Wet Spinning Process Research Articles

Rheological behavior of poly(acrylonitrile) concentrated solutions: effect of Sb2O3 nanoparticles on shear and extensional flow

This study investigates the effect of antimony trioxide (Sb2O3) nanoparticles on shear and extensional flow properties of concentrated polyacrylonitrile (PAN) solutions. Through shear rheology, a wide variety of rheological observations, such as Payne effect, applicability of Cox–Merz rule, and range of linear viscoelastic behavior (critical strain) were assessed. The presence of Sb2O3 nanoparticles was found to promote the non-linear viscoelasticity of the solutions and give rise to enhanced heterogeneous domains of PAN in the solution. In elongational flow, thinning dynamics of the nanocomposites was tracked to reproduce the dynamics of deformation in the spinline of the dry-jet wet spinning process. Increasing amounts of Sb2O3 nanoparticles in the solution were shown to improve the lifetime of the filament. All solutions were ruptured through elastocapillary behavior, while strengthened strain-hardening behavior was observed after the addition of Sb2O3 nanoparticles to the polymer solution.

Increasing washing performance of wet-spun fibers

Purpose – The wet-spinning process is very important for the development and production of new lightweight design materials. The washing process is determined as one of the most cost-expensive part of wet spinning. The purpose of this paper is to show the development of a new washing concept. It proposes to increase the washing performance by decreasing fiber-fiber-interfaces during the washing process. Design/methodology/approach – For this purpose, conventional washing concepts are investigated by means of simulations and experiments to obtain process knowledge. Computational fluid dynamics simulation and particle image velocimetry measurements are used to investigate the process. Findings – The overall deficit in conventional washing methods is the large number of fiber-fiber-interfaces, which inhibit the solvent transport out of the compact fiber bundle. Therefore, a new washing concept with included water nozzles is developed. Based on the simulations and observations it is found that the arrangement of the nozzles has direct influence on the fanning of the fiber bundle. Originality/value – With increased fanning of the fiber bundle a more efficient solvent transport is expected. The developed washing box is a prosperous concept to achieve a higher washing performance during the wet-spinning process. The variable design of the washing box makes it possible to test different nozzle configurations and designs. In this paper the two most promising nozzle arrangements are shown and compared to each other.

The formation of polysulfone hollow fiber membranes by the free fall spinning method

The basic principles of the spinning of polysulfone hollow fiber membranes by the dry-jet wet spinning process, where the polymer solution is extruded through an air gap between the spinneret and coagulation bath by the free fall spinning method, have been discussed. The main distinctive feature of the method is that the deformation of both the extruded polymer solution and the nascent hollow fiber (spinneret drawing) is due to the action of the gravity force alone without applying an external tensile force. Published data on the effect of the shear rate of the spinning solution at the spinneret outlet and nascent fiber drawing in the air gap on the structure and permeability of the hollow fiber membranes have been analyzed. The main factors affecting the spinneret drawing and dimensions of the hollow fiber membranes formed by free fall spinning have been experimentally revealed using polysulfones of different molecular weights. The factors are the dope composition, approaching ratio and viscosity, the air gap length, the temperature and the feed rate of the dope and the bore fluid, coagulation power of the bore fluid with respect to the dope. It has been found that as the spinneret draw value increases, the hydraulic permeability and the rejection coefficient of the resulting fiber generally change in a nonmonotonic manner: the pure water flux of the hollow fibers passes through a maximum and the rejection coefficient, through a maximum or minimum. The behavior is caused by the fact that the pore structure of the hollow fiber membranes is formed during uniaxial drawing and, in some cases (at increasing bore liquid flow rate), during biaxial deformation. When an external mechanical force is applied to the forming hollow fiber, an increase in the fraction of interconnected pores and the transition from cylindrical to slitlike pores are possible, which results in an increase in the hydraulic permeability of the fiber walls. A further increase in the spinneret draw ratio results in the reverse process, a decrease in the membrane matrix porosity due to the orientation and collapse of the pores, yielding a decrease in the flux and an increase in the rejection coefficient. By blocking the process of hollow fiber shrinkage through an increase in the bore fluid flow rate (increasing the internal diameter of the hollow fiber), it is possible to enhance the effective porosity of the fiber walls without substantial change in pore size, i.e., a transition from a system with isolated or partly isolated pores to a system of interconnected pores. A sharp increase in the hydraulic permeability of the hollow fiber membranes without a substantial change in their rejection is supposedly caused by this structural change.

