The formation of polyacrylonitrile nascent fibers in wet‐spinning process

The formation of polyacrylonitrile (PAN) nascent fibers in wet‐spinning process was studied by KMnO₄ back titration method and scanning electron microscopy (SEM). It has been found that the rate of DMSO diffusion was rapid at the beginning of coagulation then decreased and reached balance at 24 s. With coagulation time increase, the nascent fibers became denser and had fewer inner defects gradually, but transverse stripes appeared on the surface at 24 s, and got deeper. The main defects of nascent fibers included transverse stripes, impurity, fish tail, inner microvoids etc. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

干喷湿纺中凝固牵伸对碳纤维前驱体PAN初生纤维的影响

为了研究PAN纤维干喷湿纺中凝固浴牵伸的作用机理。采用DMso水溶液作为凝固浴,利用纤维强伸度仪、分析天平、X射线衍射仪、电子探针等手段,研究了干喷湿纺中凝固牵伸对PAN初生纤维及最终原丝结构及性能的影响。结果表明,干喷瀑纺中,在凝固浴浓度（65％）、温度（20℃）、空气层厚度（2mm）等条件下,随凝固浴牵伸的增加,初生纤维及PAN原丝的孔隙率逐步降低,结晶度逐渐增大,初生纤维表现出较高的断裂强度,纵表面更加光洁,横截面更加致密;适当调整凝固浴牵伸,得到了纤度1．01dtex,强度7．52cN,dtcx的聚丙烯腈原丝。     

Crystallinity development in polyacrylonitrile nascent fibers during coagulation

This paper has studied the crystal and thermal property of nascent fibers during the polyacrylonitrile coagulation process. A water (H₂O)/dimethyl sulphoxide (DMSO) mixture was used as the coagulation bath for the coagulation process of acrylonitrile(AN)/itaconic acid(IA) copolymer fibers in the study. By transforming the spinning conditions, especially air gap distance between the spinneret and coagulation bath, draw ratios, coagulation time, we received the crystal and thermal properties of nascent fibers under different conditions. The relationship between the property of nascent fibers and the spinning conditions has been studied by use of X-rays, SEM, differential scanning calorimetry (DSC) and so on. The results indicated that the degree of crystallization gradually increased with the rise of coagulation time and tended to a fixed value when reached some time. With the augment of draw ratios, the crystal degree appeared differently, in which it decreased when the air gap distance was 0 mm and it increased when the air gap distance was 1 mm and 2 mm. At the same time, the thermal properties showed little difference in peak position and biggish difference in heat energy, which indicated the ability to endure heat for latter spinning process and thermal stabilization process.     

Effect of coagulation on the structure and property of PAN nascent fibers during dry jet wet-spinning

The paper has studied the effect of coagulation process on the structure and property of polyacrylonitrile nascent fibers during dry jet wet-spinning. The coagulation process to form polyacrylonitrile fibers has been studied by examination of FTIR, XRD, and SEM and so on. The results indicated that compared with coagulation directly, polyacrylonitrile nascent fibers gradually formed with fine crystallites and high degree of crystallization were achieved, the flex vibration peak of S=O gradually decreased, and less solvents remained in the nascent fibers with compact cross section morphology. At the same time, nascent fibers with less DMSO under different draw ratios showed higher fracture intensity and lower elongation.     

Study on the Coagulation Process of Polyacrylonitrile Nascent Fibers during Wet-spinning

Summary The coagulation process of polyacrylonitrile (PAN) precursor during wet-spinning was studied by chemical method based on the KMnO₄ titration. Experiments were performed with gelled solutions of PAN in dimethyl sulphoxide (DMSO) to determine the diffusion rate of solvent during the coagulation. The experimental datas about solvent diffusion coeffecient were calculated by using diffusion equation, which reflected the coagulation process of nascent fibers. At the same time, the effects of coagulation on the residual solvent content, the change of morphology of nascent fibers, the crystallization degree and the stress-strain curves were studied by use of X-ray diffraction, SEM, single fiber tensible test and so on. The results elucidated the relationship between coagulation process and the structure and property of PAN nascent fibers.     

