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     

Gel‐spun polyacrylonitrile fiber from pregelled spinning solution

Polyacrylonitrile (PAN) fibers have been gel spun from pregelled PAN spinning solution. The pregelled solution had network structure with elevated spinnability, the as‐spun fiber from which had more circular cross‐section and reduced skin‐core difference. Drawing was more effective in inducing the segmental orientation and crystallization in gel‐spun fiber than in dry–wet spun fiber. The mechanical properties of the gel‐spun fiber were better than those of the dry–wet spun fiber after multi‐stage drawing. POLYM. ENG. SCI., 2010. © 2010 Society of Plastics Engineers     

Spinning and drawing properties of ultrahigh‐molecular‐weight polyethylene fibers prepared at varying concentrations and temperatures

The concentrations and temperatures of ultrahigh‐molecular‐weight polyethylene (UHMWPE) gel solutions exhibited a significant influence on their rheological and spinning properties. The shear viscosities of UHMWPE solutions increased consistently with increasing concentrations at a constant temperature above 80°C. Tremendously high shear viscosities of UHMWPE gel solutions were found as the temperatures reached 120–140°C, at which their shear viscosity values approached the maximum. The spinnable solutions are those gel solutions with optimum shear viscosities and relatively good homogeneity in nature. Moreover, the gel solution concentrations and spinning temperatures exhibited a significant influence on the drawability and microstructure of the as‐spun fibers. At each spinning temperature, the achievable draw ratios obtained for as‐spun fibers prepared near the optimum concentration are significantly higher than those of as‐spun fibers prepared at other concentrations. The critical draw ratio of the as‐spun fiber prepared at the optimum concentration approached a maximum value, as the spinning temperature reached the optimum value of 150°C. Further investigations indicated that the best orientation of the precursors of shish‐kebab‐like entities, birefringence, crystallinity, thermal and tensile properties were always accompanied with the as‐spun fiber prepared at the optimum concentration and temperature. Similar to those found for the as‐spun fibers, the birefringence and tensile properties of the draw fibers prepared at the optimum condition were always higher than those of drawn fibers prepared at other conditions but stretched to the same draw ratio. Possible mechanisms accounting for these interesting phenomena are proposed.     

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     

Structure and properties of partially cyclized polyacrylonitrile‐based carbon fiber—precursor fiber prepared by melt‐spun with ionic liquid as the medium of processing

Carbon fiber has many excellent properties. Currently, the precursor fiber of polyacrylonitrile (PAN)‐based carbon fiber is made from solution by wet or dry spinning process that requires expensive solvents and costly solvent recovery. To solve this problem, we developed a melt‐spun process with ionic liquid as the medium of processing. The melt‐spun precursor fiber exhibited partially cyclized structure. The structure and properties of the melt‐spun PAN precursor fiber were analyzed by combination of scanning electron microscope, Fourier transform infrared spectroscopy, differential scanning calorimetry, X‐ray diffraction, thermogravimetry, ultraviolet spectroscopy, flotation technique, sound velocity orientation test, linear density, and tensile strength tests. The results showed that the tensile strength of melt‐spun PAN precursor fiber was fairly high reached up to 7.0 cN/dtex. The reason was the low imperfect morphology and a cyclized structure formed by in situ chemical reaction during melt‐spun process. Due to the existence of partially cyclized structure in the melt‐spun PAN precursor fiber, exothermic process was mitigated and the heat evolved decreased during thermal stabilization stage in comparison with commercial precursor fibers produced by solution‐spun, which could shorten the residence time of thermal stabilization and reduce the cost of final carbon fiber. POLYM. ENG. SCI., 55:2722–2728, 2015. © 2015 Society of Plastics Engineers     

Development of a gel spinning process for high‐strength poly(ethylene oxide) fibers

