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Eingeladener Vortrag
- nein (42)
The thermo-oxidative stability of commercially available polymer optical fibers (POFs) and their components (cores and claddings) was investigated. All the bare POFs (core and cladding only) studied here were based on poly(methyl methacrylate) (PMMA) core. The fibers were exposed to 100 °C/low humidity for about 4200 h. Chemiluminescence (CL) technique was applied to investigate the thermo-oxidative stability and for measuring the transmission loss during exposure a prototype device called multiplexer was used. POFs exhibited variation in thermo-oxidative stability although they possessed identical core material PMMA. This was due to difference in the chemical compositions of claddings. Claddings were more susceptible to the thermo-oxidative degradation compared to cores. The thermo-oxidative degradation of both the cladding and the core was found in POFs as a result of climatic exposure. POFs showed an early drop-off followed by a slow decline of transmission. The early drop-off of transmission was attributed to physical changes like thermal expansion and the slow decline of transmission to chemical changes like oxidative degradation of POFs. A good linear relationship between optical transmission stability and thermo-oxidative stability of POFs was established from these studies.
Ansätze zur Testverkürzung
(2009)
chemiluminescence studies on the thermooxidative stability of poly(1,4-phenyl phenylene vinylene)
(1996)
Bei der Auswahl von Werkstoffen spielt deren Alterung oft eine untergeordnete Rolle, stattdessen wird häufig der ungealterte Ausgangszustand optimiert. Materialien altern aber unterschiedlich. Der Effekt der molekularen Alterung spiegelt sich in den Eigenschaften mehr oder weniger stark und in unterschiedlichem zeitlichen Verlauf wider. Da es kein physikalisch-chemisches Modell dafür gibt, sind Alterungseffekte empirisch zu bestimmen.
Combined impact of ultraviolet and chemical fluids on high-density polyethylene packaging material
(2012)
To investigate the ageing behaviour of filled plastic containers outdoors, square cuts of the wall of two high-density polyethylene (HDPE) types were exposed to ultraviolet (UV) radiation at their front side and to specific liquid chemicals (de-ionized water, surfactant or White Spirit) at their back. The UV radiant exposure at the front side was 80 MJ/m².
To compare the actions of the different exposures, separate dark backside fluid exposures were performed, in parallel. Besides, UV weathering was carried out until a UV radiant exposure of 325 MJ/m², being roughly comparable to outdoor exposure of one year in Northern Australia.
An unpigmented HDPE included in the investigation gave no sufficient protection for the White Spirit. In addition, it showed clear degradation after several of these exposures. In combination with the White Spirit, an increase of carbonyl bonds was measured, presumably assignable to degradation products of the White Spirit.
For a pigmented HDPE material, with the implemented combined exposures, no relevant damage was observed, within applied the exposure period.
Scrap tyres are widely reused in the form of granules as infill materials or component of sub-base layers in construction of sporting grounds such as synthetic turf areas and athletic track surfaces. The recycled rubber may contain organic and inorganic pollutants due to the presence of vulcanisation catalysts, stabilisers and other additives which can be released into soil and groundwater in the case of outdoor sports facilities. In order to evaluate the amount of potentially mobile pollutants, leaching tests can be employed. This study aimed particularly at the investigation of the feasibility of column tests using complete synthetic surface flooring or turf system assemblies. The release of zinc and polycyclic aromatic hydrocarbons (PAH) leached from components of sports surfaces containing recycled rubber granules was considered. Additionally, batch tests on coated and uncoated styrene butadiene rubber (SBR) granules aged by artificial weathering were performed to indicate its possible influence on the leaching behaviour of zinc and PAH. The chosen approach of column tests simulating typical complete synthetic sports surface installations has been proven to be feasible and robust. The time-dependent leaching behaviour and interactions between single components can be evaluated by column tests. Zinc was the most relevant contaminant in the eluates and its leachability was enhanced after accelerated ageing by artificial weathering. Leachable PAH were found in relatively low but well detectable amounts which increase by ageing as well.
In a laboratory test, transparent high‐density polyethylene (HDPE) jerrycans have been exposed to both UV radiation and 55 wt‐% nitric acid solution at (41 ± 2)°C, for up to 20 days. For comparison, UV radiant exposure (21 days) and nitric acid exposure (up to 6 weeks) were performed separately, at nearly equal temperatures. The damages are compared with FTIR spectroscopy in ATR and HT‐gel permeation chromatography(GPC) on a molecular level and with hydraulic internal pressure testing as a component test. For the used jerrycans, relevant oxidation can only be found after the combined exposure. This is caused by the decomposition of nitric acid into nitrous gases by UV radiation, which is also observed at lower concentrations (28 wt‐%). After 6 days of laboratory exposure, this is rated as critical, which corresponds to about 1/10 year in Central Europe, according to the UV radiant exposure. The gradual increase in oxidative damage shows the reproducibility of the test.
