Safety marked sewing threads (Source: DITF)
At the Techtextil, the DITF, Denkendorf/Germany, will showcase its developments in the research fields of new materials, lightweight construction, sustainability, digitalization and health. The main topics are high-performance fibers such as the new ceramic fiber OxCeFi, bio-based materials, fiber-based solutions for lightweight construction, smart textiles, functionalization and technical textiles.
3D knitting as an additive manufacturing process
In the AiF project AddKnit, the DITF is developing recommended actions and software modules for the production of 3D-knitted, technical textiles. Based on a 3D scan or a CAD design, a digital twin of the knitted product is generated algorithmically. This can be transferred into a parameter set for direct production on a flat knitting machine. The product type, the material used and the machine configuration are taken into account. This process model is intended to make 3D knitting technology the textile equivalent of 3D printing in terms of applicability and flexibility.
As a result, development times can significantly be reduced, machines and their components can be optimized for specific products, and new business concepts can be created.
Textile smart car door
The DITF, the Fraunhofer IAO, Stuttgart/Germany, and students of Reutlingen University, Reutlingen/Germany, have produced a functionalized textile vehicle door for a Renault Twizy. A robust, waterproof and breathable fabric was selected as the basic textile and functionalized. The integration of a textile lighting into the basic textile served to indicate the battery charge status of the vehicle and could additionally be used as lighting. Thanks to a printed capacitive textile pressure sensor, the display could be acknowledged or the lighting activated or turned off. Through shielding, the pressure sensor can only be activated from the inside of the vehicle door and is thus protected from the influence of external persons and elements. Miniaturized electronics combined with suitable programming of the integrated microcontroller ensure reliable control of the various functional elements. Parallel to the textile functionalization, a cutting pattern including a fastening concept was created so that the functionalized textile could be perfectly adapted to the door geometry and fitted.
Safety marked sewing threads
Investigators, customs authorities and textile companies have so far been unable to reliably detect counterfeit textiles. They fail time and again because of the criminals' skill and creativity. In a recently completed research project (IGF 20492 N), the DITF and the DWI – Leibniz Institute for Interactive Materials e.V., Aachen/Germany, have developed security-marked sewing threads that provide a remedy for product piracy and make life easier for investigators and customs authorities. The sewing threads contain small (approx. 100 nm) infrared light-absorbing pigments that can be made visible using an IR camera. In the project, various pigments (including LaB6, CsWO4) were investigated and compared. The sewing threads produced can easily be dyed and adapted to the needs of textile manufacturers. They can thus be used as discreet, unambiguous and easily detectable security markings.
Printed capacitive textile sensors for proximity switches
In a research project at the DITF, the basic knowledge for the production of printed sensors and switches for smart textiles was created. The sensors were manufactured by printing electrically conductive pastes and inks based on silver. The switching function could be realized with electrodes whose ohmic resistances are less than 1 kOhm/sq. The structure of the proximity sensor was multilayer and fully insulated. Pastes and inks based on textile binders were formulated for the electrical insulation of the electrodes and interlinked by adding a crosslinker. The topcoat withstood > 100,000 Martindale abrasion cycles and was resistant to water. Electrical contacting of the electrodes was achieved by mechanically anchored metallic push buttons, which were coated with a conductive PU adhesive towards the electrode. The development of versatile electronics with, among other things, an oscillating circuit and microprocessor made it possible to record and evaluate the sensor signal. It was successfully shielded by an impedance converter. The electronic component was controlled by programming the microprocessor. This made it possible to generate a light signal depending on the sensor approach as well as to trigger the heating of a textile without contact.
Particularly in the case of home textiles, flame retardancy is of elementary importance for their safe use. Flame-retardant phosphorus compounds, which are added to the polymer as additives, are widely used. However, this has disadvantages, because physical and physiological properties of the textiles deteriorate. In addition, the flame retardancy decreases with frequent washing. In a novel manufacturing process, the DITF have succeeded in chemically incorporating flame retardants into the polymer chains of polyamides. The polyamide fibers modified in this way have a permanent flame-retardant effect and also exhibit good dye receptivity and strength values.
With high technical effort, the DITF are driving forward the development of oxide ceramic fibers based on aluminum oxide and corundum. The fibers are stable at high temperatures and at the same time have high tensile strength and creep resistance. Research results contribute to increasing the long-term service temperatures of ceramic fibers and the ceramic composites made from them. Good damage tolerance and high thermal shock resistance characterize these special materials.
Self-healing glass fiber composites
Component failure of materials starts on a small scale: micro-cracks prepare in the microstructure before a component breaks. Fiber-reinforced composites are much more damage tolerant than monolithic materials. Nevertheless, microcracks initiate an advancing damage process in them as well. Recent research results on glass fiber reinforced composites have shown that component failure can be delayed or even prevented. For this purpose, the glass fibers are equipped with a microcrack self-healing function: 2 liquid monomers could be introduced separately inside hollow glass filaments. In a textile hollow glass fiber fabric, both monomers are incorporated separately in the warp or weft direction before this fabric is further processed into a composite material. When external force is applied and the first microcracks form, the monomers escape from the hollow fibers and react by means of a tin-catalyzed polyaddition to form polyurethane, which reseals the cracks that have formed.
Detect errors early and save costs
Digitalized manufacturing processes enable individualized production. A low error rate is particularly important for e-textiles, as errors in the smart additional functions in textiles are often only detected at the end of the value chain. This makes textile wearables very expensive and a value-add to non-textile wearables such as smartwatches is no longer a given. At the German Institutes of Textile and Fiber Research Denkendorf (DITF) a global
"Industry 4.0 approach" is being developed, which already starts with yarn production and extends through all process chains.
The DITF will be present these innovations during the Techtextil from June 21-24, 2022 in Frankfurt/Germany.