Manufacture and Characterization of Porous Polypropylene Fibers

Phase separation spinning, a method originally reported by Zwick [1], has been used to produce porous polypropylene fibers by spinning a solution of polypropylene in naphthalene and subsequently extracting the naphthalene with diethyl ether. In phase separation spinning, a hot solution is spun into cool air where the temperature drops below the solubility limit so that the polymer precipitates during spinning. If a relatively nonvolatile solvent in the proper concentration range is used, two continuous phases are formed. Extraction of the nonvolatile solvent produces continuous voids to form a porous fiber.     

Preparation and performances of poly(phthalazinone ether sulfone ketone) hollow fiber membranes with excellent thermotolerance

The cloud points of PPESK/NMP/H₂O ternary system at different temperatures were measured by titrimetric method. The binodal lines in the ternary phase diagram of the poly(phthalazinone ether sulfone ketone (PPESK) dope system was determined, on the basis of the cloud point experimental data being linearly fitted with the semiempirical linear cloud point correlation. Furthermore, phase separation behavior during the phase inversion of PPESK membrane‐forming system was discussed in terms of the phase diagram. Then, dry–wet spinning technique was employed in manufacturing PPESK hollow fiber membranes by immersion precipitation method. The cross‐section morphologies of hollow fibers were observed by scanning electronic microscopy. Also, the effects of dope solution composition and spinning parameters, including the coagulant composition and the spinning temperature on the separation performances of fibers, were evaluated by permeability measurements. The thermotolerance of the PPESK hollow fiber membranes prepared in the work was examined for the permeation operation at different temperatures and pressure differences. The experimental results showed that pure water flux increases several fold along with the temperature increases from 20 to 80°C at different operation pressures, while the solute rejection only decreases slightly. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 878–884, 2006     

Study on gel‐spinning process of ultra‐high molecular weight polyethylene

An ultra‐high molecular weight polyethylene (UHMW‐PE) fiber was prepared by gel spinning using general kerosene as the solvent and gasoline as the extraction solvent. The process of the phase separation of gel as‐spun, spun under various spinning conditions, was investigated. Its extracting and drying process were also studied. The results reveal that the gel as‐spun, spun under a lower spin draft and a lower spin quenching temperature, extracted in times and dried under free‐shrinkage, exhibits a good afterdrawability that eventually endows the fiber with excellent mechanical behaviors. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 670–675, 1999     

Integrally skinned polysulfone hollow fiber membranes for pervaporation

From polysulfone as polymer, integrally skinned hollow fiber membranes with a defect-free top layer have been spun. The spinning process described here differs from the traditional dry-wet spinning process where the fiber enters the coagulation bath after passing a certain air gap. In the present process, a specially designed tripple orifice spinneret has been used that allows spinning without contact with the air. This spinneret makes it possible to use two different nonsolvents subsequently. During the contact time with the first nonsolvent, the polymer concentration in the top layer is enhanced, after which the second coagulation bath causes further phase separation and solidification of the ultimate hollow fiber membrane. Top layers of ± 1 μm have been obtained, supported by a porous sublayer. The effect of spinning parameters that might influence the membrane structure and, therefore, the membrane properties, are studied by scanning electron microscopy and pervaporation experiments, using a mixture of 80 wt % acetic acid and 20 wt % water at a temperature of 70°C. Higher fluxes as a result of a lower resistance in the substructure could be obtained by adding glycerol to the spinning dope, by decreasing the polymer concentration, and by adding a certain amount of solvent to the bore liquid. Other parameters studied are the type of the solvent in the spinning dope and the type of the first nonsolvent. © 1994 John Wiley & Sons, Inc.     

硫氰酸钠法阻燃腈纶纺丝工艺及其性能的研究

探讨了阻燃剂体系的引入对阻燃腈纶纺丝原液可纺性及纤维机械性能的影响 ,确定了纺制阻燃腈纶的工艺条件 ,研究了阻燃剂在纺丝过程中的损失和纤维的耐洗涤性能     

Gel spinning of UHMWPE fibers with polybutene as a new spin solvent

Gel spinning of UHMWPE fibers using low molecular weight polybutene (PB) as a new spin solvent was investigated. A 98/2 wt% PB/UHMWPE gel exhibits a melting temperature around 115°C and shows large‐scale phase separation upon cooling the solution to room temperature. The resulting precursor fiber from this gel was hot‐drawn to a ratio of 120, yielding a fiber with tensile strength of 4 GPa and Young's modulus of over 150 GPa. Wide‐angle X‐ray diffraction indicates good molecular orientation along the fiber axis. The results also demonstrate the potential to further improve the mechanical properties. With respect to the gel spinning industry, this new solvent has a number of advantages over paraffin oil and decahydronaphthalene, and holds a promise of greatly improving the process efficiency. POLYM. ENG. SCI., 56:697–706, 2016. © 2016 Society of Plastics Engineers     

