Study on spinnability of polyacrylonitrile solution based on dynamics simulation of dry‐jet wet spinning

Spinnability of polyacrylonitrile (PAN) solution was studied based on the spinning dynamics simulation and dry‐jet wet spinning experiments. The spinnability phenomenon was observed from the extruding and extending spinning experiments. The suitable conditions of normal extruding and extending of the PAN solution were obtained and the critical spinnability conditions were simulated. The experimental and simulation results showed that pressure drop through the spinneret was similar, while the temperature, velocity, and velocity gradient through the spinneret of PAN solution changed dramatically. It suggests that pressure drop can be chosen as one of the spinnability criterion for solution extruding and filaments forming during dry‐jet wet spinning. Furthermore, the effect of spinneret parameters and spinning conditions on spinnability was simulated. It shows that spinneret entrance angle, outlet channel length and width have impacts on the pressure drop and the die swell ratio, which suggests the spinneret design can be optimized to regulate the spinnability according to the simulation results. It is also found that some bad situations of spinnability such as sticking phenomenon can be avoided by decreasing spinning temperature or increasing mass flow rate to increase the pressure drop at a certain level under the premise of extruding smoothly. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46377.     

Tackling slip effects in the nonlinear flow properties of gellan fluid gels

Gellan gum is a biopolymer widely used in the food, pharmaceutical, chemical, and agrochemical fields. Its ability to form a strong gel makes it possible to produce fluid gels. These materials present an apparent yield stress, but its value could be influenced by the wall-slip effect when performing the rheological measurements by which it is determined. In this work, the influence of the measuring surface and gap on flow behavior was first determined. The tests revealed the need to use geometries with rough surfaces, although the sample thickness using a parallel plate has no influence. Subsequently, the value of yield stress was obtained by means of creep tests (found to be 4.3 Pa), and, finally, the effect of wall slip on the dynamic viscoelastic behavior was assessed. There was an influence on the extension of the linear viscoelastic region, but not on the viscoelastic functions of the mechanical spectra. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 46900.     

Ripening time and fiber formation of chitosan spinning dope

A study was carried out on the wet spinning of chitosan fibers using 2% acetic acid as a solvent, 10% aqueous sodium hydroxide as a nonsolvent, and 4% chitosan solution as a polymer concentration. In this study, we investigated the effect of the ripening time of the spinning dope on the ability of fiber formation (i‐value), structure, thermal, and mechanical properties (such as fineness, tenacity, elongation, work of rupture, etc.) of chitosan fibers. Based on the results, it can be seen that the ripening time of spinning dope (in days), with the same polymer concentration of spinning dope, changes from 1 to 8, and the i‐value of the spinning dope increased with an increasing of the ripening time. At the ripening time of 8 days, tensile strength, elongation, and work of rupture showed minimum value attributed to the excessive degradation of the chitosan polymer chains left from the mixing operation that took place at the same time as the ripening time of the spinning dope, which means that the optimum ripening time of the spinning dope is 1 to 7 days. However, the thermal decomposition temperature and the onset of the exothermic temperature of thermal properties decreased with an increased ripening time. On the other hand, tenacity, elongation, and toughness decreased with increasing ripening time, and these qualities radically decreased with an increasing ripening time of more than a week. This indicates that the dispersion of aggregates and the degradation of chitosan polymer chains left from the mixing operation occurred at the same time during the ripening time of the spinning dope. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2870–2877, 2003     

Poly(lactic acid) fibers obtained by solution blow spinning: Effect of a greener solvent on the fiber diameter

Poly(lactic acid) (PLA) fibers has been obtained by solution blow spinning (SBS) using different solvents, however most of them are toxic and can be dangerous to human health or cause harm to the environment. Therefore, this work aimed to evaluate the use of dimethyl carbonate (DMC), a greener solvent, on the production of PLA fibers by SBS using surface response analysis to evaluate and compare the influence of three solvents (chloroform, DMC, and 1,1,1,3,3,3‐hexafluoro‐2‐propanol, HFP) in the average fiber diameter. Scanning electron microscopy (SEM) was used to analyze the fiber morphology and different ranges of fiber diameter was observed when varying the solvents (chloroform: 260–970 nm; DMC: 240–650 nm; and HFP: 220–470 nm). Regression analysis showed the polymer concentration was significant for all solvents and the air pressure was significant when using chloroform and HFP. Regardless of the air pressure, increasing the PLA concentration increased the average fiber diameters for all solvents. Chloroform and HFP indicated a tendency of reduction on the average fiber diameter when the air pressure was decreased, however this behavior was not observed for DMC. It was also observed that the standard deviation indicated to be more affected by the polymer concentration than by the air pressure. The results also indicated that lower surface tension and viscosity can reduce fiber thickness. All solvents showed to be feasible to produce PLA fibers by SBS and DMC can be used to produce PLA fibers with an affordable price using a greener process. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43379.     

