Browsing by Author "Kreis, Philipp"

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Open Access
Lignin/poly(vinylpyrrolidone) multifilament fibers dry‐spun from water as carbon fiber precursors
(2023) Kreis, Philipp; Frank, Erik; Clauß, Bernd; Bauch, Volker; Stolpmann, Heiko; Kuske, Lisa; Schneck, Tanja; König, Simon; Buchmeiser, Michael R.
The preparation of lignin-based carbon fibers by dry spinning from aqueous solution followed by stabilization and continuous carbonization to endless yarns is reported. The influence of carbonization temperature and draw ratio on the morphology and mechanical properties of the final carbon fibers is investigated by single-fiber testing, wide-angle X-ray scattering, scanning electron microscopy, and Raman spectroscopy. A draw ratio of 5% (1.05) with a carbonization temperature of 1400 °C leads to the best mechanical properties. The resulting multifilament carbon fibers have an average diameter between 10-12 µm, an average tensile strength of 1.30 ± 0.32 GPa, a Young's modulus of 101 ± 18 GPa, and an elongation at break of 1.31 ± 0.23%. The maximum Weibull strength (𝜎0) is 1.04 GPa with a Weibull modulus (m) of 5.1. The use of a water-soluble system is economically advantageous; also, unlike melt-spun lignin fibers, the dry-spun precursor fibers can be thermally converted without any additional crosslinking step.
Open Access
Melt spinning of propylene carbonate‐plasticized poly(acrylonitrile)‐co‐poly(methyl acrylate)
(2020) König, Simon; Kreis, Philipp; Reinders, Leonie; Beyer, Ronald; Wego, Andreas; Herbert, Christian; Steinmann, Mark; Frank, Erik; Buchmeiser, Michael R.
The primary use of poly(acrylonitrile) (PAN) fibers, commonly referred to as acrylic fibers, is in textile applications like clothing, furniture, carpets, and awnings. All commercially available PAN fibers are processed by solution spinning; however, alternative, more cost‐effective processes like melt spinning are still highly desired. Here, the melt spinning of PAN‐co‐poly(methyl acrylate) (PMA) plasticized with propylene carbonate (PC) at 175°C is reported. The use of methyl acrylate (MA) as comonomer and PC as an external plasticizer renders the approach a combination of internal and external plasticization. Various mixtures of PAN and PC used in this work were examined by rheology, subjected to melt spinning, followed by discontinuous and continuous washing, respectively. The best fibers were derived from a PAN‐co‐PMA copolymer containing 8.1 mol‐% of MA having a number‐average molecular weight Mn of 34 000 g/mol, spun in the presence of 22.5 wt.‐% of PC. The resulting fibers were analyzed by scanning electron microscopy and wide‐angle X‐ray scattering (WAXS), and were subjected to mechanical testing.
Open Access
Melt-spinning of an intrinsically flame-retardant polyacrylonitrile copolymer
(2020) König, Simon; Kreis, Philipp; Herbert, Christian; Wego, Andreas; Steinmann, Mark; Wang, Dongren; Frank, Erik; Buchmeiser, Michael R.
Poly(acrylonitrile) (PAN) fibers have two essential drawbacks: they are usually processed by solution-spinning, which is inferior to melt spinning in terms of productivity and costs, and they are flammable in air. Here, we report on the synthesis and melt-spinning of an intrinsically flame-retardant PAN-copolymer with phosphorus-containing dimethylphosphonomethyl acrylate (DPA) as primary comonomer. Furthermore, the copolymerization parameters of the aqueous suspension polymerization of acrylonitrile (AN) and DPA were determined applying both the Fineman and Ross and Kelen and Tüdõs methods. For flame retardancy and melt-spinning tests, multiple PAN copolymers with different amounts of DPA and, in some cases, methyl acrylate (MA) have been synthesized. One of the synthesized PAN-copolymers has been melt-spun with propylene carbonate (PC) as plasticizer; the resulting PAN-fibers had a tenacity of 195 ± 40 MPa and a Young’s modulus of 5.2 ± 0.7 GPa. The flame-retardant properties have been determined by Limiting Oxygen Index (LOI) flame tests. The LOI value of the melt-spinnable PAN was 25.1; it therefore meets the flame retardancy criteria for many applications. In short, the reported method shows that the disadvantage of high comonomer content necessary for flame retardation can be turned into an advantage by enabling melt spinning.