凝胶染色过程中腈纶沿纺程的结构性能变化的研究

采用湿法纺丝工艺制备腈纶(即聚丙烯腈(PAN)纤维),研究了凝胶染色过程中PAN纤维在不同工序段的结构和物理性能.结果表明:沿着纺程,PAN纤维的直径逐渐减小,纤维的玻璃化转变温度和结晶度逐渐提高;在水洗后PAN纤维表面有明显的微观结构缺陷、且无定形区占比高;经过热拉伸和干燥致密化之后,纤维致密化,结晶度大大增加,凝胶...     

Melt spinning and drawing of 2‐methyl‐1,3‐propanediol‐substituted poly(ethylene terephthalate)

The structure and properties of fibers prepared from copolymers of poly(ethylene terephthalate) (PET) in which 2‐methyl‐1,3‐propanediol (MPDiol® Glycol is a registered trademark of Lyondell Chemical Company) at 4, 7, 10, and 25 mol% was substituted for ethylene glycol were studied and compared with those of PET homopolymer. Filaments were melt spun over a range of spinning conditions, and some filaments that were spun at relatively low spinning speeds were subjected to hot drawing. The filaments were characterized by measurements of birefringence, differential scanning calorimetry (DSC) crystallinity, melting point, glass transition temperature, wide‐angle X‐ray diffraction patterns, boiling water shrinkage, tenacity, and elongation to break. Filaments containing 25 mol% MPDiol did not crystallize in the spinline at any spinning speed investigated, whereas the other resins did crystallize in the spinline at high spinning speeds. However, compared with PET homopolymer, increasing substitution of MPDiol reduced the rate at which the crystallinity of the melt spun filaments increased with spinning speed and reduced the ultimate crystallinity that could be achieved by high‐speed spinning. The rate of development of molecular orientation, as measured by birefringence, also decreased somewhat with increasing MPDiol content. Shrinkage in boiling water decreased at high spinning speeds as the amount of crystallinity increased; however, the shrinkage decreased more slowly with increase in spinning speed as MPDiol content increased. Tenacity also decreased slightly at any given spinning speed as MPDiol content increased, but there was no significant effect on elongation to break. The addition of MPDiol in amounts up to 7 mol% increased the maximum take‐up velocity that could be achieved at a given mass throughput. This result indicates that the use of higher spinning speeds could potentially increase the productivity of melt spun yarns. Copolymer filaments spun at low speeds were readily drawn to produce highly oriented fibers with slightly less birefringence, crystallinity, and tenacity than similarly processed PET homopolymer. Preliminary dyeing experiments showed that the incorporation of MPDiol improved the dyeability of the filaments. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2598–2606, 2003     

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.     

Investigating the jet stretch in the wet spinning of PAN fiber

The jet stretch of wet‐spun PAN fiber and its effects on the cross‐section shape and properties of fibers were investigated for the PAN‐DMSO‐H₂O system. Evidently, the spinning parameters, such as dope temperature, bath concentration, and bath temperature, influenced the jet stretch. Also, under uniform conditions, the postdrawing ratio changed as well as that of jet stretch. When coagulation temperature was 35°C simultaneously with bath concentration of 70%, jet stretch impacted obviously the cross‐section shapes of PAN fiber, but had little effect when the temperature was below 10°C or above 70°C. As the jet stretch ratio increased, the crystallinity, crystal size, sonic orientation, and mechanical properties of the as‐spun fiber changed rapidly to a major value for jet stretch ratio of 0.9 where the cross section of as‐spun fiber was circular. With further increasing of jet stretch ratio, the properties changed slightly but the fiber shape was not circular. The results indicated that appropriate jet stretch, under milder formation conditions in wet‐spinning, could result in the higher postdrawing ratio and circular profile of PAN fiber, which were helpful to produce round PAN precursor with minor titer and perfect properties for carbon fiber. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Effects of spinning speed and heat treatment on the mechanical properties and biodegradability of poly(lactic acid) fibers

