Polyacrylonitrile can be used as a base material for thermochemical conversion into carbon. Especially nanofiber mats, produced by electrospinning, are of interest to create carbon nanofibers. Optimal stabilization and carbonization parameters, however, strongly depend on the spatial features of the original material. While differences between nano- and microfibers are well known, this paper shows that depending on the electrospinning method and the solvent used, considerable differences between various nanofiber mats have to be taken into account for the optimization of the stabilization conditions. Here, we examine for the first time polyacrylonitrile nanofiber mats, electrospun with wire electrospinning from the low-toxic dimethyl sulfoxide as a solvent, instead of the typically used needle electrospinning from the toxic dimethylformamide. Additionally, we used inexpensive polyacrylonitrile from knitting yarn instead of highly specialized material, tailored for carbonization. Our results show that by carefully controlling the maximum stabilization temperature and especially the heating rate, fully stabilized polyacrylonitrile fibers without undesired interconnections can be created as precursors for carbonization.

The industrial production of prototypes made of polyurethane via silicone molds in the vacuum casting process is one of the most widespread applications of rapid tooling. The silicone molds show progressive deterioration, as the isocyanate component of the polyurethane resin diffuses into the mold cavity surface during the casting process, thus limiting their durability. Here, we present the first comprehensive description of the underlying chemical and physical mechanisms on a molecular level. It is shown that the isocyanate polymerizes inside the polydimethylsiloxane matrix with moisture to polyurea. Polyurea clusters, which emerge from the resulting interpenetrating polymer network with continuing isocyanate exposure, promote fissure formation under mechanical demolding stresses. The mechanism was investigated with a wide variety of characterization methods, and qualitative variations were demonstrated using different commercial materials. Influencing factors such as mold geometry, process flow, and different aspects of the material composition were examined experimentally. A thorough understanding of the deterioration mechanism paves the way for the development of durable molds and an economical midseries technology in plastics processing.

Electrospinning is a new technology whose scope is gradually being developed. For this reason, the number of known polymer–solvent combinations for electrospinning is still very low despite the enormous variety of substances that are potentially available. In particular, electrospinning from low-toxic solvents, such as the use of dimethyl sulfoxide (DMSO) in medical technology, is rare in the relevant scientific literature. Therefore, we present in this work a series of new polymers that are applicable for electrospinning from DMSO. From a wide range of synthetic polymers tested, poly(vinyl alcohol) (PVOH), poly(2ethyl2oxazolene) (PEOZ), and poly(vinylpyrrolidone) (PVP) as water-soluble polymers and poly(styrene-co-acrylonitrile) (SAN), poly(vinyl alcohol-co-ethylene) (EVOH), and acrylonitrile butadiene styrene (ABS) as water-insoluble polymers were found to be suitable for the production of nanofibers. Furthermore, the influence of acetone as a volatile solvent additive in DMSO on the fiber morphology of these polymers was investigated. Analyses of the fiber morphology by helium ion microscopy (HIM) showed significantly different fiber diameters for different polymers and a reduction in beads and branches with increasing acetone content.

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