Effects of water on drawability,structure, and mechanical properties of poly(vinyl alcohol) melt‐spun fibers

Poly(vinyl alcohol) (PVA) melt‐spun fibers with circular cross‐section and uniform structure, which could support high stretching, were prepared by using water as plasticizer. The effects of water content on drawability, crystallization structure, and mechanical properties of the fibers were studied. The results showed that the maximum draw ratio of PVA fibers decreased with the increase of water content due to the intensive evaporation of excessive water in PVA fibers at high drawing temperature. Hot drying could remove partially the water content in PVA as‐spun fibers, thus reducing the defects caused by the rapid evaporation of water and enhancing the drawability of PVA fibers at high drawing temperature. The decreased water content also improved the orientation and crystallization structure of PVA, thus producing a corresponding enhancement in the mechanical properties of the fibers. When PVA as‐spun fibers with 5 wt % water were drawn at 180 °C, the maximum draw ratio of 11 was obtained and the corresponding tensile strength and modulus reached ～0.9 GPa and 24 GPa, respectively. Further drawing these fibers at 215 °C and thermal treating them at 220 °C for 1.5 min, drawing ratio of 16 times, tensile strength of 1.9 GPa, and modulus of 39.5 GPa were achieved. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45436.     

Physical properties of poly(vinyl alcohol) fibers prepared from wet spinning/multi-step drawing

The preparation of poly(vinyl alcohol) (PVA) fibers by multi-step drawing was examined. The high draw ratio was attained when the drawing just before melting point was repeated. The influences of the draw ratio on mechanical and thermal properties of the fibers were studied. We utilized the wide angle x-ray diffraction (WAXD) as a medium to observe the erystallinity and the orientation of PVA fibers to study their effects on the physical properties of the fibers. With various coagulation bath concentration, both the tenacity and Young's modulus of fibers would increase as the draw ratios increased, the elongation would decrease at the same time. The tenacity was able to reach 41.0 cN/tex with the Young's modulus being 856.2 cN/tex; also, as the draw ratios increased, both crystallinity and orientation would increase. The crystallinity was about 67.2 % and the orientation was about 86.4%.     

Melt spinning of high‐strength fiber from low‐molecular‐weight polypropylene

Polypropylene (PP) with high melt flow index (MFI) or low molecular weight, although desired in melt spinning for enhanced productivity, is difficult to be spun into high‐strength fiber using the standard process where extensive jet stretching is applied. In this work, a processing route involving minimal jet stretch has been explored. A two‐stage hot drawing procedure in the solid state was found to be suitable for producing high‐strength fiber from low‐molecular‐weight PP with an ultrahigh MFI of 115 g/10 min. Fibers produced achieve a maximum tensile strength and Young's modulus of approximately 600 MPa and 12 GPa, respectively. The melt temperature of the fiber reached 170.8°C, approximately 5°C higher than that of the original resin. Wide‐angle X‐ray diffraction (WAXD) study shows that the stable α‐monoclinic crystalline structure is developed during the drawing process. A well‐oriented crystalline structure along the fiber axis is generated, having a crystalline orientation factor as high as 0.84. POLYM. ENG. SCI., 56:233–239, 2016. © 2015 Society of Plastics Engineers     

Drawing and annealing of polypropylene fibers: Structural changes and mechanical properties

A study has been carried out on the influence of cold drawing (25°C), hot drawing (140°C), and annealing (140°C) on the structure and mechanical properties of a series of four different well-characterized melt spun polypropylene filaments. The influence of the interaction between melt spinning and drawing variables was given special attention. Cold drawing increased the orientation in the samples, disrupts the initial monoclinic crystal structure and the morphology of the filaments, and it results in extensive fibrillation. Annealing restored the monoclinic structure but eliminated only a small part of the fibrillation. Hot drawing produced changes which were qualitatively similar to the combined effects of cold drawing and annealing. The orientation and morphology of the asspun filaments were found to have major effects on drawing behavior and the mechanical properties of the drawn fibers for a given draw ratio. It was found, however, that the mechanical properties (tensile strength, tangent elastic modulus, and elongation to break) of the melt spun, hot drawn and cold drawn, and annealed fibers could all be correlated with birefringence measurements.     

