In this study, the effect of spinneret geometry, including the entrance angle α of the entrance channel, the length L_s, and the diameter D₀ of the exit channel, on the spinning dynamics of dry-jet wet-spinning of cellulose/1-butyl-3-methylimidazolium chloride ([BMIM]Cl) solution was simulated by using finite element method. Based on the mathematical model of dry-jet wet-spinning established in our previous work (Xia et al., Cellulose 2015, 22, 1963) the radial and axial profiles of velocity, pressure, and shear rate in the spinneret and the profiles of diameter, temperature, and tensile stress in the air-gap region were obtained. From the simulated profiles, the effect of spinneret geometric parameters on the flow behavior and the pressure drop of polymer solution in the spinneret and the die-swell ratio near the spinneret was discussed. The entrance angle α of the entrance channel mainly influences the flow behavior of polymer solution in the spinneret and the die-swell effect near the spinneret. As the decrease of the entrance angle α of the entrance channel, the vortices in the spinneret could be removed and the die-swell ratio decreases. The increase of the length L_s of the exit channel results in the increase of pressure drop in the spinneret and the decrease of the die-swell ratio. It is also found that the increase of the diameter D₀ of the exit channel reduces the flow velocity of polymer solution and decreases the pressure drop in the spinneret at a constant mass flow rate. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43962.

The changes in performance during thermal-oxidative aging process of the aromatic co-polysulfonamide (co-PSA) fibers over a broad temperature range from 250 °C to 320 °C have been investigated. In addition, the mechanism of thermal-oxidative aging process has been studied by using structural information obtained from the fibers at varying length scales. The results showed that a significant reduction in tensile strength was observed compared with that of initial modulus during aging process. Macroscopically, thermal-oxidative aging mainly causes color changes of fibers and thermally induced macro defects begin to appear only at 320 °C for 100 h. On a micro level, the crystal structure of fibers remained stable and did not show significant changes expect that aging at 320 °C. In addition, thermo-degradation as well as crosslinking has been observed primarily in amorphous region. With the increase of temperature and time duration, the crosslinking became more dominant and crosslinking density increases. Correspondingly, the fibril length decreases due to degradation and then increases due to the formation of crosslinked structures within the fibers. The results suggest that molecular degradation is the main cause of strength loss and the formation of crosslinking structure within the fibers contributes to the retention of modulus and improvement of creep resistance. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 44078.

The structure and performance changes of aromatic copolysulfonamide (co-PSA) fibers that occurred during wet spinning process have been studied. While using different length scale characterization, including scan electron microscopy (SEM), wide-angle X-ray scattering (WAXS), and small-angle X-ray scattering (SAXS), it was found that the molecular chains of co-PSA formed an isotropic network during coagulation which further lead to extension and orientation of these chains during the subsequent stretching. As a result, only after heat stretching and heat setting the molecular chains tended to pack into crystal lattice in the fibrils. This gave rise to a much denser structure along the spinning line and the glass transition temperature of co-PSA fibers increased a little after heat setting. Before heat stretching, the co-PSA fibers were in amorphous state, and only the amorphous orientation was observed within the fibers. After heat stretching at the temperature higher than T_g, the fraction of amorphous region decreased, and the crystal structure formed in the fibers, which became more perfect during heat setting. The structure development during spinning process contributed toward the improvement of thermo-mechanical stability, tenacity and modulus of the co-PSA fibers. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42343.

The concentrated polyacrylonitrile (PAN) solutions were prepared with 1-butyl-3-methylimidazolium chloride ([BMIM]Cl) as solvent by static state, stirring, and kneading. The steady and oscillatory shear tests were carried out to investigate the viscoelastic behaviors of the PAN/[BMIM]Cl solutions by rotational rheometer. It was found that the zero shear-rate viscosity and relaxation time of the solution prepared by kneading were lowest and the non-Newtonian index was largest among the solution. During kneading, the gelation temperature of the viscous and homogenous solution was at the lowest temperature 22.7°C among the all three solutions. Only the solutions prepared by stirring and kneading could be spun by dry-jet wet spinning technology. The fiber processed with the solution prepared by kneading could be drawn with a higher draw ratio, showing the larger draw ability. The supramolecular structure and properties of the fibers were studied by synchrotron wide-angle X-ray diffraction (WAXD) technologies, dynamic mechanical analysis (DMA), and mechanical tests. All the results showed that the kneading is an efficient method for PAN fiber spinning with [BMIM]Cl as solvent. It lead to the investigation of the methods of preparation of PAN solution in [BMIM]Cl, which affect the homogeneity of the solutions and hence the resulting characteristics of PAN fibers. POLYM. ENG. SCI., 55:558–564, 2015. © 2014 Society of Plastics Engineers

