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.     

Effect of DMSO/H2O coagulation bath on the structure and property of polyacrylonitrile fibers during wet‐spinning

The effect of coagulation bath condition on the structure and property of the nascent fibers and polyacrylonitrile fibers during wet‐spinning is studied. The best coagulation condition to produce polyacrylonitrile fibers has been found by examination of EA, XRD, SEM, and so on. The results indicated that when the coagulation bath was DMSO/H₂O system, the temperature was 60°C, the concentration was 65%, the minus stretch ratio was ?10%, fine crystallites and high degree of crystallization in the nascent fibers and polyacrylonitrile fibers could be achieved, and less solvents remained in the nascent fibers with circular cross section morphology. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Structure and properties of aromatic poly(benzimidazole‐imide) copolymer fibers

A series of co‐polyimide fibers were prepared by thermal imidization of copolyamic acids derived from 3,3′,4,4′‐biphenyltertracarboxylic dianhydride (BPDA) and pyromellitic dianhydride (PMDA) in various molar ratios with 2‐(4‐aminophenyl)?5‐aminobenzimidazole (BIA). The dynamic mechanical behaviors of these polyimide (PI) fibers revealed that the glass transition temperature (T_g) was significantly improved upon increasing PMDA content. Heat‐drawing process led to dramatic change on the glass transition behavior of BPDA/BIA system, but had a small impact on BPDA/PMDA/BIA co‐polyimide fibers. This difference for PI fibers is attributed to the different degree of ordered structure of the fibers affected by heat‐drawing. The incorporation of PMDA obviously improved the dimensional stability against high temperature, due to the restricted movement of polymer chains. In addition, the obtained fibers show excellent mechanical and thermal properties because of the strong hydrogen bonding due to the incorporation of benzimidazole moieties. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41474.     

Evolution of polyacrylonitrile precursor fibers and the effect of stretch profile in wet spinning

Wet spinning of polyacrylonitrile-based polymers is a common technique to manufacture carbon fiber precursors. Understanding the role of stretch profile on structural evolution will support efforts to reduce cost and improve process robustness. Fiber stretch generally occurs in three sequential stages: jet stretch, wet stretch (first draw), and hot draw (second draw). In this study, total fiber stretch was kept constant, but distributed differently across the stretch stages yielding three different fiber variants. Samples were collected and analyzed after each stretch stage in order to correlate process parameters to structural information. For all variants, orientation of the ordered phase increases gradually for each stage of stretch while activation energy for the structural relaxation decreases. Alternatively, crystallite size increases substantially during hot draw, which is shown to have the most pronounced effect on cyclization behavior. Given the process conditions, the variant with the lowest jet stretch and highest hot draw demonstrates the highest tenacity and modulus along with the greatest orientation, crystallite size, and highest peak exotherm temperature.     

Effect of sterilization techniques on the physicochemical properties of polysulfone hollow fibers

Sterilized hollow‐fiber membranes are used in hemodialysis, ultrafiltration, bioprocessing, and tissue engineering applications that require a stable and biocompatible surface. In this study, we demonstrated significant changes in the fiber physicochemical properties with different methods of sterilization. Commercial polysulfone (PS) hollow fibers containing poly(vinyl pyrrolidone) were subjected to standard ethylene oxide (ETO), sodium hypochlorite (bleach), and electron‐beam (e‐beam) sterilization techniques followed by analysis of the surface hydrophilicity, morphology, and water‐retention ability. E‐beam sterilization rendered more hydrophilic fibers with water contact angles near 47° compared to the ETO‐ and bleach‐treated fibers, which were each near 56°. Atomic force microscopy revealed lumen root mean square (rms) roughness values near 19 nm for all three sterilization methods; however, e‐beam‐sterilized and bleach‐treated fibers had significantly higher (～ 106 nm) rms values for the outer wall compared to the ETO‐sterilized fibers (～ 39 nm). The increased hydrophilicity and surface area of the e‐beam‐sterilized fiber were reflected by a greater water evaporation rate than that of the ETO‐treated fiber. These results demonstrate that common sterilization methods may significantly and distinctly alter the polymer membrane physicochemical properties, which may, in turn, impact the performance and, in particular, surface fouling. For tissue engineering and bioprocessing applications, these changes may be leveraged to promote cell adhesion and spreading. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Influence of solvent and filler on some physical properties of a fluoroelastomer

