Enhancing PANox fiber properties through controlled oxidation and tensioning: A study on shrinkage inhibition and structural analysis

ANOX fiber is a unique organic material used in high-performance applications such as automotive and aeronautics. It is a non-flammable, infusible, and non-drip fiber, obtained from the controlled oxidation of PAN. During this process, fibers tend to shrink. The resulting chemical composition and mechanical properties of the fiber are dependent on the time and temperature of the process, as well as on the tension applied to the fiber during oxidation. In this work, it was questioned whether fiber shrinkage could be prevented by applying tension to the bundle of fibers during the stabilization process and whether the effect of fiber length variation on the chemical structure and mechanical properties of PAN fibers could be studied. Chemical reactions were investigated by differential scanning calorimetry coupled with thermogravimetric analysis, Fourier-transform infrared spectroscopy, solid-state nuclear magnetic resonance spectroscopy, while strength and Young's modulus were determined by tensile tests. Results unravel a tension-applied, stabilization-process trade-off: enhanced stress reduces the yield of cyclization and dehydrogenation reactions. Fiber elongation inhibits these processes but boosts tensile strength and elastic modulus, particularly improving Young's modulus, however, it had a marginal influence on elongation at break. When the shrinkage of fibers was about 30 % (no stress applied) the tensile strength and Young's modulus were found to be the lowest values, 130 MPa and 4 GPa, respectively. The best compromise was found when the shrinkage was kept to about 5 %, resulting in improved strength of approximately 175 MPa and a modulus of 5 GPa. Therefore, effective tension management allows precise adjustment of PANOX fiber chemistry and mechanical properties, enabling tailored product design for diverse applications.