Pre-drawn aromatic copolysulfonamide (co-PSA) fibers were prepared by wet spinning and then heat drawing at temperatures varying from 350 to 390 °C, which are below the decomposition temperature. The fibers were then characterized using tensile testing, dynamic mechanical analysis, wide-angle X-ray diffraction and small-angle X-ray scattering. The relationship between structure and properties of the co-PSA fibers drawn at different temperatures was investigated. The heat-drawn co-PSA fibers displayed similar glass transition temperature of about 355 °C, which was higher than that of pre-drawn co-PSA fibers of 345 °C. The crystal orientation was high as a crystalline structure formed during heat drawing and the crystallinity increased with the heat-drawing temperature. However, the tenacity of the co-PSA fibers did not increase linearly with the draw temperature. When the drawing temperature was higher than the glass transition temperature, a decrease in tenacity was observed, which could be attributed to an increase of crystallite size of the (100) plane and a decrease of the long period of the lamellar structure. © 2014 Society of Chemical Industry

The viscoelastic behavior of concentrated polyacrylonitrile (PAN) /1-butyl-3-methylimidazolium chloride ([BMIM]Cl) solutions at different concentrations and temperatures has been investigated by rheology. For concentrated polymer solutions at low temperature (40°C), the shear viscosity was found to show a raid decrease from the ending of Newtonian plateau. At relatively high shear rate or frequency for the concentrated PAN/[BMIM]Cl solutions, the deviation from the empirical Cox–Merz rule was quite evident, which suggested the formation of heterogeneous structures within these solutions. However, the dependence of G′ and G″ on angular frequency presented approximate linearity with similar slope at some temperatures between 100°C and 20°C. All the results lead us to the fact that the gelation has occurred within the concentrated solutions during cooling and the process was found to be thermoreversible. The gelation temperatures of the solutions have exhibited strong concentration dependence. It may be suggested that the microphase separation may be the major reason for the gelation of the concentrated PAN/[BMIM]Cl solutions during cooling process. POLYM. ENG. SCI., 54:598–606, 2014. © 2013 Society of Plastics Engineers

The effects of the type and content of comonomers on the rheological properties of acrylic copolymers in 1-butyl-3-methylimidazolium chloride ([BMIM]Cl) were explored. According to the de Gennes scaling law for solution, comparison of intrinsic viscosity and scaling analysis of the exponent in the specific viscosity- and relaxation time-concentration power law indicated that solution of both polyacrylonitrile (PAN) homo-polymer and copolymer poly(acrylonitrile-co-methyl acrylate) (poly(AN-co-MA)) in [BMIM]Cl behave in the same manner as neutral polymer in a θ-solvent. However, [BMIM]Cl acts as a more good solvent for poly(acrylonitrile-co-acrylamide) (poly(AN-co-AM)). The dissolution and unique rheological behavior of such solutions have been attributed to the interactions between copolymer chains and [BMIM]Cl. The interactions between nitrile group (−C≡N) and 1-butyl-3-methylimidazolium cation ([BMIM]⁺) should interrupt and break the dipolar-dipolar interactions of PAN resulting in the subsequent dissolution of the polymer in [BMIM]Cl. Such interactions between −C≡N and [BMIM]⁺ ion are still dominated by the solvating ability of poly(AN-co-MA) in [BMIM]Cl, even though carbonyl group (C=O) in MA repeating unit could coordinate to cation of the ionic liquid. The salvation capacity of [BMIM]Cl for poly(AN-co-AM) can be evidently improved due to the extra hydrogen bond interactions between −NH₂ group of AM and anion of [BMIM]Cl. Copyright © 2012 John Wiley & Sons, Ltd.