We undertook this study to suggest the optimal spinning process conditions that provide a proper range of tenacity and biodegradability in textile fibers. The effect of melt‐spinning speed and heat treatment on the mechanical properties and biodegradability of poly(lactic acid) (PLA) fibers were investigated. PLA was spun at a high spinning speed of 2000–4000 m/min, and each specimen was heat‐treated. Mechanical properties were estimated by measurement of the breaking stress, and the degree of crystallinity was evaluated with wide‐angle X‐ray scattering. Biodegradability was estimated from the decreases in breaking stress, weight loss, and degree of crystallinity after soil burial. The results of the experiment reveal that heat treatment of the PLA fibers increased the breaking stress and crystallinity. With increasing spinning speed, breaking stress and crystallinity also increased. An increase in spinning speed was more effective than an increase in heat treatment for enhancing the breaking stress within the range of this study. From the soil burial test, it was revealed that an increase in spinning speed and heat treatment decreased the biodegradability of the fibers. X‐ray analysis of the soil‐buried fibers showed that fibers with higher crystallinities began to degrade more slowly. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3099–3104, 2007     

Preparation of polyacrylonitrile and cellulose acetate blend fibers through wet‐spinning

Fibers containing both polyacrylonitrile (PAN) and cellulose acetate (CA) were prepared through wet‐spinning by using N,N‐dimethylformamide (DMF) as a solvent. Compatibility of PAN and cellulose acetate blend (PCB) fibers was investigated by means of scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and infrared (IR) spectrophotometry. The absorptive capacity and mechanical properties of the fibers were measured. It was observed that the surface and the cross section of PAN fibers were quite smooth and free from voids and microcracks, whereas cracks and voids were present on the surface and cross section of blend fibers, which increased with the incorporation of CA in the blend. Moisture regains of blend fibers were quite high while their tensile properties showed a partial decrease. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2000–2005, 2007     

Surface hydrolysis of filaments based on poly(trimethylene terephthalate) spun at high spinning speeds

The surface alkaline hydrolysis of fibers made from poly(trimethylene terephthalate) (PTT) was studied after extruding the polymer at high spinning speeds from 2000 to 6000 m/min and heat setting in the range of temperatures from 100 to 180°C. Fiber weight loss increased with an increasing heat‐setting temperature but it was also dependent on the spinning speed. Some of the partially hydrolyzed fibers had a well‐developed, hydrophilic surface, and pore size in the range of 0.69 to 1.20 μm. The optimum reaction and morphological conditions for increasing porosity in PTT fibers depends on spinning speed and heat‐setting temperature. A temperature of 180°C is the upper limit for heat‐setting PTT filaments but seems to be the most effective for making porous fibers. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1724–1730, 2004     

Characterization of poly(L‐lactic acid) fibers produced by melt spinning

Biodegradable poly(L ‐lactic acid) (PLLA) fibers were processed by a two‐step melt‐spinning method (melt extrusion and hot draw) from PLLA with three different viscosity‐average molecular weights (494,600, 304,700, and 262,800). Before spinning, the polymer flakes were first milled into powders and dried under vacuum. Viscosity‐average molecular weight of PLLA following the fabrication process was monitored. Tensile properties of as‐spun and hot‐drawn fibers were investigated. Morphology of the PLLA fibers was viewed under a scanning electron microscope. Crystallinity of these fibers was assessed by thermogram analysis of differential scanning calorimetry. Results showed that the extent of decrease in the viscosity‐average molecular weight of PLLA dropped sharply by 13.1–19.5% during pulverization and by 39.0–69.0% during melt‐extrusion. The hot‐draw process in this study had a little effect on the viscosity‐average molecular weight of PLLA. Smoother fibers could be obtained for the die temperature at least 230°C for raw materials with higher crystallinity (more than 75%) and at least 220°C for raw materials with lower crystallinity (about 60%). The as‐spun fibers showed crystallinity of 16.5–22.8% and the value increased to 50.3–63.7% after hot draw. Tensile moduli of the as‐spun fibers were in the range of 1.2–2.4 GPa, which were raised to 3.6–5.4 GPa after hot draw. The final PLLA fibers with 110–160 μm diameters showed tensile strengths of 300–600 MPa. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 251–260, 2001     

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

A 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.     

