Research publications

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

Raw materials Fibres Yarns Composites Textile machinery Recycling Sustainability Circular economy Technical Textiles


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.


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.


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.

Authors: Mahmud Hossain, Anwar Abdkader und Chokri Cherif

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

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Technology Development for the Sustainable Production of High-purity Chitosan Filament Yarns with High Performance and Functionality (Chion)

Raw materials Fibres Yarns Sustainability


In the IGF project 21168 BR ‘Chion’, a technology for the manufacturing of chitosan multifilament yarns from ionic liquids was developed, enabling the tailoring of the yarn properties regarding their performance and functionality in all process stages. The material costs, the field of application and the functionalities achievable by the multifilament yarns are defined by the raw material selection. By using ionic liquids, it was possible for the first time to process lower-cost chitosans in various qualities and degree of deacetylation < 90%, previously unavailable with conventional spinning processes. From the achieved and extensively evaluated project results, required process parameters for the successful transfer of the elaborated fundamentals to a pilot scale as well as the process development for the spinning of chitosan multifilament yarns with high performance and strengths up to 28 cN/tex on a pilot solvent wet spinning plant were derived and implemented. To demonstrate the textile processability of the multifilament yarns, textile demonstrators were successfully fabricated for the first time in conventional textile weaving, knitting or braiding processes on standard industrial textile machines.


Introduction and Objective

In the 21st century, society's high level of interest in using products that are manufactured in a sustainable way and minimize environmental impact grows constantly. In this context, the textile and fiber industry has the opportunity to accelerate the development of organic products from renewable raw materials, such as chitin and chitosan, in order to respond to the social, national and international demand for organic products.

The biopolymer chitin and its derivative chitosan are versatile and well-known materials used in (bio-)medicine and pharmacy. However, they are rarely available as a pure textile product. Chitin is the second abundant biopolymer after cellulose with 1.5-105 t/a [1]. The semi-crystalline structure and stable network of molecular bonds limit the solubility of chitin significantly. Therefore, chitin derivative chitosan is being primarily addressed by research and material development. The chitosan class of materials demonstrates excellent biological and antibacterial properties as well as cell colonizability and biodegradability [2, 3]. In the last few years, considerable research efforts have been made to develop efficient chitosan products; nevertheless, the availability of pure chitosan multifilament yarns with long-term stability is currently extremely limited [4]. Likewise, a robust, scalable process for manufacturing of high-performance chitosan filament yarns is urgently needed, as current products are severely limited in terms of mechanical properties. Due to the natural provenance and variability of raw material properties, such as degree of deacetylation (DD), molecular weight (Mw), etc. There are still major challenges in producing of chitosan multifilament yarns using the acid- and alkali-dominated manufacturing processes established so far.

The aim of the IGF research project ‘Chion’ (21168 BR) was therefore to develop a robust wet-spinning process based on ionic solvents for manufacturing of multifilament yarns from 100 % chitosan with high performance and functionality.

Obtained Results

By using ionic liquids (IL), lower cost chitosans with lower Mw and DD < 90% became accessible to the wet-spinning process for the first time. A high content of acetamide groups in chitosan with low DD (< 90%) leads to the increase of intermolecular interactions, which resulted in improved mechanical performance with tensile strengths up to 28 cN/tex and proper textile processing of chitosan multifilament yarns. The extensive research of chitosan-IL-systems with different chitosan proveniences, Mw and DD 60 – 90% with imidazol-based IL was initially carried out on a laboratory scale for monofilaments. Based on the results, important process parameters and promising chitosan-IL combinations were obtained and the developed process was successfully transferred to the multifilament scale. A structural-mechanical adjustment of the properties of the chitosan multifilament yarns was a fundamental object of the research work: Each development step was systematically monitored by material and process characterizations and analyses. Further investigations included the solubility of chitosan in IL, viscosity studies, fiber morphology and geometry, chemical and physical material properties, crystallinity and degradation behavior, as well as on the influence of controlled fiber drawing during the spinning process according the adjustment of the textile-physical properties. By integrating acid- and temperature-sensitive agents into the spinning dope, the functionality of the chitosan multifilament yarns was demonstrated. As a result of the precise tailoring of the molecular fiber properties and the developed spinning process parameters, a robust, scalable wet-spinning process is now available for manufacturing of pure chitosan multifilament yarns in pilot scale. Finally, the textile processability of the chitosan multifilament yarns was investigated and demonstrated by knitting, weaving and braiding processes.

