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offshore windpark Nicholas Doherty, unsplash
17.10.2023

Pyrolysis processes promise sustainable recycling of fiber composites

Wind turbines typically operate for 20 to 30 years before they are undergoing dismantling and recycling. However, the recycling of fiber composites, especially from the thick-walled rotor blade parts, has been inadequate until now. The prevailing methods involve thermal or mechanical recycling. For a sustainable and holistic recycling process, a research consortium led by Fraunhofer IFAM is pooling their expertise to recover the fibers through pyrolysis. Subsequent surface treatment and quality testing of the recyclates allow for them to be used again in industry.

Wind turbines typically operate for 20 to 30 years before they are undergoing dismantling and recycling. However, the recycling of fiber composites, especially from the thick-walled rotor blade parts, has been inadequate until now. The prevailing methods involve thermal or mechanical recycling. For a sustainable and holistic recycling process, a research consortium led by Fraunhofer IFAM is pooling their expertise to recover the fibers through pyrolysis. Subsequent surface treatment and quality testing of the recyclates allow for them to be used again in industry.

Today, the vast majority of wind turbines can already be recycled cleanly. In the case of rotor blades, however, recycling is only just beginning. Due to the 20-year operation period and the installation rates, the blade volume for recycling will be increasing in the coming years and decades. In 2000, for example, around 6,000 wind turbines were erected in Germany, which now need to be fed into a sustainable recycling process. In 2022, about 30,000 onshore and offshore wind turbines with a capacity of 65 gigawatts were in operation in Germany alone.

As wind energy is the most important cornerstone for a climate-neutral power supply, the German government has set itself the goal of further increasing its wind energy capacity by 2030 by installing larger and more modern turbines. Rotor blades will become longer, the proportion of carbon fibers used will continue to increase - and so will the amount of waste. In addition, the existing material mix in rotor blades is expected to increase in the future and precise knowledge of the structure of the components will become even more important for recycling. This underscores the urgency of developing sustainable processing methods, especially for recycling the thick-walled fiber composites in the rotor blades.

Economic and ecological recycling solution for fiber composites on the horizon
Rotor blades of wind turbines currently up for recycling consist of more than 85 percent of glass- and carbon-fiber-reinforced thermosets (GFRP/CFRP). A large proportion of these materials is found in the flange and root area and within the fiber-reinforced straps as thick-walled laminates with a wall thicknesses of up to 150 mm. Research into high-quality material fiber recycling as continuous fibers is of particular importance, not only because of the energy required for carbon fiber production. This is where the project "Pyrolysis of thick-walled fiber composites as a key innovation in the recycling process for wind turbine rotor blades" – "RE SORT" for short – funded by the German Federal Ministry of Economics and Climate Protection comes in. The aim of the project team is the complete recycling by means of pyrolysis.

A prerequisite for high-quality recycling of fiber composites is the separation of the fibers from the mostly thermoset matrix. Although pyrolysis is a suitable process for this purpose, it has not yet gained widespread adoption. Within the project, the project partners are therefore investigating and developing pyrolysis technologies that make the recycling of thick-walled fiber composite structures economically feasible and are technically different from the recycling processes commonly used for fiber composites today. Both quasi-continuous batch and microwave pyrolysis are being considered.

Batch pyrolysis, which is being developed within the project, is a pyrolysis process in which the thermoset matrix of thick fiber composite components is slowly decomposed into oily and especially gaseous hydrocarbon compounds by external heating. In microwave pyrolysis, energy is supplied by the absorption of microwave radiation, resulting in internal rapid heat generation. Quasi-continuous batch pyrolysis as well as microwave pyrolysis allow the separation of pyrolysis gases or oils. The planned continuous microwave pyrolysis also allows for the fibers to be preserved and reused in their full length.

How the circular economy succeeds - holistic utilization of the recycled products obtained
In the next step, the surfaces of the recovered recycled fibers are prepared by means of atmospheric plasmas and wet-chemical coatings to ensure their suitability for reuse in industrial applications. Finally, strength tests can be used to decide whether the recycled fibers will be used again in the wind energy industry or, for example, in the automotive or sporting goods sectors.

The pyrolysis oils and pyrolysis gases obtained in batch and microwave pyrolysis are evaluated with respect to their usability as raw materials for polymer synthesis (pyrolysis oils) or as energy sources for energy use in combined heat and power (CHP) plants (pyrolysis gases).

Both quasi-continuous batch pyrolysis and continuous-flow microwave pyrolysis promise economical operation and a significant reduction in the environmental footprint of wind energy. Therefore, the chances for a technical implementation and utilization of the project results are very good, so that this project can make a decisive contribution to the achievement of the sustainability and climate goals of the German Federal Government.

