infolge der Ladungsakkumulation im Papier tritt die höchste Beanspruchung im Ölspalt und nicht im Papier auf. Öl-Papier-isolierte Anordnungen werden somit geringer beansprucht, als eine Strömungsfeldberechnung vermuten lässt. Dies widerspricht den Annahmen der etablierten Berechnungsmodelle und wird im Weiteren durch Polaritätseffekte an homogenen, aber unsymmetrischen, papierisolierten Elektrodenanordnungen oder durch den nachweisbaren Einfluss des Ölvolumens im Prüfgefäß auf die Beanspruchung einer Anordnung verdeutlicht. Unter Mischspannungsbelastung wird weiterhin gezeigt, dass eine Überlagerung der Gleichspannung und damit auch der Polaritätswechsel keine höhere Beanspruchung des Isoliersystems im Vergleich zur reinen Gleichspannungsbelastung zur Folge hat. Die etablierten, resistiv-kapazitiven Modelle ließen jedoch den Polaritätswechsel als kritischste Beanspruchung vermuten. Somit wird nicht nur die Anwendbarkeit der ladungsträgerbasierten PNP-Modellierung an Öl-Papier-Isolieranordnungen qualitativ verifiziert. Ebenso wird demonstriert, dass die stark vereinfachten Annahmen der etablierten Berechnungsmodelle die Beanspruchungen unter Gleich- und der untersuchten Mischspannungsbelastung nicht abbilden können. Der Einsatz klassischer Strömungsfeldberechnungen zur Nachbildung der Beanspruchung des Öl-Papier-Isoliersystems unter Gleichspannungsbelastung entspricht damit nicht mehr dem Stand der Forschung. / Converter transformers of HVDC transmission systems connect HVDC and HVAC systems. To ensure a reliable operation during the entire lifetime, their oil-paper-insulation system must be designed appropriately. An optimized dielectric design demands a fundamental understanding of the dielectric stresses as well as a reliable modeling of the insulation system both under operating voltages and under superimposed, transient overvoltages. Hence, in this work the dielectric behavior of the oil-paper-insulation system is investigated. Based on dielectric tests the investigations are performed under DC voltage stress and a composite voltage stress of a DC voltage in stationary conditions superimposed by a lightning impulse voltage. The comparison of numerical calculations using a charge-carrier-based approach according to Poisson-Nernst-Planck (PNP) with breakdown experiments clarifies the dielectric stress of the oil-paper-insulation system. Furthermore, the comparison with results determined by the established, resistive-capacitive calculation models shows that it is mandatory to take the influence of the charge carrier accumulation into account. The presented results, which were obtained at oil-paper-insulated arrangements which represent the dielectic stress of real arrangements, show the influence of the charge carriers accumulating at interfaces or in the paper insulationon on the dielectric stress. The results confirm the calculations and the assumptions according to the charge-carrier-based model as well. Due to the charge carrier accumulation, the highest dielectric stress occurs in the mineral oil and not in the paper insulation. In contrast, the findings obtained assuming an ohmic conductivity would results in a higher dielectric stress of the oil-paperinsulated arrangements. Furthermore, polarity effects in homogeneous but asymmetrical, paper-insulated electrode arrangements or the influence of the surrounding oil in the test vessel demonstrate the effects of the charge carriers. Under composite voltage stresses it is also shown, that the applied superimposed voltage as well as the fast polarity reversal does not lead to a higher dielectric stress of the arrangements compared to the pure DC voltage stress. Commonly used calculation models would determine higher stresses due to the fast polarity reversal instead. Consequently, the applicability of the charge-carrier-based PNP calculation model is verified qualitatively in the presented investigations. Furthermore, it is demonstrated that the simplified assumptions of the commonly used calculation models cannot simulate the dielectric stresses under DC voltage stress and under the investigated superimposed voltage stresses. Hence, the determination of the dielectric stresses of oil-paper-insulation systems under DC voltage stress according to the commonly used calculation models assuming an ohmic conductivity does not correspond to the current state of research.

