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Depending on the specific plastic’s ageing sensitivities, the durations which plastic components remain in the environment can be very long. As, in the past, the advantages in ageing resistance and durability were highly evaluated, we now face the problem of quite stable plastic waste within the environment.
However, there is only little knowledge on the real timescales until macroscopic fragmentation for the different kinds of plastic under various environmental conditions.
Here, weathering methods are presented, which have been used for the failure prediction in specific outdoor conditions. Issues of uncertainty, reproducibility, or validation are discussed.
For the prediction of the plastic’s fragmentation, much longer time scales have to be considered. To do this within a limited project life span, various processes as well as their acceleration potential have to be evaluated separately, such as temperature increase or spectral shift.
The possibilities and limitations of such controlled acceleration will be discussed.
Weathering reference materials are used to characterize the harshness of an exposure, aiming on either reproducibility of a specific exposure or on the comparability between various kinds of weathering exposure.
The materials that are used as weathering reference materials differ in their sensitivities (as well as in interactions and interferences of the latter), conditioned by the different processes which lead to the respective property change. It is also essential to take into account the necessary measurement equipment for the respective property change, in order to allow timely intervention.
What are the key issues on choosing a weathering reference material?
What can be learned from the weathering reference materials, investigated so far?
Possibilities and limitations are discussed on the basis of existing weathering reference materials. Conclusions are drawn, for establishing new weathering reference materials.
Depending on the specific plastic’s ageing sensitivities, the durations which plastic components remain in the environment can be very long. As, in the past, the advantages in ageing resistance and durability were highly evaluated, we now face the problem of quite stable plastic waste within the environment.
However, there is only little knowledge on the real timescales until macroscopic fragmentation for the different kinds of plastic under various environmental conditions.
Here, weathering methods are presented, which have been used for the failure prediction in specific outdoor conditions. Issues of uncertainty, reproducibility, or validation are discussed.
For the prediction of the plastic’s fragmentation, much longer time scales have to be considered. To do this within a limited project life span, various processes as well as their acceleration potential have to be evaluated separately, such as temperature increase or spectral shift.
The possibilities and limitations of such controlled acceleration will be discussed.
Mass spectrometry is applied as a tool for the elucidation of molecular structures. This premises that gas-phase structures reflect the original geometry of the analytes, while it requires a thorough understanding and investigation of the forces controlling and affecting the gas-phase structures. However, only little is known about conformational changes of oligonucleotides in the gas phase. In this study, a series of multiply charged DNA oligonucleotides (n¼15–40) has been subjected to a comprehensive tandem mass spectrometric study to unravel transitions between different ionic gas-phase structures. The nucleobase sequence and the chain length were varied to gain insights into their influence on the geometrical oligonucleotide organization. Altogether, 23 oligonucleotides were analyzed using collision-induced fragmentation. All sequences showed comparable correlation regarding the characteristic collision energy. This value that is also a measure for stability, strongly correlates with the net charge density of the precursor ions. With decreasing charge of the oligonucleotides, an increase in the fragmentation energy was observed. At a distinct charge density, a deviation from linearity was observed for all studied species, indicating a structural reorganization. To corroborate the proposed geometrical change, collisional cross-sections of the oligonucleotides at different charge states were determined using ion mobility-mass spectrometry. The results clearly indicate that an increase in charge density and thus Coulomb repulsion results in the transition from a folded, compact form to elongated structures of the precursor ions. Our data show this structural transition to depend mainly on the charge density, whereas sequence and size do not have an influence.
Small, mobile propane gas vessels are widely spread and comprise additional hazards in case of a surrounding, intensive fire. The aim of the presented work is to holistically investigate the potential consequences of failure of these off-the-shelf propane gas vessels in case of an absence or malfunction of safety devices. In order to generate a statistically valid dataset, a total of 15 identical propane gas bottles without pressure relief device, each containing m = 11 kg of liquid propane, were underfired in horizontal position. For each selected fire type (wood fire, petrol pool fire, propane gas fire), five vessels were tested under identical conditions. Next to extensive camera equipment including a high-speed camera, systems to record the internal pressure of the gas cylinder, the resulting shock wave overpressure (three positions) and the flame and vessel temperature (three + three positions) during the underfiring were used. Also the unsteady, highly dynamical thermal radiation caused by the explosion of the expanding gas cloud was logged. The fragments were georeferenced and weighed after each test. The experiments prove the failure of all the gas cylinders at a burst pressure of pb = [71 … 98 bar] with a fragmentation into up to seven parts (average: four objects) and a subsequent explosion of the expanding vapour after mixing with the surrounding air. The overpressure measured in the close-up range (distance to the cylinder d = 5 m) resulting from the shockwave caused by the cylinder burst was up to pmax = 0.27 bar, which can potentially lead to significant injuries to humans and damage to building structures and infrastructure, especially in connection with the explosion and the resultant thermal radiation. The distance covered by the fragments after the failure was up to r = 260 m; 47% of the fragments hit the ground more than r = 50 m away from the position of failure.