Investigation of the solubility of chitosan in IL and spinning dope preparation

Initially, the dissolving ability of IL for chitosan was investigated and evaluated. Through systematic experiments, 19 commercially available chitosan materials of different qualities (e.g. medical grade chitosan, industrial grade chitosan, etc.), provenance (e.g. shrimps, crabs, fungal-based chitosan), degree of DD (60 – 90%) and Mw were characterized and their solubility evaluated in promising imidazole-based ILs. It was demonstrated that especially short-chain ILs in combination with acetate anions possess excellent solubility for all investigated chitosans (Figure 1). From the results of the dissolution tests, promising chitosan-IL combinations were defined for further process development steps.

The preparation of the chitosan-IL spinning dopes (Figure 2, left) was carried out using thermal processing in solids concentrations of up to 8 wt.-% and was monitored and evaluated by rheological investigations as a function of the temperature and shear rate (Figure 2, right). To investigate the stability, processability and spinnability of the homogeneous chitosan-IL-solutions, the spinning dopes were processed into monofilaments on a laboratory scale. In particular, fiber formation was analyzed as a function of the chitosan raw materials and process parameters, such as solid content, temperature, diffusion rate and residence time in the coagulation medium. The obtained results demonstrated, that all investigated chitosan-IL-combinations can be processed into pure chitosan fibers. Therefore, it was successfully proved that ILs are a suitable and promising solvent for the manufacturing of chitosan multifilament yarns.

Wet-spinning of the chitosan multifilament yarns

In the following step, the basic methods developed on the laboratory scale were successfully transferred to a wet-spinning process on a pilot scale. The chitosan multifilament yarns were spun on the wet-spinning plant (Fourné Maschinenbau GmbH) of the ITM. The pilot spinning plant is specially designed for R&D process developments and enables, in particular, test trials with 2 – 60 liters of spinning dope.

For the spinning trials, chitosan-IL spinning dope was first filtered and degassed under specific temperature and pressure conditions. Different spinneret geometries were used for multifilament spinning, including 78 holes of 90 μm (90 µm/78f) and 24 holes of 160 μm (160 µm/12f), respectively. The prepared tempered spinning dope was extruded into a coagulation bath with deionized water as medium. Overall yarn counts of about 50 – 65 tex and filament diameters of about 30 – 50 µm were achieved depending on the spinneret geometry. In order to achieve tailored functionalities, such as high mechanical strength and crystallinity as well as improved molecular orientation, the influence of fiber drawing during the spinning process was systematically investigated. The produced yarns were analyzed for their mechanical and textile-physical properties and compared with conventionally produced acetic acid (AcOH) based chitosan yarns. The DD of the raw material has an important role in this context: a high content of acetamide groups in chitosan with low DD (< 90%) leads to an increase in intermolecular interactions, resulting in improved mechanical properties. The results obtained demonstrate a high functionality as well as significantly improved mechanical properties of the IL spun chitosan multifilament yarns compared to the conventional chitosan fibers (DD 90%) (Figure 3, right). By means of elaborated drawing parameters, tailor-made textile-physical properties, such as elasticity or tensile strength, can be adjusted according to defined requirements.

Textile processing of the chitosan multifilament yarns

During the final phase of the project, the textile processing of the chitosan multifilament yarns from IL into knitted and woven patterns and braids was successfully implemented (Figure 4). The technical processing of conventional chitosan yarns on textile machines has always been a challenge due to insufficient mechanical strength and knot tearing forces. Trouble-free processing in weaving, knitting or braiding processes without special yarn pretreatment or machine adaptations could not be realized so far using conventional chitosan multifilament yarns. In contrast, the chitosan multifilament yarn produced by IL offers sufficient mechanical stability and flexibility to be processed into knitted, woven or braided structures in conventional textile processes on standard industrial production machines. Additional yarn functionalization, such as sizing, further improves the processability of the material and the quality of the finished product.


The IGF project 21168 BR 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.

The complete publication is available as download.

Authors: Kuznik, Irina; Kruppke, Iris; Cherif, Chokri

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

chitosan multifilament yarns

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