Customer SUCCESS STORY
Fire Testing of Stabilized Polyacrylonitrile (PAN) Fibers
In the future, the NETZSCH TAURUS LOI 901 oxygen index analyzer will be used at Carbon LabFactory Saxony to analyze thermally stabilized PAN fibers – also known as Preox fibers – and to research sustainable alternatives such as cellulose- or lignin-based precursors.”
This is a customer success story by Dr. Claudia Vogt, research associate at the Technical University of Chemnitz at the Department of Lightweight Structures and Polymer Technology in the research area of carbon fiber and processing technologies. She reports on investigations into future applications of Preox fibers using the NETZSCH TAURUS LOI 901 oxygen index analyzer. The investigation of Preox fibers is becoming an integral part of process monitoring at the research center currently being set up in Boxberg known as the Carbon LabFactory Saxony. A new sample holder for fiber samples was developed in successful collaboration with the NETZSCH TAURUS application laboratory.
“NETZSCH offers excellent customer service. In my search for a suitable sample holder for the limiting oxygen index instrument LOI 901, I noticed that the accessories did not include a fiber sample holder. After my enquiry, I promptly received initial ideas from NETZSCH to develop a customized sample holder based on our Preox fiber material.”
About the Chemnitz University of Technology
The Chemnitz University of Technology (figure 1) is a cosmopolitan university with strong regional, national and international networks. It is home to about 2,300 academic and administrative employees as well as more than 8,600 students from about 90 countries. It is thus the third largest university in Saxony (as of 2024).
In terms of its proportion of foreign students, Chemnitz University of Technology occupies a top position among state universities nationwide. Chemnitz, the European Capital of Culture 2025, ranks among Germany’s ten best larger cities to live in, according to a recent study, and boasts an exceptional quality of life. The city also has a notably high proportion of highly qualified employees, due in large part to the presence of the university. Chemnitz University of Technology is the intellectual heart of the city and has developed into an internationally visible research location for future value creation processes and sustainable development.
About the Carbon LabFactory Saxony
The “Carbon LabFactory Saxony” (CLFS) in Boxberg, Upper Lusatia, Germany, is a key project dedicated to the research and development of carbon fibers on a pilot line scale. The new research facility focuses on the use of sustainable alternatives to petrochemical precursors, such as polyacrylonitrile, using cellulose or lignin, for example. The carbon fibers are produced in a multi-step thermal process. The CLFS also considers the entire value chain ‒ from raw material to finished components ‒ and places particular emphasis on the sustainability of the processes.
At center stage of CLFS’s research is the manufacture of carbon fibers and their processing, for example, with the help of textile machines which will also be available on site. The stabilization and subsequent carbonization of precursors such as polyacrylonitrile, cellulose or lignin is carried out in a pilot-scale carbonization plant. This plant is used to perform the essential process steps for the production of high-quality carbon fibers. The precursor material is first thermally treated in special stabilization furnaces at temperatures between 150°C and 300°C. Carbonization then takes place in a protective gas atmosphere in two stages: in a low-temperature furnace at up to 1200°C and then in a high-temperature furnace at up to 2200°C. By fine-tuning the process parameters, the properties of the carbon fibers’ manufacture can be controlled and optimized.
Recycling and Upcycling
Another forward-looking area of research is the development of of recyclable materials and products, including recycling and upcycling strategies to increase resource efficiency and minimize environmental impact. The objective is to create closed-loop material cycles, including the recovery of materials from production waste.
CLFS, which will be established as a branch of the Chemnitz University of Technology in Upper Lusatia (figure 3), will make a significant contribution to the sustainable transformation of a region that has been severely affected by the structural change brought about by the the coal phase out. The collaboration with the Fraunhofer Institute for Applied Polymer Research(Fraunhofer IAP) and the Brandenburg University of Technology Cottbus-Senftenberg (BTU) will create an efficient research infrastructure that allows innovative lightweight products to be developed from new types of carbon fibers. IAP's main focus in this endeavor is on the production of sustainable precursors, e.g., from cellulose, and their conversion on a laboratory scale.
The particular focus of the research in Boxberg will be the industrial scalability of the technologies. The pilot-plant scale will facilitate the transfer of the developed processes and materials to industrial applications. This requires close cooperation between the research institutions and industrial partners to ensure that the solutions developed are both economically viable and sustainable.
With the approaches and opportunities described, the “Carbon LabFactory Saxony” is taking on a leading role in the European development of sustainable carbon fibers. Thanks to its holistic approach, which includes the entire value chain and targets ecological innovation, CLFS contributes to a future in which carbon fibers are not only high-performance, but also environmentally friendly. It thus makes an important contribution to the European climate targets and a greenhouse-gas-neutral future.
Claudia, please introduce yourself and your area of research and application.
My name is Claudia Vogt. I have a doctorate in chemistry and have been working as a research assistant at the Department of Lightweight Structures and Polymer Processing (SLK) at Chemnitz University of Technology since August 2023, specifically in the research area of carbon fibers and processing technologies.
I am currently involved in the laboratory planning of the Carbon LabFactory Saxony and will later be primarily responsible for questions of chemical analysis of carbon fibers, their intermediate stages (Preox fibers) or end products (e.g., composites, textile fabrics). The wide range of analytical equipment available to us ranges from flame retardancy testing using LOI to thermal analysis (e.g., STA, TMA) and the determination of surface properties using tensiometry. Our team works closely together and also hand in hand.
