Structure evolution of melt‐spun poly(vinyl alcohol) fibers during hot‐drawing

The drawability of melt‐spun poly(vinyl alcohol) (PVA) fibers and its structure evolution during hot‐drawing process were studied by differential scanning calorimetry (DSC), two dimensional X‐ray diffraction (2‐D WAXD) and dynamic mechanical analysis (DMA). The results showed that the water content of PVA fibers should be controlled before hot‐drawing and the proper drying condition was drying at 200°C for 3 min. PVA fibers with excellent mechanical properties could be obtained by drawing at 200°C and 100 mm/min. The melt point and crystallinity of PVA fibers increased with the draw ratio increasing. The 2‐D WAXD patterns of PVA fibers changed from circular scattering pattern to sharp diffraction point, confirming the change of PVA fibers from random orientation to high degree orientation. Accordingly, the tensile strength of PVA fibers enhanced by hot‐drawing, reaching 1.85 GPa when the draw ratio was 16. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Enhancing mechanical properties of gel‐spun polyvinyl alcohol fibers by iodine doping

High strength polyvinyl alcohol (PVA) fibers with a conventional degree of polymerization of 1500 were prepared by doping iodine with PVA spinning solution. The iodine‐doped PVA (I‐PVA) aqueous solution was extruded into cold methanol that provides dark purple PVA‐iodine complex gel fibers. Only a small amount of iodine was required to enhance drawability and molecular orientation by reducing the interaction between PVA chains. An increase of ca. 10% in the maximum draw ratio of the doped fibers compared with that of undoped PVA translated into values for the tensile strength, 2.2 Giga‐Pascal (GPa), and initial modulus (47 GPa) that were more than 30% higher than those of the neat PVA fiber. Easier chain slippage of molecules in the amorphous segments of the I‐PVA fiber during drawing leads to increased orientation in these segments, which is believed to be the source of the improvements in mechanical properties. POLYM. ENG. SCI., 2011. © 2010 Society of Plastics Engineers     

Influence of interchain forces and supermolecular structure on the drawing behavior of nylon 66 fibers in the presence of supercritical carbon dioxide

The drawing behavior and mechanical properties of as‐spun and highly oriented nylon 66 fibers drawn in supercritical carbon dioxide (SCCO₂) were investigated. Conditions including different temperatures, CO₂ pressures, and plasticizers with different polarity were systematically studied. Results indicate that CO₂ is an efficient plasticizer for as‐spun nylon 66 fibers as shown by decreases in the draw stress. In contrast, CO₂ shows only a slight influence on the drawability of highly oriented nylon 66 fiber. The effect of other plasticizers such as water, methanol, and ethanol on the drawability of nylon 66 fibers is very similar to that of CO₂. Tenacity and modulus of one‐stage drawn fibers were less than 0.8 and 5.0 GPa, respectively. Fibers with the highest tenacity and modulus, 0.96/5.04 and 1.06/5.04 GPa, were obtained by two‐stage drawing in SCCO₂ from as‐spun and drawn nylon 66 fibers, respectively. The main reason for the extremely low draw ratios (<6.0) of nylon 66 fibers was the presence of hydrogen bonds in the crystalline phase. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2282–2288, 2004     

High strength polyethylene fibers from high density polyethylene/organoclay composites

High strength fibers were prepared from high density polyethylene (HDPE)/organically modified montmorillonite (OMMT) composites. X‐ray diffraction study revealed that the composites were of conventional or phase‐separated type. As‐spun composite fibers were found to have higher drawability than as‐spun HDPE fiber. As a result of an increased drawability, fibers with much higher mechanical properties were obtained. The highest modulus and tensile strength obtained in the present study were 38 GPa and 1.7 GPa, respectively. Study of internal morphology suggests that the role of OMMT is to suppress a defect formation and allows the fiber to be drawn to higher draw ratio. Analysis of the mechanical properties of the fibers using a Griffith type relationship suggested that the fibers have much smaller defects and the predicted attainable strength for the fiber is much higher than that previously predicted for melt‐spun and hot drawn fiber. POLYM. ENG. SCI., 47:943–950, 2007. © 2007 Society of Plastics Engineers     

Preparation of poly(lactic acid) fiber by dry‐jet‐wet‐spinning. I. Influence of draw ratio on fiber properties

