Fiber structure formation in ultra-high-speed melt spinning of poly(ethylene 2,6-naphthalene dicarboxylate)

The high-speed melt spinning of poly(ethylene 2,6-naphthalene dicarboxylate) (PEN) was performed up to the take-up velocity of the ultra-high-speed region, 9 km/min. From the investigations of the structure and physical properties of the as-spun fibers, the high-speed spinning of PEN was divided into three regions in terms of the mechanism of fiber structure formation. The first region is the take-up velocity of up to 2.5 km/min and the birefringence of up to 0.08 where only a slight increase in molecular orientation was attained. At the take-up velocity of 2.5–4.5 km/min and the birefringence of 0.08–0.25, although some experimental evidences indicated that the orientation-induced crystallization did not occur, there was an increase in the fiber density which suggested the formation of some ordered structure. At the take-up velocity > 4.5 km/min and birefringence > 0.25, the orientation-induced crystallization occurred. The fibers obtained in this region were characterized by the formation of the crystalline structure dominated by the β form. The presence of the necklike deformation in the spinning line was also confirmed. The solidification temperature of the spinning line analyzed from the diameter profile suggested that the formation of β modification crystals occurred at relatively low crystallization temperatures in comparison with that in an isotropic state. Therefore it was indicated that the presence of elongational stress in the spinning line promoted the formation of the β modification crystals. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 1415–1427, 1997     

不同制备方法所得PEN纤维的结构性能比较

利用高速纺丝法与纺丝拉伸一步法两种不同的方法制备聚萘二甲酸乙二酯 ( PEN)纤维 ,以DSC、X射线衍射、声速、力学测试等手段分析其结构、热学及力学性能并进行比较。结果表明 :以上两种纺丝法所制备 PEN纤维的晶型、晶粒尺寸不同 ;在所采用的高速纺丝速度范围内 ,分别以 6,7,8km/m in的速度纺制的试样结构性能基本相同 ;而纺丝拉伸一步法中不同的拉伸倍数对纤维的取向度影响较大 ,进而使杨氏模量、断裂强度和断裂伸长率变化较大     

Surface modification of polypropylene fiber for hydrophilicity enhancement aided by DBD plasma

Low-wetting low-hydrophilicity polipropylene fiber has been treated by means of non-thermal dielectric barrier discharge plasma. The fiber has been characterized before and after the treatment by scanning electron microscopy (SEM), X-ray diffraction, atomic force microscopy (AFM) and industrial tests of submersion in water. The cold plasma was generated in a helium–air mixture at a 2 kHz frequency and 12–18 kV potential. The treatment periods ranged from 1 min up to 3 min. The results present an increase in the oxygen content which rose from 2.5% to 4.8%. SEM analysis reveals a surface change of the fiber with the formation of nodules, which is confirmed by AFM. Water submersion experiments show an enhancement of the hydrophilic capability of the samples.     

Stress-induced structure transition of syndiotactic polypropylene via melt spinning

Syndiotactic polypropylene (sPP) fiber was prepared by melt spinning with the taken-up velocity of 200-700 m/min, the conformation and crystallization of which were systematically investigated by a combination of Fourier transform infrared (FTIR) spectroscopy, wide-angle X-ray diffraction (WAXD) and differential scanning calorimetry (DSC). The results indicated that sPP fibers consist of form I crystal with helical conformation at the spinning velocity of 200-300 m/min, and the crystallinity and orientation are improved with the increase of spinning velocity in this range. As the spinning velocity exceeds 300 m/min, sPP fibers contain mainly mesophase with trans-planar conformation and the content of form I decreases correspondingly. The crystallization behavior of sPP fiber with spinning velocity is different from that of most other crystalline polymers, i.e., the theory of orientation-induced crystallization is not well conformed to. For sPP, form I comprising of helical conformation is thermodynamically stable, though extensional stress can lead to transition from helical to trans-planar conformation, which is not favorable for the crystallization of form I.     

Structure and properties of thermotropic liquid crystal polymer and poly(ethylene 2,6‐naphthalate) blend fibers

