Fiber Formation Process Research Articles

Computational modeling in processing flows of carbonaceous mesophases

Carbonaceous mesophases are liquid crystalline precursor materials that can be spun into high performance carbon fibers using the melt spinning process, which is a flow sequence consisting of capillary, diverging, porous media, converging, and extensional flows that modifies the precursor molecular orientation structure. Carbon fiber property optimization requires a better understanding of the principles that control the structure development during the fiber formation processes and the rheological processing properties. This paper presents the elastic and continuum theory of liquid crystals and computer simulations of structure formation for pressure-driven capillary flow of carbonaceous mesophase precursors used in the industrial carbon fiber spinning process. The simulation results capture the non-Newtonian rheology of mesophase and the formation of characteristic fiber macro-textures.

Films of self-assembled purely helical type I collagen molecules

The structural, morphological and chemical–physical characterization of films constituted of self-assembled non-helical region free type I collagen molecules has been investigated. The results indicate the presence of information at the molecular level which allow collagen I molecules to self-assemble. In the fiber formation process the collagen molecules re-establish the greater part of the native intermolecular cross-links. The films, obtained by air drying the fiber suspension, are water insoluble and characterized by a high mechanical performance. The mechanical and thermal properties of the films increase strongly as a function of the collagen fiber orientation induced in the films by uniaxial stretching.

Computational modeling of ring textures in mesophase carbon fibers

Carbon fibers are widely used in many industrial applications due the fact of their excellent properties. Carbonaceous mesophases are liquid crystalline precursor materials that can be spun into high performance carbon fibers using the melt spinning process, which is a flow cascade consisting of pressure driven flow-converging die flow-free surface extensional spinline flow that modifies the precursor molecular orientation structure. Carbon fiber property optimization requires a better understanding of the principles that control the structure development during the fiber formation processes and the rheological processing properties. This paper presents the elastic and continuum theory of liquid crystalsand computer simulations of structure formation for pressure-driven flow of carbonaceous liquid crystalline precursors used in the industrial carbon fiber spinning process. The simulations results capture the formation of characteristic fiber macro-textures and provide new knowledge on the role of viscous and elastic effects in the spinning process.

γ-Alumina Nanofibers Prepared from Aluminum Hydrate with Poly(ethylene oxide) Surfactant

Introducing poly(ethylene oxide) surfactant to aluminum hydrate colloids can effectively direct the crystal growth of boehmite and the crystal morphology of final γ-alumina crystallites. Fibrous crystallites of γ-alumina about 3−4 nm thick and 30−60 nm long are obtained. They stack randomly, resulting in a structure with a low contact area between the fibers but with a very large porosity. Such a structure exhibits strong resistance to sintering when heated to high temperatures. A sample retains a BET surface area of 68 m2/g, after being heated to 1473 K. The surfactant molecules form micelles that interact with the colloid particles of aluminum hydroxide through hydrogen bonding. This interaction is not sufficient to change the intrinsic crystal structure of boehmite, but induces profound changes in the morphology of boehmite crystallites and their growth. The surfactant-induced fiber formation (SIFF) process has distinct features from templated synthesis but shows similarities in some respects to biomineralization processes in which inorganic crystals with complex morphological shapes can be formed in biological systems. SIFF offers an effective approach to create new nanostructures of inorganic oxide from aqueous media.

Tailored Nanofiber Morphologies Using Modulated Electrospinning for Biomedical Applications

ABSTRACTThe process of electrostatic fiber formation, or electrospinning, was used to generate polymer filaments with diameters in the 50–200 nm range. We have shown that in addition to process parameters such as solution concentration, spinning voltage, and deposition distance, an oscillating electric field can also influence the morphology of the electrospun nanofibers. Specifically, effects of the oscillating field strength and frequency, spinning voltage, and deposition distance on fiber diameter as well as size and number density of the beaded structures in the fibrous thin films are examined.The results of our study demonstrate that modulated field potential produces more uniform fibers. Increasing either the oscillating field strength or frequency yields more uniform average fiber diameter. Also, for systems with the “beads on a string” fiber morphology, increasing the oscillating field strength produces more uniform bead sizes.The ability to tailor fiber morphology using an oscillating electric field has promising implications in a wide range of applications including controlled-release drug delivery systems and biocompatible implants. We show here the potential of using electrospun nanofibers as a porous template for growing fuzzy conductive polymers to modify the surface of a neural recording microelectrode device. These hairy nanostructures can increase signal transport and mediate the mechanical property differences between the device and the soft brain tissues.

Melt‐spun hollow fibers: Modeling and experiments

AbstractPolypropylene hollow fibers were prepared via melt spinning at speeds of 1000–2500 m/min. The outside diameters of the fibers were measured on‐line with high‐speed photography. The fiber formation process was modeled with momentum, energy, and two continuity equations (one for the polymer, and one for the lumen fluid). The equations were solved numerically, and the results were compared to the on‐line diameter data. Both Newtonian and viscoelastic constitutive equations were considered.

An Analysis of Lyocell Fiber Formation as a Melt–spinning Process

In order to gain an understanding of the process of Lyocell fiber formation, the melting and solidification behaviors, heat capacity and density of cellulose N-methylmorpholine-N-oxide monohydrate (NMMO-MH) solutions were studied by differential scanning calorimetry (DSC) and dilatometry, and the diameter development of Lyocell fibers in the air gap was measured online. It was found that the Lyocell process can be considered as both a melt–spinning process in the air gap and a wet-spinning process in the coagulation bath. Cellulose chains in the solutions hindered the crystallization of NMMO-MH, and the melting point of the solutions decreased with increasing cellulose concentration. The density of cellulose NMMO-MH solutions decreased linearly with increasing temperature in the solid or the liquid state, and it increased with increasing cellulose concentration. The heat capacity of the solutions increased slightly with increasing temperature and concentration. The development of fiber diameter, the velocity gradient, and the gradient of the filaments in the air gap were limited to a short distance from the spinneret orifice. The position at which the velocity and the tensile stress gradient reached their maximum values moved closer to the spinneret orifice with increasing take-up speed.

Technology of Strong Fibers: Where are We and Where Should We Direct Our Investigations?

The predictions of future successful technological developments are an important task of research organizations. The extremely poor reliability of these predictions has eroded trust in the efficiency of research laboratories which, in turn, resulted in substantial decreases in and availability of research funding. The causes of poor prediction relability are discussed and ideas are presented on how to minimize this problem. By applying the presented methodology, it is shown that, in the case of strong industrial fibers, we can learn a great deal from evolutionary processes of silk fiber formation and utilize this knowledge to solve some critical environmental problems of current man-made fiber production.

Realtime Characterization of In Situ Molecular Alignment during the Saponification Process of Polyvinyl Pivalate

The spontaneous fiber formation process during saponification of poly(vinyl pivalate) (PVPi) with syndiotactic diad content 63 to 65% to poly(vinyl alcohol)(PVA) in the presence of water was in situ examined. The variation of the revolution per minute(rpm) of a torque apparatus under a constant torque was measured for the spontaneous fibrillation system, and the actual fibrillation system was visualized in the realtime scale by in-line photographing. The in situ fibrillation mechanism was accounted for by relating the variation of the rpm with proceeding the saponifecation reaction to the change of solution morphology with saponification. At the constant torque level, the rpm changed with proceeding the saponification reaction in a complicated way. Up to the saponification time 80 s, the rpm was slightly increased with saponification, then decreased to the saponification time 400 s. From the saponification time 400 s, however, the rpm was abruptly increased. Then, the rpm was levelled off after the saponification time 700 s. Comparison of the rotational speed variation with the morphology change revealed that phase separation began from the degree of saponification 72.8%, and a clear fibrillar structure appeared from the degree of saponification 91.6%.

Up-regulation of novel intermediate filament proteins in primary fiber cells: An indicator of all vertebrate lens fiber differentiation?

The early embryonic development and expression patterns of the eye lens specific cytoskeletal proteins, CP49 and CP95, were determined for the chick and were found to be similar in both human and mouse. These proteins, as well as their homologs in other species, are obligate polymerization partners which form unique filamentous structures termed “beaded filaments.” CP49 and CP95 appeared as protein products after 3 days of embryonic development in the chick during the elongation of primary fiber cells. Although limited data were obtained for human embryos at these early developmental timepoints, they were consistent with the interpretation that the up-regulation of these lens specific proteins began only after the initiation of lens vesicle closure. In situ hybridization with the mouse lens confirmed that message levels for beaded filament proteins were greatly elevated in differentiating primary fiber cells. Nuclease protection assays established that mRNA levels for CP49 remained relatively constant while CP95 mRNA levels increased once the process of secondary fiber formation was under way. Although present in relatively low abundance, the mRNA for a unique splice variant of CP49, CP49INS, was also detected early in embryonic development and into adulthood. Peptide-specific antibodies directed against unique predicted sequences were able to confirm the protein expression of CP49INS in both embryonic and adult chick lens cells. These data present the first detailed study of the expression of CP49 and CP95 during early lens development. They suggest that the up-regulated expression of CP49 and CP95 could serve as pan-specific markers for all vertebrate lens fiber development. Anat Rec 258:25–33, 2000. © 2000 Wiley-Liss, Inc.

3C1145 分子動力学法による絹繊維化過程のシミュレーション

3C1145 分子動力学法による絹繊維化過程のシミュレーション

Processing and microstructural characterization of porous biocompatible protein polymer thin films

The process of electrostatic fiber formation, or electrospinning, was used to create biocompatible thin films for use in implantable devices. The morphology of the thin films was found to depend on process parameters including solution concentration, applied electric field strength, deposition distance, and deposition time. The microstructure of the coatings was examined by Transmission Electron Microscopy (TEM) and Wide-Angle X-ray Scattering (WAXS), with electrospun filaments being weakly oriented along the fiber axis. A shish kebab model for the filament morphology was proposed. The electrospinning process was shown to be a means of creating porous thin films with structural gradients and controlled morphology that could enhance biocompatibility.

Relevance of kinetochore size and microtubule-binding capacity for stable chromosome attachment during mitosis in PtK1 cells.

Chromosomes attach to the mitotic spindle via their kinetochores. The average number of spindle microtubules binding to each kinetochore varies with species, the stage of mitosis, and the length of time that the kinetochore has been attached to the spindle. In this report, we investigate how kinetochore microtubule number varies with kinetochore size and chromosome size in PtK1 cells. From an analysis of serial-section electron micrographs, we determined that the average surface area of metaphase, taxol-treated metaphase, and anaphase kinetochores is 0.16 +/- 0.05 microm2 (N = 181). Surprisingly, kinetochore microtubules are packed more densely on the smaller kinetochores, as seen by a reduction in the average spacing between kinetochore microtubules from 89 nm to 59 nm. Our interpretation of this result is that PtK1 cells require a minimum kinetochore microtubule-binding capacity for survival during repeated rounds of mitotic division. We estimate the lower limit to be 23 kinetochore microtubules and suggest that this capacity is required to ensure stable attachment during the dynamic and highly stochastic process of kinetochore fiber formation. There is a modest but statistically significant increase in kinetochore microtubule number with chromosome size, indicating that chromosome size is a minor determinant of kinetochore microtubule number.

Determination of the critical conditions for fiber formation by the fibroin of natural silk by polarization-optical methods

The processes of fiber formation by the fibroin of natural silk have been studied by the methods of birefringence in a longitudinal hydrodynamic field and optical rotatory dispersion. The experiments were performed with the direct drawing of a fiber from the secretion of the silk glands of the silkwormBombyx mori. The position of appearance of a longitudinal hydrodynamic field within the gland has been detected and experimental results have been obtained which permit an evaluation of the critical condition for the α-β structural transition of the fibroin chains.

On microsuperplasticity in aa7475 domes

M.G. ZELIN, formerly Post Doctoral Researcher with the Department of Chemical Engineering and Materials Science, University of California, Davis, CA 95616-5294, is Senior Engineer, Concurrent Technologies Corporation, Johnstown, PA 15904. Manuscript submitted October 24, 1995. deformed surface of unfailed materials, t6,71 Since the appearance of these fibers suggests extremely high ductility of the material, the process of fiber formation has been referred to as microsuperplasticity phenomenon.tJ,z.31 Predominately, the observations of microsuperplasticity phenomenon were reported in materials subjected to the uniaxial tension. Recent s t u d y [8'91 of the deformed surface of superplastically bulged AA7475 domes demonstrated fiber formation after biaxial stretching. This article summarizes the results of the observation of fiber formation in AA7475 domes of various shapes. AA7475 blanks, 50 X 50 x 1.5 mm 3 were bulged with the punches of hemispherical, cylindrical, and conical shape. The experimental details can be found elsewhere.[8,9~ Superplastic AA7475 sheet material with a grain size of approximately 10/~m was obtained from Kaiser Aluminum and Chemical Co. (Pleasanton, CA). The rate of punch displacement and temperature corresponded to the optimum strain rate-temperature conditions for this alloy: f6,7,1~ l] ~: = 2 x 10 4 S-I and T = 516 ~ The blanks were mechanically polished before deformation with the final polishing on alumina with 0.5 /xm particle size. Marker lines were inscribed at the polished surface by using 9/~m diamond paste parallel and perpendicular to the rolling direction. The deformed surface was examined in a scanning electron microscope (SEM). Chemical analysis was performed by us-

A synthetic peptide from the COOH-terminal heparin-binding domain of fibronectin promotes focal adhesion formation.

Cell adhesion to extracellular matrix molecules such as fibronectin involves complex transmembrane signaling processes. Attachment and spreading of primary fibroblasts can be promoted by interactions of cell surface integrins with RGD-containing fragments of fibronectin, but the further process of focal adhesion and stress fiber formation requires additional interactions. Heparin-binding fragments of fibronectin can provide this signal. The COOH-terminal heparin-binding domain of fibronectin contains five separate heparin-binding amino acid sequences. We show here that all five sequences, as synthetic peptides coupled to ovalbumin, can support cell attachment. Only three of these sequences can promote focal adhesion formation when presented as multicopy complexes, and only one of these (WQPPRARI) retains this activity as free peptide. The major activity of this peptide resides in the sequence PRARI. The biological response to this peptide and to the COOH-terminal fragment may be mediated through cell surface heparan sulfate proteoglycans because treatment of cells with heparinase II and III, or competition with heparin, reduces the response. Treatment with chondroitinase ABC or competition with chondroitin sulfate does not.

The Process of Gel Fiber Formation

ABSTRACTThe gel fiber formation was studied for the spinnable silica sols prepared from a mixture of TEOS, H2O, EtOH and HNO3 ( 1 : 2 : 2 : 0.01, in mole ratio). The effect of polysiloxane molecular size in the spinning sol on spinnability indicated that the tough skeleton of gel, which is preferable for fabrication of high-strength fiber without breakage, was formed by the selective connection of large size polymers (about 106 in M.W.) during the spinning. It was also found that the smaller size polymers in gel fiber continued to react with water in the atmosphere after the spinning, and attached to the skeleton to strengthen the fiber.

Fluid dynamics and mass transfer in the formation of fibers

A theory of the process of wet fiber formation is constructed. Calculated results are compared with experimental data.

Oriented fibrillogenesis of collagen in vitro by ordered convection.

Oriented fibers, arising from the self assembly of collagen, may be produced from in vitro fibrillogenesis of soluble collagen with gradients of fibrillogenic potential. These gradients may be introduced by either concentration gradients of pronase-treated collagen or of arginine which, in turn, create concentration gradients of collagen aggregate intermediates during the fiber formation process. These gradients are gravitationally unstable and generate ordered convective flows which guide fiber growth.

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