Microstructural effects on hot drawing syndiotactic styrene P‐methyl styrene copolymer

Crystalline syndiotactic styrene/p‐methyl styrene copolymer (SPMS) has been oriented by tensile drawing at various temperatures between the glass transition and crystalline melting point. The microstructural changes resulting from drawing have been studied using differential scanning calorimetry (DSC) and wide angle X‐ray diffraction (WAXD). WIth increasing draw temperature, both melting temperature and crystalline dimensions of the oriented samples increase. The heat of fusion increases with increasing draw temperature up to ～200°C. It also increases with draw ratio and draw rate, while the crystalline width increases only with draw ratio. THe amorphous fraction shows a clear glass transition, the temperature of which (T_g) increases with draw ratio. However, T_g decreases somewhat with increasing draw temperature. This is interpreted in terms of the stretching of the randomly coiled amorphous phase molecules.     

Preparation and characterization of high‐performance poly(ether ether ketone) fibers with improved spinnability based on thermotropic liquid crystalline poly(aryl ether ketone) copolymer

High‐performance poly(ether ether ketone) (PEEK) fibers were prepared by melt‐spinning in the presence of thermotropic liquid crystalline poly(aryl ether ketone) copolymer (FPAEKLCP). The rheological and mechanical properties, birefringence, orientation, and crystallization of the resulting PEEK/FPAEKLCP fibers were characterized by using a melt flow indexer, capillary rheometer, single fiber electronic tensile strength tester, polarized light microscopy (PLM), and wide‐angle X‐ray diffraction (WAXD), respectively. The results indicate that the melt viscosity of PEEK significantly reduced by introducing FPAEKLCP, followed by the improvements in the spinnability and the quality of as‐spun fibers. The tensile properties of PEEK/FPAEKLCP fibers mainly depend on the content of FPAEKLCP, drawing temperature, drawing ratio, and annealing processes. Moreover, the tensile strength and modulus of PEEK/FPAEKLCP fibers are obviously higher than those of neat PEEK fibers under the same processing conditions. This should be attributed to an enhancement in the orientation and crystallization of PEEK compounded with FPAEKLCP. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1406‐1414, 2013     

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     

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     

The influence of drawing,twisting, heat setting and untwisting on the structure and mechanical properties of melt spun polypropylene filament

The changes in structure and mechanical properties of melt spun polypropylene filaments were determined as the filaments were successively (i) drawn, (ii) twisted, (iii) annealed, and (iv) untwisted. Filaments spun to two different melt draw down levels were studied. The effects of draw temperature and draw ratio, extent of twist, annealing temperature, and the extent of untwisting were examined. Melt spun and twisted filaments (draw ratio of 1) were also considered. Structural characterization techniques used in this study include wide angle (WAXS) and small angle (SAXS) diffraction, scanning electron microscopy (SEM), birefringence and density measurement. Drawing increased crystalline orientation and at low temperatures disrupted the monoclinic unit. cell existing in the melt spun fibers. The drawing produced considerable fibrillation under all conditions even when carried out at 120°C. The fibrillation quid void formation due to low temperature drawing was more pronounced. The variation of WAXS patterns and mechanical properties of twisted drawn filaments was interpreted by presuming that the fibrils act in a manner analogous to that of the filaments in a continuous filament twisted yarn. In the case of incompletely drawn filaments the effect of additional drawing occurring during twistin must be considered. Twisted fibers annealed at 150°C sowed a drastic reduction in tensile properties, while those annealed at 125°C did not set the twist and caused the fibers to tend to untwist. Annealing at 140°C appeared to give satisfactory heat setting. Annealing of cold drawn and cold drawn and twisted fibers increased the density, removed many defects and reformed a well defined monoclinic crystal structure and a lamellar morphology. Untwisting of heat set filaments tended to give back the properties of hot drawn fibers. In some cases, however, the opening of cracks was noted.     

Enhanced compatibilization and orientation of polyvinyl alcohol/gelatin composite fibers using carbon nanotubes

Polyvinyl alcohol (PVA)/gelatin composite fibers containing carbon nanotubes (CNTs) had been prepared by wet‐spinning method. A remarkable increase of tensile strength of the PVA/gelatin fibers was achieved by adding small amount of CNT. The mechanism of reinforcement has been studied using a combination of differential scanning calorimetry (DSC), 2D wide‐angle X‐ray diffraction (2D‐WAXD) and scanning electron microscopy (SEM). SEM showed a decreased gelatin domain size by adding CNTs, suggesting a possible compatibilization effect between PVA and gelatin. On the other hand, an increased crystallinity and degree of orientation of PVA/gelatin fibers has been observed by adding CNTs. Thus, the increased compatibilization, crystallinity and degree of orientation in PVA/gelatin/CNTs composite fibers should be the reasons for the observed increase of mechanical properties. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

