The Effect Of PAN Solution Properties On The Behavior Of Phase Separation And The Structure Of Pan

The crystal structure of Polyacrylonitrile(PAN) precursor not only affects significantly on the process of heat treatment, but also determines the final properties of carbon fiber. The crystal structure of PAN precursor is formed in the coagulation process, which is a phase separation process. PAN changing from liquid into solid, different coagulation conditions and properties of PAN solution, can impact the phase separation process, and this is why the fiber has great difference both in macroscopic structure and supramolecular structure. Domestic and foreign scholars usually control the crystal structure of PAN fiber by factors of coagulation conditions, while they ignore the properties of PAN solution that can help explore the formation mechanism of crystal structure of PAN fiber, it is of great importance to produce the high-performance carbon fiber.This paper starts from the existing state of PAN molecular in the solution, by using changing the polar of solvent or modifying to control the solution properties. And then from the microscopic perspective, the inhibiting effect of PAN solution properties on the behavior of phase separation and the crystal structure of PAN is studied. Ultraviolet spectrum characterization means is used to test the intermolecular force in the PAN solution; The viscosity and rheology analysis method are used to find the PAN molecular chain conformation and the rheology properties of PAN solution; Turbidity titration and ternary phase diagram are used to analyze the effect of PAN solution properties on the behavior of phase separation; The formation and evolution of PAN crystal structure have been studied by using XRD, and the relationship between PAN solution properties and crystal structure has been founded. The results show that:(1)The polarity of the solvent can affect significantly on the PAN solution properties. It determines the intermolecular force between solvent and PAN molecular, and impacts the PAN molecular chain conformation. While similar results can be achieved by adding proper NH4HCO3 to change the property of DMSO;(2)The polarity of PAN solvent has effect on the ability of coagulant, cloud point and the phase separation curve. The stronger the solution polar is, the weaker ability of coagulant will be, the content of water will increase in the system after phase separation, but the content of PAN will reduce, and the phase separation curve will close to the PAN-water axis, the area of homogeneous will expand. While after solvent modification, the different of phase separation curve is mainly be seen in the area of low concentration, and the critical point of phase separation moves to the PAN-water axis;(3)The PAN solution properties directly impact the crystal structure of PAN after phase separation. The PAN molecule chain is more stretching, and the movement ability of it is weaker, the lower the crystallization is, and the bigger the grain size is;(4)The shear and drafting force during the process of coagulation can impacts the crystal structure of PAN, but the existence of two kinds of force will not cover the role of PAN solution properties, they can only decrease the effectiveness of this effect.Through the analyzing and studying, the relationship between PAN solution properties, the behavior of phase separation and the crystal structure of PAN has been founded, the crystal structure of PAN forming mechanism has been deepening, the controlling methods have been enriched and the foundation that can better control the crystal structure of PAN also has been set up.