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Relaxation behaviour of thermoplastic polyurethanes with covalently attached nitroaniline dipoles
(2002)
Thermoplastic polyurethanes with covalently attached nitroaniline chromophores exhibit a strong high-temperature relaxation associated with a glass transition rather than the typical frequency-independent loss due to the aggregation of polymer chains via hydrogen bonds. This relaxation behaviour suggests the formation of an amorphous structure without separation into soft-segment and hard-segment phases. In such a structure, a field-induced orientation of molecular dipoles is stabilised by the high viscosity of the material below its glass transition. The dipole orientation yields a pyroelectric effect caused by dipole-density changes upon thermal expansion and contraction.
The changes in phase separation are investigated by varying the chain length of the soft-phase component and studying its influence on the calorimetric, dynamic-mechanical, and dielectrical properties. Good correlation was found between differential scanning calorimetry, dynamic-mechanical analysis and dielectric spectroscopy as well as measured and calculated pyroelectric coefficients. This leads to a uniform picture of the structural changes caused by the incorporation of nitroaniline chromophores into the polyurethane structure.
Degradation effects of automotive coatings after weathering as detected by thermoluminescence
(2004)
Angesichts der spezifischen Bedeutung der Aushärtung von Phenolharzen für ihre Eigenschaften als Ingenieurwerkstoffe besteht großes Interesse an deren quantitativer Charakterisierung. Mittels DSC-Messungen unter hohem Druck (HP-DSC) kann die Vernetzungsreaktion der Phenolharzformmassen durch die Unterdrückung der Verdampfung niedermolekularer Substanzen ohne störende Überlagerungen verfolgt werden. Mittels verschiedener Vernetzungsgrade können die Einflussparameter der Aufheizrate und der Nachtemperung optimiert werden. Die Messergebnisse ermöglichen eine Modellierung der Reaktionskinetik mit dem Ziel einer verbesserten Prozessführung und Qualitätskontrolle in der industriellen Praxis.
Microbial induced corrosion (MIC) is a crucial problem in many technical plants as well as fuel tanks, leading to considerable damage and huge financial losses. Successful prevention of MIC requires the localization of first signs of corrosion as well as the identification of factors influencing the corrosion process. In this respect, also the determination of corrosion rates can be of interest for the possible prevention of MIC. Hence, there is a growing need for sensitive and preferably inexpensive tools that enable the early detection of MIC. Of special interest are methods, which provide spatially and time-resolved information and allow the study of changes on metal surfaces as prerequisites for a more detailed analysis of ongoing corrosion processes at a MIC-affected site.
Biofilm formation can lead to changes in pH, oxygen and chloride concentration as well as to the release of certain metal ions like Fe(II) and Mn(II) depending on the type of metal surface involved. Hence, optical methods enabling the detection of these analytes at very low concentration and monitoring of their changes can be used for MIC detection. Here, we propose to utilize polymeric nanosensors for MIC detection via the determination of the local pH value changes in different biofilms. Such nanosensors are known to have several advantages in imaging applications such as intracellular pH measurements including the ease of doping or labeling with a multitude of analyte-responsive and inert dye molecules for the realization of a high analyte sensitivity and ratiometric sensing. Moreover, they can be surface functionalized with target-specific ligands e.g., lectins, for the specific binding to the outer surface of certain types of bacteria. In this respect, different polymer architectures will be studied to identify an optimal candidate in terms of imaging performance in conjunction with several classes of pH-responsive fluorescent dyes like cyanines, aza-BODIPYs, and xanthenes, utilizing different mechanism of signal generation such as photo-induced electron transfer or protonation-induced changes in the spectral position of absorption and emission spectra.
Microbial induced corrosion (MIC) is a crucial problem in many technical plants as well as fuel tanks, leading to considerable damage and huge financial losses. Successful prevention of MIC requires the localization of first signs of corrosion as well as the identification of factors influencing the corrosion process.1 Hence, there is a growing need for sensitive and preferably inexpensive tools that enable the early detection of MIC. Of high importance are methods, which provide spatially and time-resolved information and allow the study of changes on metal surfaces as prerequisites for a more detailed analysis of ongoing corrosion processes at a MIC-affected site.2 In this respect, also the determination of corrosion rates can be of interest for the possible prevention of MIC.