This article describes a new gel‐spinning process for making high‐strength poly(ethylene oxide) (PEO) fibers. The PEO gel‐spinning process was enabled through an oligomer/polymer blend in place of conventional organic solvents, and the gelation and solvent‐like properties were investigated. A 92/8 wt% poly(ethylene glycol)/PEO gel exhibited a melting temperature around 45°C and was highly stretchable at room temperature. Some salient features of a gel‐spun PEO fiber with a draw ratio of 60 are tensile strength at break = 0.66 ± 0.04 GPa, Young's modulus = 4.3 ± 0.1 GPa, and a toughness corresponding to 117 MJ/m³. These numbers are significantly higher than those previously reported. Wide‐angle x‐ray diffraction of the high‐strength fibers showed good molecular orientation along the fiber direction. The results also demonstrate the potential of further improvement of mechanical properties. POLYM. ENG. SCI., 54:2839–2847, 2014. © 2014 Society of Plastics Engineers     

Processing,structure, and properties of gel spun PAN and PAN/CNT fibers and gel spun PAN based carbon fibers

Polyacrylonitrile (PAN) and PAN/carbon nanotube (PAN/CNT) fibers were manufactured through dry‐jet wet spinning and gel spinning. Fiber coagulation occurred in a solvent‐free or solvent/nonsolvent coagulation bath mixture with temperatures ranging from ?50 to 25°C. The effect of fiber processing conditions was studied to understand their effect on the as‐spun fiber cross‐sectional shape, as well as the as‐spun fiber morphology. Increased coagulation bath temperature and a higher concentration of solvent in the coagulation bath medium resulted in more circular fibers and smoother fiber surface. as‐spun fibers were then drawn to investigate the relationship between as‐spun fiber processing conditions and the drawn precursor fiber structure and mechanical properties. PAN precursor fiber tows were then stabilized and carbonized in a continuous process for the manufacture of PAN based carbon fibers. Carbon fibers with tensile strengths as high as 5.8 GPa and tensile modulus as high as 375 GPa were produced. The highest strength PAN based carbon fibers were manufactured from as‐spun fibers with an irregular cross‐sectional shape produced using a ?50°C methanol coagulation bath, and exhibited a 61% increase in carbon fiber tensile strength as compared to the carbon fibers manufactured with a circular cross‐section. POLYM. ENG. SCI., 55:2603–2614, 2015. © 2015 Society of Plastics Engineers     

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     

Fundamental understanding of the effect of air‐gap distance on the fabrication of hollow fiber membranes

The objectives of this work are, fundamentally, to understand hollow fiber membrane formation from an engineering aspect, to develop the governing equations to describe the velocity profile of nascent hollow fiber during formation in the air gap region, and to predict fiber dimension as a function of air‐gap distance. We have derived the basic equations to relate the velocity profile of a nascent hollow fiber in the air‐gap region as a function of gravity, mass transfer, surface tension, drag forces, spinning stress, and rheological parameters of spinning solutions. Two simplified equations were also derived to predict the inner and outer diameters of hollow fibers. To prove our hypotheses, hollow fiber membranes were spun from 20 : 80 polybezimidazole/polyetherimide dopes with 25.6 wt % solid in N,N‐dimethylacetamide using water as the external and internal coagulants. We found that inner and outer diameters of as‐spun fibers are in agreement with our prediction. The effects of air‐gap distance or spin‐line stress on nascent fiber morphology, gas performance, and mechanical and thermal properties can be qualitatively explained by our mathematical equations. In short, the spin‐line stresses have positive or negative effects on membrane formation and separation performance. A high elongational stress may pull molecular chains or phase‐separated domains apart in the early stage of phase separation and create porosity, whereas a medium stress may induce molecular orientation and reduce membrane porosity or free volume. Scanning electron microscopic photographs, coefficient of thermal expansion, and gas selectivity data confirm these conclusions. T_g of dry‐jet wet‐spun fibers is lower than that of wet‐spun fibers, and T_g decreases with an increase in air‐gap distance possibly because of the reduction in free volume induced by gravity and elongational stress. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 379–395, 1999     

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 copolymer mixing on elongation property of as‐spun PET fibers