Effect of coagulation temperature on the properties of poly(acrylonitrile- itaconic acid) fibers in wet spinning

A dimethyl sulfoxide (DMSO)-water system was used as the coagulation bath in the wet-spun process for poly(acrylonitrile-itaconic acid) fibers. The coagulation bath concentration of DMSO was kept constant at 65%, and the jet stretch ratio was 1. The coagulation bath temperature was varied from 40 to 70 °C. The properties of the fibers so obtained were investigated. The diffusion coefficient of solvent was calculated and the concentration profiles of solvent in a moving filament were computed by using a MOL (method of lines) method. The nascent fibers coagulated at 50 °C obtained a circular symmetrical cross section with high density and strength. The diffusion coefficients of solvent (DMSO) increase with the bath temperature increase. Simulation results show that the noncircular cross section form was the response of the rapid diffusion rate and the loose structure in the core of nascent fibers was caused by the overmuch remained solvent.     

Force field in coagulation bath at low temperature induced microfibril evolution within PAN nascent fiber and precursor fiber

The coagulation process was vital for the microfibril evolution and mechanical properties of polyacrylonitrile (PAN) fibers. The PAN nascent fibers and precursor fibers were prepared by controlling drawing ratio of coagulation bath at low temperature during the dry-jet wet spinning process. The microfibril morphological changes induced by force fields in coagulation bath were investigated by scanning electron microscopy and high-resolution transmission electron microscopy. During the coagulation process, the spinning solution evolved into an interconnected network composed of random microfibrils and tie joints as a building block of the network. At low drawing ratio, the random interconnected network existed in nascent fibers. Increasing drawing ratio, the fiber filaments underwent shrinkage and the network was transformed into the transverse lamellae. Furthermore, the lamellar thickness also decreased. After the treatment of post-spinning, similar transverse lamellae were formed in all of precursor fibers, and random microfibrillar network was stretched and oriented to develop into the aligned microfibrils in precursor fibers. The transverse fold-chain crystal layers were densely stacked in the microfibrils. Increasing drawing ratio, the lamellae and microfibrils in precursor fibers were packed more densely and orderly. Consequently, the order and homogeneity of microfibrils in nascent fibers and precursor fibers were improved by increasing drawing ratio, which were benefit to increase fiber tensile strength and modulus.     

Kinetics of diffusion in polyacrylonitrile fiber formation

A H₂O/dimethyl sulfoxide (DMSO) mixture was used as the coagulation bath of the wet‐spun process for polyacrylonitrile fibers. Diffusion behaviors of coagulate and solvent of the protofibers were studied. Diffusion coefficients of H₂O and DMSO of the protofibers, prepared by acrylonitrile (AN) homopolymers, were also determined. It was found that diffusion coefficients of H₂O and DMSO in the protofibers prepared by AN homopolymers, synthesized by DMSO solution polymerization, are highest compared with those of AN homopolymers synthesized by H₂O/DMSO mixture suspension polymerization and aqueous suspension polymerization. With increasing polyacrylonitrile concentration in the dope, diffusion coefficients of H₂O and DMSO decreased continuously. Diffusion coefficients of H₂O and DMSO increased concomitantly with increasing bath temperature, but the changes of diffusion coefficient values were less prominent when the temperature increased beyond 60°C. When DMSO concentration in the coagulation bath was 55 wt %, the values of diffusion coefficients of H₂O and DMSO were minimal. Diffusion coefficients increased with increasing jet stretch minus ratio. When the protofiber radius was increased, there was a corresponding increase of diffusion coefficients of H₂O and DMSO. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1529–1533, 2005     

