Correlation Studies Of Microcrystalline Modulus And Structure During The Preparation Process Of Carbon Fibers

Modulus is an important performance index for carbon fibers, and structure decides the modulus of carbon fiber. Predecessors just qualitatively describe the relationship between the structure and modulus of carbon fiber, not establishing the quantitative relationship.On the basis of the theory of modulus, a mathematic function of the modulus with parameters of pseudo-graphite crystallite for carbon fiber was derived in this thesis. The orientation angle and shape factor of graphite crystallite for the carbon fiber prepared in different conditions were obtained by X-ray diffraction analysis. By studying the rule of variation of fiber structure, and comparing the calculated modulus with the measured modulus, further revealed the factors affecting the structure and modulus. The results indicated that:1. By analyzing the stress of the graphite crystallite, an equation relating the structural parameter and microcrystalline modulus was deduced: The crystalline modulus of carbon fiber was affected by the shape factor and the orientation angle.2. With the increasing of shape factor, the crystalline modulus of carbon fiber was rised up firstly and then decreased. With the orientation angle decreased, the best shape factor η* increased and the modulus increased.3. The calculated modulus of carbon fiber from crystalline parameters fit well with the measured value, which imply that the equation can effectively explain the structure dependence of the modulus for carbon fiber.4. In the carbonization and graphitization process, the temperature was the determining factor affecting modulus and crystal structure of carbon fiber. The higher the temperature, the better the crystallite orientation, the higher the microcrystalline modulus and the fibers’modulus. In the carbonization process, drawing of the fiber affected the crystallite orientation and microcrystalline modulus. In the graphitization process, drawing mainly influenced the stack of microcrystalline, which led to increasing of the fibers’ modulus.5. As the microcrystalline structure in carbon fiber was not perfect, crystallite size was small, microcrystalline modulus was not high. For graphite fiber, crystallite grew and tended to arrange along the axis, microcrystalline modulus was at the upper end of the corresponding. It was difficult to adjust the stack between microcrystalline, so the difference between the microcrystalline modulus and the fiber modulus was more apparent.