Modifizierung des ABSE‐Polycarbosilazans mit Multi‐Walled Carbon Nanotubes zur Herstellung spinnfähiger Massen

Modification of the ABSE polycarbosilazane with multi‐walled carbon nanotubes for the creation of spinable masses An inexpensive method has been found to produce ceramic SiCN‐fibres via the precursor route consisting of five processing steps: synthesis of the polymer, preparation of the spinning mass, melt‐spinning, curing via electron beam and subsequent pyrolysis at 1100 °C in a nitrogen atmosphere. A special solid and meltable fibre polymer, the so‐called polycarbosilazane ABSE, has been developed in the last decade for this purpose. Due to its low molecular weight, an adequate catalytic and thermal aftertreatment was necessary to guarantee a stable melt‐spinning process. This article discusses an alternative way to prepare a qualified spinning mass, i.e. the addition of Multi‐Walled Carbon Nanotubes (MWCNTs) to the ABSE melt. For this purpose a homogeneous dispergation of the MWCNTs in the ABSE matrix is necessary. In this study, spinning masses were fabricated in different ways. By optical analysis and comparison of the level of dispergation in these spinning masses an optimized process for integration of the MWCNTs was identified. The influence of the addition of a dispersing agent is investigated as well. In using a dispersing agent, the level of homogeneous dispersion of the MWCNTs increases whereas the interactions between the particles and the precursor melt decrease. In first spinning experiments a good spinability of the masses were noticed. Thus the addition of MWCNTs represents a new way to modify the ABSE precursor for the melt‐spinning process.     

Innovative Katalysatoren zur oxidativen Dehydrierung in der Gasphase – Metallische Kurzfasern

Innovative Catalysts for Oxidative Dehydration Reactions in the Gas Phase – Metallic Short Fibres The catalytic activity of metallic short fibres with chosen alloy composition and texture was investigated in the oxidative dehydration (ODH) of propane to yield propene, and of isopropanol to yield acetone. The short fibres were synthesised using a melt extraction process and the properties of the fibres were intensely characterised. A correlation between the structure and the catalytic activity of the material was established. Thus, light‐optical microscopic‐, DSC‐, XRD‐, REM‐ and EDX‐methods were used to characterise the fibres. Selective results of the dependency of the temperature on the propane conversion are presented in this work. A yield of more than 35 % propene is obtained at a propane conversion of 50 %. The ODH of isopropanol to acetone occurred with attractive yields of over 80 %. The results demonstrate the high innovative potential of the metal fibre materials.     

Lenzing LYOCELL: Potentiale und Chancen einer neuen Fasergeneration

Lenzing LYOCELL – chances of a new generation of manmade fibres Cellulose is natures most important organic constructional and functional polymeric material and correspondigly has a variety of excellent and very specific properties. These properties can be used for a large number of products and can also be specifically modified as soon as it is possible to dissolve the cellulose and then to regenerate it in the desired shape. The progress in the development of the new Lyocell fibre, the better understanding of its performance and the possibilities to modify it, but also several completely new applications of the Lyocell process for other products show that the direct regeneration of cellulose from a solution in an organic solvent opens the path for a completely new utilisation of this outstanding property potential. Lyocell therefore not only offers the chance for a new generation of cellulosic fibres – also for new applications – but altogether also for a renaissance of cellulose for a large variety of products, where on the one side cellulose has been substituted during the last decades by synthetic polymers but where on the other side several completely new applications will be accessible for this outstanding polymer.     

Biostable highly aligned polyurethane fibres for the potential application of small calibre vascular grafting

Synthetic vascular grafting is necessarily when the autografting is not possible in some cases. Conventional polyethylene terephthalate and expanded polytetrafluoroethylene vascular grafts are found to be effective for diameter bigger than 6 mm but not for the diameter smaller than 4 mm due to the compliance mismatch and thrombogenicity. Endothelization on the surface of the graft can reduce the risks of compliance mismatch and thrombogenicity. In order to catalyst the endothelization process, fibrous morphology similar to the extracellular matrix of our body is preferable in the vascular grafts. Apart from that, the biostability of the grafts is also an essential element to be considered as the biodegradation may reduce the efficiency of the grafts. Many polyurethanes have been recognised as biostable materials. Hence, in this study, highly aligned polyurethane fibres are fabricated using a facile dry spinning technique in the view of providing effective sites for endothelization process to occur. These fibres are immersed into the simulated body fluid for as long as 24 weeks before conducting the biostability characterisations. The biostability is assessed in three aspects, physical, mechanical and chemical properties. Results show that the fibres do not have observable or significant deteriorations in all the three aspects mentioned.     

Faserverstärkte oxidkeramische Werkstoffe

Oxide ceramic matrix composites Oxide ceramics display excellent thermal and chemical stability up to high temperatures. A suitable way to overcome the inherent brittleness of oxide ceramics is the reinforcement with oxide fibers. Although both constituents, fibers and matrices are brittle, the composites display quasi‐ductile deformation behavior, due to mechanisms such as crack deflection, crack bridging or fiber pull‐out. A premise for these mechanisms to work is the relatively weak bonding between fibers and the matrix. To achieve a weak fiber/matrix bonding either suitable fiber coatings are employed or, in an alternative approach, highly porous matrices are used. WHIPOX, developed at DLR is a ceramic matrix composite belonging to the porous matrix group. These materials have a high potential for thermal protection systems and liners in gas turbine engines and beyond.