Viscosity Of Dope Research Articles

The ratio of fibroin to sericin in the middle silk gland of Bombyx mori and its correlation with the extensional behavior of the silk dope.

Understanding how native silk spinning occurs is crucial for designing artificial spinning systems. One often overlooked factor in Bombyx mori is the secretion of sericin proteins. Herein, we investigate the variation in amino acid content at different locations in the middle silk gland (MSG) of B. mori. This variation corresponds to an increase in sericin content when moving towards the anterior region of the MSG, while the posterior region predominantly contains fibroin. We estimate the mass ratio of sericin to fibroin to be ~25/75 wt% in the anterior MSG, depending on the fitting method. Then, we demonstrate that the improvement in the extensional behavior of the silk dope in the MSG correlates with the increase in sericin content. The addition of sericin may decrease the viscosity of the silk dope, a factor associated with an increase in the spinnability of silk. We further discuss whether this effect could also result from other known physicochemical changes within the MSG.

Investigations for the use and recyclability of the ionic liquid [MTBDH][AcO] as a solvent in air‐gap‐wet spinning process

AbstractThe direct dissolution of cellulose offers a pathway to production of regenerated textile fibers. However, fiber production in the Lyocell process requires a high recyclability of the solvent. Some compounds from the class of ionic liquids (IL) may have higher dissolving capacities together with a higher thermal stability than the conventional N‐methylmorpholin‐N‐oxide (NMMO), which makes them more valuable in an industrial process. A promising representative of such an advanced solvent for Lyocell process, 7‐Methyl‐1,5,7‐triazabicyclo[4.4.0]dec‐5‐ene acetate ([MTBDH][AcO]) was investigated in this study. A series of 21 consecutive cellulose dissolving and spinning trials via dry‐jet wet spinning was conducted with the same batch of solvent. In the spinning trials, the cellulose was regenerated into water consisting spinning bath. The solvent was recycled by removing the water from the spin bath via distillation in reduced pressure. Due these drastic changes in the water content of the IL during the whole process, the hydrolytic stability is an important aspect to assess the recyclability of the IL and viability of the whole process. The chemical composition of the IL was monitored by means of NMR spectroscopy. Although there was an increase of hydrolysis level of the solvent, cellulose could be dissolved constantly and spun to obtain staple fibers. The spinning behavior deteriorated slowly along the additional cycles, along with a measured increase in zero‐shear viscosity of the spinning dope. Nevertheless, the physical properties of the obtained fibers were barely influenced by the changes of the ionic liquid.

The Effects of Surfactants on the Spinnability, Structure and Properties of Dry-jet Wet Spinning Poly(m-phenylene isophalamide) Fiber

The spinnability of semi-dilute poly(m-phenylene isophalamide) (PMIA) spinning dope was regulated by a small amount of surfactants to make it suitable for dry-jet wet spinning. OP-10 shows the best effect of lowering the surface tension of PMIA spinning dope among the selected surfactants. The effects of different amounts of OP-10 on surface tension and rheological behavior of PMIA spinning dope were investigated. Results show that when the content of OP-10 reaches 0.5 wt.%, the surface tension of the PMIA dope reduces to a minimum. The apparent viscosity of the PMIA dope increases with the increment of OP-10 contents. The dynamic viscoelasticity study shows that OP-10 also enhances the elasticity of the PMIA spinning dope. The spinning dope with 0.5 wt.% OP-10 can be smoothly spun by dry-jet wet spinning, and the obtained PMIA filament shows excellent mechanical performance.

Potential Application of Nanocellulose for Filaments Production: A Review

Some researchers have reported the successful experiments to produce nanocellulose-based filaments by several spinning methods, including wet spinning and dry spinning. The addition of nanocellulose to the composites was found to improve the mechanical and thermal properties of produced filaments or continuous fibers. However, there are several parameters of spinning that needs to be considered to achieve better quality of filaments, including high aspect ratio of nanocellulose, low viscosity of dope (low solid content), high shear rate in the spinneret, and high draw ratio. This review article focuses on brief explanation of cellulose structure and how to isolate nanocellulose, nanocellulose-based filaments by wet spinning and dry spinning methods, characteristics of wet and dry spun fibers, as well as parameters that affect spinning process. For example, the strength of filament was attributed to the aspect ratio or slenderness and crystallinity of nanocellulose. Further details of the potential application of nanocellulose for filament production is presented here as the reference for application in textile, medical, and other fields.