The phase separation of ionic liquids (ILs) in water is studied by laser light scattering (LLS). For the ILs with longer alkyl chains, such as [C₈mim]BF₄ and [C₆mim]BF₄ (mim=methylimidazolium), macroscopic phase separation occurs in the mixture with water. LLS also reveals the coexistence of the mesoscopic phase, the size of which is in the order of 100–800 nm. In aqueous mixtures of ILs with shorter alkyl chains, such as [C₄mim]BF₄, only the mesoscopic phase exists. The mesoscopic phase can be effectively removed by filtration through a 0.22 μm filter. However, it reforms with time and can be enhanced by lowering the temperature, thus indicating that it is controlled by thermodynamics. The degree of mesoscopic phase separation can be used to evaluate the miscibility of ILs with water. This study helps to optimize the applications of ILs in related fields, as well as the recycling of ILs in the presence of water.

Summary: As one class of high temperature resistant aromatic polymers, polysulfonamides (PSA) are widely used in industry, physicochemical properties and conformation in solution have not been disclosed yet. In this work, the dilute solution behaviour of poly(m-diphenylsulphone terephthal amide) (m-PSA) was investigated by laser light scattering (LLS) and viscometry. The results showed that the m-PSA exists as single chains both in dimethylsulfoxide (DMSO) and dimethylformamide (DMF). The value of radius of gyration to hydrodynamic radius (s/R_h) indicats that the m-PSA has a random coil conformation in solution. Both the persistence length a and the characteristic ratio C_∞ indicate that the m-PSA chain is flexible in solution. The Mark-Houwink equation of m-PSA in DMSO was determined as [η] = 1.62 × 10⁻⁵M, and the exponent of 0.87 supports the assumption that m-PSA forms random coils in DMSO-solution at 25 °C. It was found that the flexibility of the PSA was affected when 4,4'-diphenylsulphone terephthalamide monomer was incorporated in backbone. The PSA random copolymer (r-PSA) with a comonomer ratio of 3:1 (4,4′-diaminodiphenyl- sulfone to 3,3′-diaminodiphenylsulfone) also had a random coil conformation in DMF; the rigidity increased, while the mobility of the chain was maintained.

Ionic liquid, 1-butyl-3-methylimidazolium chloride ([BMIM]Cl), was used as solvent for the polymerization of acrylonitrile (AN) and the resulting polymer solution was directly applied for spinning to produce polyacrylonitrile (PAN) fiber for the first time. Acrylic polymers with high content of AN, large molecular weight, and low polydispersity index (PDI) were prepared. The PAN macromolecules have little degradation during dissolution of PAN in [BMIM]Cl, which is completely different from the dissolution of biopolymers such as cellulose in ionic liquids. The PAN fiber with round profile and good mechanical properties was successfully spun from the PAN/[BMIM]Cl solution using dry–jet wet spinning technology. It suggests that an environmental friendly process for the acrylic fiber would be developed and the high performance PAN fiber would be obtained when the spinning conditions are optimized further. Copyright © 2008 John Wiley & Sons, Ltd.

The coagulation dynamics of acrylic polymer (PAN) with 1-butyl-3-methylimidazolium chloride [BMIM]Cl as solvent for PAN and H₂O as nonsolvent was investigated in detail. On the basis of Fick's second law of diffusion, a mass-transfer model of [BMIM]Cl from concentrated PAN/[BMIM]Cl solution was established as verified with the experimental data. The established model has a good fit with the experimental data and the diffusion coefficient D of [BMIM]Cl was calculated according to the model. The diffusion coefficient D decreased a little when the concentration of solution increased. As increasing the coagulation bath concentration, the diffusion coefficient D initially increased and then decreased, reaching a maximum of 5 wt% in the coagulation bath. The diffusion coefficient D decreased with the coagulation bath temperature. From the diffusion coefficient and the structure of the coagulated filament, it can be concluded that the diffusion rate of [BMIM]Cl from PAN concentrate solutions is relatively slow, which is prospective to prepare uniform-structure fibers. POLYM. ENG. SCI., 48:184–190, 2008. © 2007 Society of Plastics Engineers