Fluid Properties And Dynamic Simulation Of Acrylic Copolymer/1-Butyl-3-Methylimidazolium Chloride Solution During Dry-jet Wet Spinning

Diverse applications of acrylic copolymers in apparel end products, home furnishings and industrial products, particularly in high performance polyacrylonitrile fiber for carbon fibers are quite evident. However, interactions between the dipolar nitrile groups of PAN limit its solubility in some specific polar solvents, such as dimethylformamide (DMF), dimethylacetamide (DMAc) and dimethyl sulfoxide (DMSO). Recently, it is found that PAN could be polymerized and dissolved in ionic liquid. Although limitation of ionic liquids (ILs) used in industrial application due to the cost and recycle, ILs, as novel solvent, show so unique properties that are very different from the normal solvents. The unique properties suggest that the solution spinning process of PAN with ILs as solvent can not duplicate the same ones of polymer solutions in traditional solvents. The distinctive character of ILs imply that the dynamic of solution spinning need more work on it to help theoretically the formation of PAN fibers with ILs as solvents and provide the technical methods.Solution rheology and infrared spectrum were applied to investigate the dissolution mechanism of polyacrylonitrile (PAN), poly(acrylonitrile-co-methyl acrylate)(poly(AN-co-MA)), and poly(acrylonitrile-co-acrylamide)(poly(AN-co-AM)) in1-butyl-3-methylimidazolium chloride ([BMIM]Cl). It is evident from the results of infrared spectrum that the wavenumber of nitrile groups (-C=N) moved to low frequency. Simultaneously, the wavenumber of C(2)H in imidazole ring moved to higher frequency. This changes suggested that the interactions between-C≡N and [BMIM]Cl break the dipolar-dipolar interactions and facilitate the dissolving of the polymer. For poly(AN-co-MA), the polar carbonyl group (C=O) introduced does not participate in the interaction, so the solvating ability of the polymer in [BMIM]Cl is still dominated by the-C≡N group of the copolymer. However, for poly(AN-co-AM) in [BMIM]Cl, the interactions exist between not only-C≡N but the polar carbonyl group and [BMIM]Cl. According to the scaling law of the exponent in the specific viscosity-and relaxation time-concentration, the effects of the type and content of comonomers on the rheological properties of the solutions were explored. Although the weight fraction of MA incorporated in PAN backbone was increased, poly(AN-co-MA) showed the same rheological characters as PAN homo-polymer as macromolecules in θ soivent. However,[BMIM]Cl behaves as a good solvent for poly(AN-co-AM) by introducing a small amount of AM group into the PAN backbone due to the addition interaction between Cl-and NH2.The solution rheology of poly(acrylonitrile-co-itaconic acid)(poly(AN-co-IA)) in [BMIM]Cl spanning dilute, semidilute unentangled and entangled regimes were investigated. The focus was put on the dependence of viscoelasticity on the concentration and temperature for the data collection of spinning simulation. All the poly(AN-co-IA) solutions were separated into three regimes:the dilute, semidilute unentangled and entangled regimes. The rheological parameters of the solutions in various regions were obtained, such as apparent viscosity, complex viscosity, and dynamic moduli. In cooling processing of poly(AN-co-AM)/[BMIM]Cl solutions, it could be found that the microphase separation was happened leading to the gelation of the solutions. The sol-gel transition of PAN/[BMIM]Cl solutions is thermoreversible in cooling and heating process. The gelation temperature Tgel determined by Winter and Chambon method showed a considerable concentration dependence growing with increasing polymer concentration.The finite element method was employed to simulate the flow of concentrated poly(AN-co-IA)/[BMIM]Cl solution in contraction circular pipe. The constructive equations were contrasted with each other; it was evident that the difference viscoelastic PTT(Phan-Thien-Tanner) constructive equation could simulate the flow well not only at lower flow rate but also at higher flow rate. Therefore, the PTT constructive equation was used as one of governing equations to investigate the effects of contraction ration (CR), flow rate and temperature on the streamline, velocity, shear rate and shear stress in the simulation of contraction flow. The change of salient vortex size of fluid with increasing flow rate in upstream was studied. This streamline of the simulation showed that the size of salient vortex for the contraction pipe with CR-2-6increased with increasing flow rate, and the centre of the vortex moved to the lip of the contraction. But, the lip vortex was not found for the contraction pipe with CR-2-6. For the contraction flow with CR=8, the lip vortex was found clearly near the lip of the contraction with increasing flow rate up to Re=1.51×10-3(We=0.527). The effect of temperature of fluid on the size of second flow was studied. Also, the effects of CR and flow rate on the pressure drop were explored. The simulation results showed that the flow rate has more important impact on the pressure drop than the CR. The distribution of shear stress and shear rate in contraction flow were investigated, and the relationship between shear stress and shear rate was discussed. The shear stress concentration in contraction flow appeared at re-entrant corner. To eliminate the second flow including salient and lip vortex in contraction flow, the method of salient corner cutting off is proved an effective method.The dynamic model was established to simulate the spinning dynamics of concentrated poly(AN-co-IA)/[BMIM]Cl solution. The dynamic simulation of poly(AN-co-IA)/[BMIM]Cl solution was performed to investigate the die-swell in extrusion, radius, velocity and temperature profiles of the solution stream in air gap of dry-jet wet spinning. It was found the die-swell occurred near the spinneret and the length of air gap and draw ratio (DR) played a major role in the die-swell. The intensity of die-swell increased with the length of air gap and inverse of DR. The radius of the solution stream in air gap was affected only by draw ratio at a constant flow rate. From the simulation results, the axial coordinate, air gap length and the draw ratio have important effects on the velocity profiles of solution stream in air gap. The velocity of solution stream could be divided into two regions:slow-increasing zone near the spinneret and fast-increasing zone near the coagulation bath, respectively. The surface temperature of the solution stream decreased with increasing air gap length. The temperature contour of longitudinal section in air gap showed that the difference between the surface and center of the solution stream could be neglected due to the lower temperature of solution, lower draw speed and no air cooling in dry-jet wet spinning.