Forschungspublikationen

4 Ergebnisse
20.06.2023

Development of heavy tows from recycled carbon fibers for low-cost and high performance thermoset composites (rCF heavy tows)

Rohstoffe Fasern Garne Composites Textilmaschinenbau Recycling Nachhaltigkeit Kreislaufwirtschaft Technische Textilien

Zusammenfassung

Within the framework of the IGF research project (21612 BR), the entire process chain for the industrial production of novel twist-free rCF heavy tows was developed at ITM. In particular, a novel technology for the production of rCF heavy tows based on recycled carbon (rCF ≥ 90 vol.%) and hot melt adhesive fibers (< 10 vol.%) was designed, constructed and successfully implemented. This includes fiber preparation, the carding process for card sliver formation, the stretching process for drawn sliver formation, and the final fabrication of the rCF heavy tows from rCF and hot melt adhesive fibers in a newly developed test set-up. The suitability of the developed technology is demonstrated by the implementation of rCF heavy tows with different rCF types, fiber lengths and fiber volume contents and a demonstrator. The developed rCF heavy tows with finenesses between 3000-7000 tex and their further processability into textile semi-finished products were successfully demonstrated. The developed rCF Heavy Tows and composites based on them exhibit a maximum composite tensile strength and a maximum Young’s modulus of 1158±72 MPa and 80±5.7 GPa, respectively. The rCF Heavy Tows are thus applicable for low-cost thermoset composites with high performance and complex geometry. Thus, the developed rCF Heavy Tows offer a very high innovation and market potential in the fields of materials and materials, lightweight construction, environmental and sustainability research, and resource efficiency. This opens up the opportunity for SMEs in the textile industry to develop new products and technologies for the fiber composite market and to establish themselves as suppliers for the automotive, mechanical engineering and aerospace, medical and sports equipment industries.

Bericht

Introduction, problem definition and aim of the project

Carbon fiber-reinforced plastics (CFRP) are increasingly used in lightweight applications due to their high stiffness and strength as well as low density, especially in aerospace, transportation, wind energy, sports equipment or construction. Global demand of CFRP is predicted to increase to 197,000 t/a by 2024, almost tripling compared to 2011. This shows an urgent need for solutions to recycle the high quality carbon fiber (rCF) in terms of the circular economy. This is necessary not only due to strict legal regulations, but also for ecological and economic reasons. In recent years, numerous research institutes and companies developed solutions for the reuse of rCF in the fields of nonwovens, injection molding or as hybrid yarns. However, the majority of these works involve the use of rCF in combination with thermoplastic fibers for thermoplastic composites. In the field of rCF-based thermoset CFRP, mainly rCF nonwovens made of 100% rCF have been so far developed. Since the fibers in the nonwovens mostly have a limited length and a low orientation and process-related additional high fiber damage occurs, with these materials only maximum 30% of the composite characteristic values of CFRP components made of carbon filament yarns can be so far achieved.

Currently, the matrix systems used in the field of high mechanical loaded CFRPs are predominantly thermoset. Such components exhibit high dimensional stability, high stiffness and strength as well as are suitable for the implementation of complex component geometries due to low-viscosity matrix systems. However, primary carbon filament yarns are particularly used for these components due to the insufficient properties of rCF. In addition to low sustainability, the utilization of these filament yarns result in at least 200 % higher cost. The production of primary carbon filament yarn requires a high-energy demand of about 230 MJ/kg with a CO2 emission equivalent to 20 kg CO2/kg CF. Here, a significant improvement of the CO2 balance is required to make a substantial contribution to the envisaged climate protection goals of the Federal Republic of Germany and the EU. For this reason, the focus of the project work is the development of novel, sustainable rCF heavy tows made of recycled carbon fibers (rCF) and associated manufacturing technologies for the implementation of cost-effective thermoset composites with high mechanical performance.

