Göttingen, Universiẗat, Diss., 2001.

Hannover, Universiẗat, Diss., 2002.

Ulm, Univ., Diss., 2001.

Techn. Hochsch., Diss., 2004--Aachen.

No description available.

During the last years rubber nanocomposites obtained by incorporating anisotropic clay nanoparticles within a rubber matrix to tailor material properties have attracted steadily growing interest. However, one main complication preventing rubber-clay nanocomposites from many potential applications is the difficulty to achieve a high degree of exfoliation particularly in case of melt mixing or compounding (using mixing equipment like internal mixer, two roll mills which can be up-scaled in industry). Albeit commercially available organomodified montmorillonite clays (OMt) are fairly compatible with the polar rubber like Acrylo-nitrile butadiene rubber (NBR), carboxylated nitrile rubber (XNBR), chloroprene rubber (CR) etc., its dispersion in non-polar rubbers like natural rubber (NR), is rather unsatisfactory. Incorporation of only 5 phr of OMt in NR by mechanical mixing leads to very poor dispersions with larger aggregates. Large agglomerates of OMt were observed with bare eyes throughout the matrix. Even in the TEM micrographs, highly agglomerated structures of clay particle were observed. A high degree of exfoliation of such clay is achieved in NR utilizing the so called ‘Propping-open approach’ where stepwise expansion of interlayer spacing of Mt took place. A series of long chain fatty acids (C16-C22) are intercalated into the interlayer space of OMt and a gradual expansion of the interlayer space were observed as the chain length of the fatty acid increased. Wide angle X-ray diffraction (WAXD), Fourier transform infrared spectroscopy (FTIR) and contact angle measurement indicated successful intercalation of the fatty acids into the interlayer space of the clay minerals. Since the fatty acid containing 22 carbon atoms has the largest interlayer distance among the modified samples studied, it has been selected for further study to understand the reinforcing behavior in NR matrix. An unusual mechanical percolation behavior of EOMt nanoparticles was observed in a NR matrix. The value of the mechanical percolation threshold (φp) and the fractal nature of nanoparticle clusters were determined through an analysis of the experimental data based on a theory put forward by Huber and Vilgis. This phenomenon was discussed in terms of fractal dimensions of the nanoparticle cluster. The impact of filler dispersion and rubber-filler interactions on the viscoelastic behavior of NR nanocomposites was systematically investigated. Significant non-linear viscoelastic behavior (Payne effect) was observed at very low EOMt content. Kraus and Maier-Göritz models were utilized to interpret such non-linear viscoelastic behavior. The nanocomposites showed enormous improvement in different physic-mechanical properties in the presence of EOMt. Technical elastomers are generally filled with certain fillers (e.g. carbon black) in order to reinforce the rubber matrix for some typical applications like tires, conveyer belts etc. Such rubber goods are always exposed to cyclic stress and deformations attributed to their dynamic application. Under constant and repeated applied stress, cracks develop at a stress concentration point, which could lead to ultimate failure. Therefore, the crack initiation and propagation behavior in such rubber products is very fundamental and need proper attention. The role of EOMt nanoparticles on the microstructure and fracture mechanical behavior of CB filled NR composites was investigated. Using pure-shear test specimen tear fatigue analysis (TFA) tests under cyclic conditions were carried out to explicate the crack growth behavior of CB filled NR in the presence of EOMt. A significant reduction in crack growth rate was noticed in the presence of only 5 phr of EOMt. Furthermore, instrumented tensile-impact tests (IT-IT) were also performed for the characterization of the crack resistance of the materials under impact-like loading conditions. / Die Einarbeitung von nur 5 phr organisch modifizierten Montmorillonite (OMt) in Naturkautschuk (NR) durch mechanisches Mischen führt zu einer sehr schlechten Verteilung mit größeren Aggregaten. Große Agglomerate von OMt waren mit bloßem Auge in der NR Matrix sichtbar. Sogar in TEM Aufnahmen wurden stark agglomerierte Strukturen beobachtet. Ein hoher Grad der Exfolierung von diesem Clay in NR wird durch die Nutzung des so genannten ‘Propping-open’ Ansatzes erreicht, in dem eine stufenweise Aufweitung des Zwischenschichtabstandes des OMt stattfindet. Eine Reihe langkettiger Fettsäuren (C16 – C22) wurde in die Zwischenschicht des OMt eingefügt. Mit zunehmender Kettenlänge der Fettsäuren wurde eine allmähliche Aufweitung der Zwischenschicht beobachtet. Da OMt, der mit einer Fettsäure mit 22 Kohlenstoffatomen modifiziert wurde, den größten Zwischenschichtabstand aller untersuchten Proben hatte, wurde diese Fettsäure für die weiteren Untersuchungen ausgewählt, um das Verstärkungsverhalten in der NR Matrix zu verstehen. Ein ungewöhliches Perkolationsverhalten der expandierten OMt (EOMt) Nanopartikel wurde in einer NR Matrix beobachtet. Der Wert der mechanischen Perkolationsschwelle (φp) und die fraktale Natur der Nanopartikel Cluster wurden durch eine Analyse der experimentellen Daten bestimmt, wobei eine Theorie, die von Huber und Vilgis vorangetrieben wurde, zur Anwendung kam. Dieses Phänomen wurde in Bezug auf die fraktalen Dimensionen der Nanopartikel Cluster diskutiert. Die Einfluss von EOMt Nanopartikel auf die Mikrostruktur und das mechanische Bruchverhalten von russgefüllten NR Kompositen wurde untersucht. Unter Verwendung reiner Schertestproben wurden Rissermüdungsanalysen unter zyklischer Belastung ausgeführt, um das Risswachstumsverhalten von russgefülltem NR in der Gegenwart von EOMt zu untersuchen und zu erklären. Eine signifikante Reduktion der Rissausbreitungsrate wurde in Gegenwart von nur 5 phr EOMt erreicht. Des Weiteren wurden auch instrumentierte Schlagzugprüfungen zur Charakterisierung des Risswiderstandes von Materialien unter schlagartigen Belastungsbedingungen durchgeführt.

