Sensitivity of Offline and Inline Indicators for Fiber Stretching in Continuous Polyacrylonitrile Stabilization

Abstract

In carbon fiber (CF) production, the stabilization process step is the most energy- and time-consuming step in comparison with carbonization and graphitization. To develop optimization routes for energy and productivity, the stabilization needs to be monitored continuously via inline analysis methods. To prognose the evolution of high-performance CF, the density of stabilized fibers has been identified as a robust pre-indicator. As the offline analysis of density is not feasible for inline analysis, a density-soft sensor based on the stabilization indices of Fourier Transform Infrared spectrum (FTIR)-analysis and Electron Paramagnetic Resonance (EPR) Spectroscopy could potentially be used for inline monitoring. In this study, a Polyacrylonitrile-based precursor fiber (PF) stabilized in a continuous thermomechanical stabilization line with varying stretching profiles was incrementally analyzed using density, FTIR-based relative cyclization index (RCI), and EPR-based free radical concentration (FRC). Our findings show RCI and EPR dependencies for density, correlated for RCI with sensitivity by stretching to cubic model parameters, while FRC exhibits linear relationships. Therefore, this study identifies two possible soft sensors for inline density measurement, enabling autonomous energy optimization within industry 4.0-based process systems.

Potentials of Polyacrylonitrile Substitution by Lignin for Continuous Manufactured Lignin/Polyacrylonitrile-Blend-Based Carbon Fibers

“…The thermal conversion proceeded in continuous process lines, consisting of a stabilization line and a carbonization line. The continuous thermo-oxidative stabilization line [32] consists of an oven with four heating zones (HZi) and as many processing units. The temperature profile was set to 245 °C to 255 °C for HZ1 (T STAB,HZ1 ), 260 °C to 270 °C for HZ2 (T STAB,HZ2 ), 280 °C to 285 °C for HZ3 (T STAB,HZ3 ), and 290 °C to 300 °C for HZ4 (T STAB,HZ4 ).…”