Predicting the Cyclization Index and Density of Stabilized Polyacrylonitrile Tow from Processing Conditions

Abstract

The production of polyacrylonitrile (PAN)-based carbon fiber includes two major steps, stabilization (oxidization) and carbonization. Stabilization is a slow and energy-consuming process and involves using a series of ovens that need to be carefully tuned to achieve desirable quality at the lowest cost. This usually involves meeting fiber density or cyclization levels at each zone of the oxidation furnace, often achieved through trial and error by a team of skilled operators. In this work, a simple empirical model was developed to predict density from oven system parameters and cyclization onset temperature of the PAN feedstock, parametrized as Sn, representing the oxidation depth. The relative cyclization index (RCI) and density of the fibers were analyzed after various oxidation treatments and were used to derive the model parameters. The RCI of stabilized fiber was well represented by a logistic function incorporating Sn while the fiber density was well predicted by a polynomial function of RCI. The model was verified using stabilization trials conducted on the same precursor in a continuous oven system and in a batch oven, and then on a second commercial precursor using the batch oven. Statistical analysis on these trials shows good agreement with model predictions.

Exothermic Behavior and Structural Transformation of Large-Tow Polyacrylonitrile Fibers during Thermo-Oxidative Stabilization

“…In the second stage, the temperature in the tow exceeds 232 °C, and the fiber begins exothermic reaction. 31,32 Figure 6a shows the time spent by different tows. The larger the tow, the longer the central heating time.…”

“…The center temperature of the tow is raised from T 0 = 25 °C to T onset = 232 °C. In the second stage, the temperature in the tow exceeds 232 °C, and the fiber begins exothermic reaction. , …”

“…The test was conducted in air atmosphere with a scanning temperature range of 50–400 °C and a heating rate of 5 °C/min. The starting exothermic temperature T onset and the peak areas of all exothermic peaks of the samples were recorded. , …”

“…The starting exothermic temperature T onset and the peak areas of all exothermic peaks of the samples were recorded. 31,32 The tensile test of fiber monofilament according to the standard (GB-T 14337-2008) will be performed by the XQ-1A fiber tensile tester of Shanghai Xinfang Instrument Co. The tensile strength and strain at break was recorded.…”

Critical Electrospinning Parameters for Synthesis Control of Stabilized Polyacrylonitrile Nanofibers

“…The main reaction is an oxidation of the nitrile groups. The formation of polar functional groups in the fibers and of covalent bonds between adjacent nitrile groups in the polymer chains derive into the formation of ladder-like structures [39,40]. Carbonization in an inert gas atmosphere results in carbon nanofibers with tailored properties [41,42].…”