Characterization of PAN-TiO2 Nanofiber Mats and their Application as Front Electrodes for Dye-sensitized Solar Cells

In the context of the energy transition to renewables, the spotlight is on large systems connected to the power grid, but this also offers room for smaller, more specialized applications. Photovoltaics, in particular, offer the possibility of the self-sufficient supply of smaller electrical appliances on smaller scales. The idea of making previously unused surfaces usable is by no means new, and textiles such as backpacks, tent tarpaulins and other covers are particularly suitable for this purpose. In order to create a non-toxic and easily recyclable product, dye-sensitized solar cells (DSSC), which can be manufactured through electrospinning with a textile feel, are an attractive option here. Therefore, this paper investigates a needle electrospun nanofiber mat, whose spin solution contains polyacrylonitrile (PAN) dissolved in dimethyl sulfoxide (DMSO) as well es TiO2 nanoparticles. In addition to characterization, the nanofiber mat was dyed in a solution containing anthocyanins to later serve as a front electrode for a dye-sensitized solar cell. Although of lower efficiency, the DSSC provides stable results over two months of measurement

Textile based dye-sensitized solar cells with natural dyes

Natural dyes extracted from hibiscus petals, elderberries and mallow flowers were investigated in dye-sensitized solar cells. Two approaches were followed: 1. Hybrid glass/fabric cells with titanium dioxide on glass as working electrode and a textile counter electrode; 2. hybrid fabric/glass cells with zinc oxide as working electrode on textile and a glass counter electrode. The zinc oxide layer on cotton was prepared by electroless deposition whereas the titanium dioxide coated glass electrodes were obtained directly from the manufacturer. In both cases the redox couple consisted of iodine / triiodide and the counter electrode was based on an electrically conductive fabric

Design tool for automated crocheting of fabrics

In the context of developing a machine to automatically crochet fabrics, a suitable design tool tailored to the new technology and enabling its application is crucial. The paper offers first insights into the prototype of the crochet machine and presents the approach of such a design tool implemented in Python for creating, modeling and generating the machine instructions. With a graphical user interface (GUI), a flat crocheted fabric can be designed by arranging international crochet symbols for slip stitch (SL), single crochet (SC) and half double crochet (HDC). Built-in error checking mechanisms, following the rules of crochet and the machine’s constraints, will aid inexperienced crocheters in this process. Based on the resulting computer representation as an array containing short strings for the respective stitches, a topology-based 3D model at the meso scale is automatically created as a preview of the designed crocheted fabric. Also, machine instructions to automatically crochet the fabric with the crochet machine prototype are generated by mapping the computer representation of the stitches to macros of G-code and appending them in a valid order. The straightforward design tool shows the capabilities of the crochet machine and is extensible for further enhancements. Through modeling, the structure of the machine-crocheted fabrics is presented for the first time. In comparison to manually crocheted fabrics, the machine-crocheted ones exhibit a technical front and back, since stitches are formed by the machine only from one side

Stabilization and Incipient Carbonization of Electrospun Polyacrylonitrile Nanofibers Fixated on Aluminum Substrates

Storck JL, Grothe T, Tuvshinbayar K, et al. Stabilization and Incipient Carbonization of Electrospun Polyacrylonitrile Nanofibers Fixated on Aluminum Substrates. Fibers. 2020;8(9): 55.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

Necessary Parameters of Vertically Mounted Textile Substrates for Successful Cultivation of Cress for Low-Budget Vertical Farming

A growing population needs an expansion of agriculture to ensure a reliable supply of nutritious food. As a variable concept, vertical farming, becoming increasingly popular, can allow plant growth for local food produc­tion in the vertical sense on, e.g. facades in addition to the classical layered structure in buildings. As substrates, textile fabrics can be used as a sustainable approach in terms of reusability. In our experiment, we investigated which properties a textile should possess in order to be suitable for an application in vertical farming by the example of cress seeds. To determine the best-fitted fabric, four different textiles were mounted vertically, and were provided with controlled irrigation and illumination. Our results showed that a hairy textile surface as provided by weft-knitted plush is advantageous. There, the rooting of cress plants used in this experiment is easier and less complicated than along tightly meshed, flat surfaces, as for woven linen fabrics