Techn. Univ., Diss., 2002--Darmstadt

During the last years rubber nanocomposites obtained by incorporating anisotropic clay nanoparticles within a rubber matrix to tailor material properties have attracted steadily growing interest. However, one main complication preventing rubber-clay nanocomposites from many potential applications is the difficulty to achieve a high degree of exfoliation particularly in case of melt mixing or compounding (using mixing equipment like internal mixer, two roll mills which can be up-scaled in industry). Albeit commercially available organomodified montmorillonite clays (OMt) are fairly compatible with the polar rubber like Acrylo-nitrile butadiene rubber (NBR), carboxylated nitrile rubber (XNBR), chloroprene rubber (CR) etc., its dispersion in non-polar rubbers like natural rubber (NR), is rather unsatisfactory. Incorporation of only 5 phr of OMt in NR by mechanical mixing leads to very poor dispersions with larger aggregates. Large agglomerates of OMt were observed with bare eyes throughout the matrix. Even in the TEM micrographs, highly agglomerated structures of clay particle were observed. A high degree of exfoliation of such clay is achieved in NR utilizing the so called ‘Propping-open approach’ where stepwise expansion of interlayer spacing of Mt took place. A series of long chain fatty acids (C16-C22) are intercalated into the interlayer space of OMt and a gradual expansion of the interlayer space were observed as the chain length of the fatty acid increased. Wide angle X-ray diffraction (WAXD), Fourier transform infrared spectroscopy (FTIR) and contact angle measurement indicated successful intercalation of the fatty acids into the interlayer space of the clay minerals. Since the fatty acid containing 22 carbon atoms has the largest interlayer distance among the modified samples studied, it has been selected for further study to understand the reinforcing behavior in NR matrix. An unusual mechanical percolation behavior of EOMt nanoparticles was observed in a NR matrix. The value of the mechanical percolation threshold (φp) and the fractal nature of nanoparticle clusters were determined through an analysis of the experimental data based on a theory put forward by Huber and Vilgis. This phenomenon was discussed in terms of fractal dimensions of the nanoparticle cluster. The impact of filler dispersion and rubber-filler interactions on the viscoelastic behavior of NR nanocomposites was systematically investigated. Significant non-linear viscoelastic behavior (Payne effect) was observed at very low EOMt content. Kraus and Maier-Göritz models were utilized to interpret such non-linear viscoelastic behavior. The nanocomposites showed enormous improvement in different physic-mechanical properties in the presence of EOMt. Technical elastomers are generally filled with certain fillers (e.g. carbon black) in order to reinforce the rubber matrix for some typical applications like tires, conveyer belts etc. Such rubber goods are always exposed to cyclic stress and deformations attributed to their dynamic application. Under constant and repeated applied stress, cracks develop at a stress concentration point, which could lead to ultimate failure. Therefore, the crack initiation and propagation behavior in such rubber products is very fundamental and need proper attention. The role of EOMt nanoparticles on the microstructure and fracture mechanical behavior of CB filled NR composites was investigated. Using pure-shear test specimen tear fatigue analysis (TFA) tests under cyclic conditions were carried out to explicate the crack growth behavior of CB filled NR in the presence of EOMt. A significant reduction in crack growth rate was noticed in the presence of only 5 phr of EOMt. Furthermore, instrumented tensile-impact tests (IT-IT) were also performed for the characterization of the crack resistance of the materials under impact-like loading conditions. / Die Einarbeitung von nur 5 phr organisch modifizierten Montmorillonite (OMt) in Naturkautschuk (NR) durch mechanisches Mischen führt zu einer sehr schlechten Verteilung mit größeren Aggregaten. Große Agglomerate von OMt waren mit bloßem Auge in der NR Matrix sichtbar. Sogar in TEM Aufnahmen wurden stark agglomerierte Strukturen beobachtet. Ein hoher Grad der Exfolierung von diesem Clay in NR wird durch die Nutzung des so genannten ‘Propping-open’ Ansatzes erreicht, in dem eine stufenweise Aufweitung des Zwischenschichtabstandes des OMt stattfindet. Eine Reihe langkettiger Fettsäuren (C16 – C22) wurde in die Zwischenschicht des OMt eingefügt. Mit zunehmender Kettenlänge der Fettsäuren wurde eine allmähliche Aufweitung der Zwischenschicht beobachtet. Da OMt, der mit einer Fettsäure mit 22 Kohlenstoffatomen modifiziert wurde, den größten Zwischenschichtabstand aller untersuchten Proben hatte, wurde diese Fettsäure für die weiteren Untersuchungen ausgewählt, um das Verstärkungsverhalten in der NR Matrix zu verstehen. Ein ungewöhliches Perkolationsverhalten der expandierten OMt (EOMt) Nanopartikel wurde in einer NR Matrix beobachtet. Der Wert der mechanischen Perkolationsschwelle (φp) und die fraktale Natur der Nanopartikel Cluster wurden durch eine Analyse der experimentellen Daten bestimmt, wobei eine Theorie, die von Huber und Vilgis vorangetrieben wurde, zur Anwendung kam. Dieses Phänomen wurde in Bezug auf die fraktalen Dimensionen der Nanopartikel Cluster diskutiert. Die Einfluss von EOMt Nanopartikel auf die Mikrostruktur und das mechanische Bruchverhalten von russgefüllten NR Kompositen wurde untersucht. Unter Verwendung reiner Schertestproben wurden Rissermüdungsanalysen unter zyklischer Belastung ausgeführt, um das Risswachstumsverhalten von russgefülltem NR in der Gegenwart von EOMt zu untersuchen und zu erklären. Eine signifikante Reduktion der Rissausbreitungsrate wurde in Gegenwart von nur 5 phr EOMt erreicht. Des Weiteren wurden auch instrumentierte Schlagzugprüfungen zur Charakterisierung des Risswiderstandes von Materialien unter schlagartigen Belastungsbedingungen durchgeführt.