Die Grenzen der Oberflächentemperaturen von Proben, die der natürlichen oder einer künstlichen Globalstrahlung ausgesetzt sind, können grob mit sog. Schwarzstandard Thermometern BST oder Weißstandard Thermometern WST ermittelt werden [ 1a) ].
Um einige Mängel der aktuellen Konstruktion zu beseitigen, wird ein neues Konzept dieser Thermometer vorgeschlagen, das sie weniger träge und ihre physikalischen Eigenschaften ähnlicher denen einer 5 mm dicken Polymerplatte macht. Es wird auch gezeigt, dass eine Anforderung an die Reaktionszeit von weniger als 1 min in EN 513 unrealistisch ist.
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.
Jerrycans made from three different types of high-density polyethylene (HDPE) were exposed outdoors, for one Berlin summer season. They were filled with a 55 percent nitric acid solution (HN03), pure water, or air, and half of them were protected from sunlight by an UV absorbing canvas. Thus, the separate effects of UV radiation and nitric acid could be compared to the combined impact. Combined impact was mainly affected by decomposition of nitric acid, resulting in presence of reactive nitrogen oxides, increased oxygen partial pressure, and UV radiation energy, simultaneously in vapour phase.
To investigate the degradation effects after the outdoor exposure, jerrycans were exposed to a so called hydraulic internal pressure test, similar to an approval test for dangerous goods packaging. After combined impact of UV radiation and nitric acid, internal pressure tests showed very fast failures, whereas after separate impacts no remarkable deteriorations were observed, compared to unaged jerrycans.
Temperature is an important parameter in weathering tests. In many (photo-)chemical degradation processes a Variation of the specimen temperature by A t = + 1 °C can cause a Variation of AP(property change) by ± 8%.
Since the early eighties it is well known that some types of black panel thermometers can show temperatures that are far below the maximum surface temperature of a black specimen. Although, there were precise requirements for the black coating of the BPT, a replacement by a white coating - depending on the design of the BPT - did not really change the temperature shown by the thermometer. There was no correlation between the BPT and the specimen surface temperature.
In Europe and later at ISO the so-called black- and white-standard thermometers BST/WST were introduced. Now, there are BST and WST (ISO) and there are thermally uninsulated and insulated BPT and WPT (ASTM), partly for artificial or for outdoor exposure. And there are other adventurous procedures to determine surface temperatures.
The different types of thermometers and different procedures will be discussed and it will be shown that there is no procedure which establishes a correlation between outdoor surface temperatures and surface temperatures in artificial exposure tests.
The aim of the joint project ViPQuali (Virtual Product Qualification) was to describe a components ageing behaviour in a given environment, by numerical simulation.
Having chosen polypropylene (PP) as the material, which does not show sensitivity to moisture, the relevant weathering parameters of the doseresponse functions could be limited to spectral irradiance and temperature.
In artificial irradiation tests, for PP plates of varied stabiliser content, spectral sensitivity as well as temperature dependence of irradiation-caused crack formation was quantified. For that purpose, samples were exposed both to artificial weathering tests at various constant temperatures and to spectrally resolved irradiation. The temperature dependence could be modelled by an Arrhenius fit. For fitting the spectral sensitivity, a plateau function was chosen. Subsequently, the stabiliser content was parameterised and extrapolated.
The formed dose–response functions were incorporated into a Computational Fluid Dynamics (CFD) software program, simulating the environment of a sample within a Phoenix-exposed IP/DP (Instrument Panel/Door Panel box) box, based on sun position and weather conditions, including radiation interactions. Observed local effects as well as the general ageing advance of PP hats are compared with respect to simulation and experiment.
Resulting from this project, for this most simple example of PP of varied stabiliser content, the time to failure can be estimated for each weathering exposure environment with known time-resolved irradiance and temperature conditions.
The optical transmission stability was investigated for commercially available polymer optical fibers (POFs) which were exposed to a climate of 92°C and 95% relative humidity for about 3300 h. The optical transmission stability of POFs was correlated to their thermooxidative stability. POFs possessed identical core material, poly(methyl methacrylate), but they differed in the materials used for the claddings. The optical transmission was measured online using a prototype device called multiplexer. The chemiluminescence (CL) technique was applied to characterize the thermooxidative stability and degradation of POFs. CL analysis reveals the thermooxidative degradation of bare POFs (core and cladding), predominantly of the claddings, as a result of climatic exposure. Ultraviolet-visible transmittance measurements demonstrated more changes in the claddings as compared to the cores due to degradation. The CL and optical measurements data indicated that the optical transmission stability of POFs was dependent mainly on the thermooxidative stability of the claddings and their chemical compositions.
