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81.
Wouter Post Arijana Susa Rolf Blaauw Karin Molenveld Rutger J. I. Knoop 《高分子科学杂志,C辑:聚合物评论》2020,60(2):359-388
AbstractThe outstanding performance of conventional thermosets arising from their covalently cross-linked networks directly results in a limited recyclability. The available commercial or close-to-commercial techniques facing this challenge can be divided into mechanical, thermal, and chemical processing. However, these methods typically require a high energy input and do not take the recycling of the thermoset matrix itself into account. Rather, they focus on retrieving the more valuable fibers, fillers, or substrates. To increase the circularity of thermoset products, many academic studies report potential solutions which require a reduced energy input by using degradable linkages or dynamic covalent bonds. However, the majority of these studies have limited potential for industrial implementation. This review aims to bridge the gap between the industrial and academic developments by focusing on those which are most relevant from a technological, sustainable and economic point of view. An overview is given of currently used approaches for the recycling of thermoset materials, the development of novel inherently recyclable thermosets and examples of possible applications that could reach the market in the near future. 相似文献
82.
Automated determination of fatty acid methyl ester and cis/trans methyl ester composition of fats and oils 总被引:1,自引:0,他引:1
de Koning S van der Meer B Alkema G Janssen HG Brinkman UA 《Journal of chromatography. A》2001,922(1-2):391-397
The determination of the fatty acid composition (as methyl esters, FAMEs) of fats and oils and their cis/trans (CTME) distribution requires a simple, but manual and time-consuming sample preparation. The so-called BF3 method is often the preferred procedure. Because FAME/CTME analyses are encountered very frequently in the food industry, an automated, robot-based alternative is proposed which uses the sodium methylate procedure. After sample weighing and the (manual) addition of heptane (2 min), a XYZ robotic autosampler is used for all remaining work, which includes reagent addition, agitation, sample settling and the final injection into the gas chromatograph (10 min). The performance of the sodium methylate and BF3 methods are compared by analysing some 30 oil and fat samples. The novel procedure is much faster (less than 15 min versus ca. 1 h) and manual sample handling is drastically decreased. The experimental results obtained with the two methods frequently are the same, while small differences can be explained by (known) differences of the two methods in the conversion of minor oil/fat constituents, such as free fatty acids, wax esters and sterol esters. In case of FAME analyses, a hot injection is to be preferred over a cold injection. The RSDs of the peak areas were 1.5% for the major fatty acids to 11% for peaks that were just above the noise level. The detection limit were approximately 0.03%. 相似文献
83.
Veronika Gemmer-Colos und Rolf Neeb 《Fresenius' Journal of Analytical Chemistry》1978,293(4):290-294
Zusammenfassung Kleine Mengen Ni, Cu und Zn in wäßrigen Lösungen können nach Ausschütteln ihrer Dipropyldithiocarbamatochelate gas-chromatographisch bestimmt werden. Arbeitsbedingungen für den 0,01–1 ppm-Bereich werden angegeben. Die Reproduzierbarkeit der Bestimmung wird durch Zusatz eines inneren Standards verbessert.
Dialkyldithiocarbamates as reagents for the gas-chromatographic determination of metalsII. Determination of zinc, copper and nickel as dipropyldithiocarbamato chelates after extraction from aqueous solution
Summary Small amounts of Ni, Cu and Zn in aqueous solutions can be determined by gas chromatography after extraction of their dipropyldithiocarbamatochelates. Working details for the 0.01–1 ppm range are reported. Reproducibility is markedly improved by addition of an inner standard.
Die Untersuchungen wurden in dankenswerter Weise durch Mittel der Deutschen Forschungsgemeinschaft und des Verbands der chemischen Industrie unterstützt. 相似文献
84.
