Mechanical properties and microstructure of poly(ethylene terephthalate) microfiber prepared by carbon dioxide laser heating

We determined that a poly(ethylene terephthalate) microfiber was easily obtained by irradiating a carbon dioxide laser to an annealed fiber. The annealed fiber was prepared by zone drawing and zone annealing. First, an original fiber was zone drawn at a drawing temperature of 90°C under an applied tension of 4.9 MPa, and the zone‐drawn fiber was subsequently zone annealed at 150°C under 50.9 MPa. The zone‐annealed fiber had a degree of crystallinity of 48%, a birefringence of 218.9 × 10^?3, tensile modulus of 18.8 GPa, and tensile strength of 0.88 GPa. The microfiber prepared by laser heating the zone‐annealed fiber had a diameter of 1.5 μm, birefringence of 172.8 × 10^?3, tensile modulus of 17.6 GPa, and tensile strength of 1.01 GPa. The draw ratio estimated from the diameter was 9165 times; such a high draw ratio has thus far not been achievable by any conventional drawing method. Microfibers may be made more easily by laser heating than by conventional technologies such as conjugate spinning. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1955–1958, 2003     

Isotactic polypropylene microfiber prepared by carbon dioxide laser‐heating

An isotactic polypropylene (i‐PP) microfiber was obtained by irradiating a carbon dioxide laser to previously drawn fibers. To prepare the thinner i‐PP microfiber, it is necessary to previously draw original i‐PP fibers under an applied tension of 7.8 MPa at a drawing temperature of 140°C. The drawn fiber was heated under an applied tension of 0.3 MPa using the laser operated at a power density of 39.6 W cm^?2. The thinnest i‐PP microfiber obtained under optimum conditions had a diameter of 1.8 μm and a birefringence of 30 × 10^?3. Its draw ratio estimated from the diameter reached 51,630. It is so far impossible to achieve such a high draw ratio by any drawing. The wide‐angle X‐ray diffraction photograph of the microfiber shows the existence of the oriented crystallites. Laser‐heating allows easier fabrication of microfibers compared with the conventional technology such as the conjugate spinning. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1534–1539, 2004     

Zone drawing and zone annealing of poly(ethylene terephthalate) microfiber prepared by CO2 laser thinning

A zone‐drawing and zone‐annealing method was applied to a poly(ethylene terephthalate) microfiber, obtained by using CO₂ laser thinning, to develop its mechanical properties. The microfiber used for the zone drawing and zone annealing was prepared by winding at 1386 m/min the microfiber obtained by irradiating the laser at 18.1 W/cm² and had a diameter of 2.8 μm and a birefringence of 0.097. Zone drawing was carried out at a drawing temperature of 105°C under an applied tension of 53 MPa, and zone annealing at an annealing temperature of 155°C under 195 MPa applied tension. Zone drawing and zone annealing were carried out at a treatment speed of 0.21 m/min. The diameter of the microfiber decreased, and its birefringence increased, with zone drawing and zone annealing. The zone‐annealed microfiber finally obtained had a diameter of 2 μm, a birefringence of 0.234, a tensile modulus of 17.9 GPa, and a tensile strength of 1.1 GPa. The wide‐angle X‐ray diffraction photograph of the zone‐annealed microfiber showed the existence of highly oriented crystallites. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2989–2994, 2004     

Effect of zone drawing on the structure and properties of melt‐spun poly(trimethylene terephthalate) fiber

