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     

Poly(ethylene‐2,6‐naphthalate) nanofiber prepared by carbon dioxide laser supersonic drawing

Poly(ethylene‐2,6‐naphthalate) (PEN) nanofiber was prepared by a carbon dioxide (CO₂) laser supersonic drawing. The CO₂ laser supersonic drawing was carried out by irradiating the laser to the as‐spun PEN fiber in a low‐temperature supersonic jet. The supersonic jet was generated by blowing off air into a vacuum chamber from a fiber supplying orifice. The flow velocity from the orifice can be estimated by applying Graham's theorem from the pressure difference between the atmospheric pressure and the pressure of the vacuum chamber. The fastest flow velocity estimated was 396 m s^?1 (Mach 1.15) at a chamber pressure of 6 KPa. The nanofiber obtained at Mach 1.15 was the oriented nanofibers with an average diameter of 0.259 μm, and its draw ratio estimated from the diameters before and after the drawing reached 430,822 times. The CO₂ laser supersonic drawing is a new method to make nanofiber without using any solvent or removing the second component. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Reinforcing properties of poly(trimethyleneterephthalate) by a thermotropic liquid crystal polymer

A thermotropic liquid crystalline copolymer (TLCP) having a trimethylene terephthalate (TT) unit and a triad terephthaloyl mesogenic unit was synthesized and its blends with poly(trimethylene terephthalate) (PTT) were prepared for TLCP‐reinforced fiber spinning. The TLCP, PTT, and their blends were characterized in terms of their thermal, mechanical, and morphological properties. In the hot‐drawn fibers of 20 wt % TLCP/PTT blend, the well‐oriented fibrils were observed at higher temperature (>T_m) than the PTT melt by polarizing optical microscope. With scanning electron microscopy images of cryogenically fractured surfaces of the blends, the TLCP were well dispersed in 0.3 to 0.5 µm in domain size. Interfacial adhesion between the TLCP and PTT seemed fairly good. The TLCP acted effectively as a reinforcing material in PTT matrix, it led to an increase of initial modulus and tensile strength of the blend fibers as TLCP's content increased. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41408.     

Fabrication and Characterization of Glass‐Ceramic Fiber‐Containing Cr3 + ‐Doped ZnAl2O4 Nanocrystals

Glass‐ceramic fibers containing Cr³⁺‐doped ZnAl₂O₄ nanocrystals were fabricated by the melt‐in‐tube method and successive heat treatment. The obtained fibers were characterized by electro‐probe micro‐analyzer, X‐ray diffraction, Raman spectrum and high‐resolution transmission electron microscopy. In our process, fibers were precursor at the drawing temperature where the fiber core glass was melted while the clad was softened. No obvious element interdiffusion between the core and the clad section or crystallization was observed in precursor fiber. After heat treatment, ZnAl₂O₄ nanocrystals with diameters ranging from 1.0 to 6.3 nm were precipitated in the fiber core. In comparison to precursor fiber, the glass‐ceramic fiber exhibits broadband emission from Cr³⁺ when excited at 532 nm, making Cr³⁺‐doped glass‐ceramic fiber a promising material for broadband tunable fiber laser. Furthermore, the melt‐in‐tube method demonstrated here may open a new gate toward the fabrication of novel glass‐ceramic fibers.     

Structure and property relationship of thermotropic liquid crystal polymer and polyester composite fibers

Poly(ethylene 2,6‐naphthalate) (PEN) and poly(ethylene terephthalate) (PET) composite fibers reinforced with a thermotropic liquid crystal polymer (TLCP) were prepared by the melt blending and spinning process to achieve high performance fibers with improved processability. Polymer composite fibers consisting of cheap polyester and small quantity of expensive TLCP are of interest from an economic point of view and from an industrial perspective. The increase in the birefringence and density of the TLCP/PEN/PET composite fibers with the spinning speed was attributable to the enhancement of the molecular orientation and effective packing between chains in the TLCP/PEN/PET composite fibers. Annealing process resulted in the formation of more ordered and perfect crystalline structure and higher crystallinity, improving the mechanical properties of the TLCP/PEN/PET composite fibers. The increase in the crystallite size and the degree of chain extension with increasing spinning speed resulted in the gradual increment of the long period for the TLCP/PEN/PET composite fibers. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006.     