Poly(lactic acid) fiber was prepared by dry‐jet‐wet spinning of the polymer from chloroform solution and with methanol as the precipitating medium. The as‐spun fiber was subsequently made into high strength fiber by two‐step process of drawing at a temperature of 90°C and subsequent heat setting in the temperature range of 120°C. The draw ratio had significant influence on the crystallinity and the tensile strength of the fiber. The fiber with the tenacity of 0.6 GPa and modulus of 8.2 GPa was achieved at a draw ratio of 8. The differential scanning calorimetry revealed an increase in the glass‐transition temperature with the increase in the draw ratio, which suggests the orientation of chains during the drawing process. The surface morphology of the filament as revealed by scanning electron microscopy shows that fibers are porous in nature, but a significant reduction in the porosity and pore size of the fiber was observed with the increase in the draw ratio. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1239–1246, 2006     

Preparation of high-strength poly(vinyl alcohol) fibers by crosslinking wet spinning

High-strength poly(vinyl alcohol) (PVA) fiber was obtained by the crosslinking wet-spinning technique, which is an improved technique of the conventional non-crosslinked type wet-spinning of PVA. High tensile strength as well as high Young's modulus was achieved by introduction of the borate ion-aided crosslinks during the coagulation process. The drawability of the as-spun fiber greatly depends on the fiber thickness. The thinner the fiber, the higher the drawability. Since thinner fiber is subject to a very high shear rate on extrusion, the crosslinks introduced are believed to maintain topological memory of the oriented chains, which have a low density of entanglements. This allows drawing the fiber to a higher draw ratio. The strength and Young's modulus of the resultant highly drawn PVA fiber were achieved to be 22 g/d (2.3 GPa) and 430 g/d (50 GPa), respectively. The mechanism of the spinning was discussed and the spinning condition was carefully examined in order to optimize the final mechanical properties of the PVA fibers.     

Spinning and drawing properties of ultrahigh‐molecular‐weight polyethylene fibers prepared at varying concentrations and temperatures

The concentrations and temperatures of ultrahigh‐molecular‐weight polyethylene (UHMWPE) gel solutions exhibited a significant influence on their rheological and spinning properties. The shear viscosities of UHMWPE solutions increased consistently with increasing concentrations at a constant temperature above 80°C. Tremendously high shear viscosities of UHMWPE gel solutions were found as the temperatures reached 120–140°C, at which their shear viscosity values approached the maximum. The spinnable solutions are those gel solutions with optimum shear viscosities and relatively good homogeneity in nature. Moreover, the gel solution concentrations and spinning temperatures exhibited a significant influence on the drawability and microstructure of the as‐spun fibers. At each spinning temperature, the achievable draw ratios obtained for as‐spun fibers prepared near the optimum concentration are significantly higher than those of as‐spun fibers prepared at other concentrations. The critical draw ratio of the as‐spun fiber prepared at the optimum concentration approached a maximum value, as the spinning temperature reached the optimum value of 150°C. Further investigations indicated that the best orientation of the precursors of shish‐kebab‐like entities, birefringence, crystallinity, thermal and tensile properties were always accompanied with the as‐spun fiber prepared at the optimum concentration and temperature. Similar to those found for the as‐spun fibers, the birefringence and tensile properties of the draw fibers prepared at the optimum condition were always higher than those of drawn fibers prepared at other conditions but stretched to the same draw ratio. Possible mechanisms accounting for these interesting phenomena are proposed.     

Effect of coagulation conditions on solvent diffusions and the structures and tensile properties of solution spun polyacrylonitrile fibers

Polyacrylonitrile (PAN) fibers were spun by solution spinning. In this work, two coagulation compositions, dimethyl sulfoxide (DMSO)/water and methanol, were used, and coagulation temperatures were varied from ?20 to 0 to 20 °C. The coagulation compositions and temperatures strongly affected the solvent diffusion processes, the structures of as‐spun fibers, and the tensile properties of final drawn fibers. When DMSO/water was used as coagulation bath, non‐solvent (water) diffused into PAN fibers and led to a quick PAN solidification. By comparison, when methanol was used as coagulation bath, no or minimal amount of methanol diffused inward to the fibers. The different solvent diffusion behaviors in DMSO/water and methanol baths led to different structures of as‐spun PAN fibers. It was observed that the tensile properties of final drawn fibers strongly depended on the coagulation conditions. When methanol was used as coagulation bath and the bath temperature was ?20 °C, PAN fibers was found to possess the best tensile properties, a tensile strength of 0.89 GPa and young modulus of 20.4 GPa. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 44390.     