Small, mobile propane gas vessels are widely spread and comprise additional hazards in case of a surrounding, intensive fire. The aim of the presented work is to holistically investigate the potential consequences of failure of these off-the-shelf propane gas vessels in case of an absence or malfunction of safety devices. In order to generate a statistically valid dataset, a total of 15 identical propane gas bottles without pressure relief device, each containing m = 11 kg of liquid propane, were underfired in horizontal position. For each selected fire type (wood fire, petrol pool fire, propane gas fire), five vessels were tested under identical conditions. Next to extensive camera equipment including a high-speed camera, systems to record the internal pressure of the gas cylinder, the resulting shock wave overpressure (three positions) and the flame and vessel temperature (three + three positions) during the underfiring were used. Also the unsteady, highly dynamical thermal radiation caused by the explosion of the expanding gas cloud was logged. The fragments were georeferenced and weighed after each test. The experiments prove the failure of all the gas cylinders at a burst pressure of pb = [71 … 98 bar] with a fragmentation into up to seven parts (average: four objects) and a subsequent explosion of the expanding vapour after mixing with the surrounding air. The overpressure measured in the close-up range (distance to the cylinder d = 5 m) resulting from the shockwave caused by the cylinder burst was up to pmax = 0.27 bar, which can potentially lead to significant injuries to humans and damage to building structures and infrastructure, especially in connection with the explosion and the resultant thermal radiation. The distance covered by the fragments after the failure was up to r = 260 m; 47% of the fragments hit the ground more than r = 50 m away from the position of failure.
Hydroxyl radical-induced oxidation of proteins and peptides can lead to the cleavage of the peptide, leading to a release of fragments. Here, we used high-performance liquid chromatography tandem mass spectrometry (HPLC-MS/MS) and pre-column online ortho-phthalaldehyde (OPA) derivatization-based amino acid analysis by HPLC with diode array detection and fluorescence detection to identify and quantify free amino acids released upon oxidation of proteins and peptides by hydroxyl radicals. Bovine serum albumin (BSA), ovalbumin (OVA) as model proteins, and synthetic tripeptides (comprised of varying compositions of the amino acids Gly, Ala, Ser, and Met) were used for reactions with hydroxyl radicals, which were generated by the Fenton reaction of iron ions and hydrogen peroxide. The molar yields of free glycine, aspartic acid, asparagine, and alanine per peptide or protein varied between 4 and 55%. For protein oxidation reactions, the molar yields of Gly (∼32-55% for BSA, ∼10-21% for OVA) were substantially higher than those for the other identified amino acids (∼5-12% for BSA, ∼4-6% for OVA). Upon oxidation of tripeptides with Gly in C-terminal, mid-chain, or N-terminal positions, Gly was preferentially released when it was located at the C-terminal site. Overall, we observe evidence for a site-selective formation of free amino acids in the OH radical-induced oxidation of peptides and proteins, which may be due to a reaction pathway involving nitrogen-centered radicals.
Concrete spalling due to fire exposure is often defined as the sudden detachment of fragments from a concrete surface. It can be quantified by various parameters of which weight loss and spalling depth are the most common ones. The risk of spalling is influenced by many factors such as concrete composition, heating rate and applied testing methods. A reduced scale testing method should be developed to analyse the spalling behaviour and to understand its effectiveness in more detail. As a subsection of this development, this study aimed to analyse the effect of different-sized, circular heated areas in semi full-scale fire tests. Therefore, vermiculite slabs with varying cut-outs in their centre were placed between a specimen made of a spalling-sensitive concrete and the combustion chamber. The combustion chamber was heated following a standard fire curve. Our experimental results show that the thermal expansion inside of equal-sized specimens is strongly dependent on the size of the heated area. In addition, this area also affects thermal stresses. They decrease as a result of lower temperature gradients for tests with smaller unheated boundary areas. Apart from this, the analysis of fragments shows no correlation between their relative volume distribution and the heated area.