Samples of virgin and a crosslinked fluorinated rubber, containing different amounts of carbon black and solvated with methylethyl ketone, have been investigated by differential scanning calorimetry. Although the polymer–solvent interaction increases with decreasing temperature, a process of solvent separation was observed for all of the systems. This process can be attributed to a T_g regulation effect in which solvent crystallization occurs only when the crystallization temperature is higher than the T_g of the system. The interaction between rubber and filler, approximately temperature independent, was found to not influence the glass transition of the rubber–methylethyl ketone systems, even when the carbon black content is on the order of 35 wt %. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 377–384, 1999     

Effect of jet stretch on polyacrylonitrile as‐spun fiber formation

In this article, the effect of jet stretch ratio on the extrudate die‐swell effect of polyacrylonitrile spinning solution and the structure and properties of as‐spun fibers was systematically analyzed by means of X‐ray diffraction (XRD), electron microprobe analysis, and the measurement of die‐swell ratio, boiling‐water shrinkage, porosity, mechanical properties analysis, etc. It revealed the formation mechanism of the die‐swell effect and spin orientation and its influences on the structure and properties of as‐spun fibers. It showed that with the increase of the jet stretch ratio the die‐swell ratio became smaller, both the degree of spin orientation and the crystallinity increased, the microstructure of as‐spun fibers became compact and homogeneous, and the cross section tended to be circular. As a result, the breaking tenacity of as‐spun fibers and resultant precursors all increased. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3348–3352, 2007     

Effect of spinning conditions on the mechanical properties of polyacrylonitrile fibers modified with carbon nanotubes

Carbon nanotubes (CNTs) were used to modify polyacrylonitrile (PAN) polymer. The PAN/CNT composite fibers were spun from dimethylformamide solutions containing different types of CNTs. The effect of nanotube addition to the fiber precursor on the resulting mechanical properties is discussed. In this study, we examined the relationship of the rheological properties of PAN spinning solutions containing various types of CNTs and the tensile strength of the resulting PAN fibers. The presence of CNTs in the PAN spinning solution enhanced its deformability during the drawing stage. This effect resulted in a higher tensile strength in the fibers containing nanotubes, as compared to the pure fibers. The use of a three‐stage drawing process resulted in a significant increase in the tensile strength of PAN fibers modified with multiwalled nanotubes. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Carbon fibers derived from UV‐assisted stabilization of wet‐spun polyacrylonitrile fibers

A rapid, dual‐stabilization route for the production of carbon fibers from polyacrylonitrile (PAN) precursor fibers is reported. A photoinitiator, 4,4′‐bis(diethylamino)benzophenone, was added to PAN solution before the fiber wet‐spinning step. After a short UV treatment that induced cyclization and crosslinking at a lower temperature, precursor fibers could be rapidly thermo‐oxidatively stabilized and successfully carbonized. Scanning electron microscopy micrographs show no deterioration of the microstructure or hollow‐core formation in the fibers due to UV treatment or presence of photoinitiator. Fast‐thermally stabilized pure PAN‐based carbon fibers show hollow‐core fiber defects due to inadequate thermal stabilization, but such defects were not observed in carbon fibers derived from fast‐thermally stabilized fibers that contained photoinitiator and were UV treated. Tensile testing results confirm that fibers containing 1 wt % photoinitiator and UV treated for 5 min display higher tensile modulus than all other sets of thermally stabilized and carbonized fibers. Wide‐angle X‐ray diffraction results show a higher development of the aromatic structure and molecular orientation in thermally stabilized fibers. No significant increase in interplanar spacing or decrease in crystals size were observed within the UV‐stabilized carbon fibers containing photoinitiator, but such fibers retain a higher extent of molecular orientation when compared with control fibers. These results establish for the first time, the positive effect of the external addition of photoinitiator and UV treatment on the properties of the PAN‐based fibers, and may be used to reduce the precursor stabilization time for faster carbon fiber production rate. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40623.     

Alkaline dissolution monitoring of radial‐type polyester microfiber fabrics by a cationic dye‐staining method

The alkaline dissolution behavior of radial‐type polyester microfibers during high‐temperature alkali treatment and cold‐pad batch alkali treatment was successfully monitored using a cationic dye‐staining method. The weight reduction behavior of the alkali‐treated microfiber fabrics and their staining behavior with a cationic dye were compared. In addition, the termination of dissolution monitored by both methods was confirmed by scanning electron microscopy. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 279–285, 2006     