Accelerated weathering test for plastics and coatings that are exposed to acidic precipitation
(2008)
Chemiluminescence for the early detection of weathering effects of coatings - Part I: Fundamentals
(2010)
For polypropylene of varied stabilization, spectral sensitivity as well as temperature dependence of irradiation caused crack formation was determined in artificial irradiation tests. UV radiant exposure HUV necessary to generate crack formation was measured both in spectrally dispersed irradiation and artificial irradiation in a Fluorescent UV lamp device. Dependencies were fitted to a plateau function and an Arrhenius function, respectively, to describe the action of irradiation by response functions. Applied to weather data from Phoenix, the results were compared with respective outdoor exposure results.
Degradation of poly(phenylphenylene-vinylene)-films during illumination and thermal treatment
(1994)
Für Polypropylen unterschiedlicher Stabilisierung wurden in künstlichen Bestrahlungstests sowohl die spektrale Empfindlichkeit als auch die Temperaturabhängigkeit der Rissbildung quantitativ ermittelt. Dafür wurde die Dauer bis zur Rissbildung sowohl bei spektraler Bestrahlung als auch bei Bestrahlung in einem UV-Leuchtstofflampengerät bei verschiedenen Temperaturen bestimmt.
Die Temperaturabhängigkeit konnte als Arrhenius-Abhängigkeit beschrieben werden; das Wirkungsspektrum wurde an eine Stufenfunktion angepasst. Anschließend wurde auch noch der Einfluss des Stabilisatorgehalts als Potenzfit parametrisiert. Die Einzelabhängigkeiten wurden zu einer Gesamtfunktion der Wirkungen in Abhängigkeit der Dosis zusammengesetzt, die es ermöglicht die Wirkungen unterschiedlicher Dosiskombinationen abzuschätzen.
Zur Validierung der Dosis-Wirkungsfunktionen wurden Freibewitterungsergebnisse aus Phoenix/Arizona herangezogen. Mit der Dosis, die sich aus den Wetterdaten dieser Freibewitterung ergibt, wurden anhand der Dosis-Wirkungs-Funktionen die jeweiligen Lebensdauern errechnet und mit dem experimentell bestimmten Versagen in der Freibewitterung verglichen.
Die Arbeiten erfolgten im Rahmen des ViPQuali-Projektes mit dem Ziel der Bestimmung der Materialkenngrößen.
Der Anteil von Polymeren als Funktions- und Konstruktionswerkstoffe in dauerhaften medizinischen Anwendungen steigt beständig. Derartige Materialien müssen den mechanischen, biologischen und chemischen Bedingungen im Körper widerstehen (u.a. Abrieb, Hydrolyse, Degradation) und gleichzeitig gut verträglich sein. Der sichere Einsatz von polymeren Materialien erfordert die Kenntnisse über ihre Langzeitstabilität unter verschiedenen äußeren Bedingungen. Diese sind nicht nur beeinflusst durch die unmittelbare Umgebung in vivo, sondern auch durch die Historie der verwendeten Materialien. Dazu zählen u. a. erhöhte Temperaturen unter sauerstoffhaltiger Atmosphäre während der Verarbeitung oder die Exposition von ionisierender Strahlung oder reaktiven Radikalen während der Sterilisation.