This work, conceived as a second step in the development of high-performance damping materials suitable for seismic application, describes the preparation and characterization of complex natural rubber-based composites containing hybrid nano- and conventional fillers. The cluster–cluster aggregation model was used to assess the apparent filler networking energy. The values obtained suggested that the presence of the hybrid nanofiller strengthens the filler networking. The same model was used to understand the mechanisms of energy dissipation. The damping coefficient was found to be in the sought range between 10% and 20% (at 0.5 Hz and high shear strain).

Thermoplastic Vulcanizates (TPVs) are itself a commercially high valued group of polymer blend. They render technological properties of conventional vulcanized elastomers with the ease of thermoplastic melt (re)processability. With ever growing market, TPVs have got plenty of applications among various fields. Here, the technological properties of these TPVs were tailored according to the purpose by interplaying physical parameters of polymers and advanced high energy electron technology. Electron irradiation, though a well-known technique for cross-linking in polymer industry, is only restricted to final product treatment. We take it to the next level by coupling a conventional internal mixer and a high energy electron accelerator. Polypropylene (PP) and natural rubber (NR) based TPVs have been prepared using this new reactive processing technology, named Electron Induced Reactive Processing (EIReP). Various electron treatment parameters were explored to maximize technological properties of TPVs. Effects of various polyfunctional monomers (PFM) were also studied. In an endeavor to develop a potential method for customization, deep insights of macroscopic and microscopic structure of these TPVs were presented with the help of various advanced scientific characterization techniques. Commonly faced difficulties like viscosity mismatch, cure rate mismatch, and incompatibility due to different molecular structures were furnished along with plausible solutions. Investigation of phase inversion from co-continuous matrix to thermoplastic matrix was dealt with special care as it helps to understand structure property correlation for all TPVs. To make the whole effort relevant, at the end of this thesis a summary of various technological properties has been given for the newly processed and commercially available TPVs.