Characteristics of wet‐spun and thermally treated poly acrylonitrile fibers

ABSTRACTThe performance of carbon fibers depends on the quality of the precursor and the conditions of the thermal treatment. In detail, for a PAN precursor fiber the viscosity of a spinning dope and the draw ratio during the spinning process needs to be considered. Through wet spinning, different types of PAN precursor fibers with defined spinning parameters, including solid content, solvent content in a bath, and especially draw ratio resulting in defined cross section diameters, were fabricated and analyzed with tensile tests, density investigations, SEM, TGA‐MS, FTIR, and XRD. The results show that the mechanical properties of the fibers correlate to crystallinity. The cross section diameter is strongly related to the morphology of the fibers after thermal treatment. By extending the postdrawing of PAN fibers high tenacities were obtained at the cost of the cross section shape. In addition, TGA measurements reveal trapped residues of the wet spinning process as well as show several chemical reactions takes place at the same time at different temperatures. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43698.

Alginate-assisted synthesis of hollow microfibers assembled by SnO2 nanoparticles

A novel alginate-involving method has been developed to prepare hollow SnO2 microfibers, in which a wet spinning process was combined with pyrolysis oxidation to facilitate scalable production. The resulting hollow SnO2 microfibers consisted of numerous SnO2 nanoparticles with pure tetragonal phase within the microfiber walls. Successful synthesis of this 3D hierarchical and interconnected structure depends strongly on the chelation of Sn2+ and alginate into “egg-box” networks and optimized pyrolysis conditions. SnO2 with this novel structure showed comparable electrochemical performance as the anode material for lithium-ion batteries, especially in ultra-long cycling (200mAhg−1 at 200mAg−1 after 2000cycles with a Coulombic efficiency of near 100%). The natural abundance of alginate, and facile scalability of both the conventional wet-spinning and pyrolysis processes hold the promise for massive preparation and practical application of the novel nanostructured SnO2 materials.

Effective Preparation of Bamboo Cellulose Fibers in Quaternary Ammonium/DMSO Solvent

A novel, efficient, and direct blend of solvents, tetrabutylammonium acetate/dimethyl sulfoxide (TBAA/DMSO), was used for the dissolution and regeneration of bamboo pulp. Regenerated fibers were successfully prepared by a wet spinning process. The bamboo pulp without any pretreatment was readily soluble in the solvent under mild conditions. The dissolution process was observed using a confocal laser scanning microscope (CLSM). Rheological properties of the cellulose solutions at various concentrations were investigated. The regenerated fibers prepared by coagulation in ethanol were characterized with scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermal gravimetric analysis (TGA), and an electronic tensile tester. The SEM images showed that the regenerated fibers possessed a smooth surface and circular cross-section, and the XRD and FT-IR results revealed that the fibers exhibited a cellulose II structure. The thermostability and mechanical properties of the fibers was also investigated.

Advances Toward Forming Synthetic Mimetic Tendon

ABSTRACTCollagen is the most abundant protein present in the human body and found in connective tissues, bone, and tendon. It is also known as a natural resource for healing damaged skin tissues [1]. In this study, under specific microenvironment conditions, mimetic collagen gels were successfully formed synthetically from reconstituted Bovine type I collagen monomers. This was achieved by controlling ionic strength, temperature and pH, allowing fibrils with native mimetic D periodic banding structure to assemble spontaneously within the gels. In addition, by providing appropriate aging temperatures and times, mature collagen fibril growth is also realized in the gels in vitro. Mimetic gels were subsequently formed into fibers through a wet-spinning process. These spun fibers were found to preserve the native mimetic D periodic banding and fibrillar structure formed in the initial gels. As a result, the synthetic fibers resemble native tendon. Here structural development within the gel samples and fibers as a function of processing was analyzed by scanning electron microscopy (SEM). Results in this study also show a potentially new route for the fabrication of synthetic collagen fibers mimicking tendon, which may find applications as engineered tissues or scaffolding materials.

