Investigation Of Mesophase Pitch-based Carbon Fiber Spinning Process

Melt spinning is a crucial process to transform mesophase pitch precursor into pitch fiber and determine the preferred orientation of graphite layer along the fiber axis. Thus it is of great interst to clarify the spinning conditions that affect the preferred orientation within the fiber structure. In this study, the effect of spinning conditions is investigated for different types of mesophase pitch. There are mesophase pitch obtained from catalytic polymerization (MP-1), naphthalene derived mesophase pitch (MP-2) and mesophase pitch obtained from thermal treatment in laboratory (MP-3).To perform fiber spinning process, it is very important to determine the spinnablity of mesophase pitch as the precursor. A simple way to evaluate spinnability of mesophase pitch was first established based on several analytical procedures.it is find out that the mesophase pitch with good spinnability shows:1. flow domain texture in optical photomicrographs,2. smooth cuves in thermogravimetric analysis and only one peak in DTA curves.3. smooth displacement-temperature curves from capillary rheometry,4. uniform diameter and even skin of extrudate,The structure and composition of those mesophase pitch samples were characterized by capillary rheometer, polarized-light microscopy, thermogravimetric analysis, and IR spectroscopy.The softening point of MP-1, MP-2and MP-3are188℃,225℃and245℃respectively.Their viscosity-temperature curves follow Andrade’s equation. The activation energy of MP-1, MP-2and MP-3is331.1kJ/mol,373.8kJ/mol and378.2kJ/mol respectively. MP-1exhibits fully developed bulk domain texture, its weight loss begin at280℃and carbon residue rate is approximately69.3%, while MP-2shows a narrow flow domain texture, but it has a poor thermal stability, weight loss begin at380℃and carbon residue rate is about74.9%, the decomposition of gas produces holes on the cross section of fiber at high spinning temperature. MP-3shows a wide flow domain, best performance on thermal stability and the maximum residual carbon rate of75.5%, However phase transformation and separation was observed at high temperature to affect the stability of spinning process. Results show that MP-1is inclined to produce carbon fiber with radial open wedge transverse texture, and the open angle is greatly affected by spinning temperature. As spinning temperature increases, the wedge angle increases and then decreases, it reaches its maximum at spinning temperature of256℃. The radial transverse microstructure of MP-1indicates a good. thermal conductivity, the maximum of which reaches816.1W/m·K. The transverse texture of carbon fiber obtained from MP-2was random at low spinning temperature, and changed to radial-core onion-skin texture at higher temperature. Tensile strength of carbon fiber reach to the maximium of1.12GPa at the higest spinning temperature of330℃. For MP-3precursor, with increase of spinning temperatures, their transverse textures of carbon fiber transformed from random to quasi onion and then to onion skin. At spinning temperatures of353℃, both tensile strength and thermal conducitiy of produced carbon fiber reaches to their maximum of2.02GPa and401.2W/m·K. It indicated that the effect of spinning temperature on transverse microstructure of the carbon fibers is also influenced by the nature of raw materials.A novel transverse structure of carbon fiber was first discovered using home made mesophase pitch and adjusted spinning conditions. The structure contains eight petals like portions evenly distributed in four quadrants. Two different polarized microscopic structures were observed crisscross in the center and petal like. It exhibits good thermal conductivity of480.36W/m·K and tensile strength of about1.79GPa, indicating a potential candidate combining good thermal conductivity and good tensile properties for composite reinforcement.