PBT/PET conjugated fibers: Melt spinning,fiber properties,and thermal bonding

This work examines the PBT/PET sheath/core conjugated fiber, with reference to melt spinning, fiber properties and thermal bonding. Regarding the rheological behaviors in the conjugated spinning, PET and PBT show the smallest difference between their melt‐viscosity at temperatures of 290°C and 260°C respectively, which has been thought to represent optimal spinning conditions. The effect of processing parameters on the crystallinity of core material‐PET was observed and listed. In order of importance, these factors are the draw ratio, the heat‐set temperature, and the drawing temperature. The crystallinity of sheath material‐PBT, however, can be considered to be constant, independent of any processing parameters. The bulk orientation, rather than the crystallinity of PET core, dominates the tenacity of PBT/PET sheath/core fiber. Moreover, heat‐set treatment after drawing is recommended to yield a highly oriented conjugated fiber. With respect to thermal bonding, PBT/PET conjugated fibers processed via high draw ratio but low‐temperature heat setting can form optimal thermal bonds at a constant bonding temperature of 10°C above the T_m of PBT.     

Nylon 66 nanofibers prepared by CO2 laser supersonic drawing

Nylon 66 nanofibers were prepared by irradiating as‐spun nylon 66 fibers with radiation from a carbon dioxide (CO₂) laser while drawing them at supersonic velocities. A supersonic jet was generated by blowing air into a vacuum chamber through the fiber injection orifice. The fiber diameter depended on the drawing conditions used, such as laser power, chamber pressure, laser irradiation point, and fiber supply speed. A nanofiber obtained at a laser power of 20 W and a chamber pressure of 20 kPa had an average diameter of 0.337 μm and a draw ratio of 291,664, and the drawing speed in the CO₂ laser supersonic drawing was 486 m s^?1. The nanofibers showed two melting peaks at about 257 and 272°C. The lower melting peak is observed at the same temperature as that of the as‐spun fiber, whereas the higher melting peak is about 15°C higher than the lower one. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014 , 131, 40015.     

Poly(lactide) nanofibers produced by a melt‐electrospinning system with a laser melting device

A new melt‐electrospinning system equipped with a CO₂‐laser melting device was developed. Rod‐like samples were prepared from poly(lactide) pellets, and then fibers were produced from the samples using the new system. The effects of producing conditions on the fiber diameter were investigated. Furthermore, the physical properties of the fibers were investigated. The following conclusions were obtained: (i) in a special case, fibers having an average fiber diameter smaller than 1 μm could be obtained using the system developed; (ii) the fiber diameter could be decreased with increased laser output power, but the physical properties of the fibers such as the melting point and the molecular weight were decreased; and (iii) the electrospun fibers exhibited an amorphous state, and the annealed fibers exhibited an isotropic crystal orientation. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1640–1645, 2007     

Melt‐electrospinning of poly(ethylene terephthalate) and polyalirate

Rodlike polymer samples were made from three kinds of poly(ethylene terephthalate) (PET) pellets with different intrinsic viscosities (IV), and from polyalirate (Vectra) pellets. PET and Vectra fibers were produced using a melt‐electrospinning system equipped with a CO₂‐laser melting device from these rodlike samples. The effects of IV value and laser output power on the fiber diameter of PET were investigated. Furthermore, the effect of the laser output power on the fiber diameter of Vectra was investigated. The crystal orientation of these produced fibers was also investigated by X‐ray photographs. The following conclusions were reached: (i) the diameter of PET fiber decreases with increasing laser output power; (ii) the minimum average diameter of PET fibers is scarcely influenced by the value of IV; (iii) the electrospun PET fibers show isotropic crystal orientation; (iv) fibers having an average fiber diameter smaller than 1 μm cannot be obtained from PET and Vectra using the system developed; and (v) preferred liquid crystal orientation can be seen in electrospun Vectra fibers. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Influence of interchain forces and supermolecular structure on the drawing behavior of nylon 66 fibers in the presence of supercritical carbon dioxide