BACKGROUND: The melt blending of thermotropic liquid crystal polymers (TLCPs) using conventional thermoplastics has attracted much attention due to the improved strength and tensile modulus of the resulting polymer composites. Moreover, because of their low melt viscosity, the addition of small amounts of TLCPs can reduce the melt viscosity of polymer blends, thereby enhancing the processability. RESULTS: In this study, TLCP/poly(ethylene 2,6‐naphthalate) (PEN) blend fibers were prepared by melt blending and melt spinning to improve fiber performance and processability. The relation between the structure and the mechanical properties of TLCP/PEN blend fibers and the effect of annealing on these properties were also investigated. The mechanical properties of the blend fibers were improved by increasing the spinning speed and by adding TLCP. These properties of the blend fibers were also improved by annealing. The tensile strength of TLCP5/PEN spun at a spinning speed of 2.0 km h^?1 and annealed at 235 °C for 2 h was about three times higher than that of TLCP5/PEN spun at a spinning speed of 0.5 km h^?1. The double melting behavior observed in the annealed fibers depended on the annealing temperature and time. CONCLUSION: The improvement of the mechanical properties of the blend fibers with spinning speed, by adding TLCP and by annealing was attributed to an increase in crystallite size, an increase in the degree of crystallinity and an improvement in crystal perfection. The double melting behavior was influenced by the distribution in lamella thickness that occurred because of a melt‐reorganization process during differential scanning calorimetry scans. Copyright © 2007 Society of Chemical Industry     

Structure and property studies of poly(trimethylene terephthalate) high-speed melt spun fibers

Poly(trimethylene terephthalate) has been melt spun at various take-up velocities from 0.5 to 8 km/min to prepare fiber samples. The effect of take-up velocity on the structure and properties of as-spun fibers has been characterized through measurements of birefringence, density, wide-angle X-ray scattering, DSC melting behavior, tensile properties and boiling water shrinkage (BWS). The birefringence exhibits a maximum at take-up velocities between 3 and 4 km/min. The fiber samples spun at the lower take-up speeds have essentially amorphous structures, while the filaments prepared at a velocity range higher than 4 km/min all possess an obvious crystalline structure. With increasing take-up speed, a steady improvement in tensile strength, elongation to break, and BWS is found, whereas the initial modulus remains almost constant within the measurement error, over the entire take-up speed range between 0.5 and 8 km/min.     

Preparation of a carbon nanotube/carbon fiber multi-scale reinforcement by grafting multi-walled carbon nanotubes onto the fibers

To prepare a carbon nanotube (CNT)/carbon fiber multi-scale reinforcement (MSR), multi-walled carbon nanotubes (MWCNTs) functionalized at the end caps with hexamethylene diamine (HMD) are grafted onto the surfaces of carbon fibers treated with acyl chloride. The surface element concentrations, surface functional groups and morphology of the MSR were examined by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). XPS spectra indicate that sp² and sp³ carbon atoms are major components in the MSR surface, and the carbon fiber surface structure is not destroyed. There is 17.41% of C-NH_x in the surface of the MSR, which suggests that MWCNTs are covalently grafted onto carbon fiber surfaces. SEM shows that the grafted MWCNTs stick to the carbon fiber surface at different angles, and are uniformly distributed along the outer edges of the grooves in the fiber surface. The grafted MWCNTs are 50-200 nm in length and around 14 nm in diameter. It was found that the grafting increases the weight of carbon fiber by 1.2%, which implied that a considerable amount of MWCNTs were grafted onto carbon fiber surfaces.     

Structure development in high-speed spinning of polyethylene naphthalate (PEN) fibers

The structural evolution in fibers produced by high-speed fiber spinning of Polyethylene 2,6 naphthalene dicarboxylate (polyethylene naphthalate) was investigated. The fibers were found to remain amorphous at speeds up to 2500 m/min, and subsequent increases in speed resulted in highly oriented crystalline domains containing primarily α crystalline modification. The fibers processed at and above 3500 m/min were found to contain the β modification together with the α modification. At the highest speed investigated, 4000 m/min, the crystalline regions became disordered, and this was attributed to low deformation temperatures that accompany neck-like deformation. Constrained annealing of the fibers results in relatively unoriented crystalline structure at 500 m/min. Although the WAXS patterns of fibers spun in the 1000–2500 m/min range do not show any crystalline peaks, these fibers develop crystalline regions with significant orientation upon constrained annealing. In addition, these regions were found to have both α and β crystalline phases, indicating that not only the α but also the β phase can be grown from the oriented amorphous precursors upon constrained annealing. From our experimental results we extrapolated a value of 0.791 100% crystalline PEN. The estimated intrinsic birefringence value for the amorphous PEN is 0.75. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 729–747, 1997     

Analysis of the tensile modulus of poly(p‐hydroxybenzoate)/poly(ethylene terephthalate)/poly(ethylene 2,6‐naphthalate) ternary polyester composite fibers