Acknowledgments

The IGF project 21612 BR of the Research Association Forschungskuratorium Textil e.V. was funded by the Federal Ministry of Economics and Climate Protection (BMWK) via the AiF within the framework of the program for the promotion of joint industrial research and development (IGF) on the basis of a resolution of the German Bundestag. We would like to thank the above-mentioned institutions for providing the financial resources.

AutorInnen: Mahmud Hossain, Anwar Abdkader und Chokri Cherif

Technische Universität Dresden
Fakultät Maschinenwesen
Institut für Textilmaschinen und Textile Hochleistungswerkstofftechnik (ITM)
01062 Dresden

https://tu-dresden.de/mw/itm

rCF fiber yarn Composite textile machine

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16.01.2023

Increased performance and sustainability through the use of profiled textile reinforcements for concrete applications

Fasern Garne Gestricke & Gewirke Textilmaschinenbau Nachhaltigkeit Technische Textilien

Zusammenfassung

At the ITM of the TU Dresden, new, bond optimized reinforcement yarns were developed on the basis of braiding and forming technology, which can transmit up to 500 % higher bond forces in concrete than yarns without profile. The profiled rovings and braided yarns show at a bond length of only 50 mm a full anchoring. With the forming technology developed at the ITM, profiled rovings could be manufactured which, due to the patented tetrahedral geometry, can almost completely exploit the tensile potential of the carbon fibers. In the course of developing the braiding yarns, a new vario braiding structure was developed, with nearly eliminated structural elongation under load. This made it possible to manufacture profiled reinforcement yarns with very high tensile properties, which is a basic requirement for use in concrete. In addition, the multiaxial warp knitting technology has been further developed in such a way that the new bond optimized reinforcement yarns (profiled rovings and braiding yarns) can be processed without damage into profiled, grid-like textile reinforcements. This results in a significantly higher material efficiency of the textile reinforcement, so that previous necessary disproportionate oversizing and large overlapping lengths can be significantly reduced. This is of enormous importance, especially in view of the energy-intensive production of carbon fibers and consequently for the sustainability goal of the future-oriented carbon concrete technology, in order to make concrete constructions of the future resource saving and sustainable.

The project results achieved also represent a significant contribution to the production of extremely resilient textile-reinforced concrete structures with significantly improves bond properties, arising new prospects in the construction industry for component production in the field of renovation and new construction.

Bericht

Abstract
Building in a resource-saving way and still exploiting a high performance potential, is that even possible? At the Institute for Textile Machinery and High Performance Material Technology (ITM) at the TU Dresden, such composite optimized profiled textile reinforcements for concrete applications and the related manufacturing technology were developed as part of the research project IGF 21375 BR. On the basis of braiding and forming technology, a new generation of profiled reinforcement yarns was developed with the help of simulation-based investigations. Like ribbed steel reinforcements, these profiled yarns have a very high bond with the concrete matrix, but despite the profiling they almost fully exploit the performance potential of the carbon fibers in terms of tensile properties. In this way, the bond length required for complete force transmission between the textile reinforcement and the concrete can be reduced to just a few centimeters, and up to 80 % of the component-dependent oversizing of the textile reinforcement can be saved. The further development of the multiaxial warp knitting technology for the requirement-based and fiber-friendly processing of the profiled yarns into grid-like reinforcement structures enables the production of profiled textile reinforcement structures with the highest bond properties for use in carbon-reinforced concrete components with maximum material and resource efficiency.

Initial situation and problem definition
As is generally known, climate change is the greatest challenge of the 21st century, which can only be successfully overcome by consistently saving resources and CO2 emissions. Since the construction industry, with a share of approx. 38 % of global CO2 emissions, has made a significant contribution to global warming to date, in particular due to the enormous cement consumption [1], a change to more energy and resource efficiency as well as a growing awareness of sustainability is absolutely necessary. In the course of this, a resource-efficient carbon concrete, consisting of a corrosion-resistant textile reinforcement in combination with a significantly reduced concrete cover, is established in the construction industry as a convincing alternative to conventional steel reinforced concrete [2,3].