Interrelation between dyeing and thermal properties of PET fibers

The interrelation between dyeing and the thermal properties of micro and conventional poly(ethylene terephthalate) fibers is studied with conventional and modulated differential scanning calorimetry. X‐ray diffraction, density, and birefringence studies are used to confirm the obtained results. It is shown that three studied anthraquinone dyes, in contrast to three studied benzodifuranone dyes, act as plasticizers for the fibers. A comparison between fibers and partially crystallized bulk samples is made. The specific fiber morphology makes the fibers more susceptible to plasticization than are bulk samples. This ability of a dye to lower the glass transition of the fibers will influence the dye diffusion and this information is needed to optimize the dyeing process for a specific dye–fiber combination. Further, the presence of an anthraquinone dye in the fiber alters the melting endotherm by changing the stability of the original crystals. The onset of the melting and recrystallization process is lowered. Although still well above the dyeing temperature, this lowering may be critical for the dimensional stability of the fabrics during any subsequent high‐temperature process. A first investigation of the effect of variations in the thermal properties on the obtained color strength after dyeing is reported. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 105–114, 2003     

Electrospun poly(acrylic acid)/lysine fibers and the interactive effects of moisture,heat, and cross‐link density on their behavior

Poly(acrylic acid) (PAA) is an important polymer frequently used as a superabsorbent in health and hygiene products. As a polyelectrolyte that swells with absorption of water it has potential application in other fields including drug delivery, tissue scaffolds, actuators, and desiccation and humidity control. To be useful in such applications the membrane's mechanical integrity must be maintained while optimizing its moisture absorption properties. In this work PAA membranes are electrospun with lysine as cross‐linking agent. The effects of varying the concentration of the lysine on the cross‐link density and consequently on the thermo‐ and hygro‐mechanical properties of the membranes are studied through electron microscopy, FTIR spectroscopy, and dynamic mechanical thermal analysis (DMTA). Isothermal glass transitions are shown to occur with varying moisture content. The moisture content (or relative humidity) at which the transition occurs is reduced by increasing temperature and can be controlled by varying the cross‐link density. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41252.     

Polyacrylonitrile/acrylamide‐based carbon fibers prepared using a solvent‐free coagulation process: Fiber properties and its structure evolution during stabilization and carbonization

Polyacrylonitrile (PAN)/acrylamide (AM) fibers were fabricated via dry‐jet wet spinning process using a solvent‐free coagulation bath. The effects of AM loading as comonomer on the mechanical and thermal properties of PAN‐based carbon fiber have been studied. The thermal stability and mechanical stability of the fibers were characterized using differential scanning calorimetry (DSC) and tensile testing. Fibers fabricated from PAN with 5 wt% AM had the highest Young Modulus at 5.54 GPa. It also showed better exothermic trend process with broader exothermic peak and lower initiation stabilization temperature compared with homopolymer PAN. The elemental composition and chemical structure evolution of the fibers during the heat treatment processes were evaluated by elemental analyzer and Fourier Transform Infrared Spectroscopy. Crystal structure evolution of the fibers during the heat treatment process was elucidated by X‐ray diffraction (XRD) analysis. The elemental analyzer, XRD and FTIR results revealed that pyrolysis process used had successfully transformed PAN/AM fibers produced from solvent free coagulation bath into carbon fibers that were comparable with the conventional coagulation bath. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers     

Solvent‐free acetylation of lignocellulosic fibers at room temperature: Effect on fiber structure and surface properties

Acetylation is one of the most interesting chemical treatments to improve the affinity of lignocellulosic fibers with polymeric matrices for the elaboration of several types of composites. In this paper, the acetylation of flax and wood pulp (bleached softwood Kraft pulp and thermomechanical pulp) fibers was carried out at room temperature in a solvent‐free system with acetic anhydride in the presence of sulfuric acid as catalyst. The effect of acetylation on the fine structure of fibers was investigated by spectroscopic methods, while the extent of acetylation was quantified by weight percent gain. The effect of reaction time on fiber morphology was studied at macro‐ and microscale using scanning electron microscopy, optical microscopy, and fiber quality analysis. The evolution of the hydrophobic/hydrophilic character of fibers was determined by contact angle measurements. The wettability of fibers by liquid epoxy resin was also evaluated to confirm the improvement of the affinity of acetylated fibers with the epoxy matrix. It was found that the hydrophilic character of fibers decrease with increasing reaction time, whereas the trend was less pronounced beyond specific reaction times. Acetylated fibers can therefore be potential candidates for replacing nonbiodegradable reinforcing materials in composite applications. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42247.     

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.     