Coulomb dissociation of O-16 into He-4 and C-12

We measured the Coulomb dissociation of O-16 into He-4 and C-12 within the FAIR Phase-0 program at GSI Helmholtzzentrum fur Schwerionenforschung Darmstadt, Germany. From this we will extract the photon dissociation cross section O-16(alpha,gamma)C-12, which is the time reversed reaction to C-12(alpha,gamma)O-16. With this indirect method, we aim to improve on the accuracy of the experimental data at lower energies than measured so far. The expected low cross section for the Coulomb dissociation reaction and close magnetic rigidity of beam and fragments demand a high precision measurement. Hence, new detector systems were built and radical changes to the (RB)-B-3 setup were necessary to cope with the high-intensity O-16 beam. All tracking detectors were designed to let the unreacted O-16 ions pass, while detecting the C-12 and He-4

Coulomb dissociation of 16O into 4He and 12C

We measured the Coulomb dissociation of 16O into 4He and 12C at the R3B setup in a first campaign within FAIR Phase 0 at GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt. The goal was to improve the accuracy of the experimental data for the 12C(a,?)16O fusion reaction and to reach lower center-ofmass energies than measured so far. The experiment required beam intensities of 109 16O ions per second at an energy of 500 MeV/nucleon. The rare case of Coulomb breakup into 12C and 4He posed another challenge: The magnetic rigidities of the particles are so close because of the same mass-To-charge-number ratio A/Z = 2 for 16O, 12C and 4He. Hence, radical changes of the R3B setup were necessary. All detectors had slits to allow the passage of the unreacted 16O ions, while 4He and 12C would hit the detectors' active areas depending on the scattering angle and their relative energies. We developed and built detectors based on organic scintillators to track and identify the reaction products with sufficient precision

Automation of crochet technology and development of a prototype machine for the production of complex-shaped textiles