Source:

Fraunhofer-Institut für Fertigungstechnik und Angewandte Materialforschung IFAM

(c) STFI
14.12.2021

Funding Project Raw Material Classification of Recycled Fibers

For centuries, old textiles have been used to make tear fibers and processed into new textile products. This effective recycling is one of the oldest material cycles in the world. Today, it is not only clothing that is recycled, but also high-quality technical textiles. As the products of the textile industry evolve, so do the demands on textile recycling. The basis for this is a clear assessment and classification of raw materials.

For centuries, old textiles have been used to make tear fibers and processed into new textile products. This effective recycling is one of the oldest material cycles in the world. Today, it is not only clothing that is recycled, but also high-quality technical textiles. As the products of the textile industry evolve, so do the demands on textile recycling. The basis for this is a clear assessment and classification of raw materials.

In the research project of the German Institutes of Textile and Fiber Research Denkendorf (DITF) and the Sächsisches Textilforschungsinstitut e.V. (STFI - Saxony Textile Research Institute), a methodology is being developed that will make it possible to analyze the tearing as well as the subsequent processes with regard to fiber quality. The systematic analysis should make it possible to optimize the subsequent spinning processes in such a way that the recycled content of the yarn can be increased without the yarn properties differing significantly from those of a yarn consisting of 100% good fibers. These yarns can then be processed into sustainable textile products such as clothing or composite components.

The project, which is funded by the BMWi/IGF, is scheduled to run for two years and will end on December 31, 2022. The main benefits for the participating companies are to enable them to make greater use of secondary raw materials, to open up new markets through technologies or products developed in the project, to initiate synergies and long-term cooperation, and to prepare a joint market presence.    

The project includes several steps:

  • Material selection and procurement
    Cotton fibers to be processed are obtained from used textiles (T-shirts) and waste from the cotton spinning mill. Aramid fibers are processed from used protective clothing and technical textiles.
  • Optimization of the preparation / dissolution of the textiles
    To ensure that the fibers are detached from the corresponding textiles as gently as possible and with a not too high reduction, exact settings have to be found for the tearing process, which are technologically very demanding and require a lot of experience.
  • Determination of the quality criteria for the evaluation of the fiber dissolution
    In order to define the quality criteria, the fibers coming from the tearing mill are determined by means of an MDTA-4 measuring device from Textechno GmbH & Co. KG. The criteria determined are to be used to characterize the (lowest possible) fiber shortening caused by the tearing process.
  • Determination of optimized settings in the spinning process
    In order to determine the optimum settings for producing a yarn from the recycled fibers, they are spun after the rotor spinning process. By adjusting the spinning process, the aim is to produce a yarn that has good uniformity and also appropriate firmness.
  • Production and comparison of yarns from recycled raw materials
    In order that the recycled fibers - consisting of aramid and cotton - can each be used to produce an area-measured material, the material is to be processed at industrial scale. For this purpose, the fibers are processed over a complete blowroom line with following sliver production over adapted cards. After drawing and the following roving production, yarns are produced according to the rotor or ring spinning process. The finished yarns are used to produce knitted fabrics.
  • Coordination, analysis of results and preparation of reports
    The final report is prepared by the DITF and the STFI. The results will be transferred through publications, technical information to associations and trade fair presentations. Regular meetings with the participating companies are planned.

Textination spoke with Stephan Baz, Deputy Head of the Competence Center Staple Fiber, Weaving & Simulation, Head of Staple Fiber Technology and Markus Baumann, Research Associate at the Competence Center Staple Fiber, Weaving & Simulation (both DITF) as well as Bernd Gulich, Head of Department Nonwovens/Recycling and Johannes Leis, Research Associate Focus Nonwovens/Recycling (both STFI) about the current status of the funding project.

What is the current status of the project?
We are currently in the phase of carrying out trials and the iterative optimization of several project components. As expected, several loops are necessary for the mechanical preparation itself and also for the adjustment of the spinning process with the different variants. Ultimately, after all, the project aims at coordinating the processes of mechanical preparation and spinning as processing in order to achieve optimum results. At the same time, determining the quality criteria of the fibers produced is not trivial. This also requires the further development of processes and test methods that can be implemented productively in industry and that allow the quality of the fibers produced to be assessed effectively and unaffected by residual yarns, for example. What is really remarkable is the interest and willingness of the industry to drive the project work forward. The considerable quantities of materials required for our trials were purchased from ReSales Textilhandel und -recycling GmbH, Altex Textil-Recycling GmbH & Co. KG and Gebrüder Otto GmbH & Co. KG. Furthermore, with Temafa Maschinenfabrik GmbH, Nomaco GmbH & Co. KG, Schill + Seilacher GmbH, Spinnerei Neuhof GmbH & Co. KG and Maschinenfabrik Rieter AG, many members of the project-supporting committee are actively involved in the project, from consulting to the providing of technologies. The company Textechno Herbert Stein GmbH & Co. KG has provided a testing device of the type MDTA4 for the duration of the project and supports our work with regard to the evaluation of the mechanically prepared fibers. We are of course particularly pleased about this, as it has allowed us to look at and analyze several technologies in both mechanical preparation, testing and spinning. We expect to be able to make more detailed statements at the beginning of the coming year.