Thermal properties relevant to the processing of PET fibers

The thermal properties of poly(ethylene terephthalate) (PET) conventional fibers and microfibers are measured and compared to bulk samples. It is shown that the glass transition temperature (T_g) of the fibers can be monitored with modulated differential scanning calorimetry (MDSC). The T_g region is about 30°C wide and shifted to approximately 110°C for conventional as well as for micro‐PET fibers. The T_g of these fibers is compared to the T_g of cold‐crystallized bulk samples. Upon crystallization, a shift and even a split up of T_g is observed. The second T_g is much broader and is situated around 90°C. This T_g is related to the appearance of a rigid amorphous phase. In comparison, the mobility of the amorphous phase in fibers is even more restricted. The whole multiple melting profile observed on the fibers is the result of a continuous melting and recrystallization process, in contrast to bulk PET. The heat‐set temperature is shown to trigger the start of melting and recrystallization. It is seen in the MDSC as an exotherm in the nonreversing signal and an excess contribution in the heat‐capacity signal. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3840–3849, 2003     

Effects of different coagulation conditions on polyacrylonitrile fibers wet spun in a system of dimethylsulphoxide and water

Polyacrylonitrile (PAN) precursors were prepared by the wet spinning way. The effects of the coagulation conditions, such as coagulation temperature, coagulation ratio, and coagulation concentration, are discussed in detail. While keeping the coagulation bath concentration constant, as the coagulation bath temperature increased, the cross section deviated less from a circular form, and the as‐spun fiber diameter decreased. Measurement to the rate of the boundary movement has been calculated depending on the coagulation rate. While keeping the coagulation bath temperature constant, high coagulation bath concentration can cause more coagulant to diffuse into the solution to the polymer precipitated consequently, which led to a faster coagulation rate. The as‐spun fiber from high coagulation concentration was compacted than those from low concentration. The character of the formed structure reflected the system mobility and capability to crystallize. Improvement in fiber density in the as‐spun fiber resulted in improvements in the tensile strength of the as‐spun fiber. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 3723–3729, 2007     

Temperature dependence of the thermal conductivity and thermal diffusivity of treated oil‐palm‐fiber‐reinforced phenolformaldehyde composites

The effective thermal conductivity (λ_e) and effective thermal diffusivity (χ_e) of oil‐palm‐fiber‐reinforced treated composites were measured simultaneously with the transient plane source technique from 50 to 110°C. The fibers of the composites were treated with sodium hydroxide alkali, silanol, and acetic acid. The experimental results for the different treated composites showed that there were variations in λ_e and χ_e over this temperature range. However, the maximum values of λ_e and χ_e were observed at 90°C, in the vicinity of the glass‐transition temperatures of these composites. An effort was also made to predict the temperature dependence of λ_e and χ_e through the development of an empirical model. The theoretically predicted values of λ_e and χ_e for these composites were in excellent agreement with the experimental results over the entire range of investigated temperatures. Sudden increases in λ_e and χ_e in the glass‐transition region of these composites were indicative of the fact that the crosslinking density decreased and was at a minimum at the temperature at which λ_e and χ_e showed their maxima. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3458–3463, 2003     

Crosslinking studies on poly(ethylene terephthalate‐co‐1,4‐phenylene bisacrylate)

Several compositionally different poly(ethylene terephthalate‐co‐1,4‐phenylene bisacrylate) (PETPBA) copolymers were melt spun into fibers. The resulting fibers were subjected to UV irradiation to induce crosslinking. Evidence of crosslinking was obtained from FTIR, solid‐state ¹³C‐NMR, thermal analysis, and solubility. Irradiation of the fiber results in an increased glass‐transition temperature, reduced thermal shrinkage, and enhanced modulus retention at elevated temperature. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1698–1702, 2004     

Mass production of carbon nanotube‐reinforced polyacrylonitrile fine composite fibers

A facile and large‐scale production method of polyacrylonitrile (PAN) fibers and carboxyl functionalized carbon nanotube reinforced PAN composite fibers was demonstrated by the use of Forcespinning® technology. The developed polymeric fibers and carbon nanotube‐reinforced composite fibers were subsequently carbonized to obtain carbon fiber systems. Analysis of the fiber diameter, homogeneity, alignment of carbon nanotube and bead formation was conducted with scanning electron microscopy. Thermogravimetric analysis, electrical, and mechanical characterization were also conducted. Raman and FTIR analyses of the developed fiber systems indicate interactions between carbon nanotubes and the carbonized PAN fibers through π–π stacking. The carbonized carbon nanotube‐reinforced PAN composite fibers possess promising applications in energy storage applications. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40302.