Liquid crystalline polymer reinforced plastics were prepared by compounding (PHB/PEN/PET) blends. A fibrillar PHB structure was formed in situ in the PEN/PET matrix under a high elongational flow field during melt‐spinning of the composite fibers. The formation of PHB microfibrils in the composite fiber with different PHB contents and winding speeds was observed. The PHB microfibril reinforced PEN/PET composite fibers exhibited an unexpectedly low tensile modulus. We have evaluated the tensile modulus of the fibers using the non‐modified 22 and a modified 23 Halpin–Tsai model. From the analysis of both models, large differences were found between the theoretical and experimental values of the tensile modulus, and the low value of the tensile modulus of the composite fiber could not adequately be explained by either model. Thus, we analyzed the observed modulus values using the Takayanagi model, 24 which describes the concept of mechanical discontinuities in semi‐crystalline polymers. Using the Takayanagi model, the effective fraction of continuous or discontinuous microfibrils was evaluated. Consequently, we could successfully explain the very low modulus of the PHB/PEN/PET composite fiber, having a large number of PHB microfibrils, using the Takayanagi model. Copyright © 2003 Society of Chemical Industry     

Structure development and properties of high-speed melt spun poly(butylene terephthalate)/poly(butylene adipate-co-terephthalate) bicomponent fibers

Ultra-high-speed bicomponent spinning of poly(butylene terephthalate) (PBT) as sheath and biodegradable poly(butylene adipate-co-terephthalate) (PBAT) as core was accomplished with the take-up velocity up to 10 km/min. The structure development of the individual component and the properties of PBT/PBAT fibers were investigated through the measurements on differential scanning calorimetry, wide-angle X-ray diffraction, birefringence and tensile test. Due to the mutual interaction between two polymer-melts along the spinline, the processability of both components in PBT/PBAT bicomponent spinning was improved compared with those of corresponding single component spinnings. Furthermore, in PBT/PBAT fibers, the structure development of PBT component was found to be greatly enhanced, which led to the improvement in its thermal and mechanical properties; whereas the structure development of PBAT component was significantly suppressed, in which nearly non-oriented structure was observed in both crystalline and amorphous phases.     

Orientation of multiwalled carbon nanotubes in composites with polycarbonate by melt spinning

A conductive polycarbonate (PC) composite containing 2 wt% multiwalled carbon nanotubes (MWNT) and pure PC were melt spun using a piston type spinning device. Different take-up velocities up to 800 m/min and throughputs leading to draw down ratios up to 250 were used. The composite material of PC with MWNT was prepared by diluting a PC based masterbatch consisting of 15 wt% MWNT by melt mixing in an extruder. The alignment of the nanotubes within melt spun fibers with draw down ratios up to 126 was investigated by TEM and Raman spectroscopy. The nanotubes align in their length axis along the fiber axis increasingly with the draw down ratio, however, the curved shape of the nanotubes still exist in the melt spun fibers. At higher draw down ratios, the MWNT started to align by reducing their curvature. Polarized Raman spectroscopy indicated that the D/D and G/G ratios parallel/perpendicular to the fiber axis increase for both MWNT bands in a similar manner with the draw down ratio. Interestingly, with increasing alignment electrical conductivity of the fibers is lost. Mechanical investigations revealed that at low spinning speeds elongation at break and tensile strength of the composite are lower than those of the pure PC. However, at the highest take-up velocity of 800 m/min the elongation at break is higher and true stress at break of the composite fiber is comparable to the pure PC fiber.     

X-ray studies of regenerated cellulose fibers wet spun from cotton linter pulp in NaOH/thiourea aqueous solutions

Regenerated cellulose fibers were fabricated by dissolution of cotton linter pulp in NaOH (9.5 wt%) and thiourea (4.5 wt%) aqueous solution followed by wet-spinning and multi-roller drawing. The multi-roller drawing process involved three stages: coagulation (I), coagulation (II) and post-treatment (III). The crystalline structure and morphology of regenerated cellulose fiber was investigated by synchrotron wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS) techniques. Results indicated that only the cellulose II crystal structure was found in regenerated cellulose fibers, proving that the cellulose crystals were completely transformed from cellulose I to II structure during spinning from NaOH/thiourea aqueous solution. The crystallinity, orientation and crystal size at each stage were determined from the WAXD analysis. Drawing of cellulose fibers in the coagulation (II) bath (H₂SO₄/H₂O) was found to generate higher orientation and crystallinity than drawing in the post-treatment (III). Although the post-treatment process also increased crystal orientation, it led to a decrease in crystallinity with notable reduction in the anisotropic fraction. Compared with commercial rayon fibers fabricated by the viscose process, the regenerated cellulose fibers exhibited higher crystallinity but lower crystal orientation. SAXS results revealed a clear scattering maximum along the meridian direction in all regenerated cellulose fibers, indicating the formation of lamellar structure during spinning.     

