Stability of Newtonian-PTT coextrusion fiber spinning

Linear stability analysis has been applied to a coextrusion fiber spinning flow that consists of a Newtonian fluid as a core layer and a Phan-Thien/Tanner (PTT) fluid as a skin layer. These two chosen fluids show entirely different rheological behaviors. The stability of this coextrusion system was affected by the choice of three characteristic parameters: the skin layer fraction (f), the extensional parameter (ϵ), and the shear thinning parameter (ξ) in the Phan-Thien/Tanner model. The linear stability results indicate that the viscoelastic skin layer (PTT fluid) has a stabilizing effect that delays the onset of draw resonance. Under fixed compositions (f is fixed), the stability envelopes changed from upturned curves to flattened ones as extensional force dominated the system. The neutral stable curves closed to the horizontal line at a critical draw ratio of around 20, showing similar behavior to a Newtonian fluid where the system has a very high Deborah number or it is dominated by shear thinning effects.     

Interfacial flow instability in multilayer coextrusion

In coextrusion of multilayer film and sheet, one type of flow instability which can occur is a wavelike distortion of the interface under certain coextrusion conditions. Severe instability can cause intermixing of the layers, particularly in thin skin coextrusion. Observations have shown that the onset of instability is associated with a “critical interfacial shear stress”. This paper describes a mathematical model of non-Newtonian multilayer flow which was used to correlate experimental observations.     

Computer simulation of steady polymer melt spinning

An interactive computer simulation program has been developed for steady polymer melt spinning. The program includes inertial and air drag effects, and fluid viscoelasticity is described by the Phan-Thien and Tanner constitutive equation. Simulation results are compared with experiments by George on poly(ethylene terephthalate) (PET) at spinning speeds of 1000 and 3000 m/min, and the effect of elasticity under other spinning conditions is explored with computer experiments.     

Theoretical aspects of fiber spinning

A new coordinate expansion based on a Taylor series is used to derive the one‐dimensional approximation to unsteady isothermal jet flows. The expansion procedure is carried out for an isothermal, Newtonian jet with no surface tension and air drag, and it can be used to derive a higher order approximation to the flow field. Two new formulations have been derived for the eigenvalue problem for fiber spinning stability for negligible inertia and gravity. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 986–993, 2004     

Two directional coextrusion flow of two molten polymers in flat dies

A theoretical study has been carried out of the two directional isothermal flow of two molten polymers in a flat die. The viscous behavior of each fluid is described by a power-law. Using an iterative finite difference method, a numerical program predicts the influence of geometrical and Theological parameters on the variations of the interface position. Theoretical values are in good agreement with experimental results obtained on a fish-tail die. In the case of a coat hanger-die, the mean value of the interface position is correct, but the general shape may be quite different.     

A study of fiber extrusion in wet spinning. II. Effects of spinning conditions on fiber formation

A study is carried out to investigate the effects of spinning conditions on fiber formation in the wet-spinning process. The spinning conditions studied are free velocity (and hence free diameter), throughput rate, maximum take-up velocity, jet stretch (the ratio of take-up velocity to free velocity), and filament tension. The coagulating bath temperature and concentration are varied, and three spinnerette diameters are used. The spinning dope is an aqueous solution of polyacrylonitrile in sodium thiocyanate. The present study shows that the coagulating bath concentration influences the spinning tension and maximum take-up velocity. Two thread breakage mechanisms are postulated which take into account the rate of coagulation, spinning tension, and thread velocity. An attempt is made to predict the concentration profile of solvent in the moving filament by simultaneously solving the mass and force balance equations, in which the increase in elongational viscosity along the spinning way is assumed to be mainly due to the hardening process.     

An analytical model for steady coextrusion of viscoplastic fluids in thin slit dies with wall slip

Coextrusion is widely used to fabricate multilayered products with each layer providing a separate functionality, including barrier resistance to gases, strength, and printability. Here an analytical model of the coextrusion die flow of two incompressible, viscoplastic fluids in a slit die, subject to nonlinear wall slip and under fully developed and isothermal conditions, is developed to allow the prediction of the steady‐state velocity and shear stress distributions and the flow rate versus pressure gradient relationship. The resulting model is applied to the coextrusion of two layers of viscoplastic fluids in a thin rectangular slit die (slit gap, h ? slit width, W). The analytical solution recognizes a number of distinct flow conditions (eleven cases) that need to be treated separately. The solutions for all eleven cases are provided along with an apriori identification methodology for the determination of the applicable case, given the shear viscosity and wall slip parameters of the two viscoplastic fluids, the slit geometry and the flow conditions. Simplifications of the model would provide the solutions for the fully developed and isothermal coextrusion flows of any combination of Hershel‐Bulkley, Bingham, power‐law and Newtonian fluids with or without wall slip at one or both walls of the slit die. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers     

熔体直纺涤纶平行纺管道输送的设计

介绍了熔体直纺涤纶平行纺输送管道设计过程,及熔体流量、熔体管道压力降、熔体管道停留时间、管道壁厚的选择等计算方法及设计要点。     

Simulations of instability in fiber spinning of polymers

This work determines the critical regimes beyond which the melt fiber spinning for noncrystallizable polymeric liquids becomes unstable. The critical draw ratio of the process is established using linear stability analysis for both isothermal and nonisothermal fiber spinning regimes. In addition, nonlinear isothermal analysis describes the complete range of the stable and unstable conditions for fiber spinning. Unlike previous studies, this research uses quite realistic viscoelastic constitutive equations extensively tested for five polymer liquids, which provides a good comparison of our calculations with available experimental data. POLYM. ENG. SCI., 2010. © 2010 Society of Plastics Engineers     

