Rheology And Spinnability Of PAN Spinning Solution

High performance PAN spinning solution is the basis of high performance precursor. A full study about the rheology and spinnability of precursor is necessary conditions of obtaining high performance spinning solution. In this paper PAN spinning solution was made by high molecular weight polyacrylonitrile synthesized by aqueous deposited polymerization in the high dissolved ability organic solvents dimethylsulfoxide(DMSO) and dimethylacetamide (DMAc). The effect of temperature, molecular weight, solid content, shear rate and solvent ratio r(r=DMSO:DMAc, volume ratio) on the apparent viscosity of PAN spinning solution was studied systematically. We discovered that the apparent viscosity of PAN spinning solution was affected obviously by different solvent ratio. The influence of various factors on the spinnability of PAN spinning solution was explored by orthogonal experiment and fitting correspond rheological equations.The preparation progress of PAN spinning solution including:drying PAN powder, measuring solvent, solubility, stirring, defoam and so on. DMSO is added before DMAc to avoid its crystallization. The process of PAN added in solvent should be stirred slowly to avoid clumps or embedded. Conical flask should be covered before defoam to prevent volatile of solvent.PAN pinning solution belongs to the plastic fluid of non-Newtonian fluid. Its apparent viscosity decreases with the increase of temperature and shear rate and increases with the increase of molecular weight and solid content. For different PAN spinning solution, there is the same critical molecular weight(40×104), critical solid content(12%) and critical shear rate(0.5s-1). These critical points do not vary with the other conditions The variation tendency of apparent viscosity of PAN spinning solution differs at critical points. These critical points can be regarded as references, thereby obtain the suitable viscosity of pinning solution.Solvent has a significant effect on the apparent viscosity of PAN spinning solution. The apparent viscosity increases with the increase of solvent ratio and decreases after maximum value at r=1.00. The minimum value is obtained at r=2.25, which approaches good solvent of PAN. Then the apparent viscosity increases gradually. The apparent viscosity can be modulated by using this above-mentioned regularity. Besides, solvent destroys the crystallization area of PAN and affects the crystallinity of PAN. The more component solvent approaches good solvent of PAN, the lower crystallinity and the smaller crystal size. The crystal size of PAN at r=1.25is10%smaller than that of pure DMAc.The viscous flow activation energy of PAN spinning solution increases with the increase of solid content and solvent ratio and decreases with the increase of molecular weight and shear rate. The non-Newtonian index increases with the increase of temperature and decreases with the increase of molecular weight, solid content and solvent ratio. And the change extent caused by molecular weight and solvent ratio is far outweigh than that caused by solid content. The structural viscosity index of spinning solution increases with the increase of molecular weight and solid content and decreases with the increase of temperature. The structural viscosity index of PAN spinning solution increases with the increase of solvent ratio and decreases until minimum value is obtained at r=2.50, then increases gradually.The study on orthogonal experiment discovers that four factors have different impact on apparent viscosity of PAN spinning solution at different stages of solvent ratio. At r=0～1.00stage, the impact order of four factors on the apparent viscosity of PAN spinning solution is solid content> molecular weight> solvent ratio> temperature. At r=1.00～1.25stage, the order is solvent ratio>solid content> temperature>molecular weight. At r=1.25～10.0stage, the order is solid content> temperature> molecular weight> solvent ratio. The impact of solid content on apparent viscosity of PAN spinning solution is evident at every stage. Thus, we can focus on the control of solid content when making PAN spinning solution and adjust solvent ratio at the same time to obtain pinning solution at a suitable viscosity.There is a linear relationship between1gη with1/T,1gM,1g(wt) and r in regard to different solvent ratio stages of PAN spinning solution. The equation of PAN spinning solution at different solvent ratio stages are:stage r=0～1.00,1gη7=1.0464-82.7/T+0.09241gM-0.26971g(wt)+0.4806r; stage r=1.00-1.25, lgη=-1.0108+565/T+0.12461gM+0.5541g(wt)+0.785r and stage r=0-1.00, lgη=0.912-54.8/T+0.10561gM-0.54541g(wt)+0.0481r. There is a small difference between theoretical value and experimental value, which varies between2-6Pa-s. The apparent viscosity of PAN spinning solution can be predicted according to these equations and guidance for spinning process can be provided.