Showing papers on "Fiber published in 2004"

Are natural fiber composites environmentally superior to glass fiber reinforced composites

Abstract: Natural fibers are emerging as low cost, lightweight and apparently environmentally superior alternatives to glass fibers in composites. We review select comparative life cycle assessment studies of natural fiber and glass fiber composites, and identify key drivers of their relative environmental performance. Natural fiber composites are likely to be environmentally superior to glass fiber composites in most cases for the following reasons: (1) natural fiber production has lower environmental impacts compared to glass fiber production; (2) natural fiber composites have higher fiber content for equivalent performance, reducing more polluting base polymer content; (3) the light-weight natural fiber composites improve fuel efficiency and reduce emissions in the use phase of the component, especially in auto applications; and (4) end of life incineration of natural fibers results in recovered energy and carbon credits.

Direct Spinning of Carbon Nanotube Fibers from Chemical Vapor Deposition Synthesis

Abstract: Many routes have been developed for the synthesis of carbon nanotubes, but their assembly into continuous fibers has been achieved only through postprocessing methods. We spun fibers and ribbons of carbon nanotubes directly from the chemical vapor deposition (CVD) synthesis zone of a furnace using a liquid source of carbon and an iron nanocatalyst. This process was realized through the appropriate choice of reactants, control of the reaction conditions, and continuous withdrawal of the product with a rotating spindle used in various geometries. This direct spinning from a CVD reaction zone is extendable to other types of fiber and to the spin coating of rotating objects in general.

Controlling Surface Morphology of Electrospun Polystyrene Fibers: Effect of Humidity and Molecular Weight in the Electrospinning Process

Abstract: Electrospinning is a technique used to produce micron to submicron diameter polymeric fibers. The surface of electrospun fibers is important when considering end-use applications. For example, the ability to introduce porous surface features of a known size is required if nanoparticles need to be deposited on the surface of the fiber or if drug molecules are to be incorporated for controlled release. Surface features, or pores, became evident when electrospinning in an atmosphere with more than 30% relative humidity. Increasing humidity causes an increase in the number, diameter, shape, and distribution of the pores. Increasing the molecular weight of the polystyrene (PS) results in larger, less uniform shaped pores. This work includes an investigation of how humidity and molecular weight affect the surface of electrospun PS fibers. The results of varying the humidity and molecular weight on the surface of electrospun PS fibers were studied using optical microscopy, field emission scanning electron micros...

All-Cellulose Composite

Abstract: An all-cellulose composite, in which both the fibers and the matrix are cellulose, was prepared by distinguishing the solubility of the matrix cellulose into the solvent from that of the fibers through pretreatment. The structure, mechanical, and thermal properties of this composite were investigated using an X-ray diffraction, a scanning electron microscope, a tensile test, and dynamic viscoelastic and thermomechanical analyses. The tensile strength of uniaxially reinforced all-cellulose composite was 480 MPa at 25 °C, and the dynamic storage modulus was as high as 20 GPa at 300 °C. These were comparable or even higher than those of conventional glass-fiber-reinforced composites. In addition, a linear thermal expansion coefficient was about 10-7 K-1. This all-cellulose composite shows substantial advantages, that is, it is composed of sustainable resources, there is less interface between the fiber and the matrix, it possesses excellent mechanical and thermal performance during use, and it is biodegradab...