Ce projet de recherche mené en collaboration avec le CTP (Centre Technique du papier) a eu comme objectif de mettre en place une stratégie de greffage de polymères sur des fibres de cellulose via « Chimie Click » dans l’eau et dans des conditions douces et respectueuses de l’environnement afin de conférer de nouvelles propriétés mécaniques aux papiers résultants. La première étape a été d’élaborer une fonctionnalisation alcyne des fibres dans des conditions douces – dans l’eau ou dans un mélange eau/isopropanol – permettant à la fois une fonctionnalisation conséquente tout en préservant la cristallinité de la cellulose, la structure fibre et les propriétés mécaniques. Différentes méthodes de microscopie ont été utilisées pour mieux comprendre l’impact de la fonctionnalisation sur les propriétés mécaniques. Afin d’améliorer les propriétés mécaniques du papier, le greffage sur les fibres de polyéthers d’alkyle fonctionnalisés azoture a été réalisé dans l’eau par cycloaddition de Huisgen d’azoture-alcyne catalysée par le cuivre (II) (CuAAC). Plusieurs polymères de natures différentes (poly(éthylène glycol) et poly[(éthylène glycol)-stat-(propylène glycol)]), de différentes masses molaires et fonctionnalités (mono- ou difonctionnels) ont été liés aux fibres de cellulose. L’ajout de chaînes de poly(éthylène glycol) s’est avéré avoir un effet lubrifiant entraînant une légère diminution de l’indice de traction mais une augmentation importante de la flexibilité du papier. De plus, le greffage de polymères difonctionnels a démontré des propriétés originales de résistance à l’eau sans changer la nature hydrophile des fibres de cellulose. Enfin, le couplage Thiol-Yne a permis de fixer de petites molécules hydrosolubles fonctionnalisées thiol sur des fibres modifiées alcyne en s’affranchissant du cuivre nécessaire à la réalisation de la réaction de CuAAC. / This research project, in collaboration with CTP (Centre Technique du Papier), aimed at developing chemical pathway in water to graft polymers on cellulose fibers via “Click Chemistry” in eco-friendly and non-degrading conditions conferring new mechanical properties upon the resulting paper sheets. A first step was to develop a “green” alkyne derivatization method in mild conditions – through pure water or water/isopropanol mixture – allowing for a substantial alkyne functionalization without jeopardizing the cellulose crystallinity, the fiber structure, and maintaining good mechanical properties of the cellulose fibers and resulting paper sheets. To better understand how the functionalization impacts the mechanical properties, several microscopy methods were employed. Then, aiming at improving mechanical properties of the resulting paper, grafting of azidefunctionalized polyoxyalkylenes on alkyne-modified fibers was achieved via Copper(II)-Catalyzed Alkyne-Azide Cycloaddition (CuAAC) in pure water. Water soluble polymers of different nature (poly(ethylene glycol) or poly[(ethylene glycol)-stat-(propylene glycol)]), with different molar mass and functionality (one or two azide groups per macromolecular chain) were successfully attached on cellulose fibers. Grafting of PEG chains involved a slight decrease of the tensile index but a drastic increase of the flexibility of the paper sheet. Interestingly, fibers grafted with difunctional polymers demonstrated an original water resistance maintaining the hydrophilic nature of fibers. Finally, Thiol-Yne reaction was successfully carried out to attach small water soluble thiol-bearing reagents on alkyne-functionalized fibers in water as a metal-free alternative to CuAAC reaction.