Carbon Nanotube Microfiber Actuators with Reduced Stress Relaxation

Assembling carbon nanotubes (CNTs) into robust macroscopic structures remains the main challenge to efficiently exploit their electromechanical properties in actuator applications. CNT-based actuators generally suffer from creep and stress relaxation due to poor interactions between the assembled CNTs. In order to overcome this limitation, a new class of porous single wall CNT microfiber electrodes is here proposed. The present fibers are produced by a wet spinning process and generate a mechanical stress when they are stimulated at low voltage (∼1 V) in a liquid electrolyte. The used fabrication process enables the inclusion of small amounts of chemically cross-linked polymer such as poly(vinyl alcohol) within the fibers. The presence of cross-linked polymer limits the sliding of nanotubes with respect to each other, without sacrificing the porosity and electrical conductivity of the fibers. As a result, stress relaxation is greatly reduced. The fibers generate a negative stress (propensity to expand) wh...

Carbon fibers prepared from ionic liquid-derived cellulose precursors

Cellulose derivative fibers were prepared via phosphorylation of cellulose with the ionic liquid (IL) 1,3-dimethylimidazolium methyl-H-phosphonate [MMIM]+[MMP]− in the spinning dope and subsequent fiber formation in a dry–wet-spinning process. The thus obtained precursor fibers were carbonized at different temperatures. In order to receive carbon fibers in high carbonization yields, the degree of substitution (DS) was adjusted. The rheological behavior of the spinning dope was studied and the spinning and carbonization parameters were optimized. Moreover, the precursor fiber tensile and structural properties were compared to pure cellulose fibers. According to thermal analysis coupled with evolved gas analysis (TGA-EGA) of the derivative and pure cellulose fibers, the carbonization yields could be almost doubled via the applied functionalization of cellulose and differences in the relative amounts of released gases during carbonization were studied. Both, precursor and carbon fibers were analyzed by, wide-angle X-ray scattering (WAXS), Raman spectroscopy, scanning electron microscopy (SEM), and tensile testing.

A facile approach to spinning multifunctional conductive elastomer fibres with nanocarbon fillers

Electrically conductive elastomeric fibres prepared using a wet-spinning process are promising materials for intelligent textiles, in particular as a strain sensing component of the fabric. However, these fibres, when reinforced with conducting fillers, typically result in a compromise between mechanical and electrical properties and, ultimately, in the strain sensing functionality. Here we investigate the wet-spinning of polyurethane (PU) fibres with a range of conducting fillers such as carbon black (CB), single-walled carbon nanotubes (SWCNTs), and chemically converted graphene. We show that the electrical and mechanical properties of the composite fibres were strongly dependent on the aspect ratio of the filler and the interaction between the filler and the elastomer. The high aspect ratio SWCNT filler resulted in fibres with the highest electrical properties and reinforcement, while the fibres produced from the low aspect ratio CB had the highest stretchability. Furthermore, PU/SWCNT fibres presented the largest sensing range (up to 60% applied strain) and the most consistent and stable cyclic sensing behaviour. This work provides an understanding of the important factors that influence the production of conductive elastomer fibres by wet-spinning, which can be woven or knitted into textiles for the development of wearable strain sensors.

