Zugl.: Aachen, Techn. Hochsch., Diss., 2008

RWTH Aachen University, Diss., 2008.

University, Diss., 2001--Stuttgart. / Gedr. Ausg. im Inst. für Kunststofftechnologie, Univ. Stuttgart.

The production of fine filaments using the melt spinning process needs considerable effort. A thermoplastic melt is stretched from the spinneret under a constant take-up speed. The high performance thermoplastic PEEK is solidified in the melt spinning process in a small distance and short time. Therefore, the fine PEEK filaments in the fibre formation zone underwent a high deformation and cooling rate. To make the melt spinning process stable and to produce the fine PEEK filaments, material properties and material behaviour are examined using on-line and off-line measurements. The fibre speed measured using Laser Doppler Anemometry and simultaneous temperature measured using infrared thermography enable both the strain rate and consequently the apparent extensional viscosity to be estimated. This provides the apparent extensional viscosity over the spinning line, which can itself show the structural development of PEEK fibres in the fibre formation zone, i.e. necking and solidification phenomena. The one-dimensional fibre formation model must include both procedural and material parameters. The heat transfer coefficient was estimated using the filament temperature measurement and showed a relatively high contribution of radiation and free convection in comparison to forced convection near the spinneret. The improved model of PEEK fibre formation gave a good agreement to both temperature and speed measurements, and also confirmed the high deformation rate effect on the extensional viscosity, which could be simulated with a properly generalised Newtonian constitutive equation. The end properties of the fibres, such as as-spun filament fineness, orientation (expressed using total birefringence) and total crystallisation (examined using DSC) are investigated in relation to different spinning conditions, i.e. take-up speed, throughput and the draw down ratio. The tensile test diagram results, measuring phenomena such as the elongation at break, tenacity, and the Young modulus of elasticity are also analysed in order to complete the correlation of the above-mentioned spinning conditions to the structural properties of as-spun fine PEEK filaments. The melt spinning of fine PEEK fibres under different spinning conditions is examined with the purpose of finding the optimum take-up speed and throughputs. Other spinning conditions, such as the temperature of melt processing, and the arrangement and diameter of the spinneret holes, are changed in order to make the process more stable. The recommendations for further study can be used to further examine some aspects of this work; however, this work presents a new concept for fine PEEK melt spinning supported by spinnability examinations under different spinning conditions and the improved model of fibre formation, which is also relevant for typical industrial processing applications.

The production of fine filaments using the melt spinning process needs considerable effort. A thermoplastic melt is stretched from the spinneret under a constant take-up speed. The high performance thermoplastic PEEK is solidified in the melt spinning process in a small distance and short time. Therefore, the fine PEEK filaments in the fibre formation zone underwent a high deformation and cooling rate. To make the melt spinning process stable and to produce the fine PEEK filaments, material properties and material behaviour are examined using on-line and off-line measurements. The fibre speed measured using Laser Doppler Anemometry and simultaneous temperature measured using infrared thermography enable both the strain rate and consequently the apparent extensional viscosity to be estimated. This provides the apparent extensional viscosity over the spinning line, which can itself show the structural development of PEEK fibres in the fibre formation zone, i.e. necking and solidification phenomena. The one-dimensional fibre formation model must include both procedural and material parameters. The heat transfer coefficient was estimated using the filament temperature measurement and showed a relatively high contribution of radiation and free convection in comparison to forced convection near the spinneret. The improved model of PEEK fibre formation gave a good agreement to both temperature and speed measurements, and also confirmed the high deformation rate effect on the extensional viscosity, which could be simulated with a properly generalised Newtonian constitutive equation. The end properties of the fibres, such as as-spun filament fineness, orientation (expressed using total birefringence) and total crystallisation (examined using DSC) are investigated in relation to different spinning conditions, i.e. take-up speed, throughput and the draw down ratio. The tensile test diagram results, measuring phenomena such as the elongation at break, tenacity, and the Young modulus of elasticity are also analysed in order to complete the correlation of the above-mentioned spinning conditions to the structural properties of as-spun fine PEEK filaments. The melt spinning of fine PEEK fibres under different spinning conditions is examined with the purpose of finding the optimum take-up speed and throughputs. Other spinning conditions, such as the temperature of melt processing, and the arrangement and diameter of the spinneret holes, are changed in order to make the process more stable. The recommendations for further study can be used to further examine some aspects of this work; however, this work presents a new concept for fine PEEK melt spinning supported by spinnability examinations under different spinning conditions and the improved model of fibre formation, which is also relevant for typical industrial processing applications.