The change of elongation property in the melt spinning process of polyethylene terephthalate (PET) fibers, mixed with small amount of additive copolymer less than 5% by weight, was studied. The additive polymer was synthesized to improve the extensibility of matrix PET in the spinning process. The amount, molecular weight of additive polymer, and spinning conditions were changed to investigate the extensibility of as‐spun fibers. Experimental results show that the blend of copolymer improves the extensibility of as‐spun PET fibers. The elongation at break of as‐spun fibers increases with molecular weight and amount of additive polymer. The additive polymer prevents the fiber orientation and this causes the increase of extensibility of as‐spun fibers. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1426–1431, 2006     

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     

Electrospinning of methacrylate‐based copolymers: Effects of solution concentration and applied electrical potential on morphological appearance of as‐spun fibers

Three methacrylate‐based copolymers [i.e., poly(methacrylic acid‐co‐methyl methacrylate), poly(ethyl acrylate‐co‐methyl methacrylate‐co‐trimethyl‐ammonioethyl methacrylate chloride), and poly(butyl methacrylate–co‐(2‐dimethylaminoethyl) methacrylate‐co‐methyl methacrylate)] were successfully electrospun into fibers using ethanol as the solvent. For a given applied electrical potential, increasing the concentration of the spinning solutions caused the morphology of the as‐spun products to change from discrete droplets to a combination of beaded and smooth fibers and finally to completely smooth fibers. For a given spinning solution having a low concentration, increasing the applied electrical potential increased the electro‐spinnability of the spinning solution. The average diameters for all of the as‐spun fibers were found to range between about 0.2 and 5.5 μm. Generally, for a given applied potential, the average fiber diameter increased with increasing concentration of the spinning solutions, and for a given solution concentration the average fiber diameter increased with increasing applied electrical potential. POLYM. ENG. SCI., 45:1073–1080, 2005. © 2005 Society of Plastics Engineers     

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     

Investigation the jet stretch in PAN fiber dry‐jet wet spinning for PAN‐DMSO‐H2O system

The jet stretch of dry‐jet wet spun PAN fiber and its effects on the cross‐section shape of fibers were investigated for a PAN‐DMSO‐H₂O system. Clearly, the spinning parameters, such as dope temperature, bath concentration, bath temperature, and air gap, all influenced the jet stretch. Also, under uniform conditions, the postdrawing ratio as well as that of jet stretch changed. Under given conditions, as the bath temperature was below 30°C or above 45°C, jet stretch had little effect on the cross‐sectional shapes of PAN fiber. Within the temperature of 30–45°C, fiber's cross‐section shapes change obviously from round over an approximate circular shape into to an elliptical or a flat shape. The scope of jet stretch produced PAN fiber with circular cross‐section was bigger than that in wet spinning. These results indicated that appropriate air gap height, under milder formation conditions in dry‐jet wet spinning, could result in higher jet stretch and higher postdrawing ratio. The appropriate jet stretch and postdrawing ratio could result in circular profile of PAN fiber, which were helpful to produce round PAN precursor with finer size and better properties for carbon fiber. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Studies on high‐speed melt spinning of noncircular cross‐section fibers. III. Modeling of melt spinning process incorporating change in cross‐sectional shape

A numerical analysis program for high‐speed melt spinning of flat and hollow fibers was developed. Change in cross‐sectional shape along the spin line was incorporated adopting a formulation in which energy reduction caused by the reduction of surface area was assumed to be equal to the energy dissipation by viscous flow in the plane perpendicular to the fiber axis. In the case of flat fiber spinning, the development of temperature distribution in the cross section was considered. It was found that the empirical equations for air friction and cooling of the spin line of circular fibers can be applied for the flat fiber spin line if the geometrical mean of long‐axis and short‐axis lengths was adopted, instead of fiber diameter, as the characteristic length for Reynolds number and Nusselt number. Three features expected through the high‐speed spinning of noncircular cross‐section fibers could be reproduced: (1) although cooling of the flat fiber spin line was enhanced, calculated tension at the position of solidification was not affected much by the difference in cross‐sectional shape; (2) change in cross‐sectional shape proceeded steeply near the spinneret; and (3) temperature at the edge became significantly lower than that at the center in the cross section of flat fibers. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1589–1600, 2001     