Ultrafine Electrospun Polyamide‐6 Fibers: Effect of Solution Conditions on Morphology and Average Fiber Diameter

Abstract: Summary: In the present contribution, the electrostatic spinning or electrospinning technique was used to produce ultra-fine polyamide-6 (PA-6) fibers. The effects of solution conditions on the morphological appearance and the average diameter of as-spun fibers were investigated by optical scanning (OS) and scanning electron microscopy (SEM) techniques. It was shown that the solution properties (i.e. viscosity, surface tension and conductivity) were important factors characterizing the morphology of the fibers obtained. Among these three properties, solution viscosity was found to have the greatest effect. Solutions with high enough viscosities (viz. solutions at high concentrations) were necessary to produce fibers without beads. At a given concentration, fibers obtained from PA-6 of higher molecular weights appeared to be larger in diameter, but it was observed that the average diameters of the fibers from PA-6 of different molecular weights had a common relationship with the solution viscosities which could be approximated by an exponential growth equation. Raising the temperature of the solution during spinning resulted in the reduction of the fiber diameters with higher deposition rate, while mixing m-cresol with formic acid to serve as a mixed solvent for PA-6 caused the solutions to have higher viscosities which resulted in larger fiber diameters. Lastly, the addition of some inorganic salts resulted in an increase in the solution conductivity, which caused the fiber diameters to increase due to the large increase in the mass flow. Average diameter of as-spun fibers plotted as a function of the viscosity of the solutions.

Effects of solvents on electrospun polymeric fibers: preliminary study on polystyrene

Abstract: Six solvents [acetic acid, acetonitrile, m-cresol, toluene, tetrahydrofuran (THF) and dimethylformamide (DMF)] with different properties (eg density, boiling point, solubility parameter, dipole moment and dielectric constant) were used to prepare electrospun polystyrene (PS) fibers. Fiber diameters were found to decrease with increasing density and boiling point of the solvents. A large difference between the solubility parameters of PS and the solvent was responsible for the bead-on-string morphology observed. Productivity of the fibers (the numbers of fiber webs per unit area per unit time) increased with increasing dielectric constant and dipole moment of the solvents. Among the solvents studied, DMF was the best solvent that provided PS fibers with highest productivity and optimal morphological characteristics. The beadless, well-aligned PS fibers with a diameter of ca 0.7 µm were produced from the solution of 10 % (w/v) of PS in DMF at an applied electrostatic field of 15 kV/10 cm, a nitrogen flow rate of 101 ml min−1 and a rotational speed of the collector of 1500 rev min−1. Copyright © 2004 Society of Chemical Industry

Saturable absorbers incorporating carbon nanotubes directly synthesized onto substrates and fibers and their application to mode-locked fiber lasers

Abstract: We present novel carbon-nanotube-based saturable absorbers. Using the low-temperature alcohol catalytic chemical-vapor deposition method, high-quality single-walled carbon nanotubes (SWNTs) were directly synthesized on quartz substrates and fiber ends. We successfully applied the SWNTs to mode lock a fiber laser producing subpicosecond pulses at a 50-MHz repetition rate.

Large Raman gain and nonlinear phase shifts in high-purity As 2 Se 3 chalcogenide fibers

Abstract: Third-order Kerr nonlinearities and Raman gain are studied experimentally in high-purity As2Se3 optical fibers for wavelengths near 1.55 μm. Kerr nonlinear coefficients are measured to be nearly 1000 times higher than those for silica fibers. In pulsed mode, nonlinear phase shifts near 1.2-π rad are measured in fibers only 85 cm long with peak pulse powers near 3 W. However, there are nonlinear losses near 20% for nonlinear phase shifts near π. By use of a cw optical pump, large Raman gains nearly 800 times that of silica were measured. In the cw case there were losses in the form of index gratings formed from standing waves at the exit face of the fiber. Discrete Raman amplifiers and optical regenerators are discussed as possible applications.

Preparation of Antimicrobial Ultrafine Cellulose Acetate Fibers with Silver Nanoparticles

Abstract: Summary: A feasible method for the preparation of antimicrobial ultrafine fibers with silver nanoparticles was developed by direct electrospinning of a cellulose acetate (CA) solution with small amounts of silver nitrate followed by photoreduction. Silver nanoparticles in ultrafine CA fibers were stabilized by interactions with carbonyl oxygen atoms in CA. Ultrafine CA fibers with silver nanoparticles showed very strong antimicrobial activity. TEM image of an ultrafine CA fiber electrospun from 10 wt.-% CA solution with 0.5 wt.-% AgNO3.