Preparation and Performance of PET-Braid-Reinforced Poly(vinylidene fluoride)/Graphene Hollow-Fiber Membranes

Poly(ethylene terephthalate)- (PET-) braid-reinforced poly(vinylidene fluoride)/graphene (PBR–PVDF/GE) hollow-fiber membranes were prepared by a dry–wet spinning process; they consisted of an outer-coated PVDF/GE separation layer and inner PET hollow tubular braids. GE was employed to increase the hydrophobicity of the membranes. The influences of the GE concentration in the casting solution on the structure and performance of the PBR–PVDF/GE hollow-fiber membranes were investigated in terms of the pore size distribution, water contact angle (CA), water entry pressure (WEP), and differential scanning calorimetry (DSC), and the morphologies of the membranes were observed by field-emission scanning electron microscopy (FESEM). The results indicated that the as-prepared membranes completely repelled water during an 8-h continuous oil/water separation process and were hydrophobic and had a high WEP. The PBR–PVDF/GE hollow-fiber membrane with 0.5 wt % GE exhibited the optimal performance and was used for reusa...

Scalable synthesis of nanometric α-Fe2O3 within interconnected carbon shells from pyrolytic alginate chelates for lithium storage

By combining naturally abundant iron ions and sodium alginate into conventional wet-spinning and pyrolysis processes, α-Fe2O3 could be nanostructured and carbon-coated in a facile and scalable technique.

Assembly of emulsion droplets into fibers by microfluidic wet spinning

Emulsion droplets stabilized by branched copolymers and nano-sized clay are assembled into fibers using a microfluidic wet spinning process.

폴리히드록시아미드/CNT 나노복합체 섬유에 대한 연구

Polyhydroxyamide (PHA) was synthesized by low-temperature solution polymer- ization of 3,3'-dihydroxybenzidine and terephthaloyl chloride. Then, pure PHA and PHA nanocomposite fibers, including multi-walled carbon nanotube (MWNT), were prepared by a wet-spinning process. The structural characteristics, thermal properties, and mechani- cal performances, such as tensile strength, initial modulus, and compressive strength, of the PHA fibers were investigated using FT-IR, TGA, and a tensile testing machine. The TGA results show that the PHA fiber has excellent thermal stability at high temperatures and can undergo thermal cyclization to yield PBO fiber. The tensile mechanical properties of PHA nanocomposite fibers were better than those of pure PHA fiber, and they were improved on increasing the MWNT content. The highly improved mechanical properties of the nanocomposite fibers are thought to be related to the strong interfacial interactions between the PHA matrix and MWNT.

Hydrogen storage characteristics of carbon fibers derived from rice straw and paper mulberry

Highly porous carbon fibers based on rice straw and paper mulberry have been successfully prepared via wet spinning and carbonization process. From the comparison of the morphological structure and specific surface area, the porous carbon fibers derived from rice straw shows a high specific surface area of 2260m2/g. This material exhibits excellent hydrogen storage properties with a gravimetric hydrogen uptakes of 4.35wt% at 77K and 10bar.

Preparation of chitosan fibers using aqueous ionic liquid as the solvent

In this work, acidic ionic liquid glycine hydrochloride (Gly·HCl) is reported as a new solvent for dissolving chitosan. The regenerated chitosan fibers were fabricated by a wet spinning process and characterized by scanning electronic microscopy, fourier transform infrared spectroscopy, wide-angle X-ray diffraction and thermal gravimetric analysis. The result shows that the regenerated chitosan fibers had the same chemical structure as the raw chitosan flake, however, its thermal stability and crystallinity is a little low. Furthermore, a new mechanism of dissolving chitosan in ionic liquid was proposed. The chitosan fibers had soft feeling, excellent antibacterial property and have huge potential application in biomaterials.

The effects of DMSO on structure and properties of PVA/PEDOT:PSS blended fiber

In the present study, novel strong and conductive blended fibers composed of poly(3,4-ethylenedioxythiophene): poly(styrene sulfonate) (PEDOT:PSS) and polyvinyl alcohol (PVA) were successfully fabricated via a wet-spinning process using spinning formulation prepared by doping DMSO into PVA/PEDOT:PSS aqueous solution. The effects of DMSO on structure and properties of PVA/PEDOT:PSS blended fibers were systematically investigated in detail by analyzing the changes in electrical conductivity, aggregation structure, conformational PEDOT chains, morphology and mechanical properties. The results showed that doping of DMSO induced significant conformational changes in PEDOT chains which in turn led to significant enhancement in electrical conductivity and smoother surface morphology as well as better mechanical properties of PVA/PEDOT:PSS blended fibers. The resultant DMSO-doped PVA/PEDOT:PSS blended conductive fibers exhibited an enhanced electrical conductivity up to 21.16 S cm-1. In addition, as the doping concentration of DMSO increased, the surface of blended fibers became less fluted and smoother. The Young’s modulus and tensile strength increased from 3.5 GPa and 115 MPa to 4.95 GPa and 145 MPa respectively, while the elongation at break decreased from 25 % to 17 %.

