Additive manufacturing (AM) processes can provide great input for solving recently encountered challenges of the global market such as mass customization, highly dynamic environments, and the decrease of time needed from a draft to final products. This study aims at contributing to the issue of material limitations typically present in AM by researching possibilities of directly using technically relevant and commercially available polymer granules in melt extrusion processes. In order to extend the knowledge on the processing of semicrystalline polymers in melt extrusion based processes, different temperature induced influences on mechanical and morphological properties are investigated for poly(propylene). Mechanical tests are conducted to evaluate the effects and interdependencies of substrate, extrusion, and cooling temperature. Finally, based on the identified mechanical and rheological behavior of the material, a process window for the used materials is suggested.
Currently, atomic force microscopy is the preferred technique to determine roughness on membrane surfaces. In this paper, a new method to measure surface roughness is presented using a 3D laser scanning confocal microscope for high-resolution topographic analysis and is compared to conventional SEM. For this study, the surfaces of eight samples based on a poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) host polymer with different liquid interpenetrating components were analyzed. Polymethylhydrosiloxane, triethylene glycolallylmethylether, (3,3,3-trifluoropropyl)methylcyclotrisiloxane (D3-C2H4CF3), polysiloxane-comb-propyloxymethoxytriglycol (PSx), polysiloxane-comb-propyl-3,3,3-trifluoro (PSx-C2H4CF3), poly[bis(2-(2-methoxyethoxy) ethoxy) phosphazene, or poly[bis(trifluoro)ethoxy] phosphazene was chosen as interpenetrating compound to investigate the impact of comb and double-comb-structured polymer backbones, as well as their dipolar or fluorous residues on the PVDF-HFP-miscibility. Different phases of the constituting ingredients were identified via their thermal properties determined by DSC. Additionally, the COSMO-RS method supported the experimental results, and with regard to computed σ-profiles, new modified structures for polysiloxane and polyphosphazene synthesis were suggested. 相似文献
The asymmetric organocatalytic one‐pot synthesis of polyfunctionalized cyclohexanes is described. Starting from β‐keto esters, nitroalkenes and α,β‐unstaturated aldehydes and employing a bifunctional norephedrine‐based thiourea catalyst, six contiguous stereocenters including one quarternary center are generated. The one‐pot protocol follows a Michael/Michael/aldol addition sequence and affords the highly substituted cyclohexanes in moderate to very good yields (22–70%), diastereomeric ratios of dr>95:5 and excellent enantioselectivities of 91–99% ee. 相似文献
Power limitations in CW THz generation imposed by conventional photomixers (“antenna emitters”, AEs) are the major drawbacks on THz generation. From the antenna point of view, two different strategies are proposed to increase the generated power: optimized arrays and lenses arrangements and the use of new dielectric horn antennas. Then, using multiple small lenses, one per each single element, instead of a large one, bigger than the array, makes the generated power much higher. In addition, horn antennas etched in the substrate are considered in order to reduce the energy distribution scattering. Finally, some manufacturing issues are discussed. 相似文献
AbstractThis study aimed to identify sex-related differences in clothing-microclimate and subjective perceptions while wearing two outdoor jackets in a setting that is representative for outdoor sports at a leisure level. Ten male and 10 female subjects were testing a thin one-layer jacket and a wind- and waterproof three-layer membrane jacket in a climatic chamber (12?°C, 40% relative humidity) during rest, exercise and recovery. Relative humidity, temperature and sweat residues in the clothing system, perceptions of comfort and physiological parameters were measured. For females, relative humidity, sweat residues and loss of body mass were significantly lower without significantly influencing perceptions of comfort. It can be concluded that sex has a strong effect on clothing-microclimate in outdoor jackets with drier microclimate for females. Furthermore, our findings suggest that females are more sensitive to humidity within the clothing system and that they cool easier, especially in periods of rest. 相似文献
The effects of two different low calcium fly ashes on the hydration of ordinary Portland cement (OPC) pastes containing 50 wt.% of fly ash were investigated over a hydration time of 550 days. The results were compared with a reference blend of OPC containing 50 wt.% of inert quartz powder allowing the distinction between "filler effect" and pozzolanic reaction.Until 2 days, no evidence of fly ash reaction was measured and its influence on the hydration is mainly related to the “filler effect”. From 7 days on, the effects of the pozzolanic reaction were observed by the consumption of portlandite, the change of the pore solution chemistry, the formation of a presumably water-rich inner hydration product and the change of the C–S–H composition towards higher Al/Si ratio compared to the C–S–H of neat OPC. Additional strength due to the pozzolanic reaction developed after 28 days of hydration. 相似文献
The application of nitroxides for the development of new synthetic methods and their implementation in polymer chemistry, material science and beyond is one of the major research topics in our laboratory in the institute of organic chemistry at the WWU Münster. This short review focuses on our recent progress towards nitroxide-based transition-metal-free oxidative coupling reactions. The demand for organic surrogates for transition metals in such transformations is in our eyes unquestionable, since environmental and economic issues have become progressively more important in recent years. For this purpose, the 2,2,6,6-tetramethylpiperidine-N-oxyl radical (TEMPO) is shown to be a highly efficient oxidant for the homo- and cross-coupling of Grignard reagents. This powerful C-C bond forming strategy allows the generation of conjugated polymers from bifunctional Grignard reagents. Moreover, cross-coupling of alkynyl Grignard compounds and nitrones can be accomplished under aerobic atmosphere with catalytic amounts of TEMPO. It is also shown that TEMPO-derived N-oxoammonium salts can act as suitable oxidants for formation of C-N bonds between non-preactivated benzoxazoles and secondary amines under metal-free conditions. 相似文献