Scrutinizing the influence of strain‐induced fiber orientation on the melt rheological behavior of short aramid fiber/thermoplastic elastomer composite using rubber process analyzer

The effect of fiber loading and its orientational changes on the melt rheological behavior of a short aramid fiber reinforced ethylene‐octene copolymer was explored as function of dynamic strain and frequency using a Rubber Process Analyser (RPA). The rheological responses such as the storage modulus and complex viscosity to a cyclic dynamic strain sweep and subsequent linear viscoelastic (LVE) frequency sweep were performed to probe the orientational changes of the short fiber within the sample. An enhanced elastic shear modulus was observed at the low strain regime with a few numbers of repeated strain sweeps and level off thereafter. This can be attributed to the orientational changes of the short fiber from an initial random orientation to a well‐ordered concentric fiber string and the string–string packing with repeated oscillatory shear strain. The complex viscosity measured as a function of LVE frequency sweep having the influence of a pre strain history was also found to increases in first few cycles, but very interestingly the complex viscosity measured at all the frequency sweep cycles shows similar values, which are not subjected to any strain history. The optical microscopic images of the samples before and after the RPA analyses clearly support the possibility of fiber orientations and their subsequent packing with repeated strain sweeps. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

The index of dry‐jet wet spinning for polyacrylonitrile precursor fibers

A new spinning index for a PAN precursor fiber is proposed that includes the viscosity of a spinning dope, the thermodynamic affinity, and the draw ratio during the spinning process. Through dry‐jet wet spinning, six types of PAN precursor fibers with different spinning parameters, including solid content, solvent content in a bath, and draw ratio, were fabricated and analyzed with tensile tests, SEM, and XRD. The results show that the spinning index can reflect the mechanical properties of the fibers but is less indicative of crystallinity. Hence, the current spinning index is recommended for use as an indicator for the mechanical properties of PAN precursor fibers. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41265.     

Influence of particle size and fluid fraction on rheological and extrusion properties of crosslinked hyaluronic acid hydrogel dispersions

Crosslinked hyaluronic acid (HA) hydrogels are widely used in gel/HA fluid formulations as a viscosupplement to treat joint diseases; thus, it is important to characterize these hydrogels in terms of their particle size and to investigate the effects of the gel/fluid mixtures on their rheological properties and extrusion force. Hydrogels previously crosslinked with divinyl sulfone were sheared in an Ultra‐Turrax unit to produce particles with mean diameters ranging from 20 to 200 μm. Hydrogels with 75–100 μm mean diameters were also evaluated in dispersions containing a 20–40% mass fraction of HA fluid. The mean diameters were measured by laser light scattering and the rheological behavior was determined by oscillatory and steady measurements in parallel plate geometry. The HA hydrogels exhibited the typical behavior of so‐called weak gels, as analyzed by the storage and loss moduli G′ and G″, respectively. The viscoelasticity, the viscosity, and the extrusion force increased with the hydrogel particle size. The fluid phase dispersions decreased both moduli. At 40% fluid fraction, the gel characteristics were lost and the dispersion behaved as a fluid. Based on these results, the particle size and HA fluid fraction in hydrogel dispersions may be optimized to develop more efficient viscosupplement formulations. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Performance of biomimetic coating modified fiber incorporated styrene butadiene styrene modified asphalt

