Microfluidic behavior in melt-spun hollow and liquid core fibers

The development of thermoplastic fibers containing a liquid core is described. Internal morphology analysis confirms that the liquid-containing core is composed of a continuous cylindrical microchannel of constant diameter. Microfluidic experiments on both liquid core and reference hollow fibers were conducted by pumping distilled water through several filaments simultaneously. The observed fluid motions are satisfactorily described by the Hagen-Poiseuille law, indicating that the hollow and liquid core fibers have internal diameters of 31.6 and 14.8 µm, respectively. Flushing the liquid core fibers with a surfactant solution efficiently removes the saturated ester initially used during the melt spinning of the fiber.     

The influence of processing parameters on the properties of melt‐spun polypropylene hollow fibers

Isotactic polypropylene hollow fibers were produced by melt spinning. Spinning speeds up to 1880 m/min were used, and sample hollowness (percentage void in cross section) ranged from 0 to 69%. The fiber samples were characterized using dynamic mechanical analysis, birefringence, tensile testing, and differential scanning calorimetry. The hollow fibers were found to have higher crystallinity, orientation, and strength than the analogous solid fibers. In general, the polymer orientation in a hollow fiber was larger than the orientation in a solid fiber, even when the spinning speed for the latter was much larger. For a fixed outer diameter, increasing the hollowness improved fiber properties. However, as hollowness was further increased, fiber properties declined slightly. At a given percentage hollowness, increased spinning speed increased modulus and tenacity. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1759–1772, 2002     

Formation of hollow fibers in the melt‐spinning process

This article reports an investigation of the formation of hollow fibers in a melt‐spinning process. Experimental results indicate that die swelling is largely responsible for a negative effect on hole formation. The factors that positively affect die swelling, including a decrease in temperature, a decrease in capillary length, and an increase in shear rate, are thus not recommended for the spinning of hollow fibers. For vinyl‐type polymers such as polypropylene, in which the apparent elasticity leads to serious die swelling, the formation of hollow fibers is more complex than that of a typical condensation polymer. Our results further demonstrate that when hollow fibers are being made in a variety of shapes (but of the same denier), spinning a polygonal hollow fiber is significantly more unstable than spinning a circular one. Moreover, an asymmetric bridge along the polygonal contour leads to a melt twist and interrupts the entire spinning process. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2896–2902, 2001     

Preparation mechanism and characterization of a novel,regulable hollow phenolic fiber

A novel hollow phenolic fiber was successfully prepared by the dissolution of the uncrosslinked core of the partially crosslinking spun filament derived from the melt spinning of the phenolic resin. A series of hollow phenolic fibers with various degrees of hollowness were obtained through different preparation processes. The hollow phenolic fibers were characterized with scanning electron microscopy, infrared spectrometry, and thermogravimetric analysis. The formation of the hollow core in the hollow phenolic fibers was attributed to partial crosslinking of the filaments during the curing process; the prepared hollow phenolic fibers had high crosslinkage after the second cure, their thermal stability was as excellent as that of the solid phenolic fiber, and their hollowness could be regulated from 5 to 85%. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Effect of annealing on the structure and properties of polyvinylidene fluoride hollow fiber by melt‐spinning

Polyvinylidene fluoride hollow fibers were prepared by melt‐spinning technique under three spinning temperatures. The effects of annealing treatment on the structure and properties of hollow fiber were studied by differential scanning calorimetry (DSC), wide‐angle X‐ray diffraction (WAXD), tensile test, and scanning electron microscopy (SEM) measurements. DSC and WAXD results indicated that the annealing not only produced secondary crystallization but also perfected primary crystallization, and spinning and annealing temperature influenced the crystallinity of hollow fiber: the crystallinity decreased with the increase of spinning temperature; 140°C annealing increased the crystallinity, and hardly influenced the orientation of hollow fiber; above 150°C annealing increased the crystallinity as well, and furthermore had a comparative effect on the orientation. The tensile tests showed that the annealed samples, which did not present the obvious yield point, exhibited characteristics of hard elasticity, and all the hollow fiber had no neck phenomenon. Compared with the annealed sample, the precursor presented a clear yield point. In addition, the annealed samples had a higher break strength and initial modulus by contrast with the precursor, and the 140°C annealed sample showed the smallest break elongation. SEM demonstrated the micro‐fiber structure appeared in surface of drawn sample. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 935–941, 2007     