Structure and processability of iodinated poly(vinyl alcohol). IV. Drawability of the films iodinated at solution before casting

The drawability of iodinated at solution before casting (IBC) polyvinyl alcohol films prepared by casting aqueous solutions of 10 wt % PVA containing 15.2, 39.8, 83.2, 117.0, and 140.1% was examined with a tensile tester at 20–60°C. The tensile behavior of IBC films showed that the yield and breaking loads were much lower, and the breaking elongation was even higher than those of the unoriented iodinated after casting (IAC) films as well as the untreated PVA films. The maximum draw ratios of the films with the weight gain of 15.2, 39.8, 83.2, 117, and 140.1% were 4.5, 5.5, 8.5, 8.0, and 7.5, respectively, which were achieved at 20°C in all. The crystallinity of all films increased by the maximum draw, regardless of crystallinity before drawing. The crystalline structure was recovered to the original PVA crystalline lattice by deiodination. Amorphous orientation and initial moduli increased with the maximum draw ratio, while the orientation of crystals was constant. The orientation and moduli increased up to the weight gain of 83.2%, whose highest draw ratio and initial modulus were 8.5 and of 7.1 GPa, respectively, and then decreased. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Morphology and viscoelastic properties of melt‐spun HDPE/hydrotalcite nanocomposite fibers

Viscoelastic properties of nanocomposite fibers of high density polyethylene (HDPE) and organically modified hydrotalcite were studied. Neat and nanofilled HDPE fibers (with nanofiller content between 0.5 and 3 wt%) were produced by melt spinning and hot‐drawing at different draw ratios up to 20. Effect of temperature on storage modulus, loss modulus, and creep compliance were compared. Rising nanofiller content and/or drawing ratio accounted for an increase in storage modulus in the glassy (i.e., below the γ transition at −100°C) as well as in the rubbery state of non‐crystalline regions. The α relaxation temperature read‐off for the maximum of the loss modulus peak ranged from 20 to 60°C being dependent on frequency, filler content and draw ratio. Sumita model was successfully applied to evaluate the effective volume fraction of the dispersed phase; maximum fraction of immobilized matrix was observed for the composite with 1 wt% of nanofiller. Creep behavior was evaluated by fitting experimental data with the Burgers model. The addition of a small amount of well‐dispersed hydrotalcite (0.5–1 wt%) had a beneficial effect on the creep resistance of drawn fibers at room temperature as well as at 70°C. TEM analysis evidenced a good dispersion of 0.5% nanofiller in as‐spun fibers and improved interfacial adhesion after drawing. The best mechanical properties were observed for the composition with 1 wt% of hydrotalcite, due to combined effects of nanofiller reinforcement and stiffening produced by hot drawing. POLYM. COMPOS., 288–298, 2016. © 2014 Society of Plastics Engineers     

Effect of zone drawing on the structure and properties of melt‐spun poly(trimethylene terephthalate) fiber

Melt‐spun poly(trimethylene terephthalate) (PTT) fibers were zone‐drawn and the structures and properties of the fibers were investigated in consideration of the spinning and zone‐drawing conditions. The draw ratio increased up to 4 with increasing drawing temperature to 180°C, at a maximum drawing stress of 220 MPa. Higher take‐up velocity gave lower drawability of the fiber. The PTT fiber taken up at 4000 rpm was hardly drawn, in spite of using maximum drawing stress, because a high degree of orientation had been achieved in the spinning procedure. However, an additional enhancement of birefringence was observed, indicating a further orientation of PTT molecules by zone drawing. The exotherm peak at 60°C disappeared and was shifted to a lower temperature with an increase in the take‐up velocity, which means that the orientation and crystallinity of the fiber increased. The d‐spacing of (002) plane increased with increasing take‐up velocity and draw ratio, whereas those of (010) and (001) planes decreased. In all cases, the crystal size increased with take‐up velocity and draw ratio. The cold‐drawn PTT fiber revealed a kink band structure, which disappeared as the drawing temperature was raised. The physical properties of zone‐drawn PTT fibers were improved as the draw ratio and take‐up velocity increased. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 3471–3480, 2001     

TEMPO-oxidized cellulose nanofibril/poly(vinyl alcohol) composite drawn fibers

PVA/TOCN composite fiber with a weight ratio of 100:1 was prepared from a mixture of aqueous poly(vinyl alcohol) (PVA) solution and 2,2,6,6-tetramethylpiperidine-1-oxy radical (TEMPO)-oxidized cellulose nanofibril (TOCN) dispersion using spinning, drawing, and drying processes. The as-spun PVA/TOCN composite fiber was further drawn, up to a draw ratio of 20 by heating at up to 230 °C. The maximum tensile modulus of the PVA/TOCN composite drawn fiber reached 57 GPa, remarkably higher than that of commercial PVA drawn fibers. Moreover, the PVA/TOCN composite drawn fiber had storage modulus higher than that of the PVA drawn fiber at each temperature in the range from 28 to 239 °C. Structural analyses showed that amorphous PVA regions in the composite drawn fiber were more oriented than those in neat PVA fiber after the addition of the small amount of TOCN used. These results indicate that TOCN elements were individually dispersed in the PVA matrix without aggregation and formed hydrogen bonds with amorphous PVA molecules in the composite drawn fiber.     

