@article{2039, abstract = { Carbon nanofibers are used for a broad range of applications, from nano-composites to energy storage devices. They are typically produced from electrospun poly(acrylonitrile) nanofibers by thermal stabilization and carbonization. The nanofiber mats are usually placed freely movable in an oven, which leads to relaxation of internal stress within the nanofibers, making them thicker and shorter. To preserve their pristine morphology they can be mechanically fixated, which may cause the nanofibers to break. In a previous study, we demonstrated that sandwiching the nanofiber mats between metal sheets retained their morphology during stabilization and incipient carbonization at 500 °C. Here, we present a comparative study of stainless steel, titanium, copper and silicon substrate sandwiches at carbonization temperatures of 500 °C, 800 °C and 1200 °C. Helium ion microscopy revealed that all metals mostly eliminated nanofiber deformation, whereas silicone achieved the best results in this regard. The highest temperatures for which the metals were shown to be applicable were 500 °C for silicon, 800 °C for stainless steel and copper, and 1200 °C for titanium. Fourier transform infrared and Raman spectroscopy revealed a higher degree of carbonization and increased crystallinity for higher temperatures, which was shown to depend on the substrate material. }, author = {Storck, Jan Lukas and Wortmann, Martin and Brockhagen, Bennet and Frese, Natalie and Diestelhorst, Elise and Grothe, Timo and Hellert, Christian and Ehrmann, Andrea}, issn = {2073-4360}, journal = {Polymers}, keywords = {electrospinning, poly(acrylonitrile), stabilization, carbonization, metallic substrates, shrinkage, nanofiber morphology}, number = {4}, publisher = {MDPI AG}, title = {{Comparative Study of Metal Substrates for Improved Carbonization of Electrospun PAN Nanofibers}}, doi = {10.3390/polym14040721}, volume = {14}, year = {2022}, } @article{1081, abstract = { Polyacrylonitrile (PAN) nanofiber mats are typical precursors for carbon nanofibers. They can be fixed or even elongated during stabilization and subsequent carbonization to gain straight, mechanically robust carbon nanofibers. These processes necessitate additional equipment or are—if the nanofiber mats are just fixed at the edges—prone to resulting in the specimens breaking, due to an uneven force distribution. Hence, we showed in a previous study that electrospinning PAN on aluminum foils and stabilizing them fixed on these substrates, is a suitable solution to keep the desired morphology after stabilization and incipient carbonization. Here, we report on the influence of different metallic and semiconductor substrates on the physical and chemical properties of the nanofiber mats after stabilization and carbonization at temperatures up to 1200 °C. For stabilization on a metal substrate, an optimum stabilization temperature of slightly above 240 °C was found, approached with a heating rate of 0.25 K/min. Independent from the substrate material, SEM images revealed less defect fibers in the nanofiber mats stabilized and incipiently carbonized on a metal foil. Finally, high-temperature carbonization on different substrates is shown to allow for producing metal/carbon nano-composites. }, author = {Storck, Jan Lukas and Brockhagen, Bennet and Grothe, Timo and Sabantina, Lilia and Kaltschmidt, Bernhard and Tuvshinbayar, Khorolsuren and Braun, Laura and Tanzli, Ewin and Hütten, Andreas and Ehrmann, Andrea}, issn = {2311-5629}, journal = {C}, keywords = {polyacrylonitrile (PAN), nanofibers, electrospinning, aluminum, copper, tin, titanium, silicon wafer, steel, stabilization and carbonization}, number = {1}, publisher = {MDPI AG}, title = {{Stabilization and Carbonization of PAN Nanofiber Mats Electrospun on Metal Substrates}}, doi = {10.3390/c7010012}, volume = {7}, year = {2021}, } @article{1594, abstract = { Electrospun poly(acrylonitrile) (PAN) nanofibers are typical precursors of carbon nanofibers. During stabilization and carbonization, however, the morphology of pristine PAN nanofibers is not retained if the as-spun nanofiber mats are treated without an external mechanical force, since internal stress tends to relax, causing the whole mats to shrink significantly, while the individual fibers thicken and curl. Stretching the nanofiber mats during thermal treatment, in contrast, can