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     

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     

Carbon fibers derived from wet‐spinning of equi‐component lignin/polyacrylonitrile blends

Equi‐component blends of polyacrylonitrile (PAN) and lignin, i.e., with a lignin content as large as 50 wt %, were successfully used as precursors to produce carbon fibers. Rheological measurements demonstrated that increasing lignin content in spinning solution reduced shear viscosity and normal stress, indicating a decrease of viscoelastic behavior. This was confirmed by Fourier transform infrared results that show no discernable chemical reaction or crosslinking between PAN and lignin in the solution. However, the resulting carbon fibers display a large I_D/I_G ratio (by Raman spectroscopy) indicating a larger disordered as compared to that from pure PAN. The macro‐voids in the lignin/PAN blend fibers typically generated during wet‐spinning were eliminated by adding lignin in the coagulant bath to counter‐balance the out‐diffusion of lignin. Carbon fibers resulting from lignin/PAN blends with 50 wt % lignin content displayed a tensile strength and modulus of 1.2 ± 0.1 and 130 ± 3 GPa, respectively, establishing that the equi‐component wet‐spun L/P‐based carbon fibers possessed tensile strength and modulus higher than 1 and 100 GPa. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45903.     

Effect of the drawing process on the wet spinning of polyacrylonitrile fibers in a system of dimethyl sulfoxide and water

The effect of the drawing process on the structural characteristics and mechanical properties of polyacrylonitrile (PAN) fibers was comparatively studied. The protofibers extruded from the spinneret were the initial phase of stretching, which involved the deformation of the primitive fiber with the concurrent orientation of the fibrils. Wet‐spun PAN fibers observed by scanning electron microscopy exhibited different cross‐sectional shapes as the draw ratio was varied. X‐ray diffraction results revealed that the crystalline orientation of PAN fibers increased with increasing draw ratio; these differences in the orientation behaviors were attributed to the various drawing mechanisms involved. The crystalline and amorphous orientations of the PAN fibers showed different features; at the same time, the tensile properties were strongly dependent on the draw ratio. However, the stream stretch ratio had most influence on the tensile strength and the orientation of PAN fibers for the selected process parameters. Electron spin resonance proved that the local morphology and segmental dynamics of the protofibers were due to a more heterogeneous environment caused by the sequence structure. Differential scanning calorimetry indicated that the size and shape of the exotherm and exoenergic reaction were strongly dependent on the morphology and physical changes occurring during fiber formation. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1026–1037, 2007     

Structure and property development of aromatic copolysulfonamide fibers during wet spinning process

The structure and performance changes of aromatic copolysulfonamide (co‐PSA) fibers that occurred during wet spinning process have been studied. While using different length scale characterization, including scan electron microscopy (SEM), wide‐angle X‐ray scattering (WAXS), and small‐angle X‐ray scattering (SAXS), it was found that the molecular chains of co‐PSA formed an isotropic network during coagulation which further lead to extension and orientation of these chains during the subsequent stretching. As a result, only after heat stretching and heat setting the molecular chains tended to pack into crystal lattice in the fibrils. This gave rise to a much denser structure along the spinning line and the glass transition temperature of co‐PSA fibers increased a little after heat setting. Before heat stretching, the co‐PSA fibers were in amorphous state, and only the amorphous orientation was observed within the fibers. After heat stretching at the temperature higher than T_g, the fraction of amorphous region decreased, and the crystal structure formed in the fibers, which became more perfect during heat setting. The structure development during spinning process contributed toward the improvement of thermo‐mechanical stability, tenacity and modulus of the co‐PSA fibers. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42343.     

Facile fabrication of PVA composite fibers with high fraction of multiwalled carbon nanotubes by gel spinning

Poly(vinyl alcohol) (PVA) composite fibers with high fraction of multiwalled carbon nanotubes (MWCNTs) were prepared by gel spinning process. Here, a modified process was introduced to prepare concentrated PVA/MWCNTs/DMSO spinning dope, and to attain good dispersion of MWCNTs in the fibers. The final composite fibers were studied by thermogravimetric analyzer (TGA), Fourier transform infrared spectrometer (FTIR), Raman spectroscopy, differential scanning calorimetry (DSC), and WAXD analysis. The total content of MWCNTs in PVA composite fibers, from 5 to 30 wt%, was confirmed by TGA analysis. FTIR and Raman measurements demonstrated the existence of strong hydrogen interaction between MWCNTs and PVA matrix. SEM images of composite fibers showed smooth surface, regular cross‐section shape and good dispersion of MWCNTs in the fibers. DSC analysis showed that the crystallinity first increased and then decreased with the increase of MWCNTs contents. It can be concluded that low concentration of MWNCTs can act as nucleation sites for crystallization of PVA component, and large amount of MWCNTs may impede the crystallization of PVA component. The WAXD analysis results indicated that the crystal orientation of the PVA component in PVA composite fibers is almost identical at the same drawn ratio. Polarized Raman analysis indicated a small increase in MWCNTs orientation for the composite fibers. The mechanical properties tests showed that the composite fibers exhibit significant improvement in tensile strength and modulus as compared to the neat PVA fibers. The composite fibers also showed sustained growth in electrical conductivity. POLYM. ENG. SCI., 58:37–45, 2018. © 2017 Society of Plastics Engineers     

