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- Zeitschriftenartikel (48) (entfernen)
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- Weathering (15)
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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)
Polyether and -ester urethanes (PU) were exposed to artificial weathering at 40 °C and artificial UV radiation in a weathering chamber. In 3 parallel exposures, humidity was varied between dry, humid, and wet conditions. Material alteration was investigated by various analytical techniques like size exclusion chromatography
(SEC), liquid chromatography-infrared spectroscopy (LC-FTIR), thermal-desorption gas chromatography-mass spectrometry (TD-GC-MS), fluorescence mapping and dynamic mechanical analysis (DMA). Our results show that depending on the weathering conditions, different degradation effects can be observed. By means of SEC an initial strong decrease of the molar masses and a broadening of the mass distributions was found. After a material dependent time span this was followed by a plateau where molar mass changes were less significant. A minor moisture-dependent degradation effect was only found for polyester PU. Fluorescence measurements on two materials revealed an increase in the luminescence intensity upon weathering process reaching a saturation level after about 500 h. The changes in the optical properties observed after different exposure conditions and times were very similar. The TD-GC-MS data showed the fate of the stabilizers and antioxidant in the course of weathering. LC-FTIR measurements revealed a change in peak intensities and the ratio of urethane and carbonyl bands.
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.
Additively manufactured test specimens made of polyamide 12 (PA 12) by Laser Sintering as well as of acrylonitrile butadiene styrene (ABS) by Fused Layer Modelling, were characterised with active thermography directly after manufacturing and after artificial weathering. For this, two different excitation methods (flash and pulse heating) were used and compared, regarding their suitability for the detection of constructed and imprinted defects inside the test specimens. To increase the quality of the thermograms, data processing methods like thermal signal reconstruction (TSR) and Fourier Transformation after TSR were applied. To further investigate the long-term stability of the additively manufactured test specimens towards environmental stress, like UV radiation, heat, humidity, water contact and frost with active thermography, an artificial weathering test over 2000 hours (~3 months) was applied to the specimens. The monitoring of the changes in the optical properties of the weathered plastics was supplemented by spectral reflectance and UV/VIS spectroscopy.
Accelerated weathering test for plastics and coatings that are exposed to acidic precipitation
(2009)
Due to the occurrence of acidic precipitation, and due to the fact that polymers and stabilizers may be sensititve to acids, it is important to have a laboratory test that combines weathering exposure with acidic exposure. The loss of stabilization caused by an acid damage of stabilizing system gets evident only over the weathering progress. For solid samples, for wich mostly the surface properties are relevant, the "Acid Dew and Fog Test" (ADF test) was established. For woven or tufted materials, the "Acid Rain Test" (AR test) was developed. The proposed weathering tests aim at plastics as well as at coatings.
The site of Schöningen (Germany), dated to ca. 300,000 years ago, yielded the earliest large-scale record of humanly-made wooden tools. These include wooden spears and shorter double-pointed sticks, discovered in association with herbivores that were hunted and butchered along a lakeshore. Wooden tools have not been systematically analysed to the same standard as other Palaeolithic technologies, such as lithic or bone tools. Our multianalytical study includes micro-CT scanning, 3-dimensional microscopy, and Fourier transform infrared spectroscopy, supporting a systematic technological and taphonomic analysis, thus setting a new standard for wooden tool analysis. In illustrating the biography of one of Schöningen’s double-pointed sticks, we demonstrate new human behaviours for this time period, including sophisticated woodworking techniques. The hominins selected a spruce branch which they then debarked and shaped into an aerodynamic and ergonomic tool. They likely seasoned the wood to avoid cracking and warping. After a long period of use, it was probably lost while hunting, and was then rapidly buried in mud. Taphonomic alterations include damage from trampling, fungal attack, root damage and compression. Through our detailed analysis we show that Middle Pleistocene humans had a rich awareness of raw material properties, and possessed sophisticated woodworking skills. Alongside new detailed morphometrics of the object, an ethnographic review supports a primary function as a throwing stick for hunting, indicating potential hunting strategies and social contexts including for communal hunts involving children. The Schöningen throwing sticks may have been used to strategically disadvantage larger ungulates, potentially from distances of up to 30 metres. They also demonstrate that the hominins were technologically capable of capturing smaller fast prey and avian fauna, a behaviour evidenced at contemporaneous Middle Pleistocene archaeological sites.
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.
A systematic approach was used to investigate the weathering-induced degradation of a common water–based intumescent coating. In this study, the coatings are intended for humid indoor applications on steel substrates. The coating contains ammonium polyphosphate, pentaerythritol, melamine, and polyvinyl acetate. By replacing each ingredient with a less water-soluble substance, the most vulnerable substances, polyvinyl acetate and pentaerythritol, were identified. Furthermore, the weathering resistance of the system was improved by exchanging the ingredients. The coatings were stressed by artificial weathering tests and evaluated by fire tests. Thermogravimetry and Fourier-transform infrared spectroscopy were used to study the thermal decomposition. This study lays the foundation for the development of a new generation of water-based intumescent coatings.