Due to the high load-bearing capacity of the textile reinforcement with the smaller concrete cross-sections required, the bond between the textile and the concrete is extremely important. So far, R&D has focused on the development of impregnations and impregnation systems for improved material bond with the concrete matrix [4]. However, only small forces with a shear flow of about 5 - 40 N/mm can be transferred, an efficient utilization of the textile reinforcement is not possible. Solutions with profiling of the yarn surface promise significant improvements in the transmission of bond forces [5]. Therefore, new technologies for the continuous and reproducible production of profiled textile high-performance fiber yarns and their further processing into reinforcement structures were developed within a research project at the ITM of the TU Dresden. These innovative, profiled reinforcements are characterized by their ability to transmit significantly higher bond forces in concrete [6,7]. In particular, this was realized by a form-fitting effect between the textile and the concrete, that meets the specific requirements of a stiff and symmetrical surface profile of the reinforcement yarns in order to guarantee a constant and high force transmission. To generate the yarn profiling, solutions based on braiding technology and forming processes were developed and implemented with the help of simulation-supported studies. The premises were a permanently stable textile structure and a profile with a symmetrical structure. The realization of grid-like reinforcement structures, consisting of the profiled reinforcement yarns, was carried out using the multiaxial warp knitting technology. This was developed further on a modular basis with regard to the existing processes (yarn feeding, weft yarn insertion, knitting process, impregnation and winding) in accordance with the necessary adaptation measures for the fiber-friendly and requirement-based further processing of the profiled reinforcement yarns into grid-like structures.

Development of the innovative profiled reinforcement yarns
For the development of bond optimized profiled reinforcement yarns for concrete applications, a simulation-supported yarn development was carried out on the basis of braiding and forming technology. In particular, the main challenge was to realize profiled yarns with minimal structural elongation, so that, an initial force transmission of the textile reinforcement is possible and the concrete crack widths are minimized [3] if the concrete matrix fails at approx. 0.2 % elongation. For this purpose, a new type of varying braiding structure was developed. Moreover the braiding technology was further developed to enable a low-undulation and pre-stabilization of the braiding yarn structure during the braiding process, yet still ensuring further textile processing. As a result, it is now possible to implement novel vario braiding yarns as well as conventional packing braided yarns, consisting of carbon fibers with nearly eliminated structural elongation, minimal fiber damage and the required pre-stabilization of the yarn structure (see Table 1).

...

Performance potential of the new profiled reinforcement yarns
The newly developed profiled reinforcement yarns are characterized by nearly unchanged tensile properties, yet up to 500 % higher bond properties compared to carbon rovings without profile or rovings extracted from reference textiles (see Figure 1). In addition, they do not show any noticeable structural elongation, so that an initial force transmission is possible without additional crack opening after the failure of the concrete matrix. However, an increase in bond strength of more than 500 % from approx. 20 N/mm of the carbon rovings without a profile to over 100 N/mm of the profiled reinforcement yarns was achieved, which is accompanied by a significant increase in material efficiency (see Figure 1). The vario braiding yarns in particular are characterized by very high bond stiffness, which is of particular interest for an initial force transmission. The packing braiding yarns and the profiled rovings with tetrahedral geometry have almost the same bond properties. The bond stiffness is marginally lower compared to the vario braiding yarns, whereas their production is more productive than the vario braiding yarns.

Development of the multiaxial-warp knitting process
To process the newly profiled reinforcement yarns into a grid-like reinforcement structure, a biaxial warp knitting machine Malimo 14022 at the ITM and the corresponding sub-processes (yarn feeding, weft yarn insertion, knitting process, impregnation and winding) were adapted and further developed so that on the one hand the pre-stabilized braiding yarns and the consolidated tetrahedral-shaped profiled rovings can be processed further. For this purpose, the weft thread laying process in particular was modified by developing a new type of weft thread guide for the laying of the pre-stabilized braiding yarns. Since the rigid profiled rovings could not be processed with the conventional weft laying process, a new type stick placement system consisting of a stick magazine and a shaft with profile rollers was developed (see Figure 2). The pre-cut sticks were individually inserted via the stick placement system into a transport chain modified with new fixing elements.