Tailoring the morphology of self-assembled block copolymer hollow fiber membranes

Isoporous asymmetric polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) hollow fiber membranes were successfully made by a dry-jet wet spinning process. Well-defined nanometer-scale pores around 20–40 nm in diameter were tailored on the top surface of the fiber above a non-ordered macroporous layer by combining block copolymer self-assembly and non-solvent induced phase separation (SNIPS). Uniformity of the surface-assembled pores and fiber cross-section morphology was improved by adjusting the solution concentration, solvent composition as well as some important spinning parameters such as bore fluid flow rate, polymer solution flow rate and air gap distance between the spinneret and the precipitation bath. The formation of the well-organized self-assembled pores is a result of the interplay of fast relaxation of the shear-induced oriented block copolymer chains, the rapid evaporation of the solvent mixture on the outer surface and solvent extraction into the bore liquid on the lumen side, and gravity force during spinning. Structural features of the block copolymer solutions were investigated by small-angle X-ray scattering (SAXS) and rheological properties of the solutions were examined as well. The scattering patterns of the optimal solutions for membrane formation indicate a disordered phase which is very close to the disorder-order transition. The nanostructured surface and cross-section morphology of the membranes were characterized by scanning electron microscopy (SEM). The water flux of the membranes was measured and gas permeation was examined to test the pressure stability of the hollow fibers.     

Preparation of poly(lactic acid) fiber by dry–jet–wet spinning. II. Effect of process parameters on fiber properties

The dry–jet–wet spinning process was employed to spin poly(lactic acid)(PLA) fiber by the phase inversion technique using chloroform and methanol as solvent and nonsolvent, respectively, for PLA. The as spun fiber was subjected to two‐stage hot drawing to study the effect of various process parameters, such as take‐up speed, drawing temperature, and heat‐setting temperature on the fiber structural properties. The take‐up speed had a pronounced influence on the maximum draw ratio of the fiber. The optimum drawing temperature was observed to be 90°C to get a fiber with the tenacity of 0.6 GPa for the draw ratio of 8. The heat‐setting temperature had a pronounced effect on fiber properties. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3774–3780, 2006     

Preparation of a heterogeneous hollow‐fiber affinity membrane modified with a mercapto chelating resin

A high‐quality, heterogeneous hollow‐fiber affinity membranes modified with mercapto was prepared through phase separation with blends of a chelating resin and polysulfone as membrane materials, poly(ethylene glycol) as an additive, N,N‐dimethylacetamide as a solvent, and water as an extraction solvent. The effects of the blending ratio and chelating resin grain size on the structure of the hollow‐fiber affinity membrane were studied. The effects of the composition of the spin‐cast solution and process parameters of dry–wet spinning on the structure of the heterogeneous hollow‐fiber affinity membrane were investigated. The pore size, porosity, and water flux of the hollow‐fiber affinity membrane all decreased with an increase in the additive content, bore liquid, and dry‐spinning distance. With an increase in the extrusion volume outflow, the external diameter, wall thickness, and porosity of the hollow‐fiber affinity membrane all increased, but the pore size and water flux of the hollow‐fiber affinity membrane decreased. It was also found that the effects of the internal coagulant composition and external coagulant composition on the structure of the heterogeneous hollow‐fiber affinity membrane were different. The experimental results showed that thermal drawing could increase the mechanical properties of the heterogeneous hollow‐fiber affinity membrane and decrease the pore size, porosity, and water flux of the heterogeneous hollow‐fiber affinity membrane, and the thermal treatment could increase the homogeneity and stability of the structure of the heterogeneous hollow‐fiber affinity membrane. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

湿纺工艺纺制PAN中空纤维成形机理研究

利用C型喷丝板进行挤出凝固,采用湿法纺丝工艺制备聚丙烯腈(PAN)中空纤维,从PAN/二甲基亚砜(DMSO)纺丝原液的流变性能和凝固过程的相分离两个方面探讨了PAN中空纤维的成形机理。结果表明:纺丝液随剪切速率(γ)的增加逐渐发生由粘性向弹性的转变是挤出胀大的主要原因,其粘弹转变点随着温度的升高而向高γ移动,在60℃下的纺丝液弧片接触成孔的理论临界γ为212 s~(-1);纺丝液在凝固浴中表层成膜是PAN-DMSO-H_2O三元体系相分离的结果,纺丝液细流表面成膜速度是影响孔结构闭合的重要因素,可以通过凝固浴浓度和凝固浴调节剂来控制。     

