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Sol-Gel basierte Flammschutzmittel stellen einen vielversprechenden Ansatz für Textilien dar, gerade im Bereich des Ersatzes von derzeit etablierten halogenhaltigen Flammschutzmitteln. Letztere sind aufgrund ihrer toxikologisch Bedenklichkeit sowie ihrer mitunter bioakkumulierenden Eigenschaften in die Kritik geraten. In diesem Forschungsvorhaben wurde daher untersucht auf welche Weise ein Flammschutz per Sol-Gel-Ansatz auf Stickstoff- und/oder Phosphorbasis als halogenfreie Alternative verwirklicht werden kann. Die Sol-Gel-Schicht fungierte dabei zum einen als nicht brennbarer Binder, zum anderen konnten über das Einführen entsprechender funktioneller Seitenketten für den Flammschutz aktive Gruppen direkt mit eingebunden werden. Verschiedene Ansätze wurden dabei verfolgt. Vor allem durch die Nutzung von additivierten Systemen, d.h. durch Sol-Gel-Schichten mit Zusätzen von stickstoff- und/oder phosphorhaltigen Verbindungen konnte ein Flammschutz nach DIN EN ISO 15025 (Schutzkleidung – Schutz gegen Hitze und Flammen) erhalten werden. Anhand eines Modellsystems, bei dem in zwei aufeinanderfolgenden Schritten zuerst eine funktionalisierte Sol-Gel-Schicht und anschließend eine Phosphorverbindung in einem zweiten Schritt aufgebracht wurde, konnten die Vorteile des Flammschutzes auf Sol-Gel-Basis nachgewiesen werden. Dabei wurde unter anderem auch gezeigt, dass ein Mechanismus auf Basis der Bildung einer Schutzschicht hauptsächlich verantwortlich für den Flammschutz ist. Dieses Ergebnis ist für eine zukünftige, weitere Optimierung entsprechender Ausrüstungen nicht zu unterschätzen. Durch Ausrüstungsversuche im semi-industriellen Maßstab konnte weiterhin gezeigt werden, dass einer großtechnischen Umsetzung der angewandten Ausrüstungen prinzipiell nichts im Wege steht. Abstriche müssen bis dato lediglich bezüglich der Waschstabilität gemacht werden. Die Sol-Gel-Schichten überstanden zwar im allgemeinen typische Waschprozesse, eine Permanenz der Flammfestigkeit von additivierten Systemen ergab sich aber nur in einzelnen Fällen. Ausgehend von den Ergebnissen wurde ein neuer Ansatz vorgestellt, der über den hier zugrundeliegenden Ansatz hinausgeht. Dieser sieht vor, durch den Einsatz von neu-synthetisierten Silanen mit Stickstoff- und Phosphorgruppen Sol-Gel-Schichten herzustellen, die ein vielversprechendes Verhalten zeigen. Hier konnte auch nach ersten Waschtests eine Aufrechterhaltung der verbesserten Flammfestigkeit nachgewiesen werden. Insgesamt konnte innerhalb des Forschungsvorhabens gezeigt werden, dass ein Flammschutz auf Sol-Gel-Basis für Textilien erhalten werden kann. Darüberhinaus konnte auch erklärt werden auf welchem Mechanismus dieser Flammschutz begründet ist und wie die derzeit noch ungenügende Waschpermanenz verbessert werden kann.
The requirements for textiles differ greatly depending on the area of application, whereby it often does not remain with only one required functionality. For example, in the field of functional clothing or protective clothing/PPE, it is necessary to protect the textile’s wearers from UV radiation. At the same time, self-cleaning effects offer certain advantages in that field. In addition, an antimicrobial effect in functional clothing can reduce the formation of unpleasant odors, and in PPE – especially in the healthcare sector – can contribute to the interruption of the chain of infection. One way to achieve these 3 desired functions in just one finishing step is to immobilize titanium dioxide (TiO2). However, TiO2 is viewed critically for application in the textile sector due to a REACH listing. Another disadvantage is that it only takes effect under UV radiation and is therefore not suitable for indoor use. Alternatively, photocatalysts such as doped zinc oxides (ZnO) can be used, which also exhibit catalytic activity through activation by visible light, which can lead to the killing of microorganisms and the degradation of organic soiling.