result in fractures due to inhomogeneous stress. Previous studies have shown that stabilization and carbonization of PAN nanofibers electrospun on an aluminum substrate are efficient methods to retain the fiber mat dimensions without macroscopic cracks during heat treatment. In this work, we studied different procedures of mechanical fixation via metallic substrates during thermal treatment. The influence of the metallic substrate material as well as different methods of double-sided covering of the fibers, i.e., sandwiching, were investigated. The results revealed that sandwich configurations with double-sided metallic supports not only facilitate optimal preservation of the original fiber morphology but also significantly accelerate the carbonization process. It was found that unlike regularly carbonized nanofibers, the metal supports allow complete deoxygenation at low treatment temperature and that the obtained carbon nanofibers exhibit increased crystallinity. }, author = {Storck, Jan Lukas and Hellert, Christian and Brockhagen, Bennet and Wortmann, Martin and Diestelhorst, Elise and Frese, Natalie and Grothe, Timo and Ehrmann, Andrea}, issn = {1996-1944}, journal = {Materials}, keywords = {electrospinning, stabilization, carbonization, metallic substrates, shrinkage, fiber morphology}, number = {16}, publisher = {MDPI AG}, title = {{Metallic Supports Accelerate Carbonization and Improve Morphological Stability of Polyacrylonitrile Nanofibers during Heat Treatment}}, doi = {10.3390/ma14164686}, volume = {14}, year = {2021}, } @article{670, abstract = {Polyacrylonitrile (PAN) nanofibers, prepared by electrospinning, are often used as a precursor for carbon nanofibers. The thermal carbonization process necessitates a preceding oxidative stabilization, which is usually performed thermally, i.e., by carefully heating the electrospun nanofibers in an oven. One of the typical problems occurring during this process is a strong deformation of the fiber morphologies—the fibers become thicker and shorter, and show partly undesired conglutinations. This problem can be solved by stretching the nanofiber mat during thermal treatment, which, on the other hand, can lead to breakage of the nanofiber mat. In a previous study, we have shown that the electrospinning of PAN on aluminum foils and the subsequent stabilization of this substrate is a simple method for retaining the fiber morphology without breaking the nanofiber mat. Here, we report on the impact of different aluminum foils on the physical and chemical properties of stabilized PAN nanofibers mats, and on the following incipient carbonization process at a temperature of max. 600 °C, i.e., below the melting temperature of aluminum.}, author = {Storck, Jan Lukas and Grothe, Timo and Tuvshinbayar, Khorolsuren and Diestelhorst, Elise and Wehlage, Daria and Brockhagen, Bennet and Wortmann, Martin and Frese, Natalie and Ehrmann, Andrea}, issn = {2079-6439}, journal = {Fibers}, keywords = {polyacrylonitrile (PAN), nanofibers, electrospinning, stabilization, carbonization}, number = {9}, title = {{Stabilization and Incipient Carbonization of Electrospun Polyacrylonitrile Nanofibers Fixated on Aluminum Substrates}}, doi = {10.3390/fib8090055}, volume = {8}, year = {2020}, } @article{664, abstract = {Thermally stabilized and subsequently carbonized nanofibers are a promising material for many technical applications in fields such as tissue engineering or energy storage. They can be obtained from a variety of different polymer precursors via electrospinning. While some methods have been tested for post-carbonization doping of nanofibers with the desired ingredients, very little is known about carbonization of blend nanofibers from two or more polymeric precursors. In this paper, we report on the preparation, thermal treatment and resulting properties of poly(acrylonitrile) (PAN)/poly(vinylidene fluoride) (PVDF) blend nanofibers produced by wire-based electrospinning of binary polymer solutions. Using a wide variety of spectroscopic, microscopic and thermal characterization methods, the chemical and morphological transition during oxidative stabilization (280 °C) and incipient carbonization (500 °C) was thoroughly investigated. Both PAN and PVDF precursor polymers were detected and analyzed qualitatively and quantitatively during all stages of thermal treatment. Compared to pure PAN nanofibers, the blend nanofibers showed increased fiber diameters, strong reduction of undesired morphological changes during oxidative stabilization and increased conductivity after carbonization.