The drawing behavior and mechanical properties of as‐spun and highly oriented nylon 66 fibers drawn in supercritical carbon dioxide (SCCO₂) were investigated. Conditions including different temperatures, CO₂ pressures, and plasticizers with different polarity were systematically studied. Results indicate that CO₂ is an efficient plasticizer for as‐spun nylon 66 fibers as shown by decreases in the draw stress. In contrast, CO₂ shows only a slight influence on the drawability of highly oriented nylon 66 fiber. The effect of other plasticizers such as water, methanol, and ethanol on the drawability of nylon 66 fibers is very similar to that of CO₂. Tenacity and modulus of one‐stage drawn fibers were less than 0.8 and 5.0 GPa, respectively. Fibers with the highest tenacity and modulus, 0.96/5.04 and 1.06/5.04 GPa, were obtained by two‐stage drawing in SCCO₂ from as‐spun and drawn nylon 66 fibers, respectively. The main reason for the extremely low draw ratios (<6.0) of nylon 66 fibers was the presence of hydrogen bonds in the crystalline phase. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2282–2288, 2004     

Effects of ethylene content of poly(ethylene‐co‐vinyl alcohol) on diameter of fibers produced by melt‐electrospinning

Rodlike samples were made from four kinds of poly(ethylene‐co‐vinyl alcohol) (EVAL) pellets with different ethylene contents. From these rodlike samples, fibers were produced using a melt‐electrospinning system equipped with a CO₂‐laser melting device. The effects on the fiber diameter of the ethylene content and the moisture regain of the rodlike samples were investigated. Furthermore, the physical properties of the fibers were investigated. The following conclusions were reached: (i) EVAL fibers having an average fiber diameter smaller than 1 μm can be obtained using the system developed; (ii) the diameter of EVAL fiber is influenced by the ethylene content and the moisture regain of the starting rods; (iii) the laser heating does not greatly decrease the melting point and the molecular weight of EVAL; and (iv) preferred crystal orientation can be seen in electrospun EVAL fibers. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1368–1375, 2007     

In-situ analysis of fiber structure development for isotactic polypropylene

Structural development of isotactic polypropylene (iPP) fibers was analyzed in real time through in-situ WAXD/SAXS and fiber temperature measurements during CO₂ laser-heated drawing because the CO₂ laser irradiation can nearly fix the necking position on the running fiber. The in-situ WAXD/SAXS measurements were carried out with a high time-resolution of 0.4 ms. The as-spun iPP fibers of two different initial structures were laser-heat-drawn to a draw ratio of 6.5. For the drawing of PP fiber containing mesophase structure, diffraction from the oriented mesophase remained until an elapsed time of 1.0 ms, when oriented α-phase crystal started to form. Meanwhile, for the drawing of PP fiber containing both an α-phase and a mesophase structure, fragmented microcrystals were reorganized by orientation-induced crystallization before an elapsed time of 1.0 ms. The long period increased drastically with fragmentation, and decreased with reorganization. The long period was about 16 nm for both drawn fibers.     

PET microfiber prepared by carbon dioxide laser heating

In preliminary experiments to optimize the condition of a laser heating, zone drawing for poly(ethylene terephthalate) (PET) fiber, a microfiber was prepared by a continuous‐wave carbon dioxide (CW CO₂) laser heating. CW CO₂ laser heating was carried out at an extremely low applied tension (σ_a) at a higher laser power density (PD) as compared to the optimum condition for the laser heating, zone drawing of PET fiber reported previously. The microfibers were obtained by CO₂ laser heating carried out at a PD of 15.8 W cm^?2 and under a σ_a of 0.66 MPa or lower. The diameter of the fiber decreased with a decreasing σ_a and increasing PD. The smaller the diameter, the higher was its birefringence. The smallest diameter fiber obtained at σ_a = 0.17 MPa at PD = 21 W cm^?2 had a diameter of 4.5 μm and a birefringence of 0.112, and its draw ratio estimated from the diameter reached 3086 fold. Such a high draw ratio was not previously attained by any drawing method. In a wide‐angle X‐ray diffraction photograph of the smallest diameter fiber, indistinct reflections due to oriented crystallites were observed. An SEM micrograph of the smallest diameter fiber showed a smooth surface without any crack and was uniform in diameter. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 3297–3283, 2003     

Effect of Blend Ratio and Draw Ratio on the Mechanical Properties of PET/PP Blended Conjugate Fibers