This study reports the effect of polydopamine bionic coating and γ-methacryloxypropyltrimethoxysilane (KH570) composite modified polyacrylonitrile (PAN) fiber as a secondary modifier on the performance of styrene-butadiene-styrene (SBS) modified asphalt. Dynamic shear rheometer test indicated the complex shear modulu, storage modulus, and loss modulus of modified PAN (KD-PAN) incorporated SBS modified asphalt was increased by 12.4, 20.5, and 11.2%, respectively compared with PAN/SBS modified asphalt. The master curve of G^* of fiber/SBS composite modified asphalt shows that the deformation resistance of KD-PAN/SBS modified asphalt is greater than that of PAN/SBS modified asphalt in the entire loading frequency range. The cone penetration test showed significantly enhanced shear strength of KD-PAN/SBS modified asphalt. The adhesion work test results and SEM images of interface between fiber and SBS modified asphalt revealed that the adhesion effect of KD-PAN and SBS modified asphalt is better than that of PAN and SBS modified asphalt. SEM and AFM images of fiber further showed that the fiber surface becomes rough after modification. The increased surface roughness of KD-PAN facilitated the adherence of SBS modified asphalt to it, which in turn led to the enhanced performance of KD-PAN/SBS composite modified asphalt at the same fiber content and temperature.     

Evaluation of an onset of electrospun beadless poly(ethylene oxide) nanofibres

To evaluate the lowest polymer concentration within a solvent from which there appears beadless nanofibres during the process of electrospinning, is rather complicated. A widely used method is based on a determination of so called entanglement concentration c_e and the onsets of beadless nanofibres are characterized by multipliers of c_e subjected to used materials. However, a determination of c_e as an intersection point of two linear segments (in log–log coordinates specific viscosity vs. concentration) in a semi-dilute region is not applicable for all materials as for instance a solution of poly(ethylene oxide) (PEO) in water does not exhibit 'classical' three linear segments within the dilute and semi-dilute regions determining overlap and entanglement concentrations. For such cases a new approach for the evaluation of an initial concentration from which beadless nanofibres are produced is proposed. This method does not use the terms overlap and entanglement concentrations. The procedure is demonstrated using four PEO solutions differing in molecular weight. The relationship expressing initial concentration in dependence on PEO molecular weight containing no adjustable parameters is proposed.     

Viscoelastic properties and structure of poly(acrylonitrile‐co‐methacrylic acid) polymer solutions for gel spinning at long aging times

The objective of the research is to obtain a more complete understanding of how aging affects the viscoelastic properties of polymer solutions to be used as starting materials for gel spinning of polymer fibers. Specifically, poly(acrylonitrile‐co‐methacrylic acid) solutions were prepared and characterized using rheological measurements and nuclear magnetic resonance spectroscopy. The results indicate that elastic character increased with increasing polymer concentration and that gelation of these solutions continued up to aging times of several weeks. Additionally, comparing the results from the two characterization methods show that while gelation continues to occur, the viscoelastic properties decrease after a critical time point suggesting that a chemical change occurs in the solutions at long times. However, these changes impact the solution dynamics minimally as the effective network properties were similar at the aging times studied here, but considerations for long‐term storage of polymer solutions for gel spinning are warranted. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39821.     

Gelation mechanism and rheological properties of polyacrylamide crosslinking with polyethyleneimine and its plugging performance in air‐foam displacement

Gels based on polyacrylamide crosslinking with polyethyleneimine have attracted attention because of their resulting high strength and good thermal stability. This study investigated the gelation mechanism of the polymeric gel and its plugging performance in air‐foam flooding. An optic microrheology analyzer was used to monitor the gelation process. The crosslinking reaction occurred in two steps, as determined from the elasticity factor curves, and the polymeric gels adopted a semisolid state from solution, as determined from the solid liquid balance curves. The elastic modulus values were higher than the viscous modulus values, indicating that mature gels were elastic‐based materials. The yield stress increased gradually with increasing polymer dosage, which was consistent with the breakthrough pressure and the trend of displacement pressure. The mature gels showed significant thixotropy. In the core displacement test, the preferred injection volume of the gel was 0.1 pore volume, and the stable pressure of the foam flooding was increased by about three times after the core was plugged. The blocking effect for cores with small original permeability was better than that with large permeability. The best blocking resulted from simultaneous treatment of both ends of the cores, followed by front‐end treatment and rear‐end treatment. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45778.     