}, author = {Wortmann, Martin and Frese, Natalie and Mamun, Al and Trabelsi, Marah and Keil, Waldemar and Büker, Björn and Javed, Ali and Tiemann, Michael and Moritzer, Elmar and Ehrmann, Andrea and Hütten, Andreas and Schmidt, Claudia and Gölzhäuser, Armin and Hüsgen, Bruno and Sabantina, Lilia}, issn = {2079-4991}, journal = {Nanomaterials}, keywords = {electrospinning, carbon nanofiber, polymer blend, stabilization, carbonization, poly(acrylonitrile) (PAN), poly(vinylidene fluoride) (PVDF)}, number = {6}, title = {{Chemical and Morphological Transition of Poly(acrylonitrile)/Poly(vinylidene Fluoride) Blend Nanofibers during Oxidative Stabilization and Incipient Carbonization}}, doi = {10.3390/nano10061210}, volume = {10}, year = {2020}, } @article{573, abstract = {Polyacrylonitrile belongs to the most often used precursors for carbon fibers. Using electrospinning, polyacrylonitrile nanofiber mats can be prepared and afterwards stabilized and carbonized to prepare carbon nanofiber mats which, by adding other materials, will be useful for several applications. One of these materials is TiO2, which has photocatalytic properties and can thus be used as a photocatalyst for photodegradation of dyes. Here, we report on a detailed study of electrospinning, stabilization, and carbonization of electrospun polyacrylonitrile/TiO2 mats with varying TiO2 content. Depending on the amount of TiO2 in the nanofibers, the fiber morphology changes strongly, indicating an upper limit for the preparation of carbon/TiO2 nanofibers with smooth surface, but offering an even increased inner surface of the rougher carbon/TiO2 nanofibers with increased TiO2 content due to better maintenance of the fibrous structure during stabilization.}, author = {Sabantina, Lilia and Böttjer, Robin and Wehlage, Daria and Grothe, Timo and Klöcker, Michaela and García-Mateos, Francisco José and Rodríguez-Mirasol, José and Cordero, Tomás and Ehrmann, Andrea}, journal = {Journal of Engineered Fibers and Fabrics}, keywords = {Polyacrylonitrile, PAN, TiO2, nanofiber mat, electrospinning, composite, stabilization, carbonization}, pages = {1--8}, title = {{ Morphological study of stabilization and carbonization of polyacrylonitrile/TiO2 nanofiber mats}}, doi = {10.1177/1558925019862242}, volume = {14}, year = {2019}, } @article{599, abstract = {Electrospinning is a well-known technology used to create nanofiber mats from diverse polymers and other materials. Due to their large surface-to-volume ratio, such nanofiber mats are often applied as air or water filters. Especially the latter, however, have to be mechanically highly stable, which is challenging for common nanofiber mats. One of the approaches to overcome this problem is gluing them on top of more rigid objects, integrating them in composites, or reinforcing them using other technologies to avoid damage due to the water pressure. Here, we suggest another solution. While direct 3D printing with the fused deposition modeling (FDM) technique on macroscopic textile fabrics has been under examination by several research groups for years, here we report on direct FDM printing on nanofiber mats for the first time. We show that by choosing the proper height of the printing nozzle above the nanofiber mat, printing is possible for raw polyacrylonitrile (PAN) nanofiber mats, as well as for stabilized and even more brittle carbonized material. Under these conditions, the adhesion between both parts of the composite is high enough to prevent the nanofiber mat from being peeled off the 3D printed polymer. Abrasion tests emphasize the significantly increased mechanical properties, while contact angle examinations reveal a hydrophilicity between the original values of the electrospun and the 3D printed materials. }, author = {Kozior, Tomasz and Trabelsi, Marah and Mamun, Al and Sabantina, Lilia and Ehrmann, Andrea}, journal = {Polymers}, keywords = {nanofiber mat, electrospinning, water filter, 3D printing, FDM printing, adhesion, stabilization, carbonization}, number = {10}, publisher = {MDPI}, title = {{ Stabilization of Electrospun Nanofiber Mats Used for Filters by 3D Printing }}, doi = {10.3390/polym11101618}, volume = {11}, year = {2019}, }