Characteristics of wet‐spun and thermally treated poly acrylonitrile fibers

ABSTRACTThe performance of carbon fibers depends on the quality of the precursor and the conditions of the thermal treatment. In detail, for a PAN precursor fiber the viscosity of a spinning dope and the draw ratio during the spinning process needs to be considered. Through wet spinning, different types of PAN precursor fibers with defined spinning parameters, including solid content, solvent content in a bath, and especially draw ratio resulting in defined cross section diameters, were fabricated and analyzed with tensile tests, density investigations, SEM, TGA‐MS, FTIR, and XRD. The results show that the mechanical properties of the fibers correlate to crystallinity. The cross section diameter is strongly related to the morphology of the fibers after thermal treatment. By extending the postdrawing of PAN fibers high tenacities were obtained at the cost of the cross section shape. In addition, TGA measurements reveal trapped residues of the wet spinning process as well as show several chemical reactions takes place at the same time at different temperatures. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43698.

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

ABSTRACTA 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.

Dispersity and spinnability: Why highly polydisperse polymer solutions are desirable for electrospinning

We develop new criteria that describe the minimum concentration limits controlling the spinnability of dilute and semi-dilute flexible polymer solutions with high molecular weight and varying polydispersity. By asserting that the finite and bounded extensional viscosity of the solution is the key material property determining the stability of a filament during spinning, we propose a new scaling relating the minimum necessary concentration of a polymer cspin to its molecular weight M and the quality of the solvent (through the excluded volume exponent ν) of the form cspin∼M−(ν+1). This new scaling differs from the classical interpretation of the coil overlap concentration c∗ or entanglement concentration ce as the minimum concentration required to increase the viscosity of the spinning dope, and rationalizes the surprising spinnability of high molecular weight polymers at concentrations much lower than ce. Furthermore, we introduce the concept of an extensibility average molecular weight ML as the appropriate average for the description of polydisperse solutions undergoing an extension-dominated spinning process. In particular it is shown that this extensibility average measure, and thus the solution spinnability, is primarily determined by the extensibility of the highest molecular weight fractions. For highly polydisperse systems this leads to an effective lowering of the minimum required concentration for successful fibre spinning (in comparison to narrowly distributed polymer solutions of similar weight average molecular weights). These predictions are validated with experimental observations of the electrospinnablity of mono- and polydisperse poly(methyl methacrylate) (PMMA) solutions as well as a model bimodal blend, and through comparison to published literature data on the minimum spinnable polymer concentration for a variety of flexible long chain polymers over a range of molecular weights.

Effects of environment parameters on sol-gel transition and dry-spinnability of regenerated silk fibroin aqueous solution

Protein concentration, pH, the types and concentrations of metallic ions, and extensional flow are thought to be important environment parameters affecting the natural spinning process. In this study, we investigate the effects of the types and concentrations of metallic ions (Ca2+, Mg2+, and K+ ions), pH, and silk fibroin concentration on the sol-gel transition and the rheological behavior of a regenerated silk fibroin (RSF) aqueous solution. The results show that with an increase in the silk fibroin concentration, the weak acidic RSF aqueous solutions containing Mg2+ or Ca2+ ions undergo a phase transition to a weak gel state. Moreover, the rheological characterization of RSF aqueous solutions shows a dramatic change, and their apparent viscosities increase by almost three orders of magnitude and approach the apparent viscosity of the native dope in the silkworm gland. By using conventional pressure equipment, we investigate the dry-spinnability of weak gels. Further, we observe that the as-spun fibers exhibit a smooth surface and have inferior mechanical properties. The structure of the as-spun fibers is predominantly in a random coil or Silk I conformation.

Temperature and shear dependencies of rheology of poly(acrylonitrile‐co‐itaconic acid) dope in DMF