Sizing (hydrophobization) is one of the most important process steps within the added-value chain of about 1/3rd of the worldwide produced paper & board products. Even though sizing with so-called reactive sizing agents, such as alkenyl succinic anhydride (ASA) was implemented in the paper industry decades ago, there is no total clarity yet about the detailed chemical and physical mechanisms that lead to their performance. Previous research was carried out on the role of different factors influencing the sizing performance, such as bonding between ASA and cellulose, ASA hydrolysis, size revision as well as the most important interactions with stock components, process parameters and additives during the paper making process. However, it was not yet possible to develop a holistic model for the explanation of the sizing performance given in real life application. This thesis describes a novel physico-chemical approach to this problem by including results from previous research and combining these with a wide field of own basic research and a newly developed method that allows tracing back the actual localization of ASA within the sheet structure. The carried out measurements and trial sets for the basic field of research served to evaluate the stock and process parameters that most dominantly influence the sizing performance of ASA. Interactions with additives other than retention aids were not taken into account. The results show that parameters, such as the content of secondary fibers, the degree of refining, the water hardness as well as the suspension conductivity, are of highest significance. The sample sets of the trials with the major impacting parameters were additionally analyzed by a newly developed localization method in order to better understand the main influencing factors. This method is based on optical localization of ASA within the sheet structure by confocal white light microscopy. In order to fulfill the requirements at magnification rates of factor 100 optical zoom, it was necessary to improve the contrast between ASA and cellulose. Therefore, ASA was pretreated with an inert red diazo dye, which does not have any impact on neither the sizing nor the handling properties of ASA. Laboratory hand sheets that were sized with dyed ASA, were analyzed by means of their sizing performance in correlation to measurable ASA agglomerations in the sheet structure. The sizing performance was measured by ultrasonic penetration analysis. The agglomeration behavior of ASA was analyzed automatically by multiple random imaging of a sample area of approx. 8650 µm² with a minimum resolution for particles of 500 nm in size. The gained results were interpreted by full factorial design of experiments (DOE). The trials were carried out with ASA dosages between 0% and 0.8% on laboratory hand sheets, made of 80% bleached eucalyptus short fiber kraft pulp and 20% northern bleached softwood kraft pulp, beaten to SR° 30, produced with a RDA sheet former at a base weight of 100 g/m² oven dry. The results show that there is a defined correlation between the ASA dosage, the sizing performance and the number and area of ASA agglomerates to be found in the sheet structure. It was also possible to show that the agglomeration behavior is highly influenced by external factors like furnish composition and process parameters. This enables a new approach to the explanation of sizing performance, by making it possible to not only examine the performance of the sizing agent, but to closely look at the predominant position where it is located in the sheet structure. These results lead to the explanation that the phenomenon of sizing is by far not a pure chemical process but rather a more physical one. Based on the gained findings it was possible so far to optimize the ASA sizing process in industrial-scale by means of ~ 50% less ASA consumption at a steady degree of sizing and improved physical sheet properties.