Zugl.: Stuttgart, Univ., Diss., 2003. / Print-Ausg. bei Shaker, Aachen erschienen.

Universiẗat, Diss., 2003--Stuttgart.

Bei überkritisch großen Läsionen des peripheren Nervensystems, die zum Verlust von Motorik bzw. Sensibilität an Extremitäten führen und damit eine erhebliche Beeinträchtigung der Lebensqualität des Patienten bedingen, ist der Einsatz von Überbrückungsstrukturen bzw. Nervenleitkanälen notwendig. Da weder autologe Transplantate noch künstliche Konstrukte im klinischen Alltag bislang zufriedenstellende Ergebnisse lieferten, ist die Nachfrage nach alternativen Materialien und Konzepten des Tissue Engineering hoch. Im Rahmen dieser Dissertation ist es gelungen zwei thermoplastische Methoden zu etablieren, mit denen aus dem im medizinischen Sinne interessanten und relativ neuartigen Material Poly(3-hydroxybuttersäure) in Kombination mit Polycaprolacton poröse resorbierbare Hohlstrukturen bzw. Hohlfasern erzeugt werden können, die den hohen aktuellen Anforderungen an eine Nervenleitschiene gerecht werden. Neben der Entwicklung und Charakterisierung sowie Modifizierung der erzeugten Leitkanäle bezüglich Porosität, Permeationsverhalten, mechanische Eigenschaften und Oberflächenfunktionalisierung, konnten strukturelle als auch biochemische Reize in diese integriert werden, die in einer Reihe von ex-vivo Studien mit neuronalen Primärzellen hinsichtlich Adhäsion, Vitalität und Ausbreitungsverhalten untersucht werden konnten. Es konnte eine Art „Toolbox“ aus PHB basierten Strukturen erstellt werden, die es erlaubt hierarchische Strukturen zusammenzustellen, die entsprechend des peripheren Defektes zusammengesetzt und biomolekular maßgeschneidert werden könnten, um die native Struktur bestmöglich temporär bis zur vollständigen Regeneration zu imitieren und damit die Therapie größerer Defekte zu ermöglichen bzw. die als Plattform für weitere Konzepte der Grundlagenforschung im Bereich des Neuro-Tissue Engineering dienen.