Aufgrund der Klimakrise und der Notwendigkeit CO2-Emissionen zu reduzieren, ist in Zukunft mit einer steigenden Nachfrage an Leichtbaumaterialien wie textilverstärkten Verbundwerkstoffen zu rechnen. Aufgrund steigender Rohstoff- und Energiekosten verspricht der Einsatz von endkonturnahen Verbundwerkstoffen eine Reduktion der Herstellungskosten und des Abfalls. Herkömmliche Textiltechnologien sind nur begrenzt in der Lage die erforderlichen komplex geformten Textilien herzustellen. Um dieses Problem durch den Einsatz alternativer, noch nicht industriell etablierter Technologien zu lösen, beschäftigt sich diese Arbeit ausführlich mit der Entwicklung einer Häkelmaschine sowie der Untersuchung entsprechender Textilien. Häkeln ist eine maschenbildende Technologie, bei der im Gegensatz zum Stricken die Schlaufen, die eine Masche bilden, sowohl vertikal als auch horizontal aus zuvor gebildeten Maschen entspringen. Mit dem vielseitigen Häkeln ist es insbesondere möglich, komplexe dreidimensionale (3D) Formen zu erzeugen, da an jeder beliebigen Stelle eines Textils neue Maschen gebildet werden können. Bisherige Häkelmaschinenansätze sind unzureichend und bezüglich ihrer Skalierbarkeit zu einer industriell einsetzbaren Maschine stark eingeschränkt. Industriell etablierte Maschinen, die Häkelmaschinen genannt werden, sind in ihrer Bezeichnung irreführend, da es sich um Wirkmaschinen handelt, die nur grob die Häkelstruktur nachahmen, aber keine echten Häkelmaschen bilden können. Die hier entwickelte und patentierte Häkelmaschine namens Crochet Automaton (CroMat) ermöglicht erstmals die automatisierte Herstellung von Luftmaschen, Kettmaschen, festen Maschen, halben Stäbchen, Übergängen der Maschenreihen, Zunahmen sowie Abnahmen und auch anderen Operationen nach dem Prinzip des Flachhäkelns auf Basis einer Luftmaschenreihe. Darüber hinaus können neue Maschen durch ein manuelles Umhängen des produzierten Textils an nahezu beliebigen Stellen gebildet werden. Damit können komplex geformte 3D-Textilien entsprechend den Vorteilen des Häkelns hergestellt werden. Mit dem entwickelten CroMat-Prototyp lassen sich Formen herstellen, die für endkonturnahe Faserverbundwerkstoffe wie bspw. Doppel-T-Träger potenziell geeignet sind. Durch ein Aufhängen verschiedener Maschenreihen oder Textilien auf denselben Nadeln der Maschine ist es ebenfalls möglich diese mit dem Häkeln einer verbindenden Reihe zu fügen. Neben dem mechatronischen Prototyp mit zehn Achsen wird das weltweit erste Software-Tool für den Entwurf von maschinell gehäkelten Textilien entwickelt. Es beinhaltet eine Fehlerüberprüfung, die automatische Generierung des G-Codes für die Maschinensteuerung und eine Vorschau der entworfenen Textilien. Neben einer grafischen Benutzeroberfläche mit standardisierten Häkelsymbolen wird auch die Möglichkeit zur automatischen Generierung der Häkelstruktur entsprechend der Form eines zweidimensionalen (2D) Polygons geboten. Für die Vorschau wurde das erste Topologie-basierte Modellierungs-Framework für maschinell herstellbare Häkelstrukturen entwickelt. Eine ähnliche Modellierung wurde für manuell gehäkelte Stoffe entwickelt, die sich von den maschinell hergestellten nur darin unterscheiden, dass der Stoff nach jeder Reihe gewendet wird und somit die Maschen von verschiedenen Seiten aus gebildet werden. Beide Modellarten können als Grundlage für simulative Untersuchungen mit der Finite-Elemente-Methode (FEM) verwendet werden, die in dieser Arbeit zum ersten Mal zur Simulation von gehäkelten Textilien eingesetzt wurde. Darüber hinaus wurden erstmals die Zugeigenschaften von manuell gehäkelten Textilien systematisch untersucht und die Eigenschaften der ersten Faserverbundwerkstoffe mit gehäkelten Textilien erforscht. Gehäkelte Textilien (und entsprechende Verbundstoffe) haben grundsätzlich ähnliche Eigenschaften wie gestrickte Textilien, können aber tendenziell höheren Kräften standhalten. Zusammen mit den Formgebungsmöglichkeiten ist die CroMat-Häkelmaschine generell vielversprechend für die Automatisierung des Häkelns und insbesondere für die zukünftige Produktion von endkonturnahen Faserverbundwerkstoffen.:1 Introduction 