Characterization on mixed-crystal structure and properties of poly(butylene adipate-co-terephthalate) biodegradable fibers

Biodegradable ideal random copolymer poly(butylene adipate-co-terephthalate) (PBAT), with 44 mol% butylene terephthalate (BT), was melt-spun into fibers with take-up velocity up to 5 km/min. The structure development and properties of the as-spun fibers were investigated through birefringence, WAXD, SAXS, DSC and tensile test. Despite of the ideal randomness and composition (1:1) of PBAT copolymer, PBAT fiber showed well-developed PBT-like crystal structure, while its melting temperature (ca. 121 °C) was over 100 °C lower than that of PBT. Based on the quantitative analyses on the lattice spacing, the crystallinity and the fraction of crystallizable BT sequences, the crystal structure of PBAT was characterized to be formed by mixed-crystallization of BT and BA units, where BA units were incorporated into BT lattice. This mixed-crystal structure was found to undergo PBT-like reversible crystal modification with the application and removal of tensile stress. This crystal modification was found to occur in a higher strain region compared with that of PBT fibers.     

Chitin and chitosan nanofibers: electrospinning of chitin and deacetylation of chitin nanofibers

An electrospinning method was used to fabricate chitin nanofibous matrix for wound dressings. Chitin was depolymerized by gamma irradiation to improve its solubility. The electrospinning of chitin was performed with 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) as a spinning solvent. Morphology of as-spun and deacetylated chitin (chitosan) nanofibers was investigated by scanning electron microscopy. Although as-spun chitin nanofibers had the broad fiber diameter distribution, most of the fiber diameters are less than 100 nm. From the image analysis, they had an average diameter of 110 nm and their diameters ranged from 40 to 640 nm. For deacetylation, as-spun chitin nanofibous matrix was chemically treated with a 40% aqueous NaOH solution at 60 or 100 °C. With the deacetylation for 150 min at 100 °C or for 1day at 60 °C, chitin matrix was transformed into chitosan matrix with degree of deacetylation (DD) ∼85% without dimensional change (shrinkage). This structural transformation from chitin to chitosan was confirmed by FT-IR and WAXD.     

Preparation and microstructure of hollow mesophase pitch-based carbon fibers

Hollow mesophase pitch fibers with rather thin diameter were successfully prepared by spinning through a C-shaped capillary. Die-swell was found to be the main factor affecting the formation of hollow fiber, and this was controlled by varying the spinning temperature. After carbonization at 1000°C, the hollow fibers possess a relatively small outer diameter of 21 μm and an inner diameter of 6 μm, and show better mechanical properties than solid fibers with similar outer diameter. The higher mechanical properties are attributed to the orientation of mesophase molecules which is related to the shape and dimension of the spinneret. The transverse microstructure of hollow carbon fibers is illustrated by scanning electron microscopy (SEM) observations on fracture sections.     

Effect of spinning temperature and blend ratios on electrospun chitosan/poly(acrylamide) blends fibers

We report the formation of non-woven fibers without bead defects by electrospinning blend solutions of chitosan and polyacrylamide (PAAm) with blend ratios varying from 75 wt% to 90 wt% chitosan using a modified electrospinning unit wherein polymer solutions can be spun at temperatures greater than ambient up to 100 °C. Electrospinning at elevated temperature leads to further expansion of the processing window, by producing fibers with fewer defects at higher chitosan weight percentage in the blends. Effects of varying blend ratios, spinning temperatures, and molecular weights on fiber formation were studied and optimum conditions for formation of uniform non-woven fiber mats with potential applications for air and water filtration were obtained. Uniform bead-less fiber mats with fiber diameter as low as 307 ± 67 nm were formed by spinning 90% chitosan in blend solutions at 70 °C.     

Porous nano- and microfibrous polymeric membrane material for catalytic support

High surface area is essential for attachment of functional groups, ions, moieties and nanoparticles. Surface area of fibrous membrane can be enhanced by reducing the fiber diameter or producing the porous fibers. Flow properties of the fibrous membrane can be improved by placing the fibers apart in the fibrous network. By electrospinning, it is feasible to produce the fibrous membrane of specific surface area and Darcy permeability higher than 60 m²/g and 1 × 10⁻¹¹ m², respectively. The interconnected irregular shape mesopores (2-50 nm) within the fibers increase the accessible surface area. On the other hand, presence of macropores (pores larger than 50 nm) largely increases the pore volume (porosity) in fibers and helps to reduce the diffusion resistances. Beaded fibers in the membrane can be used to reduce the bulk transport resistances. We developed a method for incorporating the mesopores and macropores in the nano/microfibers made of engineering plastics. To achieve ∼60 m²/g specific surface area by reducing the fiber diameter, one needs to draw the fibers down to 50-60 nm. In present study, 60 m²/g of specific surface area is achieved through the porous fibers of average diameter of 900 nm. A specific surface area result from the porous fiber is much higher than one can achieve by reducing the diameter of fibers.     