Melt‐spun poly(trimethylene terephthalate) (PTT) fibers were zone‐drawn and the structures and properties of the fibers were investigated in consideration of the spinning and zone‐drawing conditions. The draw ratio increased up to 4 with increasing drawing temperature to 180°C, at a maximum drawing stress of 220 MPa. Higher take‐up velocity gave lower drawability of the fiber. The PTT fiber taken up at 4000 rpm was hardly drawn, in spite of using maximum drawing stress, because a high degree of orientation had been achieved in the spinning procedure. However, an additional enhancement of birefringence was observed, indicating a further orientation of PTT molecules by zone drawing. The exotherm peak at 60°C disappeared and was shifted to a lower temperature with an increase in the take‐up velocity, which means that the orientation and crystallinity of the fiber increased. The d‐spacing of (002) plane increased with increasing take‐up velocity and draw ratio, whereas those of (010) and (001) planes decreased. In all cases, the crystal size increased with take‐up velocity and draw ratio. The cold‐drawn PTT fiber revealed a kink band structure, which disappeared as the drawing temperature was raised. The physical properties of zone‐drawn PTT fibers were improved as the draw ratio and take‐up velocity increased. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 3471–3480, 2001     

High temperature zone‐drawing of nylon 66 microfiber prepared by CO2 laser‐thinning

A high temperature zone‐drawing method was applied to a nylon 66 microfiber, obtained by using CO₂ laser‐thinning, to develop its mechanical properties. The microfiber used for the high temperature zone‐drawing was prepared by winding at 150 m min^?1 the microfiber obtained by irradiating the laser at 4.0 W cm^?2 to an original fiber with a diameter of 50 μm, and had a diameter of 9.6 μm and a birefringence of 0.019. The high temperature zone‐drawing was carried out in two steps; the first drawing was carried out at a temperature of 230°C at supplying and winding speeds of 0.266 and 0.797 m min^?1, the second at 250°C at supplying and winding speeds of 0.266 and 0.425 m min^?1, respectively. The diameter of the microfiber decreased, and its birefringence increased stepwise with the processing. The high temperature zone‐drawn microfiber finally obtained had a diameter of 4.2 μm, a birefringence of 0.079, total draw ratio of 4.8, tensile modulus of 12 GPa, and tensile strength of 1.0 GPa. The wide‐angle X‐ray diffraction photograph of the drawn microfiber showed the existence of highly oriented crystallites. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 42–47, 2006     

Evaluation of the microstructure and melting behavior of drawn polypropylene fibers with a microthermal analyzer

The strong correlation of melting behavior with the microstructure of original and zone‐drawn isotactic polypropylene fibers was evaluated by microthermal analysis (micro‐TA) combined with wide‐angle X‐ray diffraction analysis. The crystal structure of both the original and zone‐drawn fibers was a monoclinic α‐form with a ～ 0.64 nm, b ～ 2.03 nm, and c ～ 0.65 nm. In contrast to the absence of any oriented polymer molecules in the original fiber, the polymer molecules in the zone‐drawn fiber were extended and highly oriented in at least two different states; one arranged along the drawn axis and the other at 40° to the drawn axis. The micro‐TA‐derived melting points corresponded to these microstructural changes caused by the zone‐drawing process and differed from the melting points obtained by differential scanning calorimetery. The micro‐TA melting point of 140°C corresponded to the z‐e‐p melting point of the original fiber, being much lower than the conventional differential scanning calorimetery melting point of 163°C. As for the zone‐drawn fiber, an increase of 19°C in the melting temperature revealed its high orientation level, and the appearance of three elevated melting peaks (161, 167, and 178°C) at the highest heating rate (1500°C/min) coincided with its several oriented states. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1306–1311, 2006     

Mechanical properties and superstructure of isotactic polypropylene fibers prepared by continuous vibrating zone‐drawing

A continuous vibrating zone‐drawing (CVZD) was applied to study the effect of vibration on the mechanical properties and superstructure of isotactic polypropylene fibers. The CVZD treatment was a new drawing method by which the fiber was continuously drawn at a rate of 0.5 m/min under vibration using the specially designed apparatus. The CVZD treatment was carried out in five steps at a drawing temperature of 150°C and a frequency of 100 Hz, and applied tensions increased step by step with processing in the range of 14.8 to 207 MPa. The obtained fiber had a birefringence of 0.0373, crystallinity of 62.4%, tensile modulus of 17.6 GPa, and tensile strength of 1.11 GPa. These values are higher than those of the continuous zone‐drawn isotactic polypropylene fiber previous reported. The vibration added to the fibers during the zone‐drawing was effective in developing amorphous orientation and improving the mechanical properties. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 600–608, 2001     