In order to guarantee textile processing, the pre-stabilized braiding yarns were impregnated and consolidated after the warp knitting process, contrary to the rigid profiled rovings, which do not require any further impregnation.. On the basis of extensive production tests, a new type of impregnation system was developed based on the kiss coater process with an additional coating roller for applying an impregnation agent to both sides of the pre-stabilized braiding yarns. Various reinforcement structures were manufactured and characterized with the implemented system technology. Figure 3 shows a new type of profiled textile reinforcement consisting of prefabricated profiled rovings with tetrahedral shape.

Acknowledgments
The IGF research project 21375 BR of the Forschungsvereinigung Forschungskuratorium Textil e. V. is funded through the AiF within the program for supporting the „Industriellen Gemeinschaftsforschung (IGF)“ from funds of the Federal Ministry for Economic Affairs and Climate Action on the basis of a decision by the German Bundestag.

The complete publication is available as download.

AutorInnen: Penzel, Paul; Hahn, Lars; Abdkader, Anwar; Cherif, Chokri

Technische Universität Dresden
Fakultät Maschinenwesen
Institut für Textilmaschinen und Textile Hochleistungswerkstofftechnik (ITM)
01062 Dresden

https://tu-dresden.de/mw/itm

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18.10.2022

Development of Textile Structures with Material-Intrinsic Shape Changing Capabilities for Regenerative Medicine (TexMedActor)

Garne Gewebe Nachhaltigkeit Technische Textilien Medizin

Zusammenfassung

In the IGF project 21022 BR/1 "TexMedActor", fabrics based on shape memory or electroactive yarns were developed which are capable of enclosing defects in hollow organs on the one hand and stimulating cells by micro-movements on the other. For this purpose, influences of spinning process and material composition on the shape memory behavior of TPU-based yarns were characterized and, in particular, the activation temperature was adjusted to values of the body core and body surface temperature. Furthermore, piezoelectric PVDF yarns were developed whose proportion of polar crystal phases was significantly increased by the spinning parameters and post-treatment, which also increased the piezoelectric behavior of the material. This allowed dynamic changes in pore size to be demonstrated in situ, which can have a stimulating effect on cells. With a new process and a new product group (textiles with intrinsic, active shape-changing capability), the results offer high innovation potential not only for medical devices, but also for a wide range of lucrative applications in a variety of niches, such as sports textiles and filter textiles. Furthermore, these can be used as a basis for the development of extracorporeal medical products such as compression textiles, bandages and orthoses.

Bericht

Introduction and Objective

In Germany, both demographic changes in society and injuries resulting from trauma are leading to a high proportion of people with cardiovascular diseases or injuries to vessels and internal organs requiring treatment. Treatment of injuries to internal organs, vessels, or nerves usually requires complex procedures (anastomoses) that involve elaborate fixation and suturing. These complicated and elaborate procedures are often associated with long procedure times, which in turn directly correlate with increased complication rates [1-3]. Tubular plastic implants are increasingly being developed to bridge such defects. These single material structures do not allow tissue/ cell ingrowth. Therefore, they run counter to the concept of regenerative medicine, which aims to restore body tissues and cells. In addition, when the defects are filled, regeneration is often disturbed due to the structural-mechanical properties that are not adapted to biomechanics. Furthermore, the lack of interconnectivity of the pore spaces of the replacement structures prevents the cell ingrowth, cell growth, nutrient supply and the removal of metabolic products.

