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Fully Renewable Biocomposites And Translucent Concrete

Researchers at the Institut für Textiltechnik of RWTH Aachen University present two technologies recently developed at the institute.

Marie-Isabel Popzyk, Yves-Simon Gloy and Thomas Gries

The Institut für Textiltechnik (ITA) is one of the largest institutes of RWTH Aachen University and one of the leading textile research institutes in Germany. Currently almost 100 researchers, including postdoctoral and doctoral candidates, do research in the field of textile machinery, new materials and recycling as well as in the field of fully renewable biobased composites. With two European partners, ITA developed a racecar seat consisting completely of flax and polylactic acid (PLA). Also, ITA developed translucent concrete, which during daytime has an optical characteristic comparable to a natural stone cladding. In addition, each concrete panel can be lit in a different color using LED panels. 
The Institute
ITA belongs to the top 10 institutes of RWTH Aachen University, Aachen, Germany. Its core competencies are the development of textile machinery and components, manufacturing technologies and comprehensive process chains; as well as high-performance fiber materials and innovative textile-based products in the sectors of mobility, civil engineering and life science, energy, and health (See Figure 1). The essential technology fields of its research are material and energy efficiency, functional integration and integrated production technologies.

Figure 1: Textile process chain and application fields at Institut für Textiltechnik (ITA) of RWTH Aachen University
One unique feature of ITA is its consistency of manufacture. ITA is able to produce carbon-fiber-reinforced plastics and all other materials through all steps of manufacturing, starting with a precursor and finishing with a laminated textile fabric. Additionally, ITA is researching the recycling of carbon-fiber-reinforced plastics and other materials. All research services are offered and handled in cooperation with 3T TextilTechnologieTransfer GmbH, a technology transfer spinoff of ITA.

The institute offers courses in mechanical engineering, specialized in textile engineering, and industrial engineering, specialized in textile engineering; and trains teachers in technical education for professional schools. Beyond that, the opportunity to earn a Dr.-Ing. degree exists. From fall 2014 on, an international Master’s program in Textile Engineering is offered.
In the field of biocomposites, ITA focuses on developing composites that are made completely of natural materials. There are several possible routes to produce fully biobased composites. Nature Wins is a recently successfully concluded project on which ITA and two other European project partners developed fully renewable thermoplastic biocomposites. The project focused on the development of biocomposites based on long/continuous industrial natural fibers as reinforcement and thermoplastic biopolymer fibers as matrix material. The scope was narrowed further by focusing on a production route based on blending both matrix and reinforcement in fiber form and using compression molding as the composite formation process.
The project goal was to produce a racecar seat consisting of a nonwoven made using a blend of flax and PLA fibers (See Figure 2). ITA selected the natural fibers and developed the textile processes as well as semi-finished parts, concluding with an ecological valuation and testing of the seat. In summary, this project shows that flax and PLA show excellent compatibility and adhesion, making these materials a very good combination for composites. Consolidation and impregnation of flax/PLA composites can therefore be achieved within an acceptable process window.

Figure 2: Production route for biocomposites made of flax and PLA fibers [1]
INF: Industrial Natural Fibers
UD: Unidirectional
MD: Multidirectional

The environmental assessment showed that flax and PLA have strong potential to reduce global warming effects, but that some attention is still needed to address other environmental effects, mostly related to agricultural practices.

Grateful acknowledgement goes to the research association Forschungskuratorium Textil e. V., a branch of the German Federation of Industrial Research Associations (AiF), for the financial funding — through AiF-CORNET — of the research project AiF-No. 48 EN. The writers would also like to thank project partners Centexbel, Belgium, and Sirris Leuven-Gent Composites Application Lab, Belgium [1].
Translucent Concrete
ITA developed translucent concrete, now generally known as LUCEM Lichtbeton (LUCEM Light Transmitting Concrete), and produced by LUCEM GmbH, Stolberg, Germany. Translucent concrete is a novel structural material with a light-conducting feature (See Figure 3). This concrete contains 3-percent optical fibers, which are constituted of a core and a sheet with different refraction indexes. The principle of total reflection is used, and if a light ray impinges upon the interface of core and sheet, it is refracted or reflected depending on its angle of entry. To achieve total reflection, the refracting angle of the core has to be higher than that of the mantle. Thus, the core is made of denser optical material than the mantle. Possible optical fibers are organic man-made fibers like polymethyl methacrylate (PMMA), polycarbonate (PC) and polystyrene (PS), as well as inorganic fibers like silica glass and quartz glass. Glass fibers are preferred because of their durability despite the alkali environment in the concrete.

The fibers are processed further into textile fabrics in order to simplify and to accelerate the production process. If smaller batches are produced, loose fibers can also be used. For concreting, the optical fiber surfaces are positioned in layers, thereby making possible a variable gap in direction of the height between each layer. Also, a high matrix viscosity is required; otherwise, an uncontrolled floating or sinking of the fiber surface is possible. After setting, the fibers are positioned in the longitudinal direction of the concrete block. The concrete block is then sawn into thin layers with translucent features. To improve the guiding of light, each layer needs to be cut and polished. Panels with a thickness of only 1.5 centimeters (cm) are possible. Each panel can be accompanied with a LED panel. During daytime, the optical characteristic of these concrete panels is comparable to that of a natural stone cladding. As seen in Figure 3, during daytime, the silhouette of an object behind a panel can be seen through the panel. However, the panel looks like natural stone if nothing is directly behind it.  

Figure 3: Hand in front of and behind translucent concrete [3]
The first facade installed at the Institute für Textiltechnik of RWTH Aachen University has 136 panels in the size of 150 cm by 50 cm. The panels become brighter with the reduction of daylight, and each panel can be lit with a different color. Thus, an individual light scenario can be programmed and controlled via iPhone App (See Figure 4) [2, 3].

Figure 4: A translucent concrete has been installed at ITA, RWTH Aachen University, Germany
Innovative solutions in the field of textile machinery and technical textiles from basic research to application-related research are offered at ITA.
Editor’s note: Dipl.-Ing. Marie-Isabel Popzyk is a research fellow, and Univ.-Prof. Prof. h. c. Dr.-Ing. Dipl.-Wirt. Ing Thomas Gries is head of research, at Institut für Textiltechnik (ITA) of RWTH Aachen University. Dr.-Ing. Yves-Simon Gloy. is division head, Textile Machinery/Production Technologies at ITA; and adjunct professor, Department of Material Science and Engineering, College of Engineering and Science, Clemson University.
For more information about ITA, visit ita.rwth-aachen.de.

[1]       Ramaswamy, S. et al.: Nature Wins. Final technical report. 2013.
[2]       Roye, A. et al.: Faser- und textilbasierte Lichtleitung in Betonbauteilen – Lichtleitender Beton. Beton- und Stahlbetonbau 104 (2009), Heft 2, 2009, Seite 121-126.
[3]       lucem.de

Posted June 17, 2014