This study analyzes the influence of blend ratio and draw ratio on the fiber properties of blend fibers composed of poly (ethylene terephthalate), or PET, and polypropylene, or PP, (hereafter referred to as PET/PP conjugate fibers). For a comparison, PET and poly (butylene terephthalate), or PBT blends, (hereafter referred to as PET/PBT conjugate fibers) are also investigated. Various blend ratios of fibers are melt spun and drawn in a multistep drawing method. The conjugate fibers are evaluated using tenacity, Young's modulus, wide-angle X-ray diffraction, differential scanning calorimetry (DSC), and scanning electron microscopy (SEM) tests. The results show that multistep drawing using a lower first-step draw ratio provides a higher tenacity and Young's modulus. Furthermore, when the blend ratio is 75/25 in a PET/PP conjugate fiber and 50/50 in a PET/PBT conjugate fiber, the polymer components undergo a phase inversion phenomenon. A PP sub-micron (10^?1 ～ 10⁰ micron) fiber of about 0.0001 ～ 0.00017 tex in fineness, or about 0.4 ～ 0.5 micron in diameter, can be obtained when PET/PP conjugate fiber is treated with a 25% NaOH aqueous solution by weight. However, A PBT sub-micron fiber cannot be achieved using a PET/PBT conjugate fiber.     

Study of the Processing and Mechanical Properties of In Situ Composite Materials of Thermoplastics with Thermotropic Liquid Crystalline Polymers

By blending thermoplastics (TPs)—polycarbonate (PC) and polyethersulfone (PES)—with thermotropic liquid crystalline polymers (TLCPs)—KU9221 and KU9231—and then extruding the blends to form fibers, the in situ reinforcing characteristics were studied. The injection experiment of blends was compared with the extrusion experiment. According to the experimental results, in situ reinforcing characteristics of these processes were analyzed theoretically. These researches have come to some important conclusions. TLCP domains can be transformed to form fibers that are oriented in the direction of flow during processing; these TLCP microfibers result in improved mechanical properties of the TP/TLCP blends. The extruding flow is more effective in orienting TLCP domains and results in better in situ reinforcement than that of injection molding, and the extruded fibers have better mechanical properties. The mechanical properties of the blend fibers are improved greatly with increasing tensile ratio of melt drawing and the content of TLCPs.     

In situ modulus enhancement of polypropylene monofilament through blending with a liquid‐crystalline copolyester

An immiscible blend of poly(propylene) (PP) with a thermotropic liquid‐crystalline polymer (TLCP, trade name Rodrun LC5000), a copolyester of 80/20 mol ratio of p‐hydroxy benzoic acid and polyethylene terephthalate was prepared in a twin‐screw extruder. The blend extrudate was fabricated as monofilament by using a single‐screw extruder equipped with a fiber line. The as‐spun filament was drawn at 120°C to enhance molecular orientation. Morphology, thermal, tensile, and dynamic mechanical properties of both as‐spun and drawn monofilaments were investigated. Almost continuously long TLCP fibers dispersed in PP matrix were obtained in the composite as‐spun monofilaments. The maximum modulus was found in 15 wt % TLCP/PP composite as‐spun filament, an increase of about 2.4 times that of the as‐spun neat PP. For the drawn filaments, the 10 wt % TLCP/PP composite showed a maximum modulus, an increase of about 1.5 times that of the drawn neat PP. The increase in the moduli was attributed not only to the reinforcement by TLCP fibrils with very high aspect ratio but also to the increases in PP crystallinity and molecular orientation through the drawing process. A remarkable improvement in the dynamic mechanical properties of the composite monofilaments was observed, especially in the high‐temperature region. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90:1337–1346, 2003     

Structure formation and characterization of PVDF hollow fiber membranes by melt‐spinning and stretching method