How long has the collaboration with NETZSCH been going on?
The SLK professorship has been working with NETZSCH for many years. They routinely use thermal analysis instruments (TGA, DSC) to solve problems in the polymer field.
Why did you choose NETZSCH? Have you also experienced our customer support and service?
Along with a variety of instruments, NETZSCH also offers excellent customer service. In my search for a suitable sample holder for the limiting oxygen index instrument, I noticed that the accessories did not include a fiber sample holder. After my initial enquiry, I promptly received an offer to develop a customized sample holder based on sample material. Within a very short time, I received the initial ideas for this sample holder from the NETZSCH development laboratory.
The Customized Sample Holder for the NETZSCH LOI 901
Stephan Strickmann, Sales and Application Solutions for Fire Testing at NETZSCH, reports:
“As an expert in fire testing and Thermal ConductivityThermal conductivity (λ with the unit W/(m•K)) describes the transport of energy – in the form of heat – through a body of mass as the result of a temperature gradient (see fig. 1). According to the second law of thermodynamics, heat always flows in the direction of the lower temperature.thermal conductivity instruments, NETZSCH TAURUS specializes in the manufacture of high-precision instruments. This includes the LOI 901, which is used to assess the burning behavior of materials by determining the oxygen index (LOI = limiting oxygen index) in accordance with ISO 4589-2 and ASTM D 2863. Chemnitz University of Technology approached us with a request to be able to perform specific fire behavior tests on Preox fibers (figure 5), a special material. To accommodate the unique characteristics of this specimen, we developed and used a special specimen holder for the tests. The objective was to document the methodology, set-up and results of these tests, which provide valuable data on the fire behavior of Preox fibers at room temperature.”
Preox fibers present a particular challenge in fire behavior testing due to their fine, filamentous nature. To ensure integrity of the specimen during the test, a special specimen holder was carefully designed and manufactured.
This customized sample holder provides a secure hold for the Preox fibers, enabling precise and reliable measurements of their fire behavior for a successful test.
Results
During the test, the ambient temperature was carefully controlled and maintained at 23 ± 2°C to ensure optimum test conditions. Normally, the initial oxygen concentration for the test is chosen based on our extensive experience with similar materials. As we had little experience with Preox fibers at the time, we consulted the relevant literature and found that this material has a remarkably high LOI, often in excess of 45%.
To be on the safe side, we started the tests with an oxygen concentration of 40%. No ignition of the Preox fibers was observed at this level. We then gradually increased the oxygen concentration, carefully monitoring each step. Between 40% and 45% oxygen, there were no visible flames, but the sample showed signs of thermal degradation: it melted and then disappeared, indicating significant conversion without combustion.
The first sustained combustion occurred at an oxygen concentration of around 60%. At this level, the Preox fiber ignited and burned uniformly, confirming its higher oxygen requirement for ignition compared to other conventional materials. Further tests are being carried out to determine the final oxygen index. This initial result is consistent with the reported benefit of a high LOI value, which highlights the resistance to burning in low-oxygen environments.
Claudia, please tell us more about your specific application. How will the results help you improve your research, quality control, development and production?
As already mentioned, the production of carbon fiber is a multi-stage thermal process. The first step, in which the precursor material is thermally stabilized, is particularly crucial for polyacrylonitrile. Without this pre-treatment, polyacrylonitrile fibers would be prone to degradation under high thermal StressStress is defined as a level of force applied on a sample with a well-defined cross section. (Stress = force/area). Samples having a circular or rectangular cross section can be compressed or stretched. Elastic materials like rubber can be stretched up to 5 to 10 times their original length.stress. The complex structural transformation of PAN fibers into Preox fibers is therefore a prerequisite for the production of carbon fibers from PAN. This thermal stabilization process can be controlled by several influencing factors (e.g., heating rate, temperature profile). The LOI (figure 7) is used to check the degree of stabilization of the Preox fibers. The higher the LOI of the Preox fibers examined, the more promising the process parameters used. This approach allows for quick adjustment of the process parameters during ongoing research campaigns. It also serves as a constant quality control of the carbon fiber’s intermediate stage.
Dear Claudia, thank you very much for your insights into this groundbreaking research. We look forward to hearing more news and research results from the Carbon LabFactory Saxony soon.
About the NETZSCH LOI 901
Plastics have specific advantages over other materials such as metals, ceramics or natural materials, especially in the automotive, aerospace, electronics and construction industries, because they are lighter, more versatile, more corrosion-resistant and, depending on the requirements, either electrically conductive or insulating and often more cost-effective.
The fire behavior of the polymers used plays an important role in assessing the safety and applicability of components and assemblies. If a plastic component ignites, the release of largely toxic gases during combustion and the rapid spread of the fire can quickly lead to dangerous, life-threatening situations for people and the environment.
The LOI 901 is a highly precise instrument for determining the burning behavior of polymers in accordance with the recognized ISO 4589-2 and ASTM D2863 standards. The instrument is equipped with a special combustion chamber and uses a controlled oxygen atmosphere to determine the oxygen index, flammability of plastics, burning time and burning distance.