1 1.1 Motivation 1 1.2 Aim 2 1.3 Work structure 3 2 Technical and scientific background 4 2.1 Crochet 4 2.1.1 Technique and stitch formation 5 2.1.2 Crocheting a fabric 8 2.1.3 Applications of crochet 11 2.1.4 Research overview on crochet 11 2.2 Knitting machines 15 2.2.1 Weft knitting 16 2.2.2 Warp knitting 19 2.2.3 Crochet gallon machines 21 2.3 Existing crochet machine approaches 23 2.3.1 First approach to automate crochet 23 2.3.2 Circular crochet machine approach 25 2.3.3 Crocheting with a robotic arm 27 2.3.4 Further attempts to automate crocheting 29 2.4 Rapid prototyping 30 2.4.1 Development approach 30 2.4.2 3D printing 31 2.5 Electric motors 33 2.5.1 Stepper 33 2.5.2 Servo motors 34 2.5.3 G-code 35 2.6 Textile composites 37 2.6.1 Composite production 37 2.6.2 Near net-shaped composites 38 3 Crochet machine development 39 3.1 CroMat innovation process 39 3.1.1 Development phases 39 3.1.2 Analyzing the first crochet machine approach 41 3.1.3 Definition of crochet machine prototype requirements 43 3.1.4 Crochet needle insertion process 47 3.1.5 Suspending stitches on auxiliary needles 55 3.1.6 Yarn guide and patent 57 3.2 Improvements beyond the patent 60 3.2.1 Analyzing the yarn feeding problem 60 3.2.2 Systematic identification of possible solutions 61 3.2.3 Implementation of the most suited solution 64 3.3 Automated crochet stitch formation 67 3.3.1 Initial situation 67 3.3.2 Slip stitch 68 3.3.3 Single crochet 71 3.3.4 Half double crochet 73 3.3.5 Turn 75 3.3.6 Chain stitch and skipping a stitch within a course 77 3.3.7 Increase stitches 79 3.3.8 Decrease stitches 82 3.3.9 Further methods for changing the fabric’s width 84 3.3.10 More complex stitches 87 3.4 Technical implementation of CroMat prototype 89 3.4.1 CroMat machine overview 89 3.4.2 Auxiliary needles 94 3.4.3 Crochet needle 100 3.4.4 Yarn guide 106 3.4.5 Stress on yarn and machine elements 109 3.4.6 Yarn tension 115 3.4.7 Firmware and motor control 117 3.5 Crocheting with the CroMat prototype 120 3.5.1 Producing an exemplary crocheted fabric 120 3.5.2 Movements for SC formation 122 3.6 Development of CroMat crochet design tool 125 3.6.1 Tool overview 125 3.6.2 User interface 126 3.6.3 Error checking 129 3.6.4 Preview of the fabric 130 3.6.5 Generating G-code 130 3.6.6 Discussing the design tool 132 3.7 CroMat requirement fulfillment 134 4 Research on crocheted fabrics 137 4.1 Modeling and simulation of manually crocheted fabrics 137 4.1.1 Modeling approaches for textiles 137 4.1.2 Developed modeling of crochet structures 138 4.1.3 FEM investigations 143 4.2 Mechanical characteristics of manually crocheted fabrics 146 4.2.1 Study overview 146 4.2.2 Materials and Methods 146 4.2.3 Influence of the crocheter 148 4.2.4 Influence of the crochet structure 150 4.2.5 Crochet composite 152 4.2.6 Evaluation of the results 155 4.3 Modeling and simulation of machine-crocheted fabrics 157 4.3.1 Modeling machine-crocheted fabrics 157 4.3.2 Modeling of INC and DEC 159 4.3.3 Simulative comparison of hand- and machine-crocheted fabrics 161 4.4 Generating machine producible crochet patterns in shapes of 2D polygons 164 4.4.1 Background 164 4.4.2 Developed polygon subdivision algorithm 165 4.4.3 Improving the subdivision’s quality 168 4.4.4 Crochet subdivision results for exemplary polygons 170 4.4.5 Discussing the results 176 4.5 Exemplary machine-crocheted fabrics 178 4.5.1 Basic fabric structure 178 4.5.2 Advanced possible structures 181 4.5.3 Poisson’s ratio investigation 185 5 Conclusion 189 5.1 Summary 189 5.2 Outlook 191 6 References 193 6.1 References of the author 193 6.2 Further references 193In the future, due to the climate crisis and the need to reduce CO2 emissions, an increasing demand for lightweight materials such as textile reinforced composites can be expected. Because of rising raw material and energy costs, the application of more near net-shaped composites is promising for reducing manufacturing costs and waste. However, conventional textile technologies are limited in their ability to produce the necessary complex-shaped textiles. In order to address this problem by using alternative technologies that