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831.
Dieter Fischer Petra Pötschke Harald Brünig Andreas Janke 《Macromolecular Symposia》2005,230(1):167-172
The superior association of the inherent good mechanical and electrical properties makes carbon nanotubes (CNT) exceptionally interesting for the production of composite fibers of thermoplastic polymers with CNT. Alignment of the CNT in the polymer fiber is important for improved mechanical properties. Especially the production of fibers makes it necessary to get a controlled orientation and/or alignment of the CNT. We applied transmission electron microscopy (TEM) and polarized Raman microscopy to quantify multiwalled carbon nanotubes (MWNT) orientation, alignment and crystallinity in polycarbonate (PC). The evaluation of the Raman measurements provided an improved alignment orientation of the MWNT in the fibers with increasing take-up velocity during melt spinning and that the crystal structure of the MWNT is not changed through melt spinning. 相似文献
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833.
Raman spectroscopy, which does not require a time‐consuming sample preparation, is described as an analytical tool for the high‐throughput characterization of polyethylenes. The content of comonomer and the amount of methyl groups per 1 000 carbon atoms of polyethylenes can be predicted from Raman spectra using multivariate data analysis. In addition, macroscopic properties, such as density and elastic modulus as well as yield stress, can be derived from Raman spectra.
834.
Dieter Schrenk 《Chemie in Unserer Zeit》2003,37(2):140-146
Food contains a variety of compounds of natural origin that may be harmful when consumed too frequently or at a very high dose level or under inappropriate conditions. Examples for such constituents include the glucosinolates in cabbage or tyrpsin inhibitors in raw beans. Other constituents such as vicin in broad beans or glycyrrhizic acid in liquorice may be harmful for a subpopulation only, e.g., in patients suffering from high blood pressure or in individuals bearing certain genetic defects of metabolism. Furthermore, food may contain compounds which have been added by purpose (legal food additives) such as emulsifiers, preservatives, synthetic colors etc. These compounds are under strict regulation and their safety has been tested rigorously. Contaminants in food such as dioxins, pesticides, drug residues etc. may originate from illegal or inappropriate production or treatment. At lower levels they may reflect background contamination, e.g., in the environment. Finally, nutritional supplements and ingredients of ‘functional food’ require special toxicological testing and evaluation since not all compounds considered as ‘healthy’ in certain concentrations are also beneficial or safe when consumed at higher doses. 相似文献
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Jaroslav Ščudla Klaus-Jochen Eichhorn Miroslav Raab Pavel Schmidt Dieter Jehnichen Liane Häußler 《Macromolecular Symposia》2002,184(1):371-387
The molecular and supermolecular orientation, morphology and structural changes observed during cold drawing of injection moulded isotactic polypropylene modified by specific α, and β nucleating agents were studied by polarised photoacoustic FTIR spectroscopy, wide-angle X-ray diffraction and differential scanning calorimetry. Significantly lower molecular orientation was found in the core of the β-nucleated injection moulded specimens as compared to unmodified and α-nucleated materials. This has been ascribed to the fast growth of the β-crystallites which inevitably dislocates the flow-induced orientation within the crystalline regions and in their vicinity. Moreover, it was found that the presence of the developed β-crystallites distinctly diminishes the efficiency of the orientational solid-state drawing assessed on both levels of the hierarchical structure (molecular and crystalline). This structural observation is directly connected with macroscopic softening effect of the β-phase: lowering the yield stress and flattening the neck shoulder. Thus, the interrelation between the microstructural and macroscopic effects of the β-phase could be described as a feedback process. 相似文献
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