Microbial induced corrosion (MIC) is a crucial problem in many technical plants as well as fuel tanks, leading to considerable damage and huge financial losses. Successful prevention of MIC requires the localization of first signs of corrosion as well as the identification of factors influencing the corrosion process.1 Hence, there is a growing need for sensitive and preferably inexpensive tools that enable the early detection of MIC. Of high importance are methods, which provide spatially and time-resolved information and allow the study of changes on metal surfaces as prerequisites for a more detailed analysis of ongoing corrosion processes at a MIC-affected site.2 In this respect, also the determination of corrosion rates can be of interest for the possible prevention of MIC.
Liquid chromatography in combination with spectroscopic methods like matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) or nuclear magnetic resonance (NMR) spectroscopy is a powerful method to characterize silsesquioxanes and silsesquioxane mixtures. As new examples, the formation of silsesquioxyl-substituted silsesquioxanes [(n-octyl)7(SiO1.5)8]2O and [(n-octyl)7(SiO1.5)8O]2[(n-octyl)6(SiO1.5)8] as well as the cage rearrangement of octa-[(n-heptyl)silsesquioxane] to larger structur es [(n-heptyl)SiO1.5)]n up to n=28 are shown.
Compressed natural gas (CNG) is a widely used automotive fuel in a variety of countries. In case of a vehicle fire where the safety device also malfunctions, a failure of the CNG automotive cylinder could occur. Such a cylinder failure is associated with severe hazards for the surrounding environment. Firstly, a comprehensive analysis is given below, summarizing various accidents involving CNG automotive cylinders and their consequences. In an extensive experimental program, 21 CNG automotive cylinders with no safety device were tested. Of the 21, burst tests were carried out on 5 Type III and 5 Type IV cylinders. Furthermore, fire tests with 8 Type III and 3 Type IV cylinders were conducted. Apart from cylinder pressure, inner temperature and cylinder mantle temperature, the periphery consequences, such as nearfield blast pressure and fragmentation are documented. The maximum measured overpressure due to a Type III cylinder failure was p = 0.41 bar. Each traceable fragment was georeferenced. All-in-all, fragment throw distances of d > 300 m could be observed. As one key result, it can be stated that the tested Type IV CNG cylinders showed less critical failure behavior then the Type III cylinders under fire impingement.
In case of a vehicle fire, an installed LPG (liquefied petroleum gas) tank with a malfunctioning safety device poses severe hazards. To investigate the consequences in case of tank failure, we conducted 16 tests with toroidal shaped LPG vehicle tanks. Three tanks were used for a Hydraulic Burst Test under standard conditions. Another three tanks were equipped with a statutory safety device and were subjected to a gasoline pool fire. The safety device prevented tank failure, as intended. To generate a statistically valid dataset on tank failure, ten tanks without safety devices were exposed to a gasoline pool fire. Five tanks were filled to a level of 20 %; the re-maining five were filled to a level of 100 %. In order to gain information on the heating process, three tem-perature readings at the tank surface, and three nearby flame temperatures were recorded. At distances of l = (7; 9; 11) m to the tank, the overpressure of the shock wave induced by the tank failure and the unsteady tem-peratures were measured. All ten tanks failed within a time of t < 5 min in a BLEVE (boiling liquid expanding vapor explosion). Seven of these resulted directly in a catastrophic failure. The other three resulted in partial failure followed by catastrophic failure. A near field overpressure at a distance of l = 7 m of up to p = 0.27 bar was measured. All ten tests showed massive fragmentation of the tank mantle. In total, 50 fragments were found. These 50 fragments make-up 88.6 % of the original tank mass. Each fragment was georeferenced and weighed. Fragment throwing distances of l > 250 m occurred. For the tanks with a fill level of 20 %, the average number of fragments was twice as high as it was for the tanks that were filled completely.