Developing porous fibers by electrocentrifuge spinning system

In this study, polysulfone fibers with various surface morphologies were developed using electrocentrifuge spinning system. The effects of a number of parameters, including the solvent system, spinning system angular velocity, and relative humidity, on the fiber morphology were studied using field emission scanning electron microscopy, porosimetry [Brunauer–Emmett–Teller (BET)], and contact angle test. The results showed that the fibers prepared from the acetone/dimethylformamide (DMF) solvent system had higher micro/nano roughness than those fabricated from the tetrahydrofuran/DMF solvent system, that is to say, the higher the vapor pressure of the solvent, the higher the surface roughness. The acetone/DMF system created fibers that had internal porosity. Also, the relative humidity had a significant effect on providing micro/nano roughness, so that increasing the relative humidity led to an increase in the surface roughness. The increase in the angular velocity caused to stretch the micro/nano patterns and increase the fiber diameter. The results of the BET confirmed the microscopic observations. With the increase in the relative humidity and the use of the acetone/DMF system, porosity, and specific surface area of the fiber increased. X-ray diffraction analysis was also performed and it was found that the presence of moisture did not affect the crystallinity of the fibers. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47513.     

Fast solvent removal by mechanical twisting for gel spinning of ultrastrong fibers

A new method for fast solvent removal in gel spinning was investigated. Instead of solvent evaporation or coagulation as conventionally used, the new method involves mechanically twisting the gel‐fiber along the fiber axis. By removing the majority of solvent in the gel‐fiber by mechanical twisting not only the emission of solvent vapor and the production of waste solvent mixture or coagulation byproducts are minimized but also the fiber production rate is significantly increased. The new solvent removal method was demonstrated through gel spinning of high‐strength ultrahigh‐molecular‐weight polyethylene fibers using both volatile and nonvolatile spin solvents. Approximately 90% of the spin solvent was removed by a single‐step twisting process and the resulting fiber retained the high mechanical properties conventionally obtained. A mechanistic model was developed for estimating the solvent removal as a function of twisting. With respect to the gel spinning industry, the new solvent removal method holds a promise of simplifying the solvent removal and recovery steps and improving the production rate, leading to more efficient and effective gel spinning processes. POLYM. ENG. SCI., 55:745–752, 2015. © 2014 Society of Plastics Engineers     

Fundamental analysis of the dynamics,mass transfer,and coagulation in wet spinning of fibers

New models are developed to analyze the wet spinning process. These involve a formulation of simultaneous overall mass, force, and solvent mass transfer balances. In the first-order model, internal concentration gradients and mass transfer resistance within the fiber are neglected. It is equivalent to the Kase–Matsuo melt spinning model. In the second-order model, concentration gradients and diffusion within the fiber are included. Comparison is made with an experimental study of wet spinning nylon-66 fibers. The first-order model seriously underpredicts final fiber diameter under conditions of specified spinline tension and spinning efflux. The second-order model gives better agreement between theory and experiment.     

Compositional changes during the wet spinning of acrylic fibers from aqueous sodium thiocyanate solvent

The compositional changes taking place during the wet spinning of acrylic fibers from an aqueous sodium thiocyanate solvent were investigated. The composition of the fibers diverted from the precipitation bath after various immersion times was determined gravimetrically, while fiber diameters were imaged to ascertain volumetric changes with time. The kinetics of phase separation were approximated using light transmission and video techniques applied to acrylic films. For coagulation into water at 20 and 40°C and into 15% aqueous NaSCN at 20°C, a greater influx of the nonsolvent to outflow of the solvent was recorded at short timescales. Unexpectedly, both the outflow of the solvent and nonsolvent against the concentration gradient was noted at longer timescales, suggested by the light transmission data to be after the primary phase separation. The consequent reduction in filament diameter, hence, the volume, is discussed in terms of a coarsening mechanism, whereby the mobile polymer lean phase has a route away from the filament into the bath during polymer coarsening. Finally, the compositional changes are plotted on a phase diagram for the system as trajectories into the two-phase region. The polymer-coarsening effect renders the interpretation at longer timescales uncertain. © 1998 John Wiley & Sons, Inc. J Appl Polm Sci 69: 1459–1469, 1998     

Thermodynamic study of a water–dimethylformamide–polyacrylonitrile ternary system

Experimental cloud‐point data were obtained by cloud‐point titration. The phase diagram for a ternary system of water–dimethylformamide–polyacrylonitrile was determined by numerical calculation on the basis of the extended Flory–Huggins theory and was found to agree well with the cloud‐point data. To construct the theoretical phase diagram, three binary interaction parameters were obtained with different methods. The ternary phase diagram was used to investigate the mechanism of fiber formation. The skin–core structure and fingerlike pores in polyacrylonitrile fiber may be effectively eliminated if the composition of the spinning solution is properly chosen, and consequently, homogeneous polyacrylonitrile fiber with a bicontinuous structure and good mechanical properties can be obtained through the spinning process. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Production of porous polylactic acid monoliths via nonsolvent induced phase separation

