Study On Formation Mechanism Of PAN-Based Carbon Fiber Precursor In Dry-jet Wet-spinning Process

PAN-based carbon fibers have some excellent properties,such as high strength,high modulus,heat-resistance and anti-erosion ect.,which have been widely used in the fields of spaceflight chemical and engineering industry.There are large gaps in the properties and production of PAN-based carbon fiber between our country and advanced foreign countries. The precursor is regarded as the primary element responsible for these gaps. There are few reports about the science research for the patents. So it is urgent to clarify the formation mechanism of precursor in the behalf of better carbon fiber. The study of thermodynamics of PAN solution system and of the relationship between the component concentration of fiber and the radial structure in fiber science should have been put more attention into. And the formation mechanism of solvent/polymer/non-solvent system hasn't been made clear.In this paper,according to Fick's laws,mathematical models are established to analyse radial diffusion of solvent and non-solvent in fiber precursor;the equations which can describe the variations of solvent and non-solvent with time and radial coordinate are derived.The results show that diffusion velocity of solvent and non-solvent is extremely fast;their radial concentration distribution is not very homogeneous;temperature alters diffusion velocity remarkably;the component concentration variety of spinning solution and coagulation bath may alter their radial distribution but can not alter their critical point location of concentration variation.The phase separation happened in coagulation bath is very important for PAN-based carbon fiber precursor.On account of importance of interaction parameters between components for the phase separation,study on interaction parameters is necessary.Based on the Gibbs free energy model of the mixing of liquids established by the paper,the equations which can describe the variations of the interaction parameters with the concentration and temperation are derived.We analysed precursor solidification mechanism,pointing out that solidification mechanism is crystallization,congelation and glass transition. Crystallization is very important for fiber precursor structure.Finally,we also discussed the mechanism of formation for skin layer and hole and the effect of air gap,pointing out that natural paste evaporation ,thermotropic phase separation,diffusion phase separation give cause for hole;stretch in air gap causes polymer chain to orientate.