Supramolecular structure of highly oriented wet-spun polyacrylonitrile fibers used in the preparation of high-performance carbon fibers

Highly oriented polyacrylonitrile (PAN) fibers, which are used in the preparation of high-performance carbon fibers, were prepared via a wet spinning process. The supramolecular structure—i.e., the degree of crystallinity, crystal size, and crystallite orientation—of the PAN fibers was characterized by X-ray diffraction (XRD) using fiber and powder techniques. Two equatorial diffraction peaks with 2θ ∼ 17° and 29.5° were observed in the fiber XRD patterns, which confirmed that the crystalline structure of the PAN fibers was pseudohexagonal with only two-dimensional order in the transverse direction. The powder XRD patterns were resolved into three constituent Lorentz peaks to determine the relative degree of crystallinity. In order to increase the reproducibility of the value for the crystallinity of the fibers, the Gupta–Singhal method was modified by assuming that the degree of crystallinity could be determined from the area under peak 1 (with 2θ ∼ 17°), rather than the combined area of peaks 1 and 3. The evolution of the supramolecular structure of the PAN fibers during the spinning process was also investigated. Results indicated that drying and steam stretching play important roles in the formation and growth of the crystalline structure of the PAN fibers, while the orientation of the structure was only strongly related to the degree of stretching. The effects of the supramolecular structure on the thermal properties and mechanical properties of the PAN fibers were also studied. The perfection of the supramolecular structure influenced the feasibility of cyclization reactions within the PAN fibers and the thermal decomposition of those fibers. The mechanical properties of the PAN fibers were significantly enhanced by increasing the perfection of the supramolecular structure.

Morphology and performance changes of aromatic polysulphonamide fibres formed by dry-jet wet spinning process

Aromatic polysulphonamides fibre, as a high-performance polymer fibre, was prepared by dry-jet wet spinning. The morphology and properties of polysulphonamides fibre along spinning line during dry-jet wet spinning process were investigated. From the development of mechanical and thermal property, it is shown that the fibre showed an improved stress, modulus and density along spinning line and the remarkable improvement was observed only as the fibre was hot stretched above its glass transition temperature (Tg). The property development of the fibre on spinning line is coordinated with the morphology and structure. When the fibre was drawn at the temperature lower than Tg, only the amorphous orientation was observed whereas the crystalline structure was formed as the fibre drawing temperature higher than Tg. The further optimisation of dry-jet wet spinning technology of polysulphonamides fibre could be supported by our results.

A controlled wet-spinning and dip-coating process for preparation of high-permeable TiO2 hollow fiber membranes.

In order to improve the permeate flux of photocatalytic membranes, we present an approach for coupling TiO2 with ceramic hollow fiber membranes. The ceramic hollow fiber membranes with high permeate flux were fabricated by a controlled wet-spinning process using polyethersulfone (PESf) and ceramic powder as precursors and 1-methyl-2-pyrrolidinone as solvent, and the subsequent TiO2 coating was performed by a dip-coating process using tetra-n-butyl titanate as precursor. It has been found that the PESf/ceramic powder ratio could influence the structure of the membranes. Here the as-prepared TiO2 hollow fiber membranes had a pure water flux of 4,450 L/(m(2)·h). The performance of the TiO2 hollow fiber membrane was evaluated using humic acid (HA) as a test substance. The results demonstrated that this membrane exhibited a higher permeate flux under UV irradiation than in the dark and the HA removal efficiency was enhanced. The approach described here provides an operable route to the development of high-permeable photocatalytic membranes for water treatment.