have not yet been industrially established, this thesis deals extensively with the development of a crochet machine and the investigation of respective textiles. Crochet is a stitch-forming technology in which, unlike knitting, the loops of a stitch originate both vertically and horizontally from previously formed stitches. With versatile crochet, it is especially possible to create complex three-dimensional (3D) shapes because new stitches can be formed at any point on a fabric. Previous crochet machine approaches are inadequate and severely limited in scalability to an industrially applicable machine. Industrially established machinery called crochet machines are misleading in their designation because they are knitting machines that can only roughly mimic crochet structure but cannot form true crocheted fabrics. The Crochet Automaton (CroMat) crochet machine developed and patented here enables for the first time the automated production of chain stitches (CHs), slip stitches (SLs), single crochet stitches (SCs), half double crochet stitches (HDCs), turns (T1 and T2), increase stitches (INCs) as well as decrease stitches (DECs) and other operations according to the principle of flat crocheting based on a chain line. In addition, by manually removing and re-hanging the produced fabric, new stitches can be formed at almost any point to produce complex-shaped 3D textiles according to the capabilities of crochet. For example, it is possible to produce shapes relevant for near net-shaped composites such as double T-beams with the developed CroMat prototype. With manually suspending different stitch rows or fabrics on the machine, it is also possible to join them by simultaneously crocheting a course through them. In addition to the mechatronic prototype with ten axes, the world's first tool for designing machine-crocheted textiles is developed. It includes error checking, generation of the G-code for machine control and a preview of the designed fabrics. Beyond a graphical user interface (GUI) with standardized crochet symbols, a higher-level programmability is added through specifying a shape by 2D polygons and automatically generating corresponding, machine-crochetable patterns. The first topology-based modeling framework for machine-producible crochet structures was developed for the preview. A similar modeling was developed for manually crocheted fabrics, which differ from the machine-produced ones only in the fact that the fabric is turned after each row and thus the stitches are formed from different sides. Both models can be used as a basis for simulative finite element method (FEM) investigations, which were used in this work to simulate crocheted fabrics for the first time. Furthermore, the tensile properties of manually crocheted fabrics were systematically investigated for the first time and the properties of the first crochet composites were researched. Crocheted textiles (and corresponding composites) have basically similar properties as knitted textiles but have a tendency to withstand higher forces. Together with the shaping capabilities, the CroMat crochet machine is generally highly promising for the automation of crochet and especially for the future production of near net-shaped composite reinforcements.:1 Introduction 1 1.1 Motivation 1 1.2 Aim 2 1.3 Work structure 3 2 Technical and scientific background 4 2.1 Crochet 4 2.1.1 Technique and stitch formation 5 2.1.2 Crocheting a fabric 8 2.1.3 Applications of crochet 11 2.1.4 Research overview on crochet 11 2.2 Knitting machines 15 2.2.1 Weft knitting 16 2.2.2 Warp knitting 19 2.2.3 Crochet gallon machines 21 2.3 Existing crochet machine approaches 23 2.3.1 First approach to automate crochet 23 2.3.2 Circular crochet machine approach 25 2.3.3 Crocheting with a robotic arm 27 2.3.4 Further attempts to automate crocheting 29 2.4 Rapid prototyping 30 2.4.1 Development approach 30 2.4.2 3D printing 31 2.5 Electric motors 33 2.5.1 Stepper 33 2.5.2 Servo motors 34 2.5.3 G-code 35 2.6 Textile composites 37 2.6.1 Composite production 37 2.6.2 Near net-shaped composites 38 3 Crochet machine development 39 3.1 CroMat innovation process 