Effect of dope extrusion rate on the formation and characterization of polyacrylonitrile nascent fibers during wet-spinning

Polyacrylonitrile nascent fibers were prepared via the wet-spinning technique and a dimethyl sulphoxide/H₂O coagulation bath system was adopted. The objective of this study was to investigate the influence of dope extrusion rates on formation and characterization of nascent fibers. Nine different dope extrusion rates were adopted when other technique parameters were kept steady. The surface morphology of nascent fibers was observed by field emission scanning electron microscopy. The results showed that the dope extrusion rates played significant effects on the cross-section structure, surface morphology, degree of crystallization, and sound velocity of the nascent fibers. With an increase of dope extrusion rate, the surface roughness increased, and the sound velocity had a point of inflexion. Moreover, the degree of crystallization had a maximum when the dope extrusion rate was 5.92 m/min.     

三角形PAN纤维湿法纺丝工艺研究

采用三角形喷丝板,以二甲基亚砜为溶剂,进行聚丙烯腈(PAN)湿法纺丝。探讨凝固成形条件及后拉伸对三角形PAN纤维截面形状、声速和力学性能的影响。结果表明:随着凝固浴浓度的升高,PAN初生纤维的异形度降低,声速和力学性能均先升高后降低;随着凝固浴温度的升高,PAN初生纤维的异形度增大,声速和力学性能均降低;随着喷丝头拉伸比的增加,PAN初生纤维的异形度增加,声速和力学性能也都呈上升趋势,随着后拉伸的进行,三角形PAN纤维的异形度基本保持不变,其力学性能和声速均逐渐升高。     

Influence of process parameters on the structure formation of man‐made cellulosic fibers from ionic liquid solution

The influence of dry‐jet wet spinning parameters on the production of man‐made cellulosic fibers from 13 wt % cellulose/1,5‐diazabicyclo[4.3.0]non‐5‐ene acetate solutions was investigated. The spinneret nozzle diameter, extrusion velocity, draw ratio, and coagulation bath temperature were the studied parameters. The production of highly oriented fibers was favored by selecting higher extrusion velocity and lower spinneret diameter. A spinneret size of 100 µm and a draw ratio of 6 were sufficient to highly orient the cellulose macromolecules and achieve tenacities above 40 cN/tex (600 MPa). Total orientation assessed via birefringence measurement, tenacity, and Young's modulus values reached a plateau at a draw of 6 and no further development in properties was observed. A temperature of the aqueous coagulation bath of 15 °C slightly promoted greater orientation of the fibers by hampering structural changes of the cellulose macromolecules in the nascent solid fibers. Furthermore, the determination of the elongational viscosity of the liquid thread via the measurement of radial force tensor was tested and showed promising results. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43718.     

Gel spinning of polyacrylonitrile fibers with medium molecular weight

A new gel‐spinning method was employed to prepare polyacrylonitrile (PAN) fibers from a PAN spinning solution with dimethylsulfoxide and water as a mixed solvent. Aging at 25 °C for 120 min brought the spinning solution to the sol–gel transition and a three‐dimensional gel formed before entering the coagulation bath. The as‐spun fibers from the solution at the sol–gel transition and in the gel state possess a circular cross‐section. Compared with dry‐jet wet‐spun fibers, the gel‐spun fibers have a more compact structure, fewer voids and better mechanical properties after a three‐stage drawing. Moreover, the gel‐spun fibers obtained from the extraction bath have a more homogeneous microstructure and better packed supermolecular structure. The physical properties of the extracted gel‐spun fibers are also better than those of coagulated gel‐spun fibers. Copyright © 2010 Society of Chemical Industry     

Structure development during dry–jet–wet spinning of acrylonitrile/vinyl acids and acrylonitrile/methyl acrylate copolymers

