Dokument-ID Dokumenttyp Autoren/innen Persönliche Herausgeber/innen Haupttitel Abstract Auflage Verlagsort Verlag Herausgeber (Institution) Erscheinungsjahr Titel des übergeordneten Werkes Jahrgang/Band ISBN Veranstaltung Veranstaltungsort Beginndatum der Veranstaltung Enddatum der Veranstaltung Ausgabe/Heft Erste Seite Letzte Seite URN DOI Lizenz Datum der Freischaltung OPUS4-30867 Zeitschriftenartikel Bajer, Kamila; Braun, Ulrike Different aspects of the accelerated oxidation of polypropylene at increased pressure in an autoclave with regard to temperature, pretreatment and exposure media The aim of this study is to investigate and compare three different factors, temperature, pretreatment and exposure media, on the oxidation and aging behavior of polypropylene (PP) bulk samples in the autoclave test under increased oxygen pressure. The aging of polypropylene, in this case syringe material, was accelerated under different conditions. The samples were aged at 75°, 80° and 85 °C under pure oxygen and at 75 °C under ultrapure water. Further samples treated with 15 kGy (e-beam) were aged at 75 °C under pure oxygen. All experiments were carried out at an oxygen partial pressure of 50 bar. The different courses of aging were evaluated and compared. Color and transparency were used to assess the visual changes; weight, geometry and tensile test for the changes in technical properties; and DSC, FTIR and TDS-GC-MS to improve our physico-chemical understanding of the aging processes. The investigations showed that all factors tested influence oxidation/aging behaviour. Dry or wet exposure has no effect on aging during the induction time. However, after the point of maximum service time the degradation process of polymer changes significantly in the presence of water. The increase of aging temperature decreases the maximum service time; however a temperature higher than 80 °C changes the relative ratio of surface and bulk oxidation. The pretreatment with irradiation decreases the maximum service time further, because the irradiation partly damages the antioxidant, and the mobility of antioxidant fragments inside the polymer changes. These diffusion effects influence the relative ratio of bulk and surface oxidation of the polymer sample. Amsterdam [u.a.] Elsevier Science 2014 Polymer testing 37 102 111 10.1016/j.polymertesting.2014.05.006 2016-02-20 OPUS4-30704 Vortrag Braun, Ulrike Einfluss der Feuchtigkeit auf die Schlichte von Glasfasern während der Lagerung 2014 DEWI-OCC DEWI-OCC Bremen, Germany 2014-05-20 2014-05-20 2016-02-20 OPUS4-30304 Vortrag Braun, Ulrike Molekulare Effekte von Alterungsreaktionen: Korrelation zu realen Proben 2014 Alterung von Polymerwerkstoffen und -bauteilen Alterung von Polymerwerkstoffen und -bauteilen Munich, Germany 2014-02-26 2014-02-27 2016-02-20 OPUS4-30603 Vortrag Braun, Ulrike Techniques for Understanding Fire Retardant Behaviour: Molecular Degradation and Decomposition Schemas 2014 Fire Retardant Technologies, FRT 14 Fire Retardant Technologies, FRT 14 Preston (Lancashire), England 2014-04-14 2014-04-16 2016-02-20 OPUS4-31420 Vortrag Braun, Ulrike Sulphur containing additives for polystyrene: influencing the decomposition behaviour in the condensed phase 2014 MoDeSt MoDeSt Portoro˛, Slovenia 2014-08-31 2014-09-04 2016-02-20 OPUS4-31584 Posterpräsentation Braun, Ulrike Cure Monitoring Using Infrared Spectroscopy 2014 Wissenschaftskolloquium "Nanotechnologie für Kunststoffverbunde Wissenschaftskolloquium "Nanotechnologie für Kunststoffverbunde Braunschweig, Germany 2014-09-30 2014-09-30 2016-02-20 OPUS4-30716 Zeitschriftenartikel Braun, Ulrike; Brademann-Jock, Kerstin; Stark, Wolfgang Cure monitoring of epoxy films by heatable in situ FTIR analysis: Correlation to composite parts The curing mechanism of an epoxy film containing dicyandiamide (DICY) and an epoxy formulation based on diglycidyl ether of Bisphenol A (DGEBA) polymer was studied as a function of various temperature programs. The investigation was performed in situ, using a thin film of the epoxy mixture on a silicon wafer substrate in a heatable transmission tool of a FTIR spectrometer. Based on these model-curing experiments, a major curing mechanism was proposed, taking into account the appearance, the decrease, and the development of characteristic bands at various temperatures. The conclusions of the model curing were correlated to FTIR measurements on a real, 50-mm-thick glass fiber reinforced component composite part from a technical process. It could be shown that characteristic bands that develop at curing temperatures above 150°C appear especially in the center of the thick sample. From the chemical or molecular point of view, this demonstrates the established technician's understanding that temperature control inside a large-scale fiber composite