Mechanical properties and microstructure of poly(ethylene terephthalate) microfiber prepared by carbon dioxide laser heating

We determined that a poly(ethylene terephthalate) microfiber was easily obtained by irradiating a carbon dioxide laser to an annealed fiber. The annealed fiber was prepared by zone drawing and zone annealing. First, an original fiber was zone drawn at a drawing temperature of 90°C under an applied tension of 4.9 MPa, and the zone‐drawn fiber was subsequently zone annealed at 150°C under 50.9 MPa. The zone‐annealed fiber had a degree of crystallinity of 48%, a birefringence of 218.9 × 10^?3, tensile modulus of 18.8 GPa, and tensile strength of 0.88 GPa. The microfiber prepared by laser heating the zone‐annealed fiber had a diameter of 1.5 μm, birefringence of 172.8 × 10^?3, tensile modulus of 17.6 GPa, and tensile strength of 1.01 GPa. The draw ratio estimated from the diameter was 9165 times; such a high draw ratio has thus far not been achievable by any conventional drawing method. Microfibers may be made more easily by laser heating than by conventional technologies such as conjugate spinning. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1955–1958, 2003     

Preparation and characterization of syndiotacticity-rich ultra-high molecular weight poly(vinyl alcohol)/imogolite blend film

To enhance the physical properties of syndiotacticity-rich (syndiotactic diad content 63·4%) ultra-high molecular weight (UHMW) (number-average degree of polymerization 12300) poly(vinyl alcohol) (PVA) film, it was solution blended with rigid-rod imogolite in dimethyl sulphoxide. In addition, the blend film prepared was stretched using a high-temperature zone drawing technique for effective orientation of the film. Through a series of experiments, it was found that imogolite caused significant changes in the structure and properties of syndiotacticity-rich UHMW PVA film, i.e. imogolite acted as an important agent which increased crystal orientation of syndiotacticity-rich UHMW PVA, resulting in enhanced tensile strength of the film. However, imogolite played a hindering role in raising the amorphous orientation of syndiotacticity-rich UHMW PVA. The maximum tensile modulus of 19·8GPa and maximum tensile strength of 1·8GPa could be obtained at the maximum draw ratio of 7·45 for PVA/imogolite blend film. In the case of PVA homo film, the highest tensile modulus and strength were 25·2GPa and 1·4GPa, respectively. © 1998 Society of Chemical Industry     

Drawing in high pressure CO2—a new route to high performance fibers in memory of late Roger Porter

In this paper, we introduce a new draw technique for polymer orientation and apply it to different polymer fibers: poly(ethylene terephthalate) or PET, nylon 6,6, and ultra‐high molecular polyethylene (UHMWPE). In this technique, a polymer is drawn uniaxially in supercritical CO₂ using a custom high‐pressure apparatus. This technique can be used in replacement of a traditional drawing process or as a post‐treatment process. With PET, the technique is not effective at temperatures at or below 130°. In contrast, the process is highly effective for nylon 6,6 where CO₂ drawn fibers show significantly higher crystallinity and orientation along with improved mechanical properties. While the fibers are plasticized, the drawability of the fibers is only slightly dependent on temperature. High pressure CO₂ drawing of ultrahigh molecular weight polyethylene (UHMWPE) fibers is equally effective. Commercial high performance fibers can be drawn up to a ratio of 1.9 in asecond stage, resulting in large increases in tensile modulus and small improvements in tensile strength.     

High‐strength regenerated cellulose fibers spun from 1‐butyl‐3‐methylimidazolium chloride solutions

High‐performance regenerated cellulose fibers were prepared from cellulose/1‐butyl‐3‐methylimidazolium chloride (BMIMCl) solutions via dry‐jet wet spinning. The spinnability of the solution was initially evaluated using the maximum winding speed of the solution spinning line under various ambient temperatures and relative humidities in the air gap. The subsequent spinning trials were conducted under various air gap conditions in a water coagulation bath. It was found that low temperature and low relative humidity in the air gap were important to obtain fibers with high tensile strength at a high draw ratio. From a 10 wt % cellulose/BMIMCl solution, regenerated fibers with tensile strength up to 886 MPa were prepared below 22 °C and relative humidity of 50%. High strengthening was also strongly linked with the fixation effect on fibers during washing and drying processes. Furthermore, an effective attempt to prepare higher performance fibers was conducted from a higher polymer concentration solution using a high molecular weight dissolving pulp. Eventually, fibers with a tensile strength of ～1 GPa and Young's modulus over 35 GPa were prepared. These tensile properties were ranked at the highest level for regenerated cellulose fibers prepared by an ionic liquid–based process. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45551.     

