Investigation Of The Solidification Forming Process And Morphology Of Polyacrylonitrile Precursor

Due to their excellent performances, carbon fibers are widely used in all kinds of fields. Polyacrylonitrile (PAN)-based carbon fibers with many advantages have become one of most important varieties in carbon fiber industries. There are large gaps in the quality of PAN-based carbon fibers between the homemade and foreign products. As is well known, PAN precursors have been the key factor for producing high-performance carbon fibers, and the property of PAN precursors depends largely on their morplology, as well as chemical constitution, crystallization and orientation structure. In fiber-forming process, the microstructure of PAN precursors is constantly evolving and transforming, but their structural defects will be likely genetic to carbon fibers. The appearance of structural defects should be avoided in spinning process; in that case, the excellent precursors with ideal morphology can be fabricated. Therefore, it can’t be achieved to foresee the fibers’ performance and provide greater researching space until the formation of morphology structure and evolution mechanism in wet or dry-jet-wet spinning process has been clearly clarified.This paper is divided into two major parts, in the first part of the study, gradient solification forming methods have been adopted to investigate the thermodynamic path in PAN-DMSO-H2O system and the forming of morphology of PAN precursor, deeply expounded the conditions on coagulation spinning of cross section and skin-core microstructue and mechanical properties. Meanwhile, the influence of fiber-forming conditions on the microstructure of PAN precursor has been discussed. In the second part, through the reasearch on the spinning forming conditions and subsequent preparation process of the porosity of PAN precursors, the formation mechanism of porostiy of precursor has been descirbed. Furthermore, the effects of the variation of opening and closing pores have been deeply expounded.Generally speaking, the physical mechanical properties of fiber can be inferred from the structure, determining the different performances of precursors with different spinning conditions. In Chapter Two and Chapter Three, by adjusting spinning of coagulation conditions controlled phase separation approach during wet spinning and dry-jet wet spinning, PAN precursors with various microstructures have been prepared. The thermodynamic path has been analyzed by component determination method. In addition, the influence of fiber-forming conditions on the microstructure of PAN precursor has been discussed. Judging from our investigation, it can be concluded that forming path of gradient solidification in ternary phase diagram is optimal thermodynamic path.In Chapter Four, the forming and evolution of porosity in PAN precursor are examined by a series of measurements. Judging from our study, it can be concluded that porosity mainly form at the stage of solidification forming and show a trend of decrease after the forming process of tension, dry compaction and steam tension. Also, the closing pores and the open pores of precursor have been chiefly affected by the tension and dry compaction.This paper deeply investigated forming process of PAN fiber and influence of spinning technical parameters on PAN fibers’ morphology structure and performance. Comprehensive and in-depth understanding of wet or dry-jet-wet spinning technical conditions, formation mechanism, structure, performance and the inevitable connection between them, the theoretical foundation is provided for preparing excellent PAN precursors.