Melt‐spinning and stretching (MS‐S) method was proposed for preparing poly(vinylidene fluoride) (PVDF) hollow fiber membranes with excellent mechanical properties. The morphology and properties of PVDF fibers and membranes were investigated by small angle X‐ray scattering (SAXS), differential scanning calorimeter (DSC), field emission scanning electron microscope, mercury porosimeter, and tensile experiment. SAXS results indicated that the stacked lamellar structure aligned normal to the fiber axis was separated and deformed when the fibers were strained, and the long period of the strained fibers increased accordingly. Factors affecting the membrane properties were mainly spin‐draw ratio, annealing temperature, time, and stretching rate. Experimental results showed that the average pore size, porosity, and N₂ permeation of the membranes all increased with the increasing spin‐draw ratios and annealing temperatures. Annealing the nascent PVDF hollow fibers at 145°C for 12 h was suitable for attaining membranes with good performance. In addition, the amount and size of the micropores of the membrane increased obviously with stretching rate. Tensile experiment indicated PVDF hollow fiber membranes made by MS‐S process had excellent mechanical properties. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Modification of PET in high‐speed melt spinning by blending with PEN

Blends of polyethylene terephthalate (PET) and polyethylene naphthalate (PEN) were melt spun using a high‐speed winding process in a single‐screw extruder combined with a spinning setup. The filaments had a single T_m and T_g, which indicates excellent compatibility in both the amorphous and crystalline phases. Birefringence and wide angle X‐ray measurements indicated that compounding PEN into PET suppresses stress‐induced orientation and decreases the stressinduced crystallization in the filaments. Adding PEN to PET relaxes the formation of skin‐core structures for as‐spun fibers and reduces the occurrence of broken filaments. Although the addition of PEN reduced crystallinity, it did not affect the tenacity and the shrinkage of the compounded filaments. The elongation of the fibers could be reduced by 30% to 40%, eliminating the need for a further drawing. These results are attributed to PEN's rigid backbone. Adding PEN to PET improves PETs spinnability during high‐speed spinning.     

Isotactic polypropylene hollow microfibers prepared by CO2 laser‐thinning

An isotactic polypropylene hollow microfiber was continuously produced by using a carbon dioxide (CO₂) laser‐thinning method. To prepare the hollow microfiber continuously, the apparatus used for the thinning of the solid fiber was improved so that the laser can circularly irradiate to the hollow fiber. Original hollow fiber with an outside diameter (OD) of 450 μm and an internal diameter (ID) of 250 μm was spun by using a melt spinning machine with a specially designed spinneret to produce the hollow fiber. An as‐spun hollow fiber was laser‐heated under various conditions, and the OD and the ID decreased with increasing the winding speed. For example, when the hollow microfiber obtained by irradiating the CO₂ laser to the original hollow fiber supplied at 0.30 m min^?1 was wound up at 800 m min^?1, the obtained hollow microfiber had an OD of 6.3 μm and an ID of 2.2 μm. The draw ratio calculated from the supplying and the winding speeds was 2667‐fold. The hollow microfibers obtained under various conditions had the hollowness in the range of 20–30%. The wide‐angle X‐ray diffraction patterns of the hollow microfibers showed the existence of the highly oriented crystallites. Further, the OD and ID decreased, and the hollowness increased by drawing hollow microfiber obtained with the laser‐thinning. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2600–2607, 2006     

Influence of viscosity ratio on processing and morphology of thermotropic liquid crystal polymer‐reinforced poly(ethylene 2,6‐naphthalate) blends

Thermotropic liquid crystal polymer (TLCP) microfibril‐reinforced poly(ethylene 2,6‐naphthalate) (PEN) composites with various intrinsic viscosities were prepared by a melt compounding method. Polymer composites consisting of bulk cheap polyester with a small amount of expensive TLCP are of interest from a commercial perspective. The TLCP acts as a nucleating agent in the TLCP/PEN composites, enhancing the crystallization of the PEN matrix through heterogeneous nucleation. The structural viscosity index of the TLCP/PEN composites was lower than that of PEN and TLCP, which was attributed to the formation of TLCP fibrillar structures with elongated fibrils in the PEN matrix. The TLCP/PEN composites with higher intrinsic viscosity than the polymer matrix contained these elongated fibrils, and had a TLCP component with a smaller average diameter, and a narrower diameter distribution than TLCP/PEN composites with lower intrinsic viscosity. The higher intrinsic viscosity of the polymer matrix, the higher shear rate and the lower viscosity ratio of TLCP to PEN can all favour TLCP fibrillation in the polymer composites. Copyright © 2006 Society of Chemical Industry