The influence of annealing treatment on the molecular structure and the mechanical properties of isotactic polypropylene fibers

An investigation was carried out on the effects of annealing treatment on the molecular structure and the mechanical properties of isotactic polypropylene fibers annealed in an air heated environment at temperatures ranging from 60 to 140°C. Analysis of the equatorial X‐ray diffraction traces showed the presence of a three phase system of amorphous‐smectic‐monoclinic forms and revealed the transformation of the metastable smectic form to the highly stable monoclinic form as the annealing temperature is increased, resulting in an enhanced degree of crystallinity and the crystallite size. The improvements in the degree of crystallinity and the crystallite size became more remarkable above 120°C. Evaluation of the crystallinity was carried out using an analysis of density, infrared spectroscopy, and X‐ray diffraction methods whereas the state of the molecular orientation was evaluated using polarized infrared spectroscopy measurements only. Polarized infra‐red spectroscopy measurements after the curve fitting procedure showed a slight increase of the molecular orientation of the helical chain segments present in the crystalline phase represented by the IR bands at 841 and 998 cm^?1 whereas the amorphous structure represented by the IR band at 974 cm^?1 showed no significant change with increasing annealing temperature. The improvement in the molecular orientation of the crystalline phase became more remarkable above 120°C. Tensile strength of the annealed fibers increased with increasing annealing temperature but the elongation at break and the initial modulus were not affected as much as the tensile strength. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.     

Novel CO2 laser drawing of thermotropic liquid crystal polymer and poly(ethylene 2,6‐naphthalate) blend fibers

Thermotropic liquid crystal polymer (TLCP)/poly(ethylene 2,6‐naphthalate) (PEN) were prepared by a melt blending, and were melt spun by a spin‐draw process. In this study, we suggest novel drawing technology using the CO₂ laser that can directly and uniformly heat up fiber inside to prevent the formation of ununiform structures in conventional heat drawing process. The properties of the heat/laser drawn TLCP/PEN blend fibers were superior to those of any other handled fibers, and were rather more excellent than those of TLCP/PEN blend fibers annealed at 135°C for 10 min. It was confirmed that the CO₂ laser drawing made it possible to achieve the optimal drawing effect by draw ratio. The combined heating and CO₂ laser‐drawing method has a great potential for industrial applications as a novel fiber‐drawing process, and it can also be applied continuously to conventional spin‐draw system. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 205–211, 2007     

Structural changes in the melt spinning,cold drawing,and annealing of poly(4‐methylpentene‐1) fibers

Isotactic poly(4‐methylpentene‐1) melt‐spun fibers were investigated. Prior investigators of melt‐spun fibers found that these fibers have a tetragonal unit cell (Form I). We obtained the same unit cell structure in melt‐spun fibers. We found that higher draw‐down‐ratio fibers had d‐spacings closer to the previously cited values of Form I. We also found that cold‐drawn fibers had similar values to those of melt‐spun fibers. However, after these were annealed at 200°C, the unit cell was changed. It is possible that this new unit cell was the orthorhombic form of He and Porter. We also observed the birefringence of these fibers. The values changed after the melt‐spun fibers were cold drawn and annealed. The melt‐spun fiber values reached 0.006. The values for the drawn fibers were as high as 0.007. We suggest that the intrinsic birefringence is about 0.0075. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 130–137, 2005     

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.     