Dry–jet–wet spinning of three copolymers, poly(acrylonitrile/methyl acrylate), poly(acrylonitrile/methacrylic acid), and poly(acrylonitrile/itaconic acid), was performed with a dimethylformamide/water (60:40 v/v) coagulation bath at different temperatures (10–40°C). The fibers were stretched to different levels (1.1–6×) in boiling water, collapsed, and annealed over a heater plate at 130°C. The effects of the polymer composition, coagulation bath temperature, and draw ratio on the cross‐sectional morphology, structure, and tensile properties are reported. The cross‐sectional shape of the gel fibers underwent a transition from a kidney shape to an oval shape, and macrovoids began to appear at higher temperatures. However, F(AN/IA) gel fibers changed from a kidney shape to an irregular shoe type with a gel network of interconnected polymer fibrils. For F(AN/MAA) gel fibers, the diameter increased from 45 to 67 μm when the coagulation bath temperature was increased from 10 to 40°C, and the denier value decreased from 17.5 to 14.3 den/filament. The strength, modulus, and elongation at break decreased with an increase in the coagulation bath temperature. For F(AN/MAA) fibers coagulated at 10°C in a spin bath, the strength increased from 0.43 to 2.213 g/den, the modulus increased from 27 to 76 g/den, and the density increased from 1.177 to 1.196 g cm^?3 when the gel fibers were drawn to 6×. However, 6× drawn F(AN/MA) fibers had a higher strength (3.1 g/den) and elongation (14.6%) in a 40°C coagulation bath. F(AN/IA) fibers could be drawn only to a draw ratio of 4× instead of the 6× draw ratio for F(AN/MAA) and F(AN/MA) fibers. Therefore, the final F(AN/IA) fibers exhibited poor mechanical properties (tenacity = 0.81 g/den, modulus = 22 g/den, and elongation at break = 8%). The crystallinity did not change significantly (χ_c = 61–63%) with the draw ratio, but the crystal size increased from 22.9 to 43.4 Å and orientation factor from 0.41 to 0.78. The dichroic ratio, measured with Fourier transform infrared, decreased with an increase in the draw ratio, but the sonic modulus and crystalline orientation values increased with an increase in the draw ratio. Thermomechanical data show a maximum physical shrinkage of 51.7% for 6× drawn F(AN/MA) and a minimum physical shrinkage of 30.5% for 4× drawn F(AN/IA) fibers. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 773–787, 2002     

Preparation and properties of conductive polyaniline/poly‐ω‐aminoundecanoyle fibers

Historically, polyaniline (PANI) had been considered an intractable material, but it can be dissolved in some solvents. Therefore, it could be processed into films or fibers. A process of preparing a blend of conductive fibers of PANI/poly‐ω‐aminoundecanoyle (PA11) is described in this paper. PANI in the emeraldine base was blended with PA11 in concentrated sulfuric acid (c‐H₂SO₄) to form a spinning dope solution. This solution was used to spin conductive PANI / PA11 fibers by wet‐spinning technology. As‐spun fibers were obtained by spinning the dopes into coagulation bath water or diluted acid and drawn fibers were obtained by drawing the as‐spun fibers in warm drawing bath water. A scanning electron microscope was employed to study the effect of the acid concentration in the coagulation bath on the microstructure of as‐spun fibers. The results showed that the coagulating rate of as‐spun fibers was reduced and the size of pore shrank with an increase in the acid concentration in the coagulation bath. The weight fraction of PANI in the dope solution also had an influence on the microstructure of as‐spun fibers. The microstructure of as‐spun fibers had an influence on the drawing process and on the mechanical properties of the drawn fibers. Meanwhile, the electrically conductive property of the drawn fibers with different percentage of PANI was measured. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1458–1464, 2002     

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.     