Which approaches do you think are particularly promising?
With regard to technologies, we must refer to the evaluation and analysis of the trials, which are currently still ongoing. We will be able to go into more detail in the first quarter of next year.

Of course, things are already emerging. With meta-aramid waste, promising approaches could be found very quickly; with post-consumer cotton, this is considerably more complex. Obviously, there is a link between the quality of the raw material and the quality of the products. In some cases, we have already been able to determine very low average fiber lengths in the procured goods; to a certain extent, these are of course directly reflected in the output of our processes. From this, and this is not a new finding, a great importance of the design of the textiles is again derived.

What are the challenges?
In addition to the expected high short fiber content, the residual yarns after the tearing process are an issue of particular focus. The proportion of these residual yarns can vary between the materials and preparation technologies, but the further dissolution of the products of the tearing process is essential.

If the processes are considered further in a utilization phase, the question of design naturally also arises for the best possible use of recycled fibers. Many problems, but also the approaches to solutions for the use of comparatively short fibers, can also be expected to apply to the (multiple) use of mechanically recycled fibers.

Can we speak of upcycling in the final product?
We see yarn-to-yarn recycling neither as upcycling nor downcycling, but as closed-loop recycling. The background is that the products are to go into the same application from which they came and have to compete with primary material. This means that certain specific requirements have to be met and at the same time there is considerable price pressure. In the case of downcycling, a significant reduction in properties is accepted, while in the case of upcycling, the higher-priced application can make up for the reprocessing effort. In the attempt to produce yarn material again from yarn material, both are only permissible to a small extent. This represents the particular challenge.

What does a recyclate prepared from used textiles mean for the spinning process?
Part of this question is to be answered in the project by the detailed classification of the processed fibers and is thus the subject of the tests currently underway. It turns out that, in addition to the rather obvious points such as significantly reduced fiber length, process disturbances due to undissolved fabrics and yarn pieces, there are also less obvious aspects to be considered, such as a significantly increased outgoing quantity for processing in the spinning process. The outgoing quantity is of particular interest here, because in the end the newly produced yarn should also contain a considerable proportion of prepared fibers.

What consequences does this have for textile machinery manufacturing?
The consequences that can already be estimated at the present time are that, particularly in the processing of cotton, the machinery in the spinning preparatory mill is specialized in the processing of (new) natural fibers with a certain amount of dirt. In contrast to new fibers, processed fibers are clean fibers with a significantly higher proportion of short fibers. Elements that are good at removing dirt also reject an increased amount of short fibers, which can lead to unintentionally high waste quantities under certain circumstances. It is therefore necessary to adapt the established machine technology to the new requirement profile of the raw material "processed fibers". Analogous adaptations are probably necessary along the entire processing chain up to the yarn. In the drafting system of the spinning machine, of course, this is due more to the high short fiber ratio than to elements that have been optimized for cleaning out dirt and foreign substances.

Source:

Textination GmbH

Photo: Pixabay
16.02.2021

Carbon with Multiple Lives: Bringing Innovations in Carbon Fiber Recycling to Market

When it comes to the future of motorized mobility, everyone talks about the power drive: How much e-car, how much combustion engine can the environment tolerate and how much do people need? At the same time, new powertrains place ineased demands not only on the engine, but also on its housing and the car body: Carbon fibers are often used for such demanding applications. Like the powertrain of the future, the materials on the vehicle should also be environmentally friendly. That is why recycling of carbon fibers is required. Institutes of the Zuse Community have developed solutions for this.

Carbon fibers consist almost completely of pure carbon. It is extracted from the plastic polyacrylonitrile at 1,300 degrees Celsius, using a lot of energy. The advantages of carbon fibers: They have almost no dead weight, are enormously break-resistant and sturdy. These properties are needed, for example, in the battery box of electric vehicles in structural components of a car body.