Sizing (hydrophobization) is one of the most important process steps within the added-value chain of about 1/3rd of the worldwide produced paper & board products. Even though sizing with so-called reactive sizing agents, such as alkenyl succinic anhydride (ASA) was implemented in the paper industry decades ago, there is no total clarity yet about the detailed chemical and physical mechanisms that lead to their performance. Previous research was carried out on the role of different factors influencing the sizing performance, such as bonding between ASA and cellulose, ASA hydrolysis, size revision as well as the most important interactions with stock components, process parameters and additives during the paper making process. However, it was not yet possible to develop a holistic model for the explanation of the sizing performance given in real life application. This thesis describes a novel physico-chemical approach to this problem by including results from previous research and combining these with a wide field of own basic research and a newly developed method that allows tracing back the actual localization of ASA within the sheet structure. The carried out measurements and trial sets for the basic field of research served to evaluate the stock and process parameters that most dominantly influence the sizing performance of ASA. Interactions with additives other than retention aids were not taken into account. The results show that parameters, such as the content of secondary fibers, the degree of refining, the water hardness as well as the suspension conductivity, are of highest significance. The sample sets of the trials with the major impacting parameters were additionally analyzed by a newly developed localization method in order to better understand the main influencing factors. This method is based on optical localization of ASA within the sheet structure by confocal white light microscopy. In order to fulfill the requirements at magnification rates of factor 100 optical zoom, it was necessary to improve the contrast between ASA and cellulose. Therefore, ASA was pretreated with an inert red diazo dye, which does not have any impact on neither the sizing nor the handling properties of ASA. Laboratory hand sheets that were sized with dyed ASA, were analyzed by means of their sizing performance in correlation to measurable ASA agglomerations in the sheet structure. The sizing performance was measured by ultrasonic penetration analysis. The agglomeration behavior of ASA was analyzed automatically by multiple random imaging of a sample area of approx. 8650 µm² with a minimum resolution for particles of 500 nm in size. The gained results were interpreted by full factorial design of experiments (DOE). The trials were carried out with ASA dosages between 0% and 0.8% on laboratory hand sheets, made of 80% bleached eucalyptus short fiber kraft pulp and 20% northern bleached softwood kraft pulp, beaten to SR° 30, produced with a RDA sheet former at a base weight of 100 g/m² oven dry. The results show that there is a defined correlation between the ASA dosage, the sizing performance and the number and area of ASA agglomerates to be found in the sheet structure. It was also possible to show that the agglomeration behavior is highly influenced by external factors like furnish composition and process parameters. This enables a new approach to the explanation of sizing performance, by making it possible to not only examine the performance of the sizing agent, but to closely look at the predominant position where it is located in the sheet structure. These results lead to the explanation that the phenomenon of sizing is by far not a pure chemical process but rather a more physical one. Based on the gained findings it was possible so far to optimize the ASA sizing process in industrial-scale by means of ~ 50% less ASA consumption at a steady degree of sizing and improved physical sheet properties.:Acknowledgment I Abstract III Table of Content V List of Illustrations XI List of Tables XVI List of Formulas XVII List of Abbreviations XVIII 1 Introduction and Problem Description 1 1.1 Initial Situation 1 1.2 Objective 2 2 Theoretical Approach 3 2.1 The Modern Paper & Board Industry on the Example of Germany 3 2.1.1 Raw Materials for the Production of Paper & Board 5 2.2 The Sizing of Paper & Board 8 2.2.1 Introduction to Paper & Board Sizing 8 2.2.2 The Definition of Paper & Board Sizing 10 2.2.3 The Global Markets for Sized Paper & Board Products and Sizing Agents 11 2.2.4 Physical and Chemical Background to the Mechanisms of Surface-Wetting and Penetration 13 2.2.4.1 Surface Wetting 14 2.2.4.2 Liquid Penetration 15 2.2.5 Surface and Internal Sizing 17 2.2.6 Sizing Agents 18 2.2.6.1 Alkenyl Succinic Anhydride (ASA) 19 2.2.6.2 Rosin Sizes 19 2.2.6.3 Alkylketen Dimer (AKD) 23 2.2.6.4 Polymeric Sizing Agents (PSA) 26 2.2.7 Determination of the Sizing Degree (Performance Analysis) 28 2.2.7.1 Cobb Water Absorption 29 2.2.7.2 Contact Angle Measurement 30 2.2.7.3 Penetration Dynamics Analysis 31 2.2.7.4 Further Qualitative Analysis Methods 33 2.2.7.4.1 Ink Stroke 33 2.2.7.4.2 Immersion Test 33 2.2.7.4.3 Floating Test 34 2.2.7.4.4 Hercules Sizing Tester (HST) 34 2.2.8 Sizing Agent Detection (Qualitative Analysis) and Determination of the Sizing Agent Content (Quantitative Analysis) 35 2.2.8.1 Destructive Methods 35 2.2.8.2 Non Destructive Methods 36 2.3 Alkenyl Succinic Anhydride (ASA) 36 2.3.1.1 Chemical Composition and Production of ASA 37 2.3.1.2 Mechanistic Reaction Models 39 2.3.1.3 ASA Application 42 2.3.1.3.1 Emulsification 42 2.3.1.3.2 Dosing 44 2.3.1.4 Mechanistic Steps of ASA Sizing 46 2.3.2 Physico-Chemical Aspects during ASA Sizing 48 2.3.2.1 Reaction Plausibility 48 2.3.2.1.1 Educt-Product Balance / Kinetics 48 2.3.2.1.2 Energetics 51 2.3.2.1.3 Sterics 52 2.3.2.2 Phenomena based on Sizing Agent Mobility 53 2.3.2.2.1 Sizing Agent Orientation 54 2.3.2.2.2 Intra-Molecular Orientation 55 2.3.2.2.3 Sizing Agent Agglomeration 55 2.3.2.2.4 Fugitive Sizing / Sizing Loss / Size Reversion 56 2.3.2.2.5 Sizing Agent Migration 58 2.3.2.2.6 Sizing Reactivation / Sizing Agent Reorientation 59 2.3.3 Causes for Interactions during ASA Sizing 60 2.3.3.1 Process Parameters 61 2.3.3.1.1 Temperature 61 2.3.3.1.2 pH-Value 62 2.3.3.1.3 Water Hardness 63 2.3.3.2 Fiber Types 64 2.3.3.3 Filler Types 65 2.3.3.4 Cationic Additives 66 2.3.3.5 Anionic Additives 67 2.3.3.6 Surface-Active Additives 68 2.4 Limitations of State-of-the-Art ASA-Sizing Analysis 69 2.5 Optical ASA Localization 71 2.5.1 General Background 71 2.5.2 Confocal Microscopy 72 2.5.2.1 Principle 72 2.5.2.2 Features, Advantage and Applicability for Paper-Component Analysis 74 2.5.3 Dying / Staining 75 3 Discussion of Results 77 3.1 Localization of ASA within the Sheet Structure 77 3.1.1 Choice of Dyes 77 3.1.1.1 Dye Type 78 3.1.1.2 Evaluation of Dye/ASA Mixtures 80 3.1.1.2.1 Maximum Soluble Dye Concentration 80 3.1.1.2.2 Thin Layer Chromatography 81 3.1.1.2.3 FTIR-Spectroscopy 82 3.1.1.3 Evaluation of the D-ASA Emulsion 84 3.1.1.4 Paper Chromatography with D-ASA & F-ASA Emulsions 85 3.1.1.5 Evaluation of the D-ASA Emulsion’s Sizing Efficiency 86 3.1.2 The Localization Method 87 3.1.2.1 The Correlation between ASA Distribution and Agglomeration 88 3.1.2.2 Measurement Settings 89 3.1.2.3 Manual Analysis 90 3.1.2.4 Automated Analysis 92 3.1.2.4.1 Automated Localization / Microscopy Measurement 92 3.1.2.4.2 Automated Analysis / Image-Processing 93 3.1.2.5 Result Interpretation and Example Results 96 3.1.2.6 Reproducibility 97 3.1.2.7 Sample Mapping 98 3.1.3 Approaches to Localization-Method Validation 102 3.1.3.1 Raman Spectroscopy 102 3.1.3.2 Confocal Laser Scanning Fluorescent Microscopy 102 3.1.3.3 