Influence of Coagulation bath temperature on Cross-sectional shapes and tensile properties of PAN fibers

Abstract

1. Introduction

Recently, many researches have been conducted on changing morphologies of fibers by controlling various process parameters. In this experiment, we manufactured the flat cross-sectional shapes of polyacrylonitrile (PAN) precursor fibers for carbon fibers with high tensile properties to fabricate thin carbon fiber papers. The coagulation bath temperature was set as a process parameter to observe how it affects the morphology and mechanical properties of PAN fibers.

2. Experimental

2.1 Fiber processing We prepared the spinning dope solution by dissolving poly(acrylonitrile-co-methacrylic acid) (Poly(AN-co-MAA)) into dimethylformamide (DMF) and then spun with dry-jet spinning method. The mixture solvent of methanol and DMF was used as a coagulant. To observe the influence of the coagulation bath temperature on the cross-sectional shape of PAN fibers, we set the range of temperature from -10 to 30 ℃. After spinning, the post-drawing process were progressed.

2.2 Characterization The cross-sectional shapes of post-drawn PAN fibers were investigated by SEM. The tensile properties were measured by single filament tensile testing (FAVIMAT+).

3. Results and Discussion

SEM images of cross-sectional shapes of PAN fibers according to the coagulation bath temperature are shown in Fig. 1. As the temperature decreased, the roundness of the fibers was decreased. This phenomenon was due to the changes of solvent-nonsolvent exchange rate between polymer solutions and coagulant. At low temperature of coagulation bath, the diffusion rate of the solvent out of the polymer solution were predominated, resulting in slow coagulation. Therefore, the cross-sectional shapes became non-circular and the density of fibers were higher [1, 2]. When we measured the tensile properties, the strength at 30 ℃ had the lowest value due to faster coagulation which allowed the skin-core structure to form more easily.

4. Conclusions

We observed the influence of the coagulation bath temperature on cross-sectional shapes and the tensile properties of PAN fibers. As the temperature were decreased, the cross-sectional shape became flat and the tensile strength was increased due to the slow coagulation. In order to manufacture the carbon fiber, the heat treatment process will be conducted. Once the conditions of heat treatment are optimized, it can be used in more various applications as well as carbon fiber papers.