Annealing-induced morphological changes in segmented elastomers

Thermal analysis has been used to study annealing-induced ordering in segmented elastomers. Twelve segmented elastomers were studied each having approximately 50% by wt hard segment content. Seven general classes of materials were examined including polyether and polyester polyurethanes, polyether polyurethane-urea, and polyether-polyester. Materials were slow cooled (?10°C min^?1) from the melt to an annealing temperature (?10°, 20°, 60°, 90° or 120°C) where they were annealed (16, 12, 8, 6 or 4 days, respectively). Annealing was followed by slow cooling (?10°C min^?1) to ?120°C after which a d.s.c. experiment was run. In general, annealing resulted in an endothermic peak at a temperature 20°–50°C above that of the temperature of annealing. This phenomenon was observed in both semicrystalline and amorphous materials. The closer the annealing endotherm was to a crystalline endotherm without exceeding it in temperature, the larger its size. Annealing endotherms resulted from hard or soft segment ordering. Only one annealing endotherm was observed for a given annealing history, even though in some materials hard and soft segments could exhibit annealing-induced morphological changes. Hard segment homopolymers were studied yielding results similar to the block polymers containing shorter sequences of the same material. This suggests that annealing-induced ordering is an intradomain phenomenon not associated with the interphase between domains, or necessarily dependent on the chain architecture of segmented elastomers.     

Study of the Ion‐Irradiation Behavior of Advanced SiC Fibers by Raman Spectroscopy and Transmission Electron Microscopy

6H–SiC single crystals and two types of SiC fibers, Hi‐Nicalon type S and Tyranno SA3, have been irradiated with 4‐MeV Au³⁺ up to 2 × 10¹⁵ cm^?2 (4 dpa) at room temperature, 100°C and 200°C. These fibers are composed of highly faulted 3C–SiC grains and free intergranular C. Stacking fault linear density and grain size estimations yield, respectively, 0.29 nm^?1 and 26–36 nm for the Hi‐Nicalon type S fibers and 0.18 nm^?1 and 141–210 nm for the Tyranno SA3 fibers. Both transmission electron microscopy and surface micro‐Raman spectroscopy reveal the complete amorphization of all the samples when irradiated at room temperature and 100°C and a remaining crystallinity when irradiated at 200°C. The latter observations reveal a multi‐band irradiated layer consisting in a partially amorphized band near the surface and an in‐depth amorphous band. Also, nanocrystalline SiC grains with high stacking fault densities can be found embedded in amorphous SiC at the maximum damage zone of the Hi‐Nicalon type S fibers irradiated at 200°C.     

Thermal Exposure Effects on the Strength and Microstructure of a Novel Mullite Fiber

The mechanical behavior of the novel fiber CeraFib75 after various thermal exposures is examined. This fully crystalline mullite fiber was developed to exceed the thermal stability of commercially available oxide fibers. Therefore, heat treatments at temperatures ranging from 1000°C to 1400°C for 25 h were performed and results compared to the well‐established Nextel^? 720 fibers. Mechanical characterization was realized with bundle tensile tests using acoustic emission sensors to determinate the fiber failure distributions. Investigations showed that the initial fiber microstructure of mullite grains with traces of alumina transforms starting at 1200°C. Changes include dissociation of the alumina‐rich mullite phase and grain growth. Thus, strength reduction is measured as a result of these microstructure transformations. Remarkably, at 1400°C, fibers become more fragile and Weibull statistics can no longer describe the failure distribution. A relation between the distribution shape and the load redistribution capability of fibers is suggested. This is more pronounced for Nextel^?720 fibers, which present much bigger grains and retain only 10% of their original strength. However, CeraFib75 fibers are more stable and exhibit a strength retention of 50% at the same conditions, which is attributed to the higher amount of mullite phase.     