AbstractPoly(acrylonitrile‐co‐itaconic acid) (poly(AN‐co‐IA)) precursor required for carbon fiber production is made into a dope and spun into fibers using a suitable spinning technique. The viscosity of the resin dope is decided by the polymer concentration, polymer molecular weight, temperature, and shear force. The shear rheology of concentrated poly(AN‐co‐IA) polymer solutions in N,N‐dimethylformamide (DMF), in the $\overline M_{\rm v} $ range of 1 × 105–1 × 106 g mol−1, has been investigated in the shear rate (γ′) range of 1 × 101–5 × 104 min−1. The zero shear viscosity (η0) has been evaluated at different temperatures. The temperature dependence of zero shear viscosity conformed to the Arrhenius–Frenkel–Eyring model. The free energy of activation of viscous flow (ΔGV) values were in the range 5–32 kJ mol−1 and this value increased with increase in polymer concentration and molecular weight. A master equation for the ΔGV value of the polymer solution of any $\overline M_{\rm v} $ and concentration (c) is suggested. The power law $(\tau \, = \,k\gamma ^n )$ fitted well for the shear dependency of viscosity of these polymer solutions. The pseudoplasticity index (n) diminished with increase in polymer concentration and molecular weight. An empirical relation between viscosity (η) and $\overline M_{\rm v} $ was found to exist at constant shear rate, concentration and temperature. For each $\overline M _{\rm v} $, the equation relating n, c, and T was established. Copyright © 2008 John Wiley & Sons, Ltd.

Rheological Behavior of Dope Solutions of Poly(acrylonitrile‐co‐itaconic acid) in N,N‐dimethylformamide: Effect of Polymer Molar Mass

The rheological behavior of dope solutions of poly(acrylonitrile‐co‐itaconic acid) or poly(AN‐co‐IA) is important from the point of view of deriving the spinning conditions for good quality special acrylic fibers. The viscosity of the resin dope is dictated by the polymer concentration, molar mass, temperature and shear force. The dynamic shear rheology of concentrated poly(AN‐co‐IA) polymer dope solutions in N, N‐dimethylformamide, in the molar mass (M¯v) range of 1×105 to 1×106 g/mol, was investigated in the shear rate (γ′) range of 1×101 to 5×104 min−1. An empirical relation between η and M¯v was found to exist at constant shear rate. The dope viscosity was dependent on the molar mass and the shear rate at a given temperature (T) and concentration. The polymer molar mass index of dope viscosity (m) was calculated as functions of concentration (c), shear rate and temperature. The m values increased with shear rate and temperature. A master equation relating m, with shear rate and temperature was derived for a given dope concentration. At higher shear rates, m tends to the value of 3.4, which is close to the molar mass index of viscosity reported for molten thermoplastics. m increased significantly with shear rate and nominally with temperature, while an increase in concentration decreased it. The onset of shear thinning of the dope shifted to a lower shear rate regime with an increase in polymer concentration and the molar mass. For a given value of molar mass, the increase in viscosity of the dope solution with polymer concentration was dependent on the shear rate.

Effect of Polyvinyl Alcohol Concentration in Spinning Dope on Diameter, Beads and HHS of Produced Nanofibers

In this study it was aimed to produce nano fibers of poly vinyl alcohol PVA polymer via electrospinning ES method and to investigate the role of PVA concentration in the spinning dope on diameter, beads and HHS of produced fibers. Spinning dopes with different concentrations of PVA at rang of 5 to 20% (wt/wt on weight of solution) prepared. The requisite voltage for ES (30 kv) was supplied by a DC high voltage power supply and for collecting the fibers a grounded aluminum foil target placed 17 cm below the tip of capillary tube (spinning nozzle). The results showed that spinning dopes with PVA concentration between 8 to 12% (wt/wt) are capable of producing PVA fibers, but those below 8% (wt/wt) concentrations because of low viscosity formed droplets known as electrospray effect. Electrospinning suppressed at spinning dope concentrations above 12% (wt/wt) due to high viscosity of dope. According to the SEM photographs of electrospun PVA fibers it revealed that in higher concentrations produced nanofibers have larger diameter with less beads and HHS in compare with lower concentrations.

Effect of oxalic acid on the rheological properties of dope solution of poly[acrylonitrile-co-(methyl acrylate)-co-(itaconic acid)

The very high dope viscosity of concentrated dope of poly[acrylonitrile-co-(methyl acrylate)-co-(itaconic acid)] (with Mv = 10.67 × 105g mol−1) in DMF could be diminished significantly by the addition of oxalic acid (OXA). The change in steady shear rheological behaviour caused by OXA has been analysed for the dope using a rheometer working in the viscosity mode. The temperature dependence of η0 conformed to the Arrhenius-Frenkel-Eyring equation. ΔGv decreased marginally with OXA concentration, and the least value was observed at an OXA concentration of 0.63 % by weight. Shear thinning behaviour was observed under higher shear rates for the terpolymer solutions in the presence and absence of OXA. The pseudoplasticity index (n) showed an abrupt initial increase on addition of OXA. The OXA concentration of 0.63 % by weight was advantageous for decreasing the viscosity of the polymer dope. The reduction in viscosity is attributed to the disturbed polymer-polymer interactions by way of H-bonding of OXA with the polymer. OXA-containing dope at higher shear rate could achieve very low viscosities. Copyright © 2004 Society of Chemical Industry