Polylactic acid (PLA) is one of the most promising polymers for use as the matrix of a bone scaffold. In this work, porous PLA monoliths are fabricated via nonsolvent induced phase separation using dichloromethane as a solvent and hexane as a nonsolvent. The PLA-dichloromethane-hexane compositions which undergo liquid–liquid phase separation followed by gelation are shown to allow for the production of high quality foams. Solvent exchange with methanol after aging the gel is found to substantially reduce shrinkage during drying. Using this simple, versatile and template-free method we produced PLA foams with porosities as high as ∼90.8%, specific surface area up to 54.14 m²/g, crystallinity up to 62.6% and compressive modulus ranging from 1.8 to 57 MPa. Depending on ternary mixture concentration and standing temperature a range of mesoporous and combined meso/macroporous morphologies suitable for use as a bone scaffold are produced.     

Direct drawing of gel fibers enabled by twist‐gel spinning process

A new twist‐gel spinning process for ultrahigh molecular weight polyethylene fibers is demonstrated which significantly increases the extraction rate of nonvolatile spin solvent while simultaneously reducing the consumption of extraction solvent by more than 75%. Applying twist to the gel fiber enables it to be directly hot‐drawn, allowing conventional solvent extraction to proceed significantly faster. While solvent extraction effectiveness is largely enhanced, the new process does not show reduced fiber properties. The tensile strength, Young's modulus, surface morphology, and geometry are relatively unaffected when compared to fibers produced using the conventional gel‐spinning process. The new twist‐gel spinning process is expected to improve the processing efficiency of gel‐spun high‐strength fibers, promoting broad expansion of these high performance fibers into applications that were previously prohibitive due to extremely slow production. POLYM. ENG. SCI., 55:1389–1395, 2015. © 2015 Society of Plastics Engineers     

In situ study on kinetic behavior during asymmetric membrane formation via phase inversion process using Raman spectroscopy

Asymmetric membrane formation has been studied by using an in situ analysis developed with a Micro Raman spectroscopy, which emphasizes kinetic aspects of the phase inversion process. Changes in composition with time was successfully measured on the gelation bath‐side as well as inside the precipitated phase for the polymer/solvent/nonsolvent system of polysulfone/1‐methyl‐2‐pyrrolidinone/ethanol. The results shows that resulting relative mass transfer rates of solvent and nonsolvent during the phase inversion process strongly influence the final membrane morphologies. In addition, ternary compositions at which phase separation initiates were explored by analyzing the coagulation front. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 135–141, 2000     

Tailoring the Morphology of Responsive Bioinspired Bicomponent Fibers

Nature is an intriguing inspiration for designing a myriad of functional materials. However, artificial mimicking of bioinspired structures usually requires different specialized procedures and setups. In this study, a new upscalable concept is presented that allows to produce two bioinspired, bicomponent fiber morphologies (side‐by‐side and coaxial bead‐on‐string) using the same electrospinning setup, just by changing the employed spinning solvent. The generated fiber morphologies are highly attractive for thermoresponsive actuation and water harvesting. Another challenge solved in this work is the compositional characterization of complex fiber morphologies. Raman imaging and atomic force microscopy is introduced as a powerful method for the unambiguous characterization of complex bicomponent fiber morphologies. The work opens the way for the construction of heterostructured fiber morphologies based on different polymers combinations, offering high potential for applications as actuators, smart textiles, water management, drug release, and catalysis.     

The kinetic study for asymmetric membrane formation via phase-inversion process

The kinetics of membrane formation by phase inversion was studied emphasizing the rate of solvent diffusion from a polymer solution during the phase separation. Diffusional behavior of the solvent can be considered Fickian. Membrane morphologies were shown to be strongly dependent on the rate of solvent diffusion, indicating that mass-transfer rates of solvent and nonsolvent during phase separation are crucial for determining the final membrane structure for the following system: polysulfone (polymer), dimethyl acetamide (solvent), and ethanol (gelation medium). Specific reference to the mechanism of macrovoid formation was explored. Macrovoid formation was found to be proportional to the square root of time, suggesting that it is governed by a diffusion process. In addition, latex particles of coagulated polymer formed by the nucleation and growth of a concentrated polymer phase was observed inside the macrovoids. Such a result implies that the macrovoids grow by a diffusive flow which results from the growth of the polymer lean phase during binodal decomposition. © 1996 John Wiley & Sons, Inc.