Decolorization 103 3.2 Factors Impacting the Sizing Behavior of ASA 104 3.2.1 ASA Type 105 3.2.2 Emulsion Parameters 107 3.2.2.1 Hydrolyzed ASA Content 107 3.2.2.2 ASA/Starch Ratio 109 3.2.2.3 Emulsion Age 110 3.2.3 Stock Parameters 111 3.2.3.1 Long Fiber/Short Fiber Ratio 111 3.2.3.2 Furnish Type 112 3.2.3.3 Degree of Refining 114 3.2.3.4 Filler Type/Content 116 3.2.4 Process Parameters 119 3.2.4.1 Temperature 119 3.2.4.2 pH-Value 120 3.2.4.3 Conductivity 122 3.2.4.4 Water Hardness 123 3.2.4.5 Shear Rate 125 3.2.4.6 Dwell Time 127 3.2.4.7 Dosing Position & Dosing Order 128 3.2.4.8 Drying 130 3.2.4.9 Aging 131 3.3 Factors Impacting the Localization Behavior of ASA 132 3.3.1 Degree of Refining 132 3.3.2 Sheet Forming Conductivity 135 3.3.3 Water Hardness 136 3.3.4 Retention Aid (PAM) 137 3.3.5 Contact Curing 138 3.3.6 Accelerated Aging 139 3.4 Main Optimization Approach 141 3.4.1 Optimization of ASA Sizing Performance Characteristics 142 3.4.2 Emulsion Modification 144 3.4.2.1 Lab Trials / RDA Sheet Forming 146 3.4.2.2 TPM Trials 147 3.4.2.3 Industrial-Scale Trials 149 3.4.2.4 Correlation between Sizing Performance Optimization and Agglomeration Behavior on the Example of PAAE 152 3.5 Holistic Approach to Sizing Performance Explanation 154 4 Experimental Approach 157 4.1 Characterization of Methods, Measurements and Chemicals used for the Optical Localization-Analysis of ASA 157 4.1.1 Characterization of used Chemicals 157 4.1.1.1 Preparation of Dyed-ASA Solutions 157 4.1.1.2 Thin Layer Chromatography 157 4.1.1.3 Fourier Transformed Infrared Spectroscopy 157 4.1.1.4 Emulsification of ASA 158 4.1.1.5 Paper Chromatography 159 4.1.1.6 Particle Size Measurement 159 4.1.2 Optical Analysis of ASA Agglomerates 160 4.1.2.1 Microscopy 160 4.1.2.2 Automated Analysis 163 4.1.2.2.1 Adobe Photoshop 163 4.1.2.2.2 Adobe Illustrator 164 4.1.2.3 Confocal Laser Scanning Fluorescent Microscopy 166 4.2 Characterization of Used Standard Methods and Measurements 166 4.2.1 Stock and Paper Properties 166 4.2.1.1 Stock pH, Conductivity and Temperature Measurement 166 4.2.1.2 Dry Content / Consistency Measurement 167 4.2.1.3 Drainability (Schopper-Riegler) Measurement 167 4.2.1.4 Base Weight Measurement 168 4.2.1.5 Ultrasonic Penetration Measurement 168 4.2.1.6 Contact Angle Measurement 169 4.2.1.1 Cobb Measurement 169 4.2.1.2 Air Permeability Measurements 170 4.2.1.3 Tensile Strength Measurements 170 4.2.2 Preparation of Sample Sheets 171 4.2.2.1 Stock Preparation 171 4.2.2.2 Laboratory Refining (Valley Beater) 171 4.2.2.3 RDA Sheet Forming 171 4.2.2.4 Additive Dosing 173 4.2.2.5 Contact Curing 174 4.2.2.6 Hot Air Curing 174 4.2.2.7 Sample Aging 174 4.2.2.8 Preparation of Hydrolyzed ASA 175 4.2.2.9 Trial Paper Machine 175 4.2.2.10 Industrial-Scale Board Machine 177 4.3 Characterization of used Materials 178 4.3.1 Fibers 178 4.3.1.1 Reference Stock System 178 4.3.1.2 OCC Fibers 179 4.3.1.3 DIP Fibers 179 4.3.2 Fillers 180 4.3.3 Chemical Additives 180 4.3.3.1 ASA 180 4.3.3.2 Starches 181 4.3.3.3 Retention Aids 181 4.3.3.4 Poly Aluminum Compounds 181 4.3.3.5 Wet Strength Resin 181 4.3.4 Characterization of used Additives 182 4.3.4.1 Solids Content 182 4.4 Description of Implemented Advanced Data Analysis- and Visualization Methods 183 4.4.1 Design of Experiments (DOE183 4.4.2 Contour Plots 184 4.4.3 Box-Whisker Graphs 185 5 Conclusion 186 6 Outlook for Further Work 191 7 Bibliography 192 Appendix 207 7.1 Localization Method Reproducibility 207 7.2 DOE - Coefficient Lists 208 7.2.1 Trial 3.3.4 – Impact of Retention Aid (PAM) on Agglomeration Behavior and Sizing Performance 208 7.2.2 Trial 3.3.5 – Impact of Contact Curing on Agglomeration Behavior and Sizing Performance 208 7.2.3 Trial 3.3.6 – Impact of Accelerated Aging on Agglomeration Behavior and Sizing Performance 209

