Effect of Coagulation Conditions on Morphology of Polyacrylonitrile Fiber

Abstract

It is well known that polyacrylonitrile (PAN) is the most suitable precursor for carbon fiber. As the quality of PAN determines the performance of carbon fiber, a number of research has been conducted on manufacturing PAN precursor fibers. In general, there are three steps in solution spinning process, one of the most widely used method to prepare the fibers: (1) polymer solution preparation, (2) fiber spinning process and (3) post-drawing process. Due to the complex process, there are various process parameters affecting the morphology and properties of fibers. Among them, the spinning process, especially coagulation process, has a great influence on polymer solution forming a fiber shape. Once the polymer solution enters the coagulation bath after extruded from the spinneret, it begins to solidify as the solvent-nonsolvent exchange occurs. In more detail, the fiber morphology depends on the coagulation rate and solvent-nonsolvent diffusion rate, which are related to the structural differences and cross-sectional shape of the fiber, respectively. In this study, the changes of fiber morphology during the coagulation process were investigated. The coagulant composition and coagulation bath temperature were set as a processing parameter to control the solvent-nonsolvent exchange. When the solvent content in coagulant increases and the bath temperature decreases, the coagulation rate becomes slower resulting in little structural differences and few voids with small size. In addition, when the solvent content and the bath temperature increase, the solvent-nonsolvent diffusion rate is in balance and thus the fiber cross-sectionals shape becomes circular. Therefore, it is possible to control the fiber morphology by controlling the coagulant composition and bath temperature. The characterization of fiber morphology was observed by OM and SEM.