Shaping conjugated hollow fibers using a four‐segmented arc spinneret

This study discusses a light‐weight bicomponent hollow fiber that is formed from a low‐density material on the inside, such as polypropylene (PP), and a regularly dyeable material outside, such as polyterephthalate (PET) or nylon. Finite elements and the Optimesh‐3D remeshing approach are adopted to identify the main controlling factors of spinning the sheath‐core hollow fiber without the consideration of winding actions are performed, based on a four‐segmented arc spinneret design. The results indicate that the deflection of melt streams under the spinneret is a major factor that controls the gluing of the gap between arc segments. A greater mismatch between the viscosities of the sheath and the core causes a greater deflection and increases the likelihood of gluing events. Beyond deflection, die swelling under the spinneret is another issue of concern in the processing of bicomponent hollow fibers. Finally, the simulation results are compared with experimental data, and the most appropriate conditions for forming a PET/PP hollow fiber were obtained. POLYM. ENG. SCI., 2011. © 2010 Society of Plastics Engineers     

Stress-induced structure transition of syndiotactic polypropylene via melt spinning

Syndiotactic polypropylene (sPP) fiber was prepared by melt spinning with the taken-up velocity of 200-700 m/min, the conformation and crystallization of which were systematically investigated by a combination of Fourier transform infrared (FTIR) spectroscopy, wide-angle X-ray diffraction (WAXD) and differential scanning calorimetry (DSC). The results indicated that sPP fibers consist of form I crystal with helical conformation at the spinning velocity of 200-300 m/min, and the crystallinity and orientation are improved with the increase of spinning velocity in this range. As the spinning velocity exceeds 300 m/min, sPP fibers contain mainly mesophase with trans-planar conformation and the content of form I decreases correspondingly. The crystallization behavior of sPP fiber with spinning velocity is different from that of most other crystalline polymers, i.e., the theory of orientation-induced crystallization is not well conformed to. For sPP, form I comprising of helical conformation is thermodynamically stable, though extensional stress can lead to transition from helical to trans-planar conformation, which is not favorable for the crystallization of form I.     

Spinning speed–throughput rate relationships for polyester,nylon, and polypropylene fibers

The relationship between spinning speed and throughput rate has been investigated for fibers having the same fiber denier in the drawn state when produced by melt spinning of poly(ethylene terephthalate), nylon 6, and polypropylene polymers over a range of take-up speed (750–3000 m min^-1) and throughput rate. To understand the structural origin of the relationship, a limited amount of characterization of structure and properties of the as-spun and drawn fibers was also done. A comparison of the results for the three polymers shows that while the increase in productivity with increase in spinning speed is relatively less for polyester and nylon 6, it is quite high for polypropylene. The birefringence data show that while molecular orientation increases rapidly with increasing wind-up speed in polyester and nylon 6, the rate of increase is relatively less in the case of polypropylene. The possible reasons for the observed differences in behavior are discussed. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:1773–1788, 1997     

Influence of the cross‐sectional shape on the structure and properties of polyester fibers

The effects of the fiber cross‐sectional shape on the structure and properties of polyester fibers were investigated. Fully drawn yarn (FDY) polyester fibers (167 dtex and 48 filaments) were produced under the same spinning conditions used in a spinning plant. The only difference between the fibers was their cross‐sectional shapes. Four different cross‐sectional shapes were chosen for the experimental work: round, hollow‐round, trilobal, and hollow‐trilobal. The crystallinity and values of the maximum stress, maximum strain, modulus, yield stress, shrinkage in boiling water, and unevenness of the fibers were determined. The difference in the cross‐sectional shapes influenced the modulus, maximum strain, yield stress, and shrinkage in boiling water. No effects on the crystallinity and maximum stress were observed. The results suggested that the hollow fibers had higher amorphous orientation than the full fibers. The hollow‐round fiber had the highest unevenness value. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2615–2621, 2007     