Effect of low‐temperature annealing on dimensional stability of poly(ethylene 2,6‐naphthalene dicarboxylate) fibers melt‐spun at high speed

To investigate structural factors, necessary to obtain a valuable industrial fiber possessing excellent thermomechanical properties, poly(ethylene 2,6‐naphthalene dicarboxylate) (PEN) fibers were produced by high‐speed melt‐spinning to a take‐up speed of 8 km/min, followed by low‐temperature annealing between the glass‐transition temperature (T_g) and exothermic cold crystallization temperature (T_{c cold}), where little transition of crystalline phase, as well as little thermal degradation, takes place. Their thermomechanical behavior, as well as structural variations, were investigated through differential scanning calorimetry, Rheovibron, thermomechanical analysis (TMA), and tensile testing. Two types of the α‐ and α′‐dispersions were observed at near T_g and at a temperature 50–60°C higher than T_g, respectively. The dispersions were affected by rearranged structures, which are generated by developing an inhomogeneous taut structure with rigidity of aromatic segment and aliphatic segment. The α‐dispersion seemed to reflect an inhomogeneous taut structure by the less nearly arranged segments. Consequently, at intermediate take‐up speeds between 2 and 6 km/min the inhomogeneous taut structure may be partially formed, but the homogeneously ordered structure may be enlarged as the take‐up speed and annealing temperature increased. Thermal shrinkage increased above the α‐dispersion temperature, which suggested that the onset point of dimensional change in PEN fibers was attributed to α‐dispersion. In the case of annealed fibers, the start of length change coincided with the respective annealing temperatures, which indicated that dimensional stability could be gained from restraining the inhomogeneous taut structure in the amorphous region without the transition of crystalline phase by annealing between T_g and T_{c cold}. Therefore, to obtain dimensional stability in PEN fibers, it is supposed that the inhomogeneous taut structure exhibited by the α‐dispersion should be controlled. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 212–218, 2005     

Fine structure and physical properties of polyethylene/poly(ethylene terephthalate) bicomponent fibers in high‐speed spinning. I. Polyethylene sheath/poly(ethylene terephthalate) core fibers

The high‐speed melt spinning of sheath/core type bicomponent fibers was performed and the change of fiber structure with increasing take‐up velocity was investigated. Two kinds of polyethylene, high density and linear low density (HDPE, LLDPE) with melt flow rates (MFR) of 11 and 50, [HDPE(11), LLDPE(50)], and poly(ethylene terephthalate) (PET) were selected and two sets of sheath/core combinations [HDPE(11)/PET and LLDPE(50)/PET bicomponent fibers] were studied. The fiber structure formation and physical property effects on the take‐up velocities were investigated with birefringence, wide‐angle X‐ray diffraction, thermal analysis, tensile tests, and so forth. In the fiber structure formation of PE/PET, the PET component was developed but the PE components were suppressed in high‐speed spinning. The different kinds of PE had little affect on the fine structure formation of bicomponent fibers. The difference in the mechanical properties of the bicomponent fiber with the MFR was very small. The instability of the interface was shown above a take‐up velocity of 4 km/min, where the orientation‐induced crystallization of PET started. LLDPE(50)/PET has a larger difference in intrinsic viscosity and a higher stability of the interface compared to the HDPE(11)/PET bicomponent fibers. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2254–2266, 2000     

Electrosyntheses of poly(neutral red), a polyaniline derivative

The electrochemical oxidation of neutral red in 0.5 mol dm⁻³ H₂SO₄ solution was carried out by using repeated potential cycling between −0.20 and 1.20 V (versus SCE). The polymer film was electrochemically deposited on a platinum anode and had an electrochemical activity in the solution of 0.5 mol dm⁻³ Na₂SO₄ with pH ≤ 4.0. The result from the X-ray photoelectron spectroscopy (XPS) experiment shows that the anions can be doped into the polymer film during the electropolymerization reaction of neutral red. The scanning electron microscopy (SEM) micrograph shows the surface of poly(neutral red) film deposited on the platinum foil is covered with a micro-structured network of mass interwoven fibers with a diameter of 2-4 μm. A straight fiber of the unsystematic micro-fibers is longer than 0.4 mm. The UV-vis spectrum and infrared spectrum (IR) of the polymer are different from those of the monomer.