Ingenieurbauwerke wie Brücken, hoch beanspruchte Verkehrsflächen oder auch Hochhäuser und deren Bauwerksteile wie z.B. Hochhausfassaden werden aus technischen und ästhetischen Gründen durch Fugen in Einzelabschnitte unterteilt. Zur Sicherstellung der Gebrauchsfähigkeit und zum Schutz des Gesamtbauwerks, aber in zunehmendem Maße auch zur statisch-konstruktiven Anbindung der Bauwerksteile, werden diese Fugenspalte in aller Regel durch spezielle Fugenfüllsysteme verschlossen. Aufgrund der hohen Sicherheitsrelevanz bei Fugenfüllungen im Glasfassadenbau fordert das Baurecht auch bei diesen Bauprodukten als Voraussetzung für die baupraktische Verwendbarkeit neben dem Nachweis der Funktionsfähigkeit auch den Nachweis der Dauerhaftigkeit. Da die hierfür bekannten Nachweismethoden zur Dauerhaftigkeit keine allgemeine Zulassungsakzeptanz finden, kann das ästhetische, bauphysikalische und ökonomische Potential von modernen geklebten Ganzglasfassaden (sogenannte SSG-Fassaden) in der Baupraxis der Bundesrepublik Deutschland derzeit nicht ausgenutzt werden. Grund dafür sind die ungenügend erfassten und in den Bewertungsverfahren simulierten Wechselwirkungen derartiger Baukonstruktionen mit der Umwelt. In diesem Beitrag soll am Beispiel moderner Fugen im Glasfassadenbau (SSG-Fassaden) eine ganzheitliche gebrauchsbezogene Versuchsmethodik zur kontrollierten Ansprache der Funktionsfähigkeit und Dauerhaftigkeit von Fugensystemen unter realitätsnah und reproduzierbar simulierten Umwelteinwirkungen vorgestellt werden. Dazu werden die maßgebenden Umwelteinflüsse und die Quantifizierung der daraus folgenden Beanspruchungen auf derartige Fugensysteme dargestellt. Basierend darauf werden eine repräsentative Beanspruchungsfunktion zur Nachstellung der maßgebenden Umwelteinflüsse und Beanspruchungen auf das System Tragrahmen - Fugenfüllung- Glasscheibe sowie eine geeignete Probendimensionierung abgeleitet. In der Konsequenz werden die Erkenntnisse in den Aufbau einer neuartigen komplexen Versuchseinrichtung überführt. Funktionsprinzip und Leistungsparameter dieser Anlage zur Umweltsimulation werden vorgestellt. Die Möglichkeiten der Systemkennzeichnung werden vorgestellt. Erste Versuchsergebnisse zeigen das Potential der neuartigen Bewertungsmethodik auf, die Kunst der Fuge im Bauwesen gebrauchsorientiert weiter zu entwickeln.
The surface temperature of test specimens exposed to natural and artificial solar radiation are roughly ascertained with black standard thermometers BST and white standard thermometers WST. For the calibration of these thermometers a new European Standard prEN 16465 was published in 2015, describing the well-known contact method and a new contactless method with a pyrometer. It can be confirmed that the temperature calibrations according to the two methods provide different calibration results which are not interchangeable (which is already stated in the scope of this standard). The described contactless method to determine the surface temperature 'under radiation load' results in clearly too high temperatures. This paper tries to highlighting the reasons.
A new irradiation device for the exposure of plastic products is presented. Developed in the BAM division 3.1 "Dangerous Goods Packaging" it can be used for artificial UV irradiation of plastic Containers filled with hazardous liquids.
Present regulations and tests only investigate the exposure effects of UV and of media separately, but as the damaging effect is expected to be synergistic for at least some media, a combined test was looked for.
A chamber of 60 cm by 60 cm base area and 1 m height gives space for up to 40 cm wide objects. Two fluorescent UV lamp arrays are arranged on opposite walls, separated from the chamber by quartz glass panes. By continuously rotating the exposure object by means of a rotary disc that the object is placed on, spatial irradiation homogeneity is achieved over the exposure duration. The spectral irradiance of the chosen UVA 340 nm lamps gives the best match of global solar radiation in the short wavelength ränge. The close arrangement of the UVA lamps (15 each side) results in 60 W m'2 UV irradiance.
Constant temperature is adjusted to typically 40 °C by the control of the fan speed. This temperature is chosen, as it is the required temperature for three week storage of filled polyethylene Containers, for proving Chemical compatibility in the field of dangerous goods. To ensure homogeneity, an interiorfan provides for air circulation.
Häufig ist es wünschenswert, für neue Materialien oder Anwendungen künstliche Bewitterungsverfahren zu benutzen, die auf die spezifischen Anforderungen besser zugeschnitten sind, als es bei bestehenden standardisierten Verfahren der Fall ist. Nachdem man die spezifischen Parameter der Beanspruchung unter Anwendungsbedingungen und die spezifische Empfindlichkeit des Materials erfasst hat, beginnt ein Prozess, der als „Test Tailoring“ häufig abstrakt verwendet, auf den aber nur selten näher eingegangen wird. Genau dieser Prozess soll hier am Beispiel der Entwicklung eines künstlichen Bewitterungstests unter saurer Beaufschlagung, dem in der BAM entwickelten Acid Dew and Fog Test, beispielhaft erläutert werden.
Additively manufactured test specimens made of polyamide 12 (PA 12) by Laser Sintering (LS) as well as of acrylnitril-butadien-styrol (ABS) by Fused Layer Modeling (FLM), were tested with active thermography. For this, two different excitation methods (flash and impulse excitation) were used and compared, regarding the suitability for the detection of constructed and imprinted defects. To increase the quality of the thermograms, data processing methods like thermal signal reconstruction (TSR) and Fourier-Transformation were applied. Furthermore, the long-term stability of the probes towards environmental stress, like UV-radiation, heat, water contact and frost is being investigated in the presented project with artificial weathering tests.