高密度聚乙烯熔纺纤维的拉伸工艺

相对分子质量为１４万的高密度聚乙烯（ＨＤＰＥ）通过螺杆挤出机熔纺成形,然后经过高温超拉伸可制成强度为９．７ｃＮ／ｄｔｅｘ的中强聚乙烯纤维。讨论了拉伸温度、拉伸比对纤维力学性能的影响,并通过声速取向、热分析（ＤＳＣ）、广角Ｘ射线衍射（ＷＡＸＤ）和纤维力学性能的测试研究了拉伸过程中聚乙烯纤维结构与性能的变化。结果表明：拉伸温度对纤维稳定拉伸影响较大,最佳温度为１０５～１１５℃;且初生纤维的纤度越小,高倍拉伸纤维强度越大,随拉伸倍数的提高,纤维的强度和声速取向都显著提高并改善了纤维的热性能和力学性能,但断裂伸长却呈下降趋势。     

Novel CO2 laser drawing of thermotropic liquid crystal polymer and poly(ethylene 2,6‐naphthalate) blend fibers

Thermotropic liquid crystal polymer (TLCP)/poly(ethylene 2,6‐naphthalate) (PEN) were prepared by a melt blending, and were melt spun by a spin‐draw process. In this study, we suggest novel drawing technology using the CO₂ laser that can directly and uniformly heat up fiber inside to prevent the formation of ununiform structures in conventional heat drawing process. The properties of the heat/laser drawn TLCP/PEN blend fibers were superior to those of any other handled fibers, and were rather more excellent than those of TLCP/PEN blend fibers annealed at 135°C for 10 min. It was confirmed that the CO₂ laser drawing made it possible to achieve the optimal drawing effect by draw ratio. The combined heating and CO₂ laser‐drawing method has a great potential for industrial applications as a novel fiber‐drawing process, and it can also be applied continuously to conventional spin‐draw system. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 205–211, 2007     

Melt spinning of poly(vinylidene fluoride) fibers and the influence of spinning parameters on β‐phase crystallinity

The effects of melt‐spinning and cold‐drawing parameters on the formation of β‐phase crystallinity in poly(vinylidene fluoride) (PVDF) fibers and ways of increasing such crystallinity were studied. Fibers were melt‐spun with four different melt draw ratios (MDRs) and were subsequently cold‐drawn at different draw ratios (λ). The maximum λ value in cold drawing was dependent on the MDR used in melt spinning. The crystalline structure of the fibers was studied mainly with differential scanning calorimetry (DSC) and X‐ray diffraction (XRD). The results showed that the degree of crystallinity in the fibers was determined by the MDR and that before cold drawing the crystalline structure of the fibers was predominantly in the α form. By cold drawing, α‐phase crystallites could be transformed into the β phase. It was established that, under certain conditions of melt spinning and cold drawing, PVDF fibers of up to 80% crystallinity, mainly in the β form, could be prepared. It was further proposed that fibers spun at a sufficiently high MDR consist to a large extent of extended‐chain crystals, and this greatly affects the melting point of PVDF. Thus, DSC melting‐point data were shown to be insufficient for determining the crystalline phase of PVDF. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Morphology and structure changes of aromatic copolysulfonamide fibers heat‐drawn at various temperatures

Pre‐drawn aromatic copolysulfonamide (co‐PSA) fibers were prepared by wet spinning and then heat drawing at temperatures varying from 350 to 390 °C, which are below the decomposition temperature. The fibers were then characterized using tensile testing, dynamic mechanical analysis, wide‐angle X‐ray diffraction and small‐angle X‐ray scattering. The relationship between structure and properties of the co‐PSA fibers drawn at different temperatures was investigated. The heat‐drawn co‐PSA fibers displayed similar glass transition temperature of about 355 °C, which was higher than that of pre‐drawn co‐PSA fibers of 345 °C. The crystal orientation was high as a crystalline structure formed during heat drawing and the crystallinity increased with the heat‐drawing temperature. However, the tenacity of the co‐PSA fibers did not increase linearly with the draw temperature. When the drawing temperature was higher than the glass transition temperature, a decrease in tenacity was observed, which could be attributed to an increase of crystallite size of the (100) plane and a decrease of the long period of the lamellar structure. © 2014 Society of Chemical Industry     

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     

Fine‐structure and physical properties of polyethylene fibers in high‐speed spinning. I. Effect of melt‐flow rate in the high‐density polyethylene