In the context of in vitro tissue engineering, in addition to static cell culture systems, dynamic systems are also being developed. These are based, for example, on continuous or pulsating fluid flows or on a cyclic stretching of a clamped cell support system or substrate [4]. However, a replication of natural mechanical growth stimuli is not possible with such bioreactor systems because, especially in larger structures, there is a locally increased flow velocity along the largest pores or only an overflow of the entire cell support system. Additionally, undesirable stress peaks and undefined distortions occur in the region of the clamps and supports in mechanically stimulated systems.

Since the native structure of the four most important tissue types (connective and supporting tissue, nervous, muscular and epithelial tissue) from which organs, such as bones, blood vessels, muscles, tendons and ligaments, are formed, consists of fiber-like constructs, these can be particularly well biomimicked with textile structures. With the help of pre-designed fiber arrangements, three-dimensional, complex geometries with interconnecting pore spaces can be built up. The cells can use these structures to orient themselves in their growth direction [5]. Therefore, fiber-based high-tech structures are particularly predestined to overcome the limitations of currently available implants.

Therefore, within the framework of the IGF research project TexMedActor (21022 BR/1) novel textile structures with material-intrinsic shape changing capabilities were developed for regenerative medicine with a variety of different application fields, especially anastomosis. The concept pursued envisages the textile-technological realization of structures with a shape memory effect. The textiles should be able to assume predetermined geometries in order to adapt interactively to defects and to simplify complex interventions to bridge or support defects in internal organs like vessel and nerves. Furthermore, these textiles are intended to enable electromechanical stimulation for the actively targeted stimulating of cell growth. In this way, regeneration is accelerated or even made possible in the first place, since the necessary stimuli for tissue- and cell-adapted growth stimulation are lacking, especially in the case of body tissues with weak or no blood supply, such as cartilage, tendons, ligaments, or in the case of wound healing disorders or chronic wounds. Furthermore, novel bioreactors based on the intrinsic properties of the textile structures will be developed, which use the mechanism of action for electromechanical stimulation to uniformly stimulate the cells at each site even in highly complex and large-scale cell carrier structures. Here, the mechanical stimuli originate from the material itself. This material-intrinsic stimulation represent a new method for optimal cell cultivation, by stimulating cell on the textile cell carrier structures without externally applied fluid flows or mechanical deformation. This is intended to overcome two recognized medical technology problems: 1) complicated, costly operations on internal organs, vessels or nerves that are difficult or impossible to perform with minimally invasive procedures, and 2) lack of tissue- and cell-adapted stimuli for promotion of growth in previously used replacement structures and materials as well as currently available dynamic cell culture systems.

Acknowledgement

The IGF project 21022 BR/1 of the Research Association Forschungskuratorium Textil e.V. was funded by the Federal Ministry of Economics and Climate Protection via the AiF within the framework of the program for the promotion of joint industrial research (IGF) on the basis of a resolution of the German Bundestag. We would like to thank the above-mentioned institutions for providing the financial resources. Furthermore, we want to thank the member of the “Projektbegleitender Ausschuss” (project accompanying committee) for their support during the project.

AutorInnen: Benecke, Lukas; Aibibu, Dilbar; Cherif, Chokri

Technische Universität Dresden
Fakultät Maschinenwesen
Institut für Textilmaschinen und Textile Hochleistungswerkstofftechnik (ITM)
01062 Dresden

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30.09.2022

CF/AR/thermoplastic hybrid yarns for requirement-based thermoplastic composites with outstanding, scalable stiffness, strength, crash and impact property combinations

Fasern Garne Composites Textilmaschinenbau

Zusammenfassung

Within the framework of the IGF research project (21004 BR/1), material concepts based on two yarn formation technologies were realized at the ITM and CF/AR/PA6 and rCF/rAR/PA6 hybrid yarns for thermoplastic composites meeting requirements with outstanding, scalable stiffness, strength, crash and impact property combinations were produced. The influence of carding, draw frame and roving frame (MK1) and air texturing unit (MK2) parameters and fiber volume fractions on the mechanical properties were analyzed to develop requirements-based and defined engineered yarns and composites based on them. The investigated yarn formation technologies complement or partly compete with each other, but thereby also represent a broad technology spectrum. This generates a broad effect for the application of the results for product development in numerous German and often on few technologies specialized SMEs of textile technology.