Im Fokus dieser Studie stehen mehrere Gruppen von tragbaren Skulpturen unterschiedlicher Größe und aus unterschiedlichem Material gefertigt (Bronze bzw. Papiermaché), die eine bestimmte Überlieferungslinie von Lehrern der Lamdre-Tradition darstellen. Lamdre („Der Weg und das Resultat“) bildet das zentrale religiöse Lehrsystem der Sakya-Schule des tibetischen Buddhismus und ihrer wichtigsten Zweigschule, der Ngor-Schule. Diese wenig bekannten oder weitgehend unerforschten Skulpturen und Skulpturengruppen befinden sich in der Sammlung des Klosters Namgyal in Mustang (Nepal), dem ehemaligen Königreich von Lowo (Glo bo), an der Grenze zu Tibet gelegen. Sie stammen aus dem späten 15. bis frühen 16. Jahrhundert, einer höchst innovativen Phase buddhistischer Kunstproduktion in Tibet und dem Himalaya, in der sich regionale Stile entwickelten und neue künstlerische Gestaltungsformen erprobt wurden, einschließlich verschiedener Arten des Porträts. Hierzu zählen idealisierte, typisierte, und gelegentlich hoch-expressive, Darstellungen von Lehrern innerhalb einer Überlieferungslinie ebenso wie individualisierte, realistische Einzelporträts von bedeutenden buddhistischen Meistern, die offensichtlich nach dem lebenden Modell geschaffen wurden. Basierend auf einer vergleichenden kunsthistorischen Analyse zeigt die Arbeit, dass der Repräsentation der Überlieferungslinie als Ganzes eine höhere Stellung beigemessen wurde als der Schaffung von Ähnlichkeit mit den einzelnen Figuren innerhalb einer Skulpturengruppe. Die Bildwerke reflektieren außerdem die religiösen, historischen und künstlerischen Verbindungen zwischen Mustang und angrenzenden Königreichen in West-Tibet, der Provinz Tsang und dem Kathmandu-Tal. Sie zeigen, dass die lokalen Klöster auf ein etabliertes Netzwerk von buddhistischen Klostergemeinschaften, machtvollen und wohlhabenden Stiftern und künstlerischen Traditionen aufbauen konnten, und dass sich die Region als ein Zentrum skulpturaler Produktion von höchster Qualität und Innovation etablierte. / This two-volume dissertation on lineage portraiture in Tibetan Buddhist art investigates in its core a body of portable sculpture preserved in a monastery in Mustang, Nepal. Most of these sculptures were originally part of sets documenting the person-to-person transmission of the most important teaching of the Ngor tradition, the Lamdre or “Path with the Result.” The Ngor tradition is a sub-tradition of the Sakya school of Tibetan Buddhism to which this teaching traces back. Accordingly, most Sakyapa and Ngorpa monasteries may have had one or more Lamdre lineage sets in painting and/or sculpture. The focus of the study is on the iconographic and overall visual conceptions of different sets representing the same teacher lineage produced for or within the same regional context (Mustang in the fifteenth and sixteenth centuries). A comparative analysis of the different sets shows that depicting the lineage teachers as a collective entity was deemed more important than creating physical likenesses of the individual teachers. This is reflected in the variation of the depiction of individual teachers from one set to another in terms of facial features, hand gestures, and even the type of practice a teacher may be associated with. The study also considers the emergence and evolution of teacher lineages within the Sakya school, introducing lineage representations on monumental backrest arches in repoussé work at the Sakya Lhakhang Chenmo in south-western Tibet. It also discusses teacher portraits produced outside the Lamdre lineage to reflect on questions of individuality, realism and likeness in Tibetan portraiture. A special focus is on portraits of two princely monks from the ruling house of Mustang, Lowo Khenchen and Lodrö Gyaltsen Pelzangpo. Overall, the lineage depictions and individual portraits are analyzed in relation to art history research on portraiture, Tibetan religious and political history, as well as their religious significance and ritual use.