Study on the effect of spinning conditions and surface treatment on the geometry and performance of polymeric hollow-fibre membranes

Hollow-fibre membranes were prepared by the wet-dry spinning technique from polyether sulfone (PES). The effect of spinning conditions such as the flow-rate of the internal coagulant and the flow-rate, composition and temperature of the polymer solution on the geometry and performance of hollow fibres was studied. In particular, five different ratios of pore former/polymer covering the range 0.2–1.0 were investigated while the polymer content was kept constant. Since the viscosity of the spinning dope affects the morphology of the hollow-fibre membrane, hollow fibres were prepared at different temperatures of the spinning dope from 25 to 60°. By scanning electron microscopy (SEM) two layers sandwiching a finger-like cavity structure were observed. Also, the surface on the bore side of the hollow fibre was modified by grafting polyethylene glycol (PEG) with γ-ray irradiation to improve the ultrafiltration performance.

The formation of asymmetric hollow fibre membranes for gas separation, using PPE of different intrinsic viscosities

A range of intrinsic viscosities of poly (2,6-dimethyl-1,4-phenylene ether) (PPE) has been used to produce skinned asymmetric hollow fibre membranes for gas separation and to study the effect of intrinsic viscosity on membrane properties. With all the PPE samples used it proved possible to produce asymmetric hollow fibre membranes with an oxygen over nitrogen selectivity of 4 to 5 at room temperature. It is shown that a clear relation exists between the intrinsic viscosity of the PPE and the attainable apparent minimal thickness of the selective layer, the skin. When using a higher intrinsic viscosity of the polymer, the minimal skin thickness of the membrane is reduced. The minimal skin thickness ranges from more than 20μm using PPE with an intrinsic viscosity of 0.25 (dl/g) to less than 0.02 μm using PPE with an intrinsic viscosity of 1.4 (dg/l), while the selectivity remains the same. As yet, the reason of the effect of intrinsic viscosity on membrane formation is not clearly understood. However, it can not be ascribed to the viscosity of the spinning dope. If the viscosity of the spinning dope is increased by an increasing polymer concentration or a higher solvent/non-solvent ration, the resulting hollow fibres have poor membrane properties. However, if the viscosity of the spinning dope is increased by increasing the intrinsic viscosity of the polymer, the resulting fibres have improved properties.

Measurement of dynamic viscoelastic properties of polymer melts and liquids by the modified rheovibron

A new technique is presented which permits the quantitative characterization of the dynamic viscoelastic properties of polymer melts and liquids. A new sample holding system with oscillatory shear platen and modification of the amplifier and oscillating unit made it possible to measure rheological properties of the viscous liquids using the Rheovibron. The dynamic shear modulus, viscosity, and internal friction of acrylic dope, and silicone fluids are obtained by using the new procedure and developed mathematical expressions. This technique will be useful in studies on the rheological properties characterization of polymer melts and liquids in conjunction with process parameters.

RHEOLOGICAL PROPERTIES AND SPINNABILITY OF SINGLE‐CELL PROTEIN/ADDITIVE MIXTURES

ABSTRACTThe rheological properties of single‐cell protein (SCP) extracted from Torula dried yeast, under a wide range of shear, and the potential for forming a continuous and uniform filament were studied. Additions of various reagents to the extracted SCP were made to investigate their effects on flow behavior and spinnability. A cone‐and‐plate viscometer was applied to obtain rheological measurements. At higher shear rates, a capillary rheometer was used and the spinnability of these SCP/additive mixtures was observed simultaneously. Among the alkali‐modified samples, pH 9 dope containing 20% SCP showed best spinnability with a moderately high apparent viscosity. When the reagents which induce intermolecular linkage were incorporated, the apparent viscosity of the alkali SCP dope changed and also the spinnability. Formaldehyde appeared to affect the dope's behavior most drastically. The formalde‐hyde/SCP dope formed a gel‐like structure at ambient temperature and rendered the highest apparent viscosity, but was poor in filament forming capability. With the addition of carboxymethyl cellulose or carrageenan, spinnability improved accompanied with a slight increase in the apparent viscosity of the SCP dope.