TY - JOUR A1 - Bajer, Kamila A1 - Braun, Ulrike T1 - Different aspects of the accelerated oxidation of polypropylene at increased pressure in an autoclave with regard to temperature, pretreatment and exposure media N2 - 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. KW - Autoclave test KW - Accelerated aging KW - Polypropylene KW - Electron radiation PY - 2014 U6 - https://doi.org/10.1016/j.polymertesting.2014.05.006 SN - 0142-9418 VL - 37 SP - 102 EP - 111 PB - Elsevier Science CY - Amsterdam [u.a.] AN - OPUS4-30867 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Braun, Ulrike A1 - Brademann-Jock, Kerstin A1 - Stark, Wolfgang T1 - Cure monitoring of epoxy films by heatable in situ FTIR analysis: Correlation to composite parts N2 - 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. KW - Crosslinking KW - Resins KW - Spectroscopy KW - Thermosets KW - Thermal properties PY - 2014 U6 - https://doi.org/10.1002/APP.39832 SN - 0021-8995 SN - 1097-4628 VL - 131 IS - 3 SP - 39832, 1 EP - 10 PB - Wiley InterScience CY - Hoboken, NJ AN - OPUS4-30716 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Dümichen, Erik A1 - Braun, Ulrike A1 - Senz, R. A1 - Fabian, G. A1 - Sturm, Heinz T1 - 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 N2 - 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. KW - TDS-GC-MS KW - TGA-FTIR KW - TGA-MS KW - Degradation KW - Polymer KW - Solid-phase extraction PY - 2014 U6 - https://doi.org/10.1016/j.chroma.2014.05.057 SN - 0021-9673 VL - 1354 SP - 117 EP - 128 PB - Elsevier B.V. CY - Amsterdam AN - OPUS4-31046 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Grabmayer, K. A1 - Wallner, G.M. A1 - Beißmann, S. A1 - Braun, Ulrike A1 - Steffen, R. A1 - Nitsche, D. A1 - Röder, B. A1 - Buchberger, W. A1 - Lang, R.W. T1 - Accelerated aging of polyethylene materials at high oxygen pressure characterized by photoluminescence spectroscopy and established aging characterization methods N2 - 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. KW - Polyethylene KW - PE-RT KW - High oxygen pressure KW - Photoluminescence spectroscopy KW - Aging PY - 2014 U6 - https://doi.org/10.1016/j.polymdegradstab.2014.06.021 SN - 0141-3910 SN - 1873-2321 VL - 109 SP - 40 EP - 49 PB - Applied Science Publ. CY - London AN - OPUS4-31349 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Meyer, S. A1 - Timmel, S. A1 - Gläser, M. A1 - Braun, Ulrike A1 - Wachtendorf, Volker A1 - Hagendorf, C. T1 - Polymer foil additives trigger the formation of snail trails in photovoltaic modules N2 - 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. KW - Snail trails KW - Encapsulation foil KW - Back-sheet foil KW - Additives KW - Silver nanoparticles PY - 2014 U6 - https://doi.org/10.1016/j.solmat.2014.06.028 SN - 0927-0248 VL - 130 SP - 64 EP - 70 PB - Elsevier B.V. CY - Amsterdam [u.a.] AN - OPUS4-31249 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Meyer, S. A1 - Timmel, S. A1 - Richter, S. A1 - Werner, M. A1 - Gläser, M. A1 - Swatek, S. A1 - Braun, Ulrike A1 - Hagendorf, C. T1 - Silver nanoparticles cause snail trails in photovoltaic modules N2 - After some months of operation, a number of PV modules develop a discolouration defect called 'snail trails', or 'snail traces', which appear as irregular dark stripes across the cells. Whereas these traces were soon identified as discoloured silver contacts along the cell edges or at micro cracks, the chemical and mechanistic reasons for this phenomenon have not yet been resolved in detail. In this work we show that silver nanoparticles accumulating within the encapsulation foil cause the brownish discolouration, and that certain additives of encapsulation and back sheet foils trigger the formation of these nanoparticles. KW - Snail trails KW - Cell cracks KW - Encapsulation foil KW - Ag contact finger KW - Nanoparticles PY - 2014 U6 - https://doi.org/10.1016/j.solmat.2013.11.013 SN - 0927-0248 VL - 121 SP - 171 EP - 175 PB - Elsevier B.V. CY - Amsterdam [u.a.] AN - OPUS4-30059 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Ressnig, A. A1 - Corbiere, T. A1 - Lunkenbein, T. A1 - Braun, Ulrike A1 - Willinger, M. G. A1 - Antonietti, M. T1 - Decomposition synthesis of tuneable, macroporous carbon foams from crystalline precursors via in situ templating N2 - A flexible, sustainable, one-step thermal decomposition route for the synthesis of hierarchical, heteroatom doped carbon foams is presented. Task-specific semi-organic crystals combine functions for three different purposes: the carbon and heteroatom source, a foaming agent (CO2) and an in situ generable template (NaCl). Insights to the decomposition pathway were gained through FTIR/MS coupled TGA and an ultrafast out-of-furnace heating procedure and the products were analysed with (HR)SEM/TEM, EELS, FTIR, and N2 sorption. The resulting macroporous carbon foams are excellent supports for metallic nanoparticles due to their hierarchical structure, high surface area and tuneable heteroatom contents. This was demonstrated for catalytically active copper or the magnetic CoNi alloy for water purification. KW - macroporous carbon KW - thermal decomposition KW - synthesize heteroatom KW - in situ template (NaCl) PY - 2014 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:b43-318641 SN - 2050-7496 SN - 2050-7488 VL - 2 IS - 42 SP - 18076 EP - 18081 PB - RSC CY - London [u.a.] AN - OPUS4-31864 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -