Preparation Of PAN Spinning Solution And Rheological Research

High performance precursor is the basis of high quality carbon fiber, while high performance polyacrylonitrile (PAN) and high quality of PAN spinning solution are necessary conditions of obtaining high performance precursor. In polymerization stage, aqueous deposited polymerization is utilized to synthesize high molecular weight PAN polymers using by acrylonitrile (AN) and itaconic acid (IA) as monomers. In dissolving stage, the high dissolved ability organic solvents dimethylsulphoxide (DMSO) and dimethylacetamide (DMAc) were choosed to prepare PAN spinning solution. After defoaming and filtering, the experimental PAN spinning solution was obtained. The influence of various factors such as solid content,temperature, molecular weight, shear rate and solvents on the apparent viscosity of spinning solution was explored by orthogonal experiment and spinning solution rheological research of PAN spinning solution. And fitting correspond rheological equations. In the process of above research for spinning solution findings:using different solvents, experimental data and analysis results of spinning solution vary greatly. Therefore, after getting PAN polymer powder by membrance, washing, drying and grinding of spinning solution, the thermal properties and structure were analysised by using DSC, TG and XRD.The preparation techniques of PAN spinning solution including:dry, solubility, defoam, shear and pre-filtering. Through optimize the preparation technology, high quality PAN spinning solution can be obtained. Meanwhile, the spinning solution preparation technology is connectted with solvent. Compared with DMSO, using DMAc as solvent, the stir and defoam time was shorter, the solubility temperature was lower, but due to its volatile, the dissolving process of PAN/DMAc spinning solution should be under pressure in the atmosphere of N2.As the orthogonal test of PAN spinning solution shown, the influence of four factors on apparent viscosity is connect with solvent. To PAN/DMSO and PAN/DMAc spinning solution, the influence degree of four factors on apparent viscosity respectively is:content of solid> molecular weight> temperature> shear rate; temperature> content of solid> molecular weight > shear rate, and the influence of temperature on PAN/DMAc spinning solution apparent viscosity is more degree than the other three factors.The rheological properties research of PAN spinning solution shows that, the PAN spinning solution displays thinning shear phenomenon obviously, belongs to the plastic fluid of non-newtonian fluid, its apparent viscosity increases with the increasing of the molecular weight and the content of solid. Meanwhile, the PAN spinning solution exists critical molecular weight and critical shear rate, the critical molecular weight and critical shear rate of PAN/DMSO spinning solution and they are approximately to:35×104,4S-1～8S-1; the critical molecular weight and critical shear rate of PAN/DMAc spinning solution are approximately to:27×104,1.5S-1～2S-1, and the critical point is not changed with temperature. Under the same conditions, the apparent viscosity of PAN/DMAc spinning solution is far less than that of PAN/DMSO spinning solution. Therefore, when the PAN spinning solution is in the configuration, the relationship of polymer molecular weight, temperature and the solid content, and adopt the appropriate solvent should be fully coordinate to get the suitable viscosity of spinning solution.The rheological curves of PAN spinning solution finds that:before the critical molecular weight, linear relationship exists between 1gηwith 1gM, 1gγ, 1g(wt),1/T. The equation of PAN/DMSO and PAN/DMAc spinning solution respectively are:1gη=-31.45+5.331gM+377/T+3.531g(wt)-0.2631gγ, 1gη=-10.70+2.601gM+1767/T+7.931g(wt)-0.0891gγ. According the regression equation, the apparent viscosity of PAN spinning solution with certain conditions can be predicted and guidance for spinning process can be provided.The study on rheological property indexs of the PAN spinning solution discovers that:sticky flow activation energy increases with the increasing of solid content, decreases with the increasing of molecular weight and shear rate; non-newtonian index increases with the increasing of temperature, decreases with the increasing of molecular weight and solid content; structure index increases with the increasing of solid content and molecular weight, decreases with the increasing of temperature; and the change extent caused by molecular weight is far outweigh than that caused by temperature and solid content. Meanwhile, compared to PAN/DMSO spinning solution, the sticky flow activation energy and structure index of PAN/DMAc spinning solution is greater, the non-newtonian index is smaller.The analysis of DSC, TG, XRD explores that:the PAN polymer group unchanged during the dissolving process; solvent destroys the crystallization area of PAN, making the crystallinity decrease. Compared to DMSO, the content of the damaged crystallization caused by DMAc is deeper; compared to PAN polymer, the PAN polymer of spinning solution is more stable, maximum weightlessness rate and the corresponding temperature are greatly reduced, exothermic peak is wider and the corresponding rate is lower; compared to the polymer of PAN/DMAc spinning solution, the polymer of PAN/DMSO spinning solution thermal stability is better, maximum weightlessness rate and the corresponding temperature are lower, exothermic peak is wider and the corresponding rate is lower.