Mechanism Of Diffusion And Coagulation Of Concentrated Polyacrylonitrile Solution

Mass exchange takes place violently in coagulation process, which is crucially important for solution spinning in preparing polyacrylonitrile (PAN) precursor with quality for carbon fibers, leading to precipitation of PAN solution; meanwhile, the structure is dramatically changed when the solution transformed into gel or solid. The morphology and structure of PAN precursor is determined in quite large extension resulting from genetic structure formed during coagulation. Considering the decisive impact, quite amount of work has been done by many researchers attempting to figure out the mechanism of coagulation from various perspectives including the thermodynamics and kinetics. However, the obtained results so far are mainly refined from observation on phase separation, which are far from satisfactory and with little significance for industrial production due to the lack of profound theory of concentrated polymer solution and appropriate measurements.A different research perspective has been carried out and the inner mechanism of coagulation of PAN solution is demonstrated in this thesis based on evolution of inter/intra-molecular interaction between components in PAN/solvent system. Attenuated total reflection (ATR) FT-IR was used to trace the process of PAN/solvent (DMSO) system coagulated by non-solvent (ethylene glycol) in the form of IR spectra, which was treated by two-dimensional correlation analysis method to resolve the overlapped bands and figure out relationships between the specific bands. The evolution of intra-and interactions of PAN-DMSO-EG molecularly explains the mechanism of the coagulation. The main results obtained are as follows:1. Two dimensional correlation analysis method was used to verify the existence of interaction between-CN and S=O in PAN/DMSO solution, which ensured the stability of the solution. A physical quantity Iv (Interaction value) was put forward to characterize the interaction intensity between groups.2. Three types of interactions, namely free, cyclic and linear type between PAN and DMSO, were defined according to the molecular patterns of DMSO in solution. And the ratio of each type was calculated by the quantitative method.3. The relationship between PAN/DMSO interactions and concentration was revealed. PAN was prone to interact with free unimolecule DMSO in relative dilute solution, with PAN concentration increasing, however, the interaction type was transformed to linear and cyclic.4. Hydrogen bond was immediately formed between non-solvent EG and solvent DMSO when former added in the coagulation system. Meanwhile, the DMSO interacted with-CN of PAN was "grabbed" by EG weakening the force between them through interaction transformation.5. The evolution of interaction between components in the coagulation system motivated by non-solvent EG disclosed movement behavior of PAN segments and DMSO molecules which were gradually expelled from inner polymer chains while the process proceeding. EG molecule was prone to form hydrogen bond with S=O resulting in the change of the arrangement of PAN chains. The solidification then took place when PAN chains began to gather together by the interaction between-CNs...