Analysis of steady conditions for spinning of viscose cord fibre

Production of viscose cord fibre was analyzed. Two basic conditions for spinning the fibre were determined. A technological interpretation of the identified conditions was given. A method for determining the optimum amount of surfactants added in the stage of cellulose mercerization was proposed. The results of processing experimental batches of cellulose without preliminary treatment with Proxanol CL-3 are reported. A number of changes in the organization of introduction of SF in the technological process at the Svetlogorsk Khimvolokno Industrial Association was proposed.Ivanovo Institute of Chemical Technology. Translated from Khimicheskie Volokna, No. 3, pp. 23–26, May–June, 1994.     

Stability of fiber spinning of power-law fluids

A stability analysis of fiber spinning of isothermal power-law fluids has been carried out. The analysis for purely viscous fluids indicates that the critical extension ratio increases with an increase in power-law constant q above 1. For q greater than approximately 1.5, very high values of critical extension ratio are obtained. A stability analysis in the presence of viscous and inertial forces indicates that for q > 1 critical extension ratio can be correlated to a quantity Rq = q ? 1 + 3Re, wherein Re is the Reynolds number. For the values of Rq greather than approximately 0.5, very high values of critical extension ratios are obtained.     

熔体直纺上纺制多功能聚酯纤维的设备改造

介绍了在熔体直纺生产线上,生产在线可控多功能聚酯纤维的生产工艺流程、设备改造,熔体直纺在线添加技术的关键点,采用球窝型动态混合器对添加组分进行均匀混合。改造后生产高附加值的功能纤维,产品品质达到用户要求。     

An integrated numerical study of coextrusion flow inside and outside the die

The three‐dimensional coextrusion flow of two polymer melts is solved over the die‐extrudate region using the finite element method. As elastic recovery is known to be the main source of extrudate swelling, a viscoelastic constitutive model (the Phan‐Thien‐Tanner or PTT model) is adopted to characterize the rheological behavior of the elastomers. A major challenge in the simulation of multilayer flow inside and outside the die is to update multiple moving surfaces (material interface and extrudate free surface) simultaneously. This difficulty is resolved by introducing a two‐step updating algorithm which decouples the iterations of the interface and the free surface. The effects of extrudate swelling and bending on interface deformation are investigated herein, together with the interface shape dependency on flow elasticity. The numerical method is also applied to an industrial profile and the simulation result is in quantitative agreement with the experimental coextrusion data. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43522.     

熔体静电纺丝的工艺条件对纺丝纤维直径的影响

主要研究纺丝温度、纺丝电压、接收距离等参数对聚丙烯(PP)熔体静电纺丝纤维直径的影响。采用了只变一个参数,其它参数固定的常规实验方法。在实验条件范围内,随着纺丝温度的升高,纤维的平均直径逐渐减小,得到PP的最佳纺丝温度240℃。在固定电压的情况下,得到最佳接收距离7cm。在固定接收距离的情况下,随着电压的增加,电场中的喷射流熔体受到的电场力逐渐增大,得出最佳纺丝电压35kV。     

抗起球腈纶纺丝工艺的优化

采用纺丝工艺调整法生产抗起球腈纶。结果表明:在抗起球腈纶生产工艺基础上,选择孔径相对较小的喷丝板,提高负拉伸比,有利于纤维成形;干燥机丝束堆积密度下调3%,湿球温度上调至77～80℃,采用加压过热蒸汽为热定型介质,热定型温度110～115℃,生产的抗起球腈纶抗起球级数达4.0～4.5。     

Fabrication of segmented cladding fiber by bicomponent spinning

Fabrication of segmented cladding fiber (SCF) by bicomponent spinning was proposed in this article. In the new designed spin pack, we considered the high refractive component of cladding and core as a whole to control the cross section of the fiber. Quenching system in current bicomponent melting spinning system was modified according to the requirement of quenching fiber with a large size. The polymer SCF with required cross section was successfully fabricated using polycarbonate and polymethyl methacrylate. The transmission loss in the wavelength of 500–1000 nm was tested by the cut‐back method. The result showed that the transmission loss of the obtained fiber was comparatively high, being up to 30 dB/m. The output light pattern of the obtained fiber of 60 cm was collected by using a charge‐coupled device camera with laser light of 532 nm as the input. The output light pattern for the far field was a uniform circle and that for the near field was similar to the cross‐section designed. The results showed that the obtained fiber was still a multimode optical fiber because of the comparatively large refractive index difference between the two materials used. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Gel spinning of PVA/SWNT composite fiber

Single wall carbon nanotubes (SWNT), polyvinyl alcohol (PVA), dimethyl sulfoxide (DMSO) and water, homogeneous dispersion has been prepared by stirring and sonication. This dispersion was extruded into fiber via gel spinning. The modulus of the PVA/SWNT (3 wt%) composite fiber was 40% higher than that of the control PVA gel spun fiber. Fiber structure and properties have been studied. The PVA orientation in the control and the composite fibers were comparable while the composite fiber exhibited lower crystallinity.