Schmidt EM Gleiter R Rominger F 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(8):1814-1822
The synthesis of 1-alkyl and 1-aryl-1-azacyclotetradeca-3,5,10,12-tetraynes was achieved in a stepwise approach. The key intermediate was 1,13-dibromotrideca-2,4,9,11-tetrayne (18). Reaction with methyl- (19 a), ethyl- (19 b), isopropyl- (19 c), n-butyl- (19 d), and tert-butylamine (19 e) as well as aniline (19 f) and p-methoxyaniline (19 g) gave the corresponding 14-membered tetraynes 20 a-20 g. The ring inversion process of 20 b was studied by variable temperature (1)H NMR spectroscopy. From these measurements a value of 10.6 kcal mol(-1) was calculated for DeltaG(not equal). X-ray investigations on single crystals of 20 b, 20 c, and 20 f revealed the axial position for the substituent at each nitrogen atom. For 20 b we encountered the chair conformation, for 20 c both chair and boat conformations, and for 20 f the boat conformation in the solid state. The reaction of 20 c with concentrated HCl in ethanol yielded 2,10-dichloro-6-isopropyl-6-azatricyclo[9.3.0.0(4,8)]tetradeca-1(11),2,4(8),9-tetraene (25 c). Compound 25 c was oxidized by 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) to 27 c. The structure of the latter was confirmed by X-ray investigations. The reaction of 20 c in aqueous HCl lead to the formation of 10-chloro-2-isopropyl-1,3,4,6,7,8-hexahydro-2H-benzo[g]isoquinolin-9-one (37 c). The structure of 37 c was verified by X-ray studies on single crystals. 相似文献
85.
Ernst Schaumann Erwin Kausch Karl-Heinz Klaska Rolf Klaska Otto Jarchow 《Journal of heterocyclic chemistry》1977,14(5):857-860
The crystal and molecular structures of the cycloadduct from isopropyl[α-(dimethylthio-carbamoyl)isopropyl]carbodiimide and methyl isothiocyanate were determined by single-crystal X-ray methods. The product was established to be 2-(1-isopropyl-3,5-dimethyl-4,6-dithioxo-hexahydro-1,3,5-triazine-2-ylidenamino)-N,N-dimethylthioisoburyramide, in which contrary to expectations based on hybridisation the heterocyclic ring adopts a boat conformation. 相似文献
86.
Gies P Roy C McLennan A Pailthorpe M Hilfiker R Osterwalder U Monard B Moseley H Sliney D Wengraitis S Wong J Human S Bilimis Z Holmes G 《Photochemistry and photobiology》2003,77(1):58-67
In recent years the need to standardize measurement protocols for quantifying the degree of ultraviolet radiation (UVR) protection provided by clothing has led to the introduction of a number of standards around the world. To date, these standards have specified spectral measurements of UVR transmission by clothing and fabrics. Development of a standard test method has become an important part of the testing process, and this article presents results from an intercomparison involving 10 independent testing laboratories and 11 different UVR transmission measurement instruments. In addition to comparing the measured ultraviolet protection factors (UPF), this intercomparison also incorporates detailed scan results from all 10 laboratories and highlights differences in performance of the various instruments in different wavelength regions. Careful examination of these differences can indicate where changes to the systems could be made to allow improvements both in equipment performance and in agreement of the final results. The variability in the measurements of UPF in this study suggest that the protection categories in standards may need to be broadened. 相似文献
87.
Two different injectors, a split/splitless injector and a programmed temperature vaporizer (PTV) injector were investigated as the interface in on-line supercritical fluid extraction (SFE)-capillary gas chromatography (cGC). The parameters affecting the chromatographic peak shapes as well as the quantitative performance of the interfaces in on-line SFE-cGC were identified and studied. Particular attention was paid to the case where modified extraction fluids were used. Experiments were performed on two different samples. The first sample consisted of PAHs spiked on sand at different concentration levels. The other sample was a polymeric material. 相似文献
88.
89.
On the Preparation of Arsenic Dichloride Trifluoride, AsCl2F3 AsCl2F3 is prepared by pyrolysis of [AsCl4]+ [AsF6]?. The vibrational spectra of the new low temperature compound are reported and the valence force constants are calculated. The formation of AsCl2F3 by ligand exchange reactions is discussed. 相似文献
90.
Kollmar M Steinhagen H Janssen JP Goldfuss B Malinovskaya SA Vázquez J Rominger F Helmchen G 《Chemistry (Weinheim an der Bergstrasse, Germany)》2002,8(14):3103-3114
All possible (eta(3)-allyl)palladium complexes (1-4) of the ligand (4S)-[2-(2'-diphenylphosphanyl)phenyl]-4,5-dihydro-4-(2-propyl)-oxazole (L 1) and eta(3)-allyl ligands with one to three phenyl substituents at the terminal allylic centers were synthesized and characterized by X-ray crystal structure analysis and, with respect to allylic isomers, by NMR investigations. Equilibrium geometries, electronic structures, and relative energies of isomeric complexes were computed by restricted Hartree-Fock (RHF) and density functional theory (DFT) calculations; experimentally determined isomer ratios could be reproduced. The results allowed important conclusions to be drawn regarding the mechanism of Pd-catalyzed asymmetric allylic substitutions. 相似文献