Processing,structure, and properties of gel spun PAN and PAN/CNT fibers and gel spun PAN based carbon fibers

Polyacrylonitrile (PAN) and PAN/carbon nanotube (PAN/CNT) fibers were manufactured through dry‐jet wet spinning and gel spinning. Fiber coagulation occurred in a solvent‐free or solvent/nonsolvent coagulation bath mixture with temperatures ranging from ?50 to 25°C. The effect of fiber processing conditions was studied to understand their effect on the as‐spun fiber cross‐sectional shape, as well as the as‐spun fiber morphology. Increased coagulation bath temperature and a higher concentration of solvent in the coagulation bath medium resulted in more circular fibers and smoother fiber surface. as‐spun fibers were then drawn to investigate the relationship between as‐spun fiber processing conditions and the drawn precursor fiber structure and mechanical properties. PAN precursor fiber tows were then stabilized and carbonized in a continuous process for the manufacture of PAN based carbon fibers. Carbon fibers with tensile strengths as high as 5.8 GPa and tensile modulus as high as 375 GPa were produced. The highest strength PAN based carbon fibers were manufactured from as‐spun fibers with an irregular cross‐sectional shape produced using a ?50°C methanol coagulation bath, and exhibited a 61% increase in carbon fiber tensile strength as compared to the carbon fibers manufactured with a circular cross‐section. POLYM. ENG. SCI., 55:2603–2614, 2015. © 2015 Society of Plastics Engineers     

Extension‐induced mechanical reinforcement in melt‐spun fibers of polyamide 66/multiwalled carbon nanotube composites

In this work, polyamide 66 (PA66) and its composites with multiwalled carbon nanotubes (MWNTs) were melt spun into fibers at different draw ratios. PA66 fibers at high draw ratio demonstrate a 40% increase in tensile strength, 66% increase in modulus and a considerable increase in toughness. It is demonstrated that this reinforcement can be mainly attributed to high‐draw‐ratio‐induced good dispersion and orientation of MWNTs, particularly the enhanced interfacial adhesion between MWNT and matrix thanks to interfacial crystallization. Our work provides a simple but efficient method to achieve good dispersion and strong interfacial interaction through melt spinning. Copyright © 2011 Society of Chemical Industry     

High modulus/tenacity filaments from blends of different molecular weights of polypropylene

Polypropylene (PP) filaments are prepared by blending two different molecular weight components of PP. A melt‐spinning process to produce filaments includes mixing of components, extrusion, and two‐stage drawing, followed by a unique Gradient Drawing? process. Blending results in highly deformable as‐spun filaments with high draw ratios. For 90:10 blends of PP samples with melt flow indexes of 35 and 3, a high level of crystallinity and crystalline and amorphous orientations are obtained. A sonic modulus of 28 GPa, dynamic modulus of 20 GPa, tensile modulus of 16 GPa, and tenacity of 667 MPa are achieved. These samples are dimensionally stable up to ～100°C. All steps in the production of the filaments are continuous. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1021–1028, 2005     

Effects of the coagulation temperature on the properties of wet‐spun poly(vinyl alcohol)–graphene oxide fibers

Graphene oxide (GO) as a positive reinforcement filler was dispersed into a poly(vinyl alcohol) (PVA) dope and wet‐spun into composite fibers. The effects of two EtOH coagulation baths maintained at ?5 and 25 °C, respectively, on the morphology, structure, and mechanical properties of the composite fibers were investigated. The results show that gel spinning at ?5 °C led to a relatively large shrinkage ratio, thin diameter, and low porosity of the as‐spun fibers. Simultaneously, the low coagulation temperature also greatly contributed to the formation and preservation of the liquid‐crystalline phase of the GO sheets and interrupted the crystalline zone of PVA less. As a result, either the tenacity or the elongation at break of the fibers spun at ?5 °C was higher than those of the fibers spun through a coagulation bath at 25 °C. In particular, 1 wt % GO showed the highest reinforcement effects among all of the wet‐spun composite fibers. Hence, controlling the gelling–demixing process at a low temperature will provide more instructive insights for tailoring functional industrial textiles with excellent mechanical properties. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 45463.