Study of the coagulated structure and fiber strength with wet spinning of aliphatic polyketone with aqueous composite metal salt solutions

Poly(1‐oxotrimethylene) (ECO) was dissolved in aqueous calcium chloride (CaCl₂)/zinc chloride (ZnCl₂) composite metal salt solutions, and the solutions had phase‐separation temperatures greater than 0°C. A higher proportion of CaCl₂ with respect to ZnCl₂ increased the phase‐separation temperature of the ECO solutions. When wet spinning was carried out with a coagulation bath at 2°C, an ECO solution with a higher phase‐separation temperature tended to produce greater ECO fiber strength. Therefore, a higher phase‐separation temperature resulted in coagulated filaments with a denser and more homogeneous cross‐sectional structure. When the metal salt concentration of the coagulation bath was increased with an ECO solution with a phase‐separation temperature of 22°C and a coagulation‐bath temperature of 2°C, the strength of the ECO fibers tended to be lower. Although little difference was observed in the uniformity of the fiber cross sections, a higher metal salt concentration in the coagulation bath facilitated greater spherical growth of the coagulated particles. Large, spherical coagulated particles promoted defects during drawing and thus lowered the strength of the ECO fibers. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1250–1258, 2005     

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     

Effect of the solvent type on the formation and physical properties of polyacrylonitrile fibers via a solvent‐free coagulation bath

Polyacrylonitrile (PAN) fibers were fabricated via a dry‐jet wet‐spinning technique, and a solvent‐free coagulation bath system was adopted. The effects of different types of dope solvent on the formation and physical properties of the PAN fibers were investigated. Dimethylformamide and dimethyl sulfoxide (DMSO) were selected as the solvents and were added to a spinning solution consisting of 18 wt % PAN. The PAN fibers were examined with field emission scanning electron microscopy, differential scanning calorimetry, and thermogravimetric analysis. The field emission scanning electron micrographs revealed that the PAN fibers with the DMSO solvent exhibited a more circular shape and a smoother skin. The PAN fibers with the DMSO solvent had their glass‐transition temperature (T_g) at 121°C. This study indicated that the different types of dope solvent used in the dope preparation did not affect T_g of the PAN fibers because of the solvent‐free coagulation bath system; however, they significantly affected the physical formation of the PAN fibers. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Impact of the wet spinning parameters on the alpaca-based polyacrylonitrile composite fibers: Morphology and enhanced mechanical properties study

The study examined the effect of different wet spinning parameters (e.g., total solid content, coagulation bath concentration, drawing, and stretching) on the morphology and mechanical properties of the wet spun alpaca/polyacrylonitrile (PAN) composite fibers. The alpaca/PAN composite fibers were wet spun using 10, 20, and 30% of alpaca particles along with the PAN polymer. The shear-thinning or non-Newtonian flow behavior was observed among the dope solutions with different solid content. The cross-sectional fiber morphology showed the bean-shaped characteristic for the control PAN fibers, whereas the alpaca/PAN composite fibers exhibited almost circular shape. “Cavity healing” was observed, where noticeable voids and porous areas were demolished in the cross section of the composite fibers, by changing the total solid content and coagulation bath concentration. Although the control PAN fibers exhibited the highest tenacity with lower fiber diameter, the alpaca/PAN composite fibers showed a gradual deterioration in tenacity while adding alpaca particles into the PAN polymeric matrix. Nevertheless, due to the increment in the total solid content, higher draw ratio, and stretching of the fibers, the tenacity, molecular orientation, and the crystallinity of the composite fibers were increased.     

Development of novel film using paramylon prepared from Euglena gracilis

A novel film was developed using paramylon from Euglena gracilis and its physical properties were investigated. Formic acid was suitable for the preparation of a solution of paramylon, and a transparent even yellow film was obtained by casting the solution on a glass plate and drying the cast film in air without using coagulation bath. However, the spinability of a paramylon solution was fairly low. The spinability was a little enhanced by blending polyvinyl alcohol (PVA) up to 70%. The paramylon/PVA blend fibers were produced through wet spinning using coagulation bath of conc. Na₂SO₄ at a room temperature. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3495–3497, 2006