A Review on Pineapple Leaf Fibers, Sisal Fibers and Their Biocomposites

Abstract: Summary: The use of lignocellulosic fibers, pineapple leaf fiber (PALF) and sisal as reinforcements in thermoplastic and thermosetting resins for developing low cost and lightweight composites is an emerging field of research in polymer science and technology. Although, these biofibers have several advantages, such as low densities, low cost, nonabrasive nature, high filling level possible, low energy consumption, high specific properties, biodegradability, etc., over synthetic fibers, the absorption of moisture by untreated biofibers, poor wettability, and insufficient adhesion between the polymer matrix and fiber deteriorate the mechanical properties of composites made up of these biofibers. Therefore, the modification of these fibers is a key area of research at present to obtain optimum fiber-matrix properties. This review article is concerned with the structure, composition and properties of PALF and sisal, the chemical modifications of these fibers and PALF/sisal-reinforced thermosets, thermoplastics, rubber, cement, hybrids and biocomposites. Scanning electron micrograph of tensile fractured surface of alkali treated sisal fiber (magnification ×500).

Mechanical Properties of Electrospun Silk Fibers

Abstract: The morphology and microstructure of electrospun B. mori silk/poly(ethylene oxide) (PEO) fibers with diameters less than 1 μm were characterized using birefringence, wide-angle X-ray diffraction, differential scanning calorimetry, and atomic force microscopy (AFM). In the as-spun fibers, silk fibroin is present in a coil conformation due to rapid fiber formation during electrospinning. After treatment with methanol, the silk fibroin was transformed into a β-sheet-containing structure. Evidence for nanofibrils within the as-spun fibers was observed by AFM, and the PEO phase was dispersed as small, elongated islands within the silk fibroin matrix and oriented along the fiber direction. The mechanical properties of single fibers were characterized by AFM nanoindentation. The results were consistent with uniaxial tensile tests and with the morphological analysis. After methanol treatment and extraction with water, the electrospun silk fiber exhibits a lateral modulus of 8.0 GPa, within a factor of 2 of degumm...

Palladium nanoparticles by electrospinning from poly(acrylonitrile-co-acrylic acid)-PdCl2 solutions. Relations between preparation conditions, particle size, and catalytic activity

Abstract: Catalytic palladium (Pd) nanoparticles on electrospun copolymers of acrylonitrile and acrylic acid (PAN-AA) mats were produced via reduction of PdCl2 with hydrazine. Fiber mats were electrospun from homogeneous solutions of PAN-AA and PdCl2 in dimethylformamide (DMF). Pd cations were reduced to Pd metals when fiber mats were treated in an aqueous hydrazine solution at room temperature. Pd atoms nucleate and form small crystallites whose sizes were estimated from the peak broadening of X-ray diffraction peaks. Two to four crystallites adhere together and form agglomerates. Agglomerate sizes and fiber diameters were determined by scanning and transmission electron microscopy. Spherical Pd nanoparticles were dispersed homogeneously on the electrospun nanofibers. The effects of copolymer composition and amount of PdCl2 on particle size were investigated. Pd particle size mainly depends on the amount of acrylic acid functional groups and PdCl2 concentration in the spinning solution. Increasing acrylic acid concentration on polymer chains leads to larger Pd nanoparticles. In addition, Pd particle size becomes larger with increasing PdCl2 concentration in the spinning solution. Hence, it is possible to tune the number density and the size of metal nanoparticles. The catalytic activity of the Pd nanoparticles in electrospun mats was determined by selective hydrogenation of dehydrolinalool (3,7-dimethyloct-6- ene-1-yne-3-ol, DHL) in toluene at 90 °C. Electrospun fibers with Pd particles have 4.5 times higher catalytic activity than the current Pd/Al2O3 catalyst.