Schweißerschutzkleidung muss unterschiedlichen Anforderungen genügen. Sie muss u.a. flammfest sein, den Schweißer vor Metallspritzern schützen, die beim Schweißen entstehen, und auch einen Schutz vor UV-Licht sicherstellen, das im Schweißbogen entsteht. Besonders der Schutz vor Metallspritzern wird durch das Flächengewicht der Textilien bestimmt. Der entsprechende Schutzfaktor wird durch Tropfen flüssigen Eisens bestimmt, die auf ein Gewebe fallen. Dabei gilt: je höher das Flächengewicht, desto höher der Schutz vor Schweißspritzern. Jedoch gilt auch: je höher das Flächengewicht, desto schlechter ist der Tragekomfort und desto wärmender ist die Kleidung und damit die körperliche Belastung des Trägers. Durch die Applikation von Nanopartikeln ist es möglich, das benötigte Flächengewicht der Kleidung zu reduzieren.
Flame-retardant finishing of cotton fabrics using DOPO functionalized alkoxy- and amido alkoxysilane
(2023)
In the present study, DOPO-based alkoxysilane (DOPO-ETES) and amido alkoxysilane (DOPO-AmdPTES) were synthesized by one-step and without by-products as halogen-free flame retardants. The flame retardants were applied on cotton fabric utilizing sol–gel method and pad-dry-cure finishing process. The flame retardancy, the thermal stability and the combustion ehaviour of treated cotton were evaluated by surface and bottom edge ignition flame test (according to EN ISO 15025), thermogravimetric analysis (TGA) and micro-scale combustion calorimeter (MCC). Unlike CO/DOPO-ETES sample, cotton treated with DOPO-AmdPTES nanosols exhibits self-extinguishing ehaviour with high char residue, an improvement of the LOI value and a significant reduction of the PHRR, HRC and THR compared to pristine cotton. Cotton finished with DOPO-AmdPTES reveals a semi-durability after ten laundering cycles keeping the flame-retardant properties unchanged. According to the results obtained from TGA-FTIR, Py-GC/MS and XPS, the major activity of flame retardant occurs in the condensed phase via catalytic induced char formation as physical barrier along with the activity in the gas phase derived mainly from the dilution effect. The early degradation of CO/DOPO-AmdPTES compared to CO/DOPO-ETES, triggered by the cleavage of the weak bond between P and C=O, as the DFT study indicated, provides the beneficial effect of this flame retardant on the fire resistance of cellulose.
Energy consumption by air-conditioning is expansive and leads to the emission of millions of tons of CO2 every year. A promising approach to circumvent this problem is the reflection of solar radiation: Rooms that would not heat up by irradiation will not need to be cooled down. Especially, transparent conductive metal oxides exhibit high infrared (IR) reflectivity and are commonly applied as low-emissivity coatings (low-e coatings). Indium tin oxide (ITO) coatings are the state-of-the-art application, though indium is a rare and expensive resource. This work demonstrates that aluminum-doped zinc oxide (AZO) can be a suitable alternative to ITO for IR-reflection applications. AZO synthesized here exhibits better emissivity to be used as roofing membrane coatings for buildings in comparison to commercially available ITO coatings. AZO particles forming the reflective coating are generated via solvothermal synthesis routes and obtain high conductivity and IR reflectivity without the need of any further post-thermal treatment. Different synthesis parameters were studied, and their effects on both conductive and optical properties of the AZO nanoparticles were evaluated. To this end, a series of characterization methods, especially 27Al-nuclear magnetic resonance spectroscopy (27Al-NMR) analysis, have been conducted for a deeper insight into the particles’ structure to understand the differences in conductivity and optical properties. The optimized AZO nanoparticles were coated on flexible transparent textile-based roofing membranes and tested as low-e coatings. The membranes demonstrated higher thermal reflectance compared with commercial ITO materials with an emissivity value lowered by 16%.
Protective welding clothing must meet various requirements. Among other things, it must be flame-resistant, protect against splashes of metal or sparks and also ensure protection against radiant heat and UV light caused by exposure to the welding arc. The protection against molten metal splashes is directly related to the fabric weight per unit area of the protective welding clothing and the level of protection is normally determined by the number of molten metal droplets that fall on the fabric. The higher the weight per unit area, the greater the protection against welding spatter. However, increasing the fabric weight per unit area also leads to psychologically uncomfortable wearing and thus increasing the physical strain on the wearer. The required basis weight per unit area of protective welding clothing can be reduced by applying nanoparticles as a protective layer while preserving other indispensable properties.