Molecular order in spider major ampullate silk (dragline): Effects of spinning rate and post‐spin drawing

Optical birefringence measurements are used to characterize how the molecular order of spider (Nephila clavipes) major ampullate silk is affected by linear spinning rate, by the extent of post‐spin drawing, and by post‐spin drawing rate. Results are interpreted qualitatively in terms of a simple microstructural model, in which birefringence depends on both the overall degree of molecular orientation and the extent to which crystalline regions are present. In contrast to the behavior of conventional, synthetic polymers, birefringence is found to be an unreliable predictor of tensile stiffness: microstructural changes that lead to increased birefringence may leave stiffness unchanged or, in some cases, lower than before. It is unlikely that economic processing of silk‐like polymers into fiber that exhibits biomimetic tensile properties can be achieved with spinning followed by drawing, or with a single spinning step. Instead, spinning followed by thermochemical treatment under load may be needed to obtain the critical combination of molecular orientation and crystallinity in commercially satisfactory time scales. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 895–903, 1999     

Spinning fibers from poly(ethylene terephthalate) bottle‐grade waste

Poly(ethylene terephthalate) bottle‐grade (BG) waste was converted into spinnable chips and spun on a laboratory‐scale melt‐spinning apparatus into filaments. Virgin fiber‐grade (FG) polyester chips were blended with BG waste during melt spinning so that the influence of blending on the fiber properties could be studied. Subsequently, the scaling‐up of the process was carried out in a polyester recycling plant so that staple fibers could be obtained. In this part of the study, the spinning of blends of BG waste and FG waste was carried out. The BG waste was found to be superior feed stock for melt processing. Fibers with unique properties were obtained from the BG waste. Staple fibers obtained by the blending of FG and BG waste showed properties different from those of fibers spun from BG waste alone. This study also showed that using blends of BG and FG waste could improve the melt processing and staple‐fiber properties. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3536–3545, 2003     

Effect of gel spinning accompanied with cross‐linking using boric acid on the structure and properties of high‐molecular‐weight poly(vinyl alcohol) fiber

To enhance the thermal stability of poly(vinyl alcohol) (PVA) fiber, the fiber was prepared from the gel spinning of high molecular weight (HMW) PVA by using dimethyl sulfoxide/water (8/2, v/v) as a solvent, accompanied with the cross‐link by boric acid (B‐PVA). In addition, the structure and properties of the B‐PVA fiber were compared with those of the HMW PVA fiber obtained by using the same spinning system without cross‐linking (NB‐PVA). Through a series of experiments, it turned out that cross‐linking actualized by an optimum amount of boric acid (0.3 wt % based on PVA) and zone drawing caused significant changes in the properties of HMW PVA gel fiber. That is, cross‐linking increased thermal degradation temperatures at each degradation step and amounts of final residues, resulting in improving thermal properties of the PVA fiber. On the contrary, it was found that in the case of the B‐PVA fiber, some broadening of the original PVA unit cell occurred, which was identified by the peak shift to lower angle in X‐ray diffractogram. The tensile strength and Young's modulus of B‐PVA fiber with draw ratio of 15 are 23.1 and 308.3 g/d, respectively. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Melt‐spinning process of a tetrafluoroethylene– hexafluoropropylene copolymer

An industrial melt‐spinning process of tetrafluoroethylene– hexafluoropropylene copolymer (FEP) using an extruder was studied. The novel “spinneret,” having both a large‐diameter spinning nozzle and a high‐temperature vessel, was used to solve the problem of filament breakage on the spinning line caused by high melting viscosity of FEP. The extruder, with its long feed zone, was newly designed to function with a geared pump. The strength of fibers increased with drawing of as‐spun fiber. FEP fibers up to six denier were continuously produced through long‐run production. According to this new process, FEP fibers can be supplied for textile or industrial application. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2366–2371, 2002