Preparation and radar wave absorbing characterization of bicomponent fibers with infrared camouflage

Sheath‐core bicomponent fibers were prepared by a general melt‐spinning method with polypropylene chips and various particles. The melt‐spun fibers were characterized by DSC and mass specific electrical resistance (MSER) apparatus. The electromagnetic constant was measured using a network analyzer and the absorbing wave effect was evaluated by an arch method. The results of the DSC thermogram indicated that the crystallinity of polypropylene containing particles in the core‐part slightly increased first and then kept steadily with the particles content increase. Nanoparticles in the sheath‐part did not make the crystallinity of fibers change markedly. The MSER of fibers rapidly decreased with the metal particles input. The complex permeability of fibers with Ba/Mn‐Zn ferrite was improved compared with that of fiber with single Mn‐Zn ferrite and the complex permittivity of fiber containing the 20 wt % Ba/Mn‐Zn ferrite increased with the increasing bronze content. The fibers filled with the Ba/Mn‐Zn ferrite and bronze particles had good radar absorbing effect. The input of Al particles in the sheath‐part of the fibers showed a limited effect on the radar wave absorbing properties of the fibers. The lowest infrared emissivity of the fibers including 15 wt % Al particles in sheath‐part reached 0.62. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 2180–2186, 2007     

Melt spinning and characterization of hollow fibers from poly(4-methyl-1-pentene)

In this article, the melt spinning behavior of poly(4-methyl-1-pentene) (PMP) hollow fibers (HF) is examined. The melt spinning trials are carried out on a pilot scale melt spinning plant with different settings while a 10-hole 2c-shaped spinneret is used. It is found that the winding speed mainly affects the outer fiber diameter. The influence of different melt spinning parameters is investigated, in particular temperatures, take-up velocities, and the use of quench air. For this purpose, the shape and crystalline structure of the fibers are analyzed using a light microscope, a scanning electron microscope, and wide-angle X-ray scattering. The shape of the fibers is mainly influenced by the temperature settings in the melt spinning process. As a reasonable lower limit, a melt spinning temperature of 280°C is identified. Concerning the crystallinity, a saturation going along with a slight reduction of the polymer chain orientation is observed at elevated take-up velocities.     

Preparation and characterization of polypropylene/silver nanocomposite fibers

Bicomponent sheath‐core fibers were prepared by a general melt‐spinning method with polypropylene chips and silver nanoparticles. The melt‐spun fibers were characterized by DSC, WAXS and SEM. The antibacterial effect was evaluated by an AATCC 100 test, a quantitative method. The results of the DSC thermogram and the intensity pattern of X‐ray diffraction indicated that the crystallinity of polypropylene including silver nanoparticles was slightly decreased compared with that of pure polypropylene fibers. SEM micrographs showed that the average diameter of the silver nanoparticles was approximately 30 nm and some particles had aggregated. The fibers, which contained silver in the core part, did not show antibacterial effects. Fibers with added silver in the sheath part, however, exhibited excellent antibacterial effects. Copyright © 2003 Society of Chemical Industry     

聚丙烯纺丝中纤维不均匀性的研究

本文研究了聚丙烯树脂、纺丝条件等对聚丙烯纺丝过程中纤维不均匀性的影响。试验证明仅仅从流变学的角度来研究聚丙烯纺丝过程中纤维直径的不均匀性是不够的,因为初生纤维的屈服应力和初始模量的不均匀性主要取决于其取向的不均匀性和结晶性的差别。因而为了改善初生纤维的牵伸性能、提高聚丙烯纤维的质量,应该以控制初生纤维的织构和织构的均匀性为原则来合理选择聚丙烯树脂原料和控制纺丝工艺条件。     