Bericht

Introduction, problem definition and aim

Fiber-reinforced plastic composites are designed according to required stiffness and strength or impact and crash properties. Complex, overlapping load scenarios are only taken into account to a very limited extent. There are first practical approaches for realizing composite components, e.g. the B-pillar of an automobile [1]. In which composites (e.g., carbon fiber prepregs) are combined with metallic components (e.g. steel sheets) in order to achieve the necessary damage tolerance along with high weight-specific stiffness and strength. In such concepts, hybridization takes place at the macro (structural level) or meso (yarn level) level and requires extremely complex and cost-intensive manufacturing processes [2-4]. Furthermore, these components also have highly pronounced interlaminar interfaces, where complex stresses generate high shear stresses. As a result, premature structural failures occurs due to delamination [5-8]. In order to overcome these disadvantages and for use in future developments, a concept is developed and implemented in the project presented here. The approach provides the design of the combination of various fiber components by hybridization at the micro-level (within a yarn/fiber level), thus maximizing their property potentials. The use of recycled high-performance fibers also results in significant advantages over conventional composites in terms of sustainability, resource efficiency and cost-effectiveness.

The project aims to create a new three-component class of materials hybridized at the micro level for thermoplastic lightweight applications. By combining the reinforcing fibers such as carbon and aramid, it is possible to combine high stiffness and strength with high crash and impact properties by varying the reinforcing fiber proportions and fiber makeup in a way appropriate to the load case. Fig. 1a schematically shows the properties of state-of-the-art CF/AR hybrid composites (Fig. 1a bottom, highlighted by an ellipse) according to state of the art, from engineered yarns to be developed (top, area within the dashed lines) and the theoretical material potentials (top, colored lines), each depending on the fiber volume fractions. The systematic investigation of the influence of the material-specific fiber volume fractions for a scalable composites design was carried out in five stages (CF/AR or rCF/rAR: 50/0 %; 40/10 %; 25/25 %; 10/40 %; 0/50 %).

The development work focused on three main areas. The first focus was the further development of the process technology so that the composites based on engineered yarns exhibit high strength and stiffness due to low fiber damage, high uniformity and high fiber orientation. The second focus was the first-time implementation of the homogeneous blending of three fiber materials at the micro-level. The third focus was designing the engineered yarns so that outstanding, scalable stiffness, strength, crash and impact property combinations can be set explicitly for a wide range of requirements (Fig. 1a).

For the concrete realization of the desired goal, CF/AR/PA6 or rCF/rAR/PA6 hybrid yarns were developed using two material concepts (Fig. 1b) based on two yarn formation technologies (Fig. 1a) for the production of thermoplastic composites with outstanding, scalable stiffness, strength, crash and impact property combinations. The interrelationships between process parameters and material-yarn composite properties were analysed. A sound knowledge for the material-dependent design of the engineered yarns could be achieved. Furthermore, the best possible material and process parameters for specific applications was derived and a process guide was prepared for the control of the manufacturing processes for the SMEs. A detailed description of the development work can be taken from the final report.

Acknowledgement

The IGF project 21004 BR/1 of the Forschungsvereinigung Forschungskuratorium Textil e. V. is funded through the AiF within the program for supporting the „Industriellen Gemeinschaftsforschung (IGF)“ from funds of the Federal Ministry for Economic Affairs and Climate Action on the basis of a decision by the German Bundestag.

AutorInnen: Matthias Overberg, Anwar Abdkader, Chokri Cherif

Technische Universität Dresden
Fakultät Maschinenwesen
Institut für Textilmaschinen und Textile Hochleistungswerkstofftechnik (ITM)
01062 Dresden

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