39 3.1.1 Development phases 39 3.1.2 Analyzing the first crochet machine approach 41 3.1.3 Definition of crochet machine prototype requirements 43 3.1.4 Crochet needle insertion process 47 3.1.5 Suspending stitches on auxiliary needles 55 3.1.6 Yarn guide and patent 57 3.2 Improvements beyond the patent 60 3.2.1 Analyzing the yarn feeding problem 60 3.2.2 Systematic identification of possible solutions 61 3.2.3 Implementation of the most suited solution 64 3.3 Automated crochet stitch formation 67 3.3.1 Initial situation 67 3.3.2 Slip stitch 68 3.3.3 Single crochet 71 3.3.4 Half double crochet 73 3.3.5 Turn 75 3.3.6 Chain stitch and skipping a stitch within a course 77 3.3.7 Increase stitches 79 3.3.8 Decrease stitches 82 3.3.9 Further methods for changing the fabric’s width 84 3.3.10 More complex stitches 87 3.4 Technical implementation of CroMat prototype 89 3.4.1 CroMat machine overview 89 3.4.2 Auxiliary needles 94 3.4.3 Crochet needle 100 3.4.4 Yarn guide 106 3.4.5 Stress on yarn and machine elements 109 3.4.6 Yarn tension 115 3.4.7 Firmware and motor control 117 3.5 Crocheting with the CroMat prototype 120 3.5.1 Producing an exemplary crocheted fabric 120 3.5.2 Movements for SC formation 122 3.6 Development of CroMat crochet design tool 125 3.6.1 Tool overview 125 3.6.2 User interface 126 3.6.3 Error checking 129 3.6.4 Preview of the fabric 130 3.6.5 Generating G-code 130 3.6.6 Discussing the design tool 132 3.7 CroMat requirement fulfillment 134 4 Research on crocheted fabrics 137 4.1 Modeling and simulation of manually crocheted fabrics 137 4.1.1 Modeling approaches for textiles 137 4.1.2 Developed modeling of crochet structures 138 4.1.3 FEM investigations 143 4.2 Mechanical characteristics of manually crocheted fabrics 146 4.2.1 Study overview 146 4.2.2 Materials and Methods 146 4.2.3 Influence of the crocheter 148 4.2.4 Influence of the crochet structure 150 4.2.5 Crochet composite 152 4.2.6 Evaluation of the results 155 4.3 Modeling and simulation of machine-crocheted fabrics 157 4.3.1 Modeling machine-crocheted fabrics 157 4.3.2 Modeling of INC and DEC 159 4.3.3 Simulative comparison of hand- and machine-crocheted fabrics 161 4.4 Generating machine producible crochet patterns in shapes of 2D polygons 164 4.4.1 Background 164 4.4.2 Developed polygon subdivision algorithm 165 4.4.3 Improving the subdivision’s quality 168 4.4.4 Crochet subdivision results for exemplary polygons 170 4.4.5 Discussing the results 176 4.5 Exemplary machine-crocheted fabrics 178 4.5.1 Basic fabric structure 178 4.5.2 Advanced possible structures 181 4.5.3 Poisson’s ratio investigation 185 5 Conclusion 189 5.1 Summary 189 5.2 Outlook 191 6 References 193 6.1 References of the author 193 6.2 Further references 19

Investigation of Low-Cost FDM-Printed Polymers for Elevated-Temperature Applications

While fused deposition modeling (FDM) and other relatively inexpensive 3D printing methods are nowadays used in many applications, the possible areas of using FDM-printed objects are still limited due to mechanical and thermal constraints. Applications for space, e.g., for microsatellites, are restricted by the usually insufficient heat resistance of the typical FDM printing materials. Printing high-temperature polymers, on the other hand, necessitates special FDM printers, which are not always available. Here, we show investigations of common polymers, processible on low-cost FDM printers, under elevated temperatures of up to 160 °C for single treatments. The polymers with the highest dimensional stability and mechanical properties after different temperature treatments were periodically heat-treated between -40 °C and +80 °C in cycles of 90 min, similar to the temperature cycles a microsatellite in the low Earth orbit (LEO) experiences. While none of the materials under investigation fully maintains its dimensions and mechanical properties, filled poly(lactic acid) (PLA) filaments were found most suitable for applications under these thermal conditions

Comparative Study of Metal Substrates for Improved Carbonization of Electrospun PAN Nanofibers

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