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Zhang M.,University of Stuttgart | Zhang M.,Institute of Textile Chemistry and Chemical Fibers ITCF | Denes I.,Robert Bosch GmbH | Buchmeiser M.R.,University of Stuttgart | Buchmeiser M.R.,Institute of Textile Chemistry and Chemical Fibers ITCF
Macromolecular Materials and Engineering | Year: 2016

Silicone-based elastomers are promising materials for future dielectric elastomer actuators. To ensure optimum performance and the long-term reliability of the actuators, it is essential to gain a fundamental understanding of the correlation between the elastomer's network structure and the mechanical and electrical responses of the material. For this purpose, mechanical and electrical tests are performed on a series of silicone elastomer films with different crosslinking densities, which are prepared by changing the stoichiometric imbalance of the network. It is determined that higher cross-linking density leads to a higher elastic modulus and a longer fatigue lifetime, whereas reduced permittivity is observed because of lower chain mobility. Dielectric breakdown strength is also observed to increase in line with increasing cross-linking density, and the variations in relation to the measured elastic modulus and permittivity agree well with the Stark-Garton model based on electromechanical instability. Alternation of network structure of silicone elastomers leads to changes in both mechanical and electrical properties. With increased cross-linking density and reduced chain mobility of the network, the elastic modulus and fatigue lifetime are found to increase significantly. Meanwhile, minor increase of dielectric breakdown strength and slight decrease of permittivity of the material are also observed. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source


Mundsinger K.,Institute of Textile Chemistry and Chemical Fibers ITCF | Mundsinger K.,University of Stuttgart | Muller A.,Institute of Textile Chemistry and Chemical Fibers ITCF | Beyer R.,Institute of Textile Chemistry and Chemical Fibers ITCF | And 3 more authors.
Carbohydrate Polymers | Year: 2015

Cellulose and chitin, both biopolymers, decompose before reaching their melting points. Therefore, processing these unmodified biopolymers into multifilament yarns is limited to solution chemistry. Especially the processing of chitin into fibers is rather limited to distinctive, often toxic or badly removable solvents often accompanied by chemical de-functionalization to chitosan (degree of acetylation, DA, <50%). This work proposes a novel method for the preparation of cellulose/chitin blend fibers using ionic liquids (ILs) as gentle, removable, recyclable and non-deacetylating solvents. Chitin and cellulose are dissolved in ethylmethylimidazolium propionate ([C2mim]+[OPr]-) and the obtained one-pot spinning dope is used to produce multifilament fibers by a continuous wet-spinning process. Both the rheology of the corresponding spinning dopes and the structural and physical properties of the obtained fibers have been determined for different biopolymer ratios. With respect to medical or hygienic application, the cellulose/chitin blend fiber show enhanced water retention capacity compared to pure cellulose fibers. © 2015 Elsevier Ltd. All rights reserved. Source


Scholz R.,Kelheim Fibres GmbH | Bauer D.,Kelheim Fibres GmbH | Hermanutz F.,Institute of Textile Chemistry and Chemical Fibers ITCF | Ingildeev D.,Institute of Textile Chemistry and Chemical Fibers ITCF | Ota A.,Institute of Textile Chemistry and Chemical Fibers ITCF
Reinforced Plastics | Year: 2016

The focus of the work was to clarify the influence of the cross section shape of the viscose fibers and additives on the carbonization process and the resulting carbon fiber properties. Overall, the shape of cross section of carbon fibers produced was determined by the initial fiber morphology of the precursor viscose fibers. The carbon yield was independent of the geometric structure of the viscose fibers and a certain degree of shrinkage was observed for all types of fibers due to the loss of water, hydrocarbons and other volatile products. Several additives, such as carbon black, a nitrogen containing carbohydrate and lignin, were homogenously incorporated into the precursor fiber and resulted in slight increase of the carbon yield. Carbon black particles became distinctive and visible on the surface of the carbon fibers. In particular, the thermal and chemical course of the carbonization was altered by the nitrogen containing additive, while the structure and properties of the carbonized fibers remained basically unchanged. © 2016 Elsevier Ltd. Source

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