of, for example, aircraft, wind-turbine, automotive applications component is of major importance. Hoboken, NJ Wiley InterScience 2014 Journal of applied polymer science 131 3 39832, 1 10 10.1002/APP.39832 2016-02-20 OPUS4-31046 Zeitschriftenartikel Dümichen, Erik; Braun, Ulrike; Senz, R.; Fabian, G.; Sturm, Heinz Assessment of a new method for the analysis of decomposition gases of polymers by a combining thermogravimetric solid-phase extraction and thermal desorption gas chromatography mass spectrometry For analysis of the gaseous thermal decomposition products of polymers, the common techniques are thermogravimetry, combined with Fourier transformed infrared spectroscopy (TGA-FTIR) and mass spectrometry (TGA-MS). These methods offer a simple approach to the decomposition mechanism, especially for small decomposition molecules. Complex spectra of gaseous mixtures are very often hard to identify because of overlapping signals. In this paper a new method is described to adsorb the decomposition products during controlled conditions in TGA on solid-phase extraction (SPE) material: twisters. Subsequently the twisters were analysed with thermal desorption gas chromatography mass spectrometry (TDS-GC-MS), which allows the decomposition products to be separated and identified using an MS library. The thermoplastics polyamide 66 (PA 66) and polybutylene terephthalate (PBT) were used as example polymers. The influence of the sample mass and of the purge gas flow during the decomposition process was investigated in TGA. The advantages and limitations of the method were presented in comparison to the common analysis techniques, TGA-FTIR and TGA-MS. Amsterdam Elsevier B.V. 2014 Journal of chromatography A 1354 117 128 10.1016/j.chroma.2014.05.057 2016-02-20 OPUS4-31349 Zeitschriftenartikel Grabmayer, K.; Wallner, G.M.; Beißmann, S.; Braun, Ulrike; Steffen, R.; Nitsche, D.; Röder, B.; Buchberger, W.; Lang, R.W. Accelerated aging of polyethylene materials at high oxygen pressure characterized by photoluminescence spectroscopy and established aging characterization methods Two commercial polyethylene grades were exposed to water at elevated temperatures and enhanced oxygen pressure. To characterize their aging behavior laser-induced photoluminescence spectroscopy was applied. Additionally, aging characterization was performed by established methods such as tensile testing, infrared (IR) spectroscopy, high performance liquid chromatography (HPLC), differential scanning calorimetry (DSC) and UV-VIS spectroscopy. During the initial stages of aging, the overall concentration of phenolic antioxidants as well as oxidation onset temperatures decreased exponentially. Simultaneously, significant discoloration due to the formation of conjugated degradation products from phenolic antioxidants (e.g., quinone methides) was detected. After the consumption of antioxidants, photoluminescence started to grow continuously presumably due to the formation of photoluminescent unsaturated carbonyls. In the final stages of aging, embrittlement of the materials as characterized by the degradation of mechanical properties (i.e., loss in ductility) coincided with rising carbonyl index values as well as an increase in crystallinity due to chemicrystallization. Between integrated photoluminescence intensity and carbonyl index, a linear correlation was established. In the induction period, the photoluminescence method exhibited a significantly higher sensitivity to reflect aging induced material changes. London Applied Science Publ. 2014 Polymer degradation and stability 109 40 49 10.1016/j.polymdegradstab.2014.06.021 2016-02-20 OPUS4-31249 Zeitschriftenartikel Meyer, S.; Timmel, S.; Gläser, M.; Braun, Ulrike; Wachtendorf, Volker; Hagendorf, C. Polymer foil additives trigger the formation of snail trails in photovoltaic modules After several months of operation, many photovoltaic (PV) modules develop a discolouration defect called snail trails which appear as irregular dark traces across the cells. These traces are caused by silver nanoparticles accumulating within the encapsulation foil directly above the grid finger. In this work we systematically investigate combinations of encapsulation and back-sheet foils with respect to their susceptibility for snail trails. We can show that certain additive compositions within the encapsulation and back sheet foils are critical for the formation of the discolouring silver nanoparticles. We suggest a reaction model explaining the formation of snail trails from a chemical point of view. This fundamental understanding allows the rapid testing of foils for their snail trail sensitivity as well as the special design of resistant foils. Amsterdam [u.a.] Elsevier B.V. 2014 Solar energy materials & solar cells 130 64 70 10.1016/j.solmat.2014.06.028 2016-02-20