Electrically conductive poly(3,4‐ethylenedioxythiophene)–polystyrene sulfonic acid/polyacrylonitrile composite fibers prepared by wet spinning

Composite conductive fibers based on poly(3,4‐ethylenedioxythiophene) (PEDOT)–polystyrene sulfonic acid (PSS) blended with polyacrylonitrile (PAN) were prepared via a conventional wet‐spinning process. The influences of the PEDOT–PSS content on the electrical conductivity, thermal stability, and mechanical properties of the composite fibers were investigated. The fibers with 1.83 wt % PEDOT–PSS showed a conductivity of 5.0 S/cm. The breaking strength of the fibers was in the range 0.36–0.60 cN/dtex. The thermal stability of the PEDOT–PSS/PAN composite fibers was similar to but slightly lower than that of the pure PAN. The X‐ray diffraction results revealed that both the pure PAN and PEDOT–PSS/PAN composite fibers were amorphous in phase, and the crystallization of the latter was lower than that of the former. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Effect of processing parameters of the continuous wet spinning system on the crystal phase of PVDF fibers

Poly(vinylidene difluoride) (PVDF) has been widely used in piezoelectric applications as films and nanofiber mats, but there are limited publications on piezoelectric wet‐spun fibers. In this work, PVDF fibers were prepared using the wet spinning method, and the processing parameters, including the drawing ratio and heat setting temperature, were controlled in the continuous wet spinning system to increase the β‐phase crystallinity of the fibers. In addition, the wet‐spun PVDF fibers were compressed by a rolling press to eliminate voids in the fibers. Then, the compressed PVDF fibers were poled to align the molecular dipoles. The crystal structures of the PVDF fibers were investigated using X‐ray diffraction and Fourier‐transform infrared spectroscopy. Single filament tensile tests were performed to measure the tensile strength of the fibers. The morphologies of the PVDF fibers with respect to the processing parameters were observed by scanning electron microscope (SEM) and polarization optical microscopy. The piezoelectric constant of the prepared PVDF fibers was then measured using a d₃₃ meter. The wet‐spun PVDF fibers showed the highest β‐phase and piezoelectric constants when the drawing ratio and heat setting temperature were 6 and 150 °C, respectively. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45712.     

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.     

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.     

Correlation between inhomogeneity in polyacrylonitrile spinning dopes and carbon fiber tensile strength

The nano‐scale and micro‐scale inhomogeneity of polyacrylonitrile (PAN) spinning dopes obtained from dynamic light scattering (DLS) experiment is correlated with the tensile strength of the resulting carbon fiber. The nanoscale inhomogeneity was estimated by calculating the diffusion coefficients from the slow relaxation mode of polymer solutions in DLS. The nanoscale inhomogeneity in the spinning dopes was found to be in the range of 1–45 nm. We also demonstrate mean of the count rate (MCR) obtained from DLS of PAN solution as a tool to detect the microscale inhomogeneity in the spinning dope for the first time. The MCR of spinning dopes varied from ~10.0 to 77.5 kcps (kilo‐counts per second). The tensile strength of carbon fibers from the precursor fiber spun from the spinning dopes in this study varied from 3 to 5.2 GPa. Correlation studies show that the microscale inhomogeneity in the spinning dope was a major contributor to the decrease in the tensile strength of carbon fibers in the range of 3–4.5 GPa. Contaminants causing microscale inhomogeneity in PAN powder were removed by using micelles, reverse micelles and frothing. The surfactant treated PAN polymer was characterized using a fourier transform infrared spectroscope, differential scanning calorimeter, and thermal gravimetic analyzer to demonstrate complete removal of surfactants. POLYM. ENG. SCI., 59:478–482, 2019. © 2018 Society of Plastics Engineers