Electrospinning of polycaprolactone nanofibers using H2O as benign additive in polycaprolactone/glacial acetic acid solution

Considerable efforts have been devoted to the production of polycaprolactone (PCL) nanofibrous structures by electrospinning. However, some toxic solvents have often been used to achieve bead‐free nanofibers. At present, a benign solvent such as glacial acetic acid (GAC) only leads to beaded or microscale fibers. Therefore a study is done to extend the electrospinnability of the PCL/GAC system by the addition of H₂O. The solution properties of conductivity, viscosity, and surface tension were altered by the addition of H₂O, especially increasing the conductivity and viscosity. These properties essential to electrospinning could remain stable for 6 h when the H₂O content was less than or equal to 9 vol %. Then ultrafine PCL fibers with diameters from 188 to 200 nm, 10 times smaller than when dissolved in pure GAC, were electrospun from solutions of PCL with concentrations in the range of 17 to 20 wt % with H₂O content at 9 vol %. Finally, the crystallinity and crystallite size of the resulting fibers were smaller than that of raw PCL pellets. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45578.     

Solvent‐solubility‐parameter‐dependent homogeneity and sol–gel transitions of concentrated polyacrylonitrile solutions

In this study, we systematically explored the dependence of the homogeneity and sol–gel transition temperatures of various polyacrylonitrile (PAN) solutions on the solvent solubility parameters. The Cole–Cole slope was used to characterize the solution homogeneity, and we found that the PAN/dimethyl sulfoxide (DMSO) solution, which had a smaller Hansen solubility parameter distance between the solvent and PAN, showed better solution homogeneity than the PAN/dimethylformamide and PAN/dimethylacetamide solutions. Additionally, we found that both heating and cooling were able to cause the gelation of the PAN solution, although their mechanisms were totally different. The gelation caused by heating was ascribed to the nitrile–nitrile coupling of PAN chains, whereas the gelation caused by cooling was due to the solvent bridge effect. In this case, DMSO, which had the highest polarity and the strongest interactions with nitrile groups, caused the highest gelation temperature of the PAN solution during cooling. The gelation temperature of the PAN solution exhibits dependence on its solvent polarity. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45405.     

Characterization of soda hardwood lignin and the formation of lignin fibers by melt spinning

Lignin fibers were developed from a commercial available soda hardwood lignin (SHL) with a melt‐spinning approach. SHL showed spinnability to form the fine fibers when poly(ethylene oxide) was used as a plasticizer with lignin. The thermal properties of lignin provided valuable information to assist the processing steps of the lignin fiber formation. The guaiacyl/syringyl ratio in SHL was determined by ³¹P‐NMR because it had great influence on the thermal mobility of lignin. A suitable temperature profile for the melt spinning was predicted through rheological studies of lignin. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

The study of short-shot water-assisted injection molding of short glass fiber reinforced polypropylene

water penetration length and fiber orientation (along the melt flow direction) are important indicators for water-assisted injection molding products of the fiber-reinforced polymer. The effects of melt short shot size, water injection delay time and water injection pressure on these two important indexes are analyzed theoretically and experimentally. The study found that with the increase of the melt short shot size, the extension of the water injection delay time and the increase of the water injection pressure, the water penetration length changed from 216 to 96 mm, 170 to 210 mm, and 215 to 180 mm, respectively. Therefore, it can be known that melt short shot size has the greatest influence on water penetration length, followed by water injection delay time, and finally water injection pressure. Meantime, due to the fiber orientation and change degree of water-assisted injection-molded products along the melt flow direction, the fiber orientation in the water channel layer along the melt flow direction has the highest and lowest change degree, followed by the wall layer and finally the core layer. It can be known that the melt short shot size has the greatest influence on the fiber orientation and the degree of change along the melt flow direction, followed by the water injection delay time, and finally the water injection pressure.     

Numerical investigation of spinneret geometric effect on spinning dynamics of dry‐jet wet‐spinning of cellulose/[BMIM]Cl solution

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.     