Hochleistungsfähige Lithium-Ionen-Batterien sind insbesondere von der hohen spezifischen Kapazität ihrer Elektrodenmaterialien abhängig. Intermetallische Phasen sind vielversprechende Kandidaten für alternative Anodenmaterialien mit verbesserten spezifischen Kapazitäten (LiAl: 993 Ah/kg; Li22Si5: 4191 Ah/kg) gegenüber den derzeit vielfach verwendeten Kohlenstoff-Materialien (LiC6: 372 Ah/kg). Nachteilig ist jedoch, dass die kristallinen Phasenumwandlungen während der Lade-Entlade-Prozesse Volumenänderungen von 100-300% verursachen. Durch die Sprödigkeit der intermetallischen Phasen führt dies zum Zerbrechen des Elektrodenmaterials und damit zum Kontaktverlust. Um Lithiierungs- und Delithiierunsprozesse ohne kristalline Phasenumwandlungen zu realisieren und somit große Volumenänderungen zu vermeiden, wurden amorphe Al-Legierungen untersucht. In amorphe, mittels Schmelzspinnen hergestellte Legierungen (Al86Ni8La6 und Al86Ni8Y6) kann beim galvanostatischen Zyklieren nur sehr wenig Li eingelagert werden. Da kristalline Phasenumwandlungen im amorphen Zustand nicht möglich sind, wird für die Diffusion und Einlagerung von Li-Ionen ein ausreichendes freies Volumen im amorphen Atomgerüst benötigt. Die Dichtemessung der Legierungen zeigt, dass dieses freie Volumen für eine signifikante Lithiierung nicht ausreichend ist. Wird Li bereits in die amorphe Ausgangslegierung integriert, können Li-Ionen auf elektrochemischem Wege aus ihr entfernt und auch wieder eingebaut werden. Die neuartige Legierung Al43Li43Ni8Y6, die Li bereits im Ausgangszustand enthält, konnte mittels Hochenergiemahlung als amorphes Pulver hergestellt werden. Verglichen mit den Li-freien amorphen Legierungen Al86Ni8La6 bzw. Al86Ni8Y6 und ihren kristallisierten Pendants zeigt diese neu entwickelte, amorphe Legierung eine signifikant höhere Lithiierungsfähigkeit und erreicht damit eine spezifische Kapazität von ca. 800 Ah/kg bezogen auf den Al-Anteil. Durch den Abrieb des Stahlmahlbechers enthält das Pulver Al43Li43Ni8Y6 einen Fe-Anteil von ca. 15 Masse%. Dieses mit Fe verunreinigte Material zeigt besonders bei niedrigen Laderaten eine bessere Zyklenstabilität als ein im abriebfesten Siliziumnitrid-Becher gemahlenes Pulver der gleichen Zusammensetzung. Mittels Mössbauerspektroskopie wurde nachgewiesen, dass das Pulver z.T. oxidisches Fe enthält. Dieses kann über Konversionsmechanismen einen Beitrag zur spezifischen Kapazität leisten. / High-energy Li-ion batteries exceedingly depend on the high specific capacity of electrode materials. Intermetallic alloys are promising candidates to be alternative anode materials with enhanced specific capacities (LiAl: 993 Ah/kg; Li22Si5: 4191 Ah/kg) in contrast to state-of-the-art techniques, dominated by carbon materials (LiC6: 372 Ah/kg). Disadvantageously the phase transitions during the charge-discharge processes, induced by the lithiation process, cause volume changes of 100-300 %. Due to the brittleness of intermetallic phases, the fracturing of the electrode material leads to the loss of the electrical contact. In order to overcome the huge volume changes amorphous Al-based alloys were investigated with the intension to realize the lithiation process without a phase transformation. Amorphous powders (Al86Ni8La6 and Al86Ni8Y6) produced via melt spinning and subsequent ball milling only show a minor lithiation during the electrochemical cycling process. This is mainly caused by the insufficient free volume, which is necessary to transfer and store Li-ions, since phase transitions are impossible in the amorphous state. If Li is already integrated into the amorphous alloy, Li-ions can easily be removed and inserted electrochemically. The new alloy Al43Li43Ni8Y6 contains Li already in its initial state and could be prepared by high energy milling as an amorphous powder. Compared with the Li-free amorphous alloys Al86Ni8La6 or Al86Ni8Y6 and their crystalline counterparts, this newly developed amorphous alloy achieves a significantly higher lithiation and therefore reaches a specific capacity of 800 Ah/kg, based on the Al-content. By the abrasion of the steel milling vials the powder contains a wear debris of 15 mass% Fe. This contaminated material shows a better cycling stability than a powder of the same composition, milled in a non-abrasive silicon nitride vial. By means of Mössbauer spectroscopy has been shown that the wear debris contains Fe oxides. This may contribute to the enhancement of the specific capacity about conversion mechanisms.

Multifunctional polymer fibers with strain and liquid sensing capabilities were fabricated and characterized. The Hansen Solubility Parameters (HSPs) were used as a tool for selecting a suitable polymer to employ as matrix for the sensing material before fiber fabrication. The addition of conductive carbon particles to a polymer matrix provides it with sensing capabilities, such as against tensile strain and the presence of liquids as it was evaluated in this work. Multiwall carbon nanotubes (MWCNTs, MW) as well as a mixture of carbon black (CB) and MWCNTs in weight concentration of 1:1 were used as conductive fillers. The route followed to achieve electrically conductive polymer fibers necessary for sensing evaluations was a combined process of melt-mixing and subsequent melt-spinning. Melt-mixing and melt-spinning are processing techniques widely used in the polymer industry that could enable the up-scaling of the fibers developed in this work. Additionally to single component fibers, bi-component (BICO) fibers consisting of a polycarbonate (PC)+CB+MW sheath and a neat PC core were also fabricated, characterized and their performance was compared to the single component fibers. The state of dispersion of the carbon nanoparticles (CNPs) as well as tensile behavior, electrical resistivity, strain and liquid sensing properties of the composite fibers were evaluated. Finally a specific fiber composition with potential to be used as sensing material for mechanical strain and liquid exposition was proposed to be tested under two real situations (strain monitoring of a rigid structure and leakage detection of a chemical substance). Sensing fibers as the developed in this work have many potential applications such as real-time deformation and structural health monitoring and early cracking detection of any kind of structure. On the other hand, fibers able to sense the presence of liquids can perceive the leakage of chemicals that are hazardous to life. Moreover, this technology can also be applied in smart clothing manufacture by combining sensing fibers with flexible woven electronics.