Filtern
Erscheinungsjahr
Dokumenttyp
- Zeitschriftenartikel (47) (entfernen)
Sprache
- Englisch (42)
- Deutsch (4)
- Mehrsprachig (1)
Schlagworte
- Weathering (15)
- Chemiluminescence (7)
- Degradation (5)
- Artificial weathering (4)
- Flame retardant (4)
- Nanocomposite (4)
- UV radiation (4)
- Durability (3)
- Polymer (3)
- Ageing (2)
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)
- 5.3 Polymere Verbundwerkstoffe (2)
- 6.6 Physik und chemische Analytik der Polymere (2)
- 1 Analytische Chemie; Referenzmaterialien (1)
Polarized fluorescence and orientational order parameters of a liquid-crystalline conjugated polymer
(1999)
We report a study of the orientational order of aligned thin films of the liquid crystalline conjugated polymer poly(9,9-dioctylfluorene). Steady state polarized fluorescence measurements were used to determine the orientational order parameter <P2> and <P4>. The influence of intermolecular and intramolecular excitation energy transfer on the degree of polarization is discussed. The role of film morphology is also examined by comparison of the results for glassy and crystalline films.
The thermo-oxidative degradation of a polymeric optical cable is investigated by chemiluminescence, The results are reliable and reproducible. Two distinct processes are reported marked by a peak and a plateau behavior versus the time, respectively. Both processes are ruled by thermally activated processes. Beside the dependencies of temperature and time, the influence of absorbed water is discussed. Chemiluminescence is proposed as a promising candidate for a suitable testing method assessing the thermo-oxidative stability of plastic optical fibers and cables. it requires not more than a simple one-day testing procedure and has the advantage that it can be carried out even within the lo cv temperature ranges of the cables' intended use.
The excitation energy transfer (EET) of a bichromophoric cross-shaped molecule was investigated by stationary polarized fluorescence spectroscopy in the solid state. For this purpose 2,2[prime],7,7[prime]-tetrakis(biphenyl-4-yl)-9,9[prime]-spirobifluorene was embedded in a polymeric bisphenol-A-polycarbonate (PC) matrix. The dependence of the fluorescence on concentration and wavelength was determined. The role of the intermolecular and intramolecular EET is dealt with separately and discussed by means of the degree of polarization. The intermolecular excitation energy transfer is described in terms of a Förster transfer mechanism. The intramolecular transfer is prevented for the zero-point vibrational levels by the molecular cross-shaped structure, but is found for a wide range of wavelength, presumably based on vibrationally excited states.
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.
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 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.