Optimising protective clothing for potentially endangered occupational groups such as the police or security companies - that is the goal of the "StereoTex" research project at Bielefeld University of Applied Sciences. In the project, researchers are currently developing a process that makes it possible to produce stab-resistant protective clothing from a combination of textiles and synthetic resins.

A transparent box just under 25 centimetres high with orange-tinted panes and a small black basin with a glass bottom: What seems rather unimpressive at first glance is a complex 3D printer with state-of-the-art technology in the Laboratory for Textile Technologies at the University of Applied Sciences (FH) Bielefeld. The truly spectacular thing, however, is what goes on inside it: A hitherto globally unique, innovative process for combining textiles and synthetic resins.

Unique research project worldwide

"According to our literature research, we are the first scientific team in the world to work on combining 3D printing using the stereolithographic manufacturing process and textiles." Timo Grothe, StereoTex project manager

This process is currently being developed by scientists at Bielefeld UAS as part of the "StereoTex" research project. The project from the Department of Engineering and Mathematics uses the so-called stereolithographic 3D printing process (SLA) as the basis for its research - a process in which 3D objects are modelled from resin. The starting point is liquid synthetic resin, which is filled into a basin and cured layer by layer into the desired 3D objects with the help of a light source, such as a laser or UV light - a well-known and frequently used technique in the 3D printing sector. What is special about the FH project's process? The 3D objects are printed directly onto textiles, which are fixed to the print bed with a self-developed holder. This is a hitherto unique process, as Timo Grothe, StereoTex project manager, tells us: "According to our literature research, we are the first scientific team in the world to deal with the combination of 3D printing according to the stereolithographic manufacturing process and textiles - the combination of resin and textile has never been investigated before."

Concrete application scenario available

The StereoTex team is working towards a very specific application scenario for their research: The goal is to develop customisable resin-textile composites that have a stab- and cut-resistant effect. "In very concrete terms, this means that we want to use the resin-textile composites to produce protective clothing for potentially vulnerable occupational groups such as the police, security companies or bus and taxi drivers, for example," Grothe reveals. It is particularly important to him that the composites are breathable and have a long-term stability of at least ten years. "Especially for protective equipment that has to be worn very close to the body for several hours a day, it is necessary that it is light and comfortable, and still offers good as well as long-term protection."

Development of a porous, printable resin is the focus

But how can all these requirements be realised in reality? The lynchpin is the nature of the resin used to print the various textiles. Timo Grothe explains: "Since the synthetic resins available on the market are not optimised for our novel process, we are working with a company for casting resin systems, ALWA GmbH, to jointly develop an innovative, porous resin that can be printed on textiles without any problems and is at the same time permeable to air and water." So far, this resin only exists as a casting resin and is to be further developed as a printable resin in the next step.

First results are promising

Although the project is still in its early stages, it has already achieved some initial successes, as Elise Diestelhorst, a research assistant at StereoTex, points out: "In order to find out which textiles are best suited for the application scenario, we have printed various textiles with commercially available UV resin. At the moment we are investigating which textile properties are best suited for adhesion of the resin as well as in long-term performance as a textile-resin composite. In the process, we have also tested various shapes and sizes of 3D objects on the textiles - smaller and larger cylinders as well as elongated square structures overlapping like roof tiles, modelled on historical armour and armour from the animal kingdom." With success: "We are currently working on the publication of our first research results, building on the world's first publication on the subject by our working group. This much we can already reveal: It works!" adds Timo Grothe with a smile.

Hybrid printer to make work easier

In the next step, the Bielefeld experts want to develop a hybrid 3D printer that uses liquid synthetic resin and UV light for curing, similar to the SLA process, but applies the synthetic resin to the textile comparable to the so-called "Fused Deposition Modelling" (FDM) technology - one of the most widespread 3D printing technologies worldwide. In this process, normally molten plastic is applied layer by layer in the desired shape to a work platform with the help of a print head, where it cools and hardens - the 3D object is ready. "Transferred to StereoTex, our goal is for liquid resin to be applied to the textile underneath with millimetre precision from above, as in FDM printers, and at the same time to be cured directly by a UV source," says Diestelhorst. This would have a decisive advantage: "The textiles would no longer have to be placed in a basin of liquid resin, which means the time-consuming step of removing the excess, uncured resin from the fabric would no longer be necessary. It could also save materials and protect the environment."
www.fh-bielefeld.de

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