For the work of the Textile Technologies WG not only the researchers are important, but also extensive equipment for creating, finishing, reinforcing, and measuring a wide variety of textiles and textile compounds.
Production of Textile Fabrics and Textile Composites
3D printing is one of the most modern types of additive manufacturing. Building layers of various possible materials creates a versatile product after printing. This type of production is not limited to the print itself but can also be combined with textiles and nano-nonwovens. The printers used by the WG Textile Technologies are mainly the Orcabot XXL (Prodim) as well as the MakerBot Replicator 2X Experimental 3D printer (Stratasys GmbH). In addition to the common printers, which mainly work with plastic filaments, food printers (here: Food-Printer from ByFlow) and epoxy resin printers are also used for research with textiles.
The crocheting machine was patented by the Bielefeld University of Applied Sciences after a successfully completed research project. Currently, students are working within study programs on the further development and improvement of the machine. The crocheting machine works with several motors, which move a cam needle in interaction. This needle is moved along a series of linearly moving cam needles so that fixed stitches are formed. The motors are controlled by an Arduino, which receives stored movement patterns of the four axes as G-code from a Raspberry Pi. This in turn provides a user interface and a wireless connection to the crocheting machine. The latch needles in the needle bed ensure the correct stitch spacing, and the movable latch needle, which sits in the opposite direction, carries out the actual crocheting process.
Warp knitting machine
The warp knitting machine HKS 3-M-EL with 42’’ working width (Karl Mayer, Obertshausen, Germany) enables producing diverse patterns and is regularly used in student projects and research. Especially combining warp knitted fabrics with 3D printing belongs to the foci of our recent investigations.
The climatic chamber CTC256 from the Memmert company offers the possibility of exposing samples to different climatic variants. With a temperature range from -42°C to +190°C and an adjustable humidity of 10% to 98%, almost any environmental situation can be simulated. Particularly interesting in this regard is the use for the samples of the Vertical Farming project, in which agricultural plants are grown on textile substrates. In order not only to consider the local (room) climate, these samples could be tested even under very adverse conditions.
The Nanospider is used to create textiles which are characterized by a thread thickness of a few µm. The device was manufactured by the company “Elmarco”. For spinning, dissolved substances such as polyacrylonitrile (PAN) are needed in solution. This basis can be additionally extended with further additives. Various biopolymers, for example, are suitable for this purpose. The solution that has been created in this way is then inserted into the Nanospider. This is done by a carriage, which applies the solution to a wire by continuously moving it along the wire. The solution thus applied is then shot onto an interception nonwoven attached over the upper wire. A voltage of up to 80 kV is applied between these two wires. The wire charged in this way charges parts of the applied solution, which is then shot in the direction of the upper cable due to the charge difference, but does not reach the upper wire as it is caught on the substrate nonwoven. During the flight the solvent also evaporates, because the volume is small in relation to the surface during the flight. Finally, the threads produced in this way are caught by the interception nonwoven, which leads to the overall result of a nanofiber mat.
Optical and Mechanical Investigations
The atomic force microscope, the Nanosurf FlexAFM, offers the possibility to examine the surfaces of textiles in the nanometre range. The cantilever is moved by the impulse on a microscopic needle which is guided over the surface. Depending on the surface structure or roughness, this needle bends. Evaluated by optical sensors, the surface is analysed with a very high resolution. Thanks to a successfully completed research project, it is now also possible to magnetize and demagnetize the sample during the measurement. For this purpose, two large coils were installed in the measurement setup and connected accordingly.
An Axio Observer inverse fluorescence microscope (Carl Zeiss Microscopy GmbH) is used to take images of diverse samples in reflected or transmitted light. While a white light source is used for most images related to surface properties, fluorescence imaging with different filter cubes allows for detecting biological samples, mostly stained with corresponding fluorescence dyes, as well as investigating different phases in polymers or other materials which show auto-fluorescence.
The two abrasion testers developed in study projects (Martindale and linear abrasion tester) serve to test the abrasion resistance of fabrics. A test head with a previously selected fabric is pressed down by a counterweight and moved linearly or in circular movements on the fabric sample. The number of friction cycles can be set here, for example. An example for the application of these testing devices is the automotive industry. Here it is tested how long denim, for example, can rub on the upholstery fabric of the seat cover without visibly destroying it.
The SourceMeter 2450 from Keithley Instruments is mainly used in the WG Textile Technologies for measuring the efficiency of solar cells. However, it also offers a variety of other applications. The meter can be programmed either via a related application or directly on the touch screen. Here, for example, it is possible to have a current-voltage characteristic curve output over time in a defined range. The advantage is that one or both values can be pre-set, and they are still recorded repeatedly during the measurement.