Several ionic liquids are excellent solvents for cellulose. Starting from that finishing of PET fabrics with cellulose dissolved in ionic liquids like 1-ethyl 3-methyl imidazolium acetate, diethylphosphate and chloride, or the chloride of butyl-methyl imidazolium has been investigated. Finishing has been carried out from solutions of different concentrations, using microcrystalline cellulose or cotton and by employing different cross-linkers. Viscosity of solutions has been investigated for different ionic liquids,concentrations, cellulose sources, linkers and temperatures. Since ionic liquids exhibit no vapor pressure,simple pad-dry-cure processes are excluded. Before drying the ionic liquid has to be removed by a rinsing step. Accordingly rinsing with fresh ionic liquid followed by water or the direct rinsing with waterhave been tested. The amount of cellulose deposited has been investigated by gravimetry, zinc chlorideiodine test as well as reactive dyeing. Results concerning wettability, water up-take, surface resistance,wear-resistance or washing stability are presented.
The sol-gel approach offers a new class of flame retardants with a high potential for textile applications. Pure inorganic sol-gel systems do, however, typically not provide an effect sufficient for a sel-fextinguishing behavior on its own. We therefore employed compounds with nitrogen and phosphorous containing groups. Especially the combination of compounds with both elements, using the synergism, is promising for the aim to find well-applicable, environmental friendly, halogen-free flame retardants. In our approach, the sol-gel network ensured on the one hand the link to the textile as nonflammable binder. On the other hand, the sol-gel-based networks modified with functional groups containing nitrogen groups provided flame retardancy. In this way, a flame retardant finishing for textiles could be obtained by simple finishing techniques as, e.g., padding. Besides a characterization with various flame tests (e.g., according to EN ISO 15025 e protective clothing), we used a combination of cone calorimetry, thermogravimetry coupled with infrared spectroscopy analysis and scanning electron microscopy to analyze the mechanism of flame retardancy. Thus, we could show that the main mechanism is based on the formation of a protection layer. This work provides a model system for sol-gel-based flame retardants and has the potential to show the principle feasibility of the sol-gel approach in flame retardancy of textiles. It therefore lays the groundwork for tailoring sol-gel layers from newly synthesized sol-gel precursors containing nitrogen and phosphorous groups.
Three established test methods employed for evaluating the abrasion or wear resistance of textile materials were compared to gain deeper insight into the specific damaging mechanisms to better understand a possible comparability of the results of the different tests. The knowledge of these mechanisms is necessary for a systematic development of finishing agents improving the wear resistance of textiles. Martindale, Schopper, and Einlehner tests were used to analyze two different fabrics made of natural (cotton) or synthetic (polyethylene terephthalate) fibers, respectively. Samples were investigated by digital microscopy and scanning electron microscopy to visualize the damage. Damage symptoms are compared and discussed with respect to differences in the damaging mechanisms.
The wet chemical deposition of solution processed transparent conducting oxides (TCO) provides an alternative low cost and economical deposition technique to realize large-areas of conducting films. Since the price for the most common TCO Indium Tin Oxide rises enormously, Aluminum Zinc Oxide (AZO) as alternative TCO reaches more and more interest. The optoelectronical properties of nanoparticle coatings strongly depend beneath the porosity of the coating on the shape and size of the used particles. By using bigger or rod-shaped particles it is possible to minimize the amount of grain boundaries resulting in an improvement of the electrical properties, whereas particles bigger than 100 nm should not be used if highly transparent coatings are necessary as these big particles scatter the visible light and lower the transmittance of the coatings. In this work we present a simple method to synthesize AZO particles with different shape and size, but comparable electronical properties. We use a simple, well reproducible polyol method for synthesis and influence the shape and size of the particles by adding different amounts of water to the precursor solution. We can show that the addition of aluminum as dopant strongly hinders the crystal growth but the addition of water counteracts this, so that both, spherical and rod-shaped particles can be obtained.