PBT/PET conjugated fibers: Melt spinning,fiber properties,and thermal bonding

This work examines the PBT/PET sheath/core conjugated fiber, with reference to melt spinning, fiber properties and thermal bonding. Regarding the rheological behaviors in the conjugated spinning, PET and PBT show the smallest difference between their melt‐viscosity at temperatures of 290°C and 260°C respectively, which has been thought to represent optimal spinning conditions. The effect of processing parameters on the crystallinity of core material‐PET was observed and listed. In order of importance, these factors are the draw ratio, the heat‐set temperature, and the drawing temperature. The crystallinity of sheath material‐PBT, however, can be considered to be constant, independent of any processing parameters. The bulk orientation, rather than the crystallinity of PET core, dominates the tenacity of PBT/PET sheath/core fiber. Moreover, heat‐set treatment after drawing is recommended to yield a highly oriented conjugated fiber. With respect to thermal bonding, PBT/PET conjugated fibers processed via high draw ratio but low‐temperature heat setting can form optimal thermal bonds at a constant bonding temperature of 10°C above the T_m of PBT.     

Melt spinning of isotactic polypropylene: Structure development and relationship to mechanical properties

An extensive experimental study of structure development during the melt spinning of polypropylene and is as-spun polypropylene filaments is reported. Five polymers representing different molecular weights and polymerization methods were studied. WAXS, SAXS, and birefringence measurements were used to characterize the structure of the filaments. Spinning through air gives rise to monoclinic crystalline structures and spinning into cold water, the paracrystalline smectic form. Both crystalline and amorphous orientation factors were found to correlate with spinline stress for the different polymers studied. Mechanical properties of as-spun fibers such as modulus, yield strength, tensile strength, and elongation to break also correlate with spinline stress.     

Radial crystallization difference of melt-spun polypropylene fiber along spinning line

The radial crystallization difference of polypropylene (PP) fiber along spinning line was investigated via synchrotron radiation microbeam X-ray diffraction (μ-XRD) analysis for the first time. Running fibers were collected at different spinning line positions to study its radial crystallization difference. The distribution of crystallinity, crystal form, and crystal size of PP fiber were obtained based on peak deconvolution. The relation between radial crystallization difference and processing condition was also investigated. The results indicate that the crystallinity of PP in the center region is found higher than the surface due to the radial temperature gradient during melt spinning, and the structure of fiber is highly sensitive to the radial temperature gradient. The crystallinity increased along spinning line and reaches a steady rate after 50 cm of spinning line position. The crystallite size increased before 50 cm of spinning line position and has a slight decrease after 50 cm due to the growth and splitting of crystal. These results display a 2D view of crystallization development of fiber during the melt spinning and give us a basic knowledge about the relation between structure evolution and processing conditions both in axis and radial directions. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47175.     

Melt spinning of β‐phase poly(vinylidene fluoride) yarns with and without a conductive core

When poly(vinylidene fluoride) (PVDF) is to be used as a piezoelectric material, the processing must include the formation of polar β‐phase crystallites, as well as the application of electrically conducting charge collectors, that is, electrodes. In this article, results from the melt spinning of PVDF yarns and a novel bicomponent PVDF‐yarn with a conductive carbon black/polypropylene (CB/PP) core are presented. Melt spinning has been done under conditions typical for industrial large‐scale fiber production. The effects on the resulting crystalline structure of varying the spinning velocity, draw rate, and draw temperature are discussed. The results show that, for maximum α‐to‐β phase transformation, cold drawing should take place at a temperature between 70 and 90°C, and both the draw ratio and the draw rate should be as high as possible. It was observed that the cold drawing necessary to form β‐phase crystallinity simultaneously leads to a decrease in the core conductivity of the bicomponent yarns. In this work, the melt spinning of bicomponent fibers with high‐β‐phase PVDF in the sheath and a CB/PP core was successfully accomplished. The core material remained electrically conductive, paving the way for the use of a CB‐polymer compound as inner electrode in the melt spinning of piezoelectric bicomponent fibers. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Structure and properties of thermotropic liquid crystal polymer and poly(ethylene 2,6‐naphthalate) blend fibers