High‐density polyethylene (HDPE) fibers, obtained from a melt‐flow rate (g/10 min) of 11 and 28, was produced by a high‐speed melt‐spinning method in the range of take‐up velocity from 1 to 8 km/min and from 1 to 6 km/min, respectively. The change of fiber structure and physical properties with increasing take‐up velocity was investigated through birefringence, wide‐angle X‐ray diffraction (WAXD), differential scanning calorimetry (DSC), a Rheovibron, and a Fafegraph‐M. With an increase in take‐up velocity, the birefringence showed a sigmoidal increase, which has distinct changes in the range of 1–5 km/min. Throughout the whole take‐up velocities, the birefringence of HDPE(11) was higher than that of HDPE(28). With increasing take‐up velocity, the crystalline orientation was transformed from a‐axis orientation to c‐axis orientation. These crystalline relaxations are confirmed by the tan δ peak of high‐speed spun HDPE fibers. The intensity of the crystalline relaxation peak decreases with increasing take‐up velocity in both HDPE(11) and HDPE(28). As above, the crystalline relaxation peaks shift to lower temperature with increasing take‐up velocity. With increasing take‐up velocity, the ultimate strain decreases while both specific stress and the initial modulus increase. The mechanical behavior may be closely related to, as investigated by birefringence, orientation of the amorphous region, etc., the take‐up velocity. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1182–1195, 2000     

Densifying and strengthening of electrospun polyacrylonitrile‐based nanofibers by uniaxial two‐step stretching

The effects of alignment of polyacrylonitrile (PAN) nanofibers and a two‐step drawing process on the mechanical properties of the fibers were evaluated in the current study. The alignment was achieved using a high‐speed collector in electrospinning synthesis of the nanofibers. Under optimal two‐step drawing conditions (e.g., hot‐water and hot‐air stretching), the PAN nanofiber felts exhibited large improvements in both alignment and molecular chain‐orientation. Large increase in crystallinity, crystallite size, and molecular chain orientation were observed with increasing draw ratio. Optimally, stretched PAN‐based nanofibers exhibited 5.3 times higher tensile strength and 6.7 times higher tensile modulus than those of the pristine one. In addition, bulk density of the drawn PAN nanofibers increased from 0.19 to 0.33 g/cm³. Our results show that fully extended and oriented polymer chains are critical in achieving the highest mechanical properties of the electrospun PAN nanofibers. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43945.     

Cellulose fibers from cellulose/1‐ethyl‐3‐methylimidazolium acetate solution by wet spinning with increasing spinning speeds

Cellulose fibers from cellulose/1‐ethyl‐3‐methylimidazolium acetate solution were prepared by wet spinning with increasing extrusion speeds and draw ratios. The effects of spinning speeds on the structures and mechanical properties of these fibers were investigated by using scanning electron microscopy, wide angle X‐ray diffraction, birefringence, thermogravimetric analysis, tensile‐fineness tester, and wet friction. The results showed that the crystallinity, orientation, and mechanical properties of the fibers were improved with increasing draw ratio. The break draw ratios, degrees of crystallinity and orientation, tenacities, and wet friction time of the cellulose fibers decreased with increasing extruding speeds. The wet friction time decreased with increasing draw ratio and decreased faster under higher extrusion speed. Due to the high dope concentration and the increased draw ratio, the maximum tenacity of the regenerated cellulose fibers reached 2.73 cN/dtex. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40225.     

Structure and mechanical properties of multi‐hollowed fibers produced by CO2 laser irradiated neck drawing

Multi‐hollowed fibers with a hollowness ratio of over 20% were successfully produced using a neck‐drawing technique accompanied by CO₂ laser irradiation on unoriented and amorphous polytrimethylene terephthalate (PTT) fibers with diameters of approximately 104 µm. The structure and mechanical properties of the multi‐hollowed fibers were characterized using scanning electron microscopy, wide angle X‐ray diffraction (WAXD), birefringence measurements, and tensile tests. Crystal orientation factors in the direction normal to the (010) and (002) planes, which were obtained from WAXD patterns, were lower in comparison to values obtained in previous studies on fibers that did not feature these hollows [9] because of the development of these internal hollows. The PTT fibers in this study also displayed high toughness, about 465 MPa (3.5 cN/dtex) strength and about 40% elongation, and had excellent elastic recovery (>95%) after 10 stretch cycles. POLYM. ENG. SCI., 56:609–616, 2016. © 2015 Society of Plastics Engineers     

热拉伸倍数对芳砜纶结构和性能的影响

通过应力—应变和动态力学热分析研究了热拉伸倍数对芳砜纶力学性能和动态热力学性能的影响,同时利用广角X-射线衍射(WAXD)对不同热拉伸倍数的芳砜纶的结晶度和晶区取向度进行了分析。结果表明:随着热拉伸倍数的增加,纤维的断裂强度提高,在拉伸倍数为2.6倍时,断裂强度达到3.83 cN/dtex;纤维的玻璃化较变温度随拉伸倍数的增加变化不大,而结晶度和晶区取向度则显著增加。