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- Weathering (12)
- Chemiluminescence (5)
- Artificial weathering (4)
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- Multilayer graphene (2)
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- Packaging (2)
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- Accelerated weathering (1)
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- Aluminum hydroxide (ATH) (1)
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- Outdoor weathering (1)
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- Polarized fluorescence measurements (1)
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- Polymer optical fibers (POFs) (1)
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- Size exclusion chromatography (1)
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- degradation (1)
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Organisationseinheit der BAM
- 7 Bauwerkssicherheit (13)
- 7.5 Technische Eigenschaften von Polymerwerkstoffen (13)
- 6 Materialchemie (5)
- 6.3 Strukturanalytik (4)
- 3 Gefahrgutumschließungen; Energiespeicher (3)
- 3.1 Sicherheit von Gefahrgutverpackungen und Batterien (3)
- 5 Werkstofftechnik (3)
- 4 Material und Umwelt (2)
- 5.3 Polymere Verbundwerkstoffe (2)
- 6.6 Physik und chemische Analytik der Polymere (2)
Artificial weathering of LDPE under dry conditions (<10% of relative humidity) by UV radiation was monitored
by dielectric spectroscopy. For an apolar polymer like LDPE, dielectric study yields information
about the change in structure and dynamics of the system. The fluctuations of the polar groups which
are generated as a result of photooxidation such as carbonyl groups can be monitored as characteristic
relaxation processes like the αc or β mode. The dielectric loss characterized by typical dielectric parameters
like the activation energy and dielectric strength are strongly dependent upon changes induced
by photooxidation in the amorphous and crystalline domains. This paper discusses in detail how the foil
reached its mechanical disintegration. It was found that initial stages of weathering induce chain scission
and/or crosslinking in the amorphous domains of the polymer and the motional processes in the crystalline
regions are not affected. After this induction period, an increase in the degree of crystallization was
observed by employing differential calorimetry. The increasing crystallinity is considered as one of the
reasons for embrittlement which finally leads to the complete loss of the structural integrity.
Chemiluminescence (CL) is a sensitive method of investigating the thermo-oxidative stability of polymers in the early stages of degradation. Therefore, CL measurements were applied to different automotive coatings to evaluate their degradation behavior during artificial weathering. In this work, CL measurements were carried out for different automotive coatings to follow their degradation behavior during artificial weathering. The CL emission depends on sample-specific parameters like stabilizer, matrix, or hardener; experimental parameters like the oxygen partial pressure; and exposure parameters like the duration of weathering. The potential of CL could be demonstrated by classifying materials into categories of good, medium, and low degradation performance at a much earlier stage of weathering exposure than in combination with the usual visual detection of weathering effects.
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.
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.
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.
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.
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.