When it comes to the future of motorized mobility, everyone talks about the power drive: How much e-car, how much combustion engine can the environment tolerate and how much do people need? At the same time, new powertrains place ineased demands not only on the engine, but also on its housing and the car body: Carbon fibers are often used for such demanding applications. Like the powertrain of the future, the materials on the vehicle should also be environmentally friendly. That is why recycling of carbon fibers is required. Institutes of the Zuse Community have developed solutions for this.

Carbon fibers consist almost completely of pure carbon. It is extracted from the plastic polyacrylonitrile at 1,300 degrees Celsius, using a lot of energy. The advantages of carbon fibers: They have almost no dead weight, are enormously break-resistant and sturdy. These properties are needed, for example, in the battery box of electric vehicles in structural components of a car body.

The Saxon Textile Research Institute (STFI), for instance, is currently working with industrial partners on combining the static-mechanical strengths of carbon fibers with vibration damping properties to improve the housings of electric motors in cars. The project, which is funded by the German Federal Ministry for Economic Affairs and Energy, is aimed at developing hybrid nonwovens that contain other fibers, in addition to carbon fiber, as a reinforcement. "We want to combine the advantages of different fiber materials and thereby develop a product that is optimally tailored to the requirements", explains Marcel Hofmann, head of department of Textile Lightweight Construction at STFI.

The Chemnitz researchers would therefore complement previous nonwoven solutions. They look back on 15 years of working with recycled carbon fibers. The global annual demand for the high-value fibers has almost quadrupled in the past decade, according to the AVK Industry Association to around 142,000 t most recently. "Increasing demand has brought recycling more and more into focus", says Hofmann. According to him, carbon fiber waste is available for about one-tenth to one-fifth of the price of primary fibers, but they still need to be processed. The key issue for the research success of recycled fibers is competitive applications. STFI has found these not only in cars, but also in the sports and leisure sector as well as in medical technology, for example in components for computer tomography. "While metals or glass fibers cast shadows as potential competing products, carbon does not interfere with the image display and can fully exploit its advantages", explains Hofmann.
 
Using Paper Know-How
If recycled carbon fibers can pass through the product cycle again, this significantly improves their carbon footprint. At the same time it applies: The shorter the carbon fibers, the less attractive they are for further recycling. With this in mind, the Cetex Research Institute and the Papiertechnische Stiftung (PTS), both members of the Zuse Community, developed a new process as part of a research project that gives recycled carbon fibers, which previously seemed unsuitable, a second product life. "While classic textile processes use dry processing for the already very brittle recycled carbon fibers in fiber lengths of at least 80 mm, we dealt with a process from the paper industry that processes the materials wet. At the end of the process, in very simplified terms, we obtained a laminar mat made of recycled carbon fibers and chemical fibers", says Cetex project engineer Johannes Tietze, explaining the process by which even 40 mm short carbon fibers can be recycled into appealing intermediates.

The resulting product created in a hot pressing process serves as the base material for heavy-duty structural components. In addition, the mechanical properties of the semi-finished products were improved by combining them with continuous fiber-reinforced tapes. The researchers expect the recycled product to compete with glass-fiber-reinforced plastics, for example in applications in rail and vehicle construction. The results are now being incorporated into further research and development in
the cooperation network of Ressourcetex, a funded association with 18 partners from industry and science.

Successful Implementation in the Automotive Industry
Industrial solutions for the recycling of carbon fiber production waste are being developed at the Thuringian Institute of Textile and Plastics Research (TITK). Several of these developments were industrially implemented with partners at the company SGL Composites in Wackersdorf, Germany. The processing of the so-called dry waste, mainly from production, is carried out in a separate procedure. "Here, we add the opened fibers to various processes for nonwoven production", says the responsible head of the department at TITK, Dr. Renate Lützkendorf . In addition to developments for applications e.g. in the BMW i3 in the roof or rear seat shell, special nonwovens and processes for the production of Sheet Molding Compounds (SMC) were established at TITK. These are thermoset materials consisting of reaction resins and reinforcing fibers, which are used to press fiber-plastic composites. This was used, for example, in a component for the C-pillar of the BMW 7 Series. "In its projects, TITK is primarily focusing on the development of more efficient processes and combined procedures to give carbon fiber recycling materials better opportunities in lightweight construction applications, also in terms of costs", says Lützkendorf. The focus is currently on the use of CF recycled fibers in thermoplastic processes for sheet and profile extrusion. "The goal is to combine short- and continuous-fiber reinforcement in a single, high-performance process step."

1) Since February 1st, 2021, Dr.-Ing. Thomas Reussmann succeeds Dr.-Ing. Renate Lützkendorf, who retired 31 January.

Source:

Zuse Community