Effect of inulin formulation on the microstructure and viscoelastic properties of low‐fat mayonnaise containing modified starch

Combinations of three types of inulin differing in the degree of polymerization, that is, short, medium, and long chained (0–10%), and modified starch (0–3%) with different composition ratios were prepared according to the D‐optimal design of experiments. The microstructural and rheological characteristics of the prepared samples were analyzed to study the effect of the inulin composition on the low‐fat mayonnaise. Rheological characterizations, including oscillatory frequency sweep tests, transient creep, and stress relaxation analysis, were carried out on the samples. An optical microscope was used to observe the microstructure. According to the results, the effects of all types of inulin were precarious in the presence of starch (≥1.5%). In fact, a relationship was found between the inulin type and concentration and also the starch content in all of the prepared samples; with increasing starch content (≥1.5%), inulin chain length, and concentration of long‐chain inulin (≥5%), the elastic properties of the emulsion were improved and showed a higher resistivity against deformation. Furthermore, a more packed structure with a larger average particle diameter and dominant monodispersity were observed under such conditions. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 801‐809, 2013     

Preparation and characterization of hyperbranched poly(ether sulfone) and its application as a coating additive for linear poly(ether sulfone)

Hyperbranched poly(ether sulfone) (HPES), a suitable coating additive for improving the rheological properties of linear poly(ether sulfone) (LPES), was easily produced via polymerization of commercially available bisphenol S (A₂ monomer, BPS) and synthesized 2,4′,6‐trifluoro‐phenylsulfone (BB′₂ monomer, TF). During this reaction, fluoro‐ or phenolic‐terminated HPES (F‐HPES or OH‐HPES) could be facilely obtained by controlling the feed mole ratios of the two monomers. The polymerization mode A₂ + BB′₂ was confirmed by analyzing the model compounds and the degree of branching (DB) was calculated systematically. In addition, the synthesized polymers' chemical structures were exhibited by FTIR, ¹H NMR as well as ¹⁹F NMR spectroscopy. Notably, the addition of 1 wt % HPES reduced the melt viscosity and improved the high temperature liquidity of LPES because of its unique spherical shape. Furthermore, the addition of HPES did not have a negative impact on the performance of LPES, which was attributed to the good miscibility between HPES and LPES. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43892.     

Shear rheology and scaling of semiflexible polymers: Effect of polymer-solvent interactions in the semidilute regime

Semiflexible polymers and their assemblies are important in biology as cross-linked networks of semiflexible polymers form a major structural component of tissue and living cells. This research used shear rheology to demonstrate the tuning from worm-like to rod-like conformation in semiflexible polymers by polymer-solvent interactions. The conformation was assessed by the persistence length l_p, and its influence, in the semidilute regime, was assessed by the scaling of zero-shear viscosity η_o with concentration c and molecular weight . The polymers were poly n-butyl and poly n-octyl isocyanate (PBIC and POIC, respectively). PBIC exhibited the largest l_p in chlorinated solvents, and the solutions obeyed the scaling law . However, when PBIC was dissolved in benzene the l_p was greatly reduced and the scaling law now was , consistent with a worm-like conformation. On the other hand, POIC dissolved in chlorinated and benzenic solvents exhibited a worm-like conformation and the scaling was . These results were contrasted with those of hydroxypropyl cellulose (HPC) aqueous solutions, which exhibit worm-like conformation, the solutions obeyed the scaling η_o ∝ c^2.5 . Finally, the shear viscosity of the polyisocyanates and HPC obeyed the Saito scaling, valid for anisotropic particles in solution.     

Application of time–stress superposition to viscoelastic behavior of polyamide 6,6 fiber and its “true” elastic modulus

The viscoelastic behavior of semi‐crystalline polyamide 6,6 fiber is exploited in viscoelastically prestressed polymeric matrix composites. To understand better the underlying prestress mechanisms, strain–time performance of the fiber material is investigated in this work, under high creep stress values (330–665 MPa). A latch‐based Weibull model enables prediction of the “true” elastic modulus through instantaneous deformation from the creep‐recovery data, giving 4.6 ± 0.4 GPa. The fiber shows approximate linear viscoelastic characteristics, so that the time–stress superposition principle (TSSP) can be implemented, with a linear relationship between the stress shift factor and applied stress. The resulting master creep curve enables creep behavior at 330 MPa to be predicted over a large timescale, thus creep at 590 MPa for 24 h would be equivalent to a 330 MPa creep stress for ～5200 years. Similarly, the TSSP is applied to the resulting recovery data, to obtain a master recovery curve. This is equivalent to load removal in the master creep curve, in which the yarns would have been subjected to 330 MPa creep stress for ～4.56 × 10⁷ h. Since our work involves high stress values, the findings may be of interest to those involved with long‐term load‐bearing applications using polyamide materials. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44971.