All-optical modulation in dye-doped nematic liquid crystal photonic bandgap fibers.

Abstract: Photonic crystal fibers (PCFs) have attracted significant attention during the last years and much research has been devoted to develop fiber designs for various applications, hereunder tunable fiber devices. Recently, thermally and electrically tunable PCF devices based on liquid crystals (LCs) have been demonstrated. However, optical tuning of the LC PCF has until now not been demonstrated. Here we demonstrate an all-optical modulator, which utilizes a pulsed 532nm laser to modulate the spectral position of the bandgaps in a photonic crystal fiber infiltrated with a dye-doped nematic liquid crystal. We demonstrate a modulation frequency of 2kHz for a moderate pump power of 2–3mW and describe two pump pulse regimes in which there is an order of magnitude difference between the decay times.

Mechanical and shape memory behavior of composites with shape memory polymer

Abstract: Shape memory polymers (SMPs) are playing a prominent role for biomedical, self-repairing and smart materials. Among various SMPs, shape memory polyurethanes (PUs) are receiving much attention for their easy control of glass transition temperature (Tg) around the room temperature and excellent shape memory effect even at the room temperature. In this paper, the glass fiber reinforced PUs were developed for the improvement of the mechanical weakness of PUs bulk and for wider practical engineering uses. The specimens with different fiber weight fractions were fabricated and their mechanical behavior and shape memory effect were investigated. As a result, the tensile strength and the resistance against mechanical and thermal mechanical cycle loading in the developed materials increased due to the role of reinforcement fiber. It was shown there is an optimum fiber weight fraction between 10 and 20 wt% to have an extremely low residual strain during cyclic loading. Although the shape memory effect of developed glass fiber reinforced shape memory PUs composites was affected by glass fiber weight fraction, it was confirmed that the shape memory effect was kept in the developed composite materials.

Utilization of waste fibers in stone matrix asphalt mixtures

Abstract: Waste fibers produced from manufacturing processes such as scrap tire processing and automotive carpet manufacturing are sometimes used in other applications, but commonly are disposed of in landfills. If these fibers could be beneficially utilized in any application, it would reduce the load on the nation’s landfills. Also, since these are waste materials, the cost of using these fibers compared to fibers manufactured for a specific application could be considerably less. The major objective of this research was to determine the feasibility of utilizing waste tire and carpet fibers in stone matrix asphalt (SMA). Many states utilize such rut resistant SMA mixtures on heavily traveled highways. Fibers are included in SMA mixtures as a stabilizing additive to prevent excessive draindown caused by relatively high contents of polymer modified asphalt binder. The common types of fiber used in SMA include cellulose and mineral fibers. This study compared the performance of SMA mixtures containing waste tire and carpet fibers with mixes made with commonly used cellulose and other polyester fibers produced specifically for use in hot mix asphalt (HMA). No significant difference in permanent deformation or moisture susceptibility was found in mixtures containing waste fibers compared to cellulose or polyester. Also, the tire, carpet, and polyester fibers significantly improved the toughness of the mixtures compared to the cellulose fibers.

Nanometer surface roughness increases select osteoblast adhesion on carbon nanofiber compacts

Abstract: Carbon nanofibers have exceptional theoretical mechanical properties (such as low weight-to-strength ratios) that, along with possessing nanoscale fiber dimensions similar to crystalline hydroxyapatite found in bone, suggest strong possibilities for use as an orthopedic/dental implant material. To determine, for the first time, cytocompatibility properties pertinent for bone prosthetic applications, osteoblast (bone-forming cells), fibroblast (cells contributing to callus formation and fibrous encapsulation events that result in implant loosening), chondrocyte (cartilage-forming cells), and smooth muscle cell (for comparison purposes) adhesion were determined on carbon nanofibers in the present in vitro study. Results provided evidence that, compared to conventional carbon fibers, nanometer dimension carbon fibers promoted select osteoblast adhesion. Moreover, adhesion of other cells was not influenