The Control Of The Microstructure Mesophase Pitch-based Carbon Fibers In The Spinning Process

Mesophase pitch-based carbon fiber(MPCF) is considered to have incredible potential for development with various kinds of excellent performances like low coefficient of thermal expansion, high modulus, and high thermal conductivity. As a type of advanced composites reinforcement material, it has a broad application prospect applied to the aviation, aerospace, automotive sector and other areas. The preparation of MPCF needs to go through mesophase pitch refining, melt spinning,oxidation and carbonation. Due to the melt spinning process, the orientation and configuration of the liquid crystal molecules were greatly affected, which then impacted the structure and properties of MPCF. Therefore, it is of great significance to explore the influence of the melt spinning process on structure and properties of MPCF.The physical and chemical properties of two kinds of mesophase pitch are studied by employing characterization methods including aromatic component analysis, polarized light microscopy analysis, TG analysis, rheological analysis, in order to investigate the spinnability of MP-1 and MP-2. Based on finding out suitable spinning process conditions, influences of spinning temperature and the L/D of spinneret die on structures and properties of two kinds of MPCF are especially investigated. Taguchi experimental design is employed to probe into the influences of fiber spinning conditions on the diameter and cracking angle of the MP-1 based carbon fibers.Drawn from the polarized light microscopy analysis results, the optical texture of MP-1 and MP-2 is flow domain structure. The softening point of MP-1 and MP-2 are209 ? and 243 ? respectively. MP-2's thermal stability is better than MP-1's but both have acceptable stability.With the increasing of the L/D of spinneret die, the spinnability of the MP-1increases at first, followed by decreasing later. The MP-1 based carbon fibers show radial textures in their transverse alignments. With the growing of the L/D of spinneret die, the spinnability of the MP-2 decreases, the transverse texture of carbon fiber obtained from MP-2 was radial with crack at low L/D, and then changed to radial-core random-skin texture and part-radial textures. With the rising of the spinning temperature, the transverse textures of carbon fiber obtained from MP-1 are radial textures with crack without any temperature shifts. With the increasing of thespinning temperature, the transverse textures of carbon fiber obtained from MP-2 are radial textures. With the increasing of spinning temperature, modulus decrease for both MP-1 and MP-2 fibers. MP-2 carbon fibers have slightly higher modulus than MP-1 carbon fibers.The Taguchi experiment results show that the spinning speed is the most important factor to affect the diameter of the MPCF. With the increasing of the winding speed and the entry angle of spinneret die, the diameter of the MPCF decreases significantly. Also, as spinning temperature decreases, the diameter of the MPCF decreases.