BACKGROUND: The melt blending of thermotropic liquid crystal polymers (TLCPs) using conventional thermoplastics has attracted much attention due to the improved strength and tensile modulus of the resulting polymer composites. Moreover, because of their low melt viscosity, the addition of small amounts of TLCPs can reduce the melt viscosity of polymer blends, thereby enhancing the processability. RESULTS: In this study, TLCP/poly(ethylene 2,6‐naphthalate) (PEN) blend fibers were prepared by melt blending and melt spinning to improve fiber performance and processability. The relation between the structure and the mechanical properties of TLCP/PEN blend fibers and the effect of annealing on these properties were also investigated. The mechanical properties of the blend fibers were improved by increasing the spinning speed and by adding TLCP. These properties of the blend fibers were also improved by annealing. The tensile strength of TLCP5/PEN spun at a spinning speed of 2.0 km h^?1 and annealed at 235 °C for 2 h was about three times higher than that of TLCP5/PEN spun at a spinning speed of 0.5 km h^?1. The double melting behavior observed in the annealed fibers depended on the annealing temperature and time. CONCLUSION: The improvement of the mechanical properties of the blend fibers with spinning speed, by adding TLCP and by annealing was attributed to an increase in crystallite size, an increase in the degree of crystallinity and an improvement in crystal perfection. The double melting behavior was influenced by the distribution in lamella thickness that occurred because of a melt‐reorganization process during differential scanning calorimetry scans. Copyright © 2007 Society of Chemical Industry     

聚丙烯／新型聚烯烃弹性体皮芯型复合纤维的纺靛

对新型聚烯烃弹性体Vistamaxx进行了差示扫描热（DSC）、核磁共振（NMR）分析，结果表明：弹性体Vistamaxxr的软化点较低，熔点与聚丙烯接近，主要由等规丙烯组成，其中含有少量聚乙烯，这些乙烯单元的存在破坏了原有丙烯单元的结晶，使其具有较好的弹性，以Vistamaxxr为芯层、丙烯为皮层，采用熔融纺丝工艺制备出了聚丙烯/Vistamaxxr皮芯复合纤维，确定了最佳熔融纺丝工艺，皮芯复合比为50/50,纺丝温度为230℃,泵供量为12-20g/min,卷绕速度可在800-1000m/min内调节，与聚丙烯纤维相比，此皮芯复合纤维具有更好的韧性.     

Controlling of threadline dynamics via a novel method to develop ultra‐high performance polypropylene filaments

A detailed study was conducted to investigate the effects of horizontal isothermal bath (hIB) on the production of ultra‐high performance polypropylene filaments. Two different commercial PP polymers were used with the melt flow rate of 4.1 and 36 g/10 min. The optimum process conditions depended on polymer molecular weight. Fibers showed distinct precursor morphology for each at each optimum process condition. However, two sets of filaments demonstrated similar fiber tenacity and modulus of about 7 and 75 g d^?1, respectively, for as‐spun and more than 12 g d^?1 for tenacity and more than 190 g d^?1 for modulus values of drawn fibers after just 1.49 draw ratio. The mean value for the modulus after the drawing process for the high melt flow rate was 196 g d^?1. The theoretical modulus of PP is 35–42 GPa¹⁹, (275–330 g d^?1), shows the hIB fiber's modulus performance is approaching its theoretical maximum value. Fibers had greatly improved thermal properties, degree of crystallinity, crystalline and amorphous orientation factors. The hIB spinning system produced highly oriented and predominantly amorphous structure for as‐spun fibers and a well‐defined, highly oriented crystalline fibrillar and amorphous structure after drawing process with the draw ratios lower than 1.5. POLYM. ENG. SCI., 55:327–339, 2015. © 2014 Society of Plastics Engineers