Creep of Nextel™ 610 Fiber at 1100°C in Air and in Steam

Creep of Nextel^?610 fibers was investigated at 1100°C and 100–500 MPa in air and in steam. The effect of loading rate on fiber tensile strength was also explored. The presence of steam accelerated creep and reduced fiber lifetimes. Loading rate had a considerable effect on tensile strength in steam, but not in air. A linear elastic crack growth model was used to predict the creep lifetimes from the constant loading rate data. The dependence of tensile strength on loading rate and the predictability of creep lifetimes suggest that the failure mechanism in steam was environmentally assisted subcritical crack growth. The creep‐rupture data were analyzed in terms of a Monkman‐Grant (MG) relationship. Monkman‐Grant parameters for creep‐rupture data were the same in steam and air, and predicted creep‐rupture at 1100°C in both environments. A grain‐size increase of about 25% was observed by TEM after 100 h at 1100°C in steam, which was about two times that observed in air.     

Design of carbon nanotube fiber microelectrode for glucose biosensing

BACKGROUND: Carbon nanotube (CNT) fiber directly spun from an aerogel has a unique, well‐aligned nanostructure (nano‐pore and nano‐brush), and thus provides high electro‐catalytic activity and strong interaction with glucose oxidase enzyme. It shows great potential as a microelectrode for electrochemical biosensors. RESULTS: Cyclic voltammogram results indicate that post‐synthesis treatments have great influence on the electrocatalytic activity of CNT fibers. Raman spectroscopy and electrical conductivity tests suggest that fibers annealed at 250 °C remove most of the impurities without damaging the graphite‐like structure. This leads to a nano‐porous morphology on the surface and the highest conductivity value (1.1 × 10⁵ S m^?1). Two CNT fiber microelectrode designs were applied to enhance their electron transfer behaviour, and it was found that a design using a 30 nm gold coating is able to linearly cover human physiological glucose level between 2 and 30 mmol L^?1. The design also leads to a low detection limit of 25 µmol L^?1. CONCLUSIONS: The high performance of CNT fibers not only offers exceptional mechanical and electrical properties, but also provides a large surface area and electron transfer pathway. They consequently make excellent bioactive microelectrodes for glucose biosensing, especially for potential use in implantable devices. Copyright © 2011 Society of Chemical Industry     

Alkali–methanol–anthraquinone pulping of Miscanthus x giganteus for thermoplastic composite reinforcement

The potential of pulp fiber–reinforced thermoplastics is currently not fully explored in composites. One of the main reasons is that pulp fibers are extracted for the use in papermaking and are thus not optimized for use as reinforcements in thermoplastics. Furthermore, currently used processing methods constitute several severe thermomechanical steps inducing premature degradation of the fibers. A systematic development of these composite materials requires the study of both these aspects. The goal of this work was to optimize fiber extraction against properties relevant to the reinforcement of thermoplastics. To this end, thick‐walled Miscanthus x giganteus pulp fibers were selected. The fibers were pulped by the alkaline–methanol–anthraquinone process. An unreplicated factorial design was applied to determine the effect of key operating variables on fiber thermal stability and mechanical properties. The thermomechanical properties of pulp fibers depend primarily on the morphology and chemical composition of the fiber resource in terms of the respective amounts of lignin, hemicellulose, and cellulose, all strongly influenced by the choice of pulping conditions. Optimal pulping parameters were identified, allowing production of fibers thermally stable up to 255°C with an aspect ratio of 40, a straightness of 95%, and tensile strength as high as 890 MPa. Specific stiffness and strength values with respect to density and material cost of 56 GPa m^?3 $^?1 and 820 MPa m^?3 $^?1 were highly competitive with glass fibers, with corresponding values of 15 GPa m^?3$^?1 and 270–490 MPa m^?3 $^?1, respectively. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2132–2143, 2004     

Preparation and characterization of carbon fibers from polyacrylonitrile precursors

The present work deals with the preparation of carbon fibers from polyacrylonitrile (PAN) fibers. The chemical composition and physical properties of the starting fibers were determined. The PAN fibers were stabilized in air at the temperatures (230, 270, and 300°C) with the heating time from 40 to 420 min. The effects of both final stabilization temperature and heating rate on the chemical and physical properties of the prepared stabilized fibers were studied. The chosen stabilized fibers samples were carbonized in argon atmosphere at the temperatures (1000, 1200, and 1400°C) with different heating rates 5, 10, 15, and 20°C min^?1. The effects of both carbonizing temperature and heating rate on the weight loss, density, elemental composition, and IR absorption spectra of carbonized fibers were also studied. The fiber sample, which was carbonized at 1400°C, contains 97.55% carbon, 1.75% nitrogen, and 1.4% hydrogen. This means that carbonizing the stabilized fibers at 1400°C in argon atmosphere is suitable to get oxygen‐free carbon fibers. Therefore, the used carbonizing temperature in the present work (1400°C) is suitable to produce moderate heat‐treated carbon fibers with the heating rate of 15°C min^?1. The modulus of the prepared carbon fibers was compared to that of industrially produced fibers using the results of X‐ray analysis. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Effect of annealing on the structure and properties of polyvinylidene fluoride hollow fiber by melt‐spinning

Polyvinylidene fluoride hollow fibers were prepared by melt‐spinning technique under three spinning temperatures. The effects of annealing treatment on the structure and properties of hollow fiber were studied by differential scanning calorimetry (DSC), wide‐angle X‐ray diffraction (WAXD), tensile test, and scanning electron microscopy (SEM) measurements. DSC and WAXD results indicated that the annealing not only produced secondary crystallization but also perfected primary crystallization, and spinning and annealing temperature influenced the crystallinity of hollow fiber: the crystallinity decreased with the increase of spinning temperature; 140°C annealing increased the crystallinity, and hardly influenced the orientation of hollow fiber; above 150°C annealing increased the crystallinity as well, and furthermore had a comparative effect on the orientation. The tensile tests showed that the annealed samples, which did not present the obvious yield point, exhibited characteristics of hard elasticity, and all the hollow fiber had no neck phenomenon. Compared with the annealed sample, the precursor presented a clear yield point. In addition, the annealed samples had a higher break strength and initial modulus by contrast with the precursor, and the 140°C annealed sample showed the smallest break elongation. SEM demonstrated the micro‐fiber structure appeared in surface of drawn sample. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 935–941, 2007     

Effect of thermal aging on electrical conductivity of the 2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid‐doped polyaniline fiber

The thermal characteristics of inherently conductive polyaniline (PANi) fiber have been studied using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Fibers show five major weight losses at ∼100°C, 165°C, 215°C, 315°C, and 465°C, which are associated with the removal of moisture, residual solvent, decompositions of the sulfonic acid and degradation of PANi fiber, respectively. The 2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid (AMPSA) that dopes the PANi (in fiber form) performs two‐stage decompositions. The conductivity of the drawn fibers aged at 50°C, 100°C, 150°C, and 190°C under vacuum for various periods of time decreases, particularly at temperatures higher than 100°C. The reduction in conductivity of the fiber aged at temperatures lower than 100°C is mainly due to the evaporation of the residual solvent (15–20% in the as‐spun fiber). Further decrease in conductivity of the fiber aged at temperatures higher than 100°C is caused by the decomposition of the dopant AMPSA. The temperature‐dependent conductivity of the fiber was measured at 15 K (−258.5°C) to 295 K (21.5°C). The conductivity of both aged and un‐aged fibers is all temperature activated, however, the conductivity of the un‐aged fibers is higher than that of the aged fibers. Although a negative temperature coefficient was observed in the temperature range from 240 K (–24.5°C) to 270 K (–3.5°C) for the un‐aged fibers, it was disappeared when the fibers were thermal aged at 100°C for 24 h in vacuum oven. These results indicate that the residual solvent trapped inside the fiber enhanced the electrical conductivity of the fibers and its “metallic” electrical conductivity at temperatures ∼263 K (–10°C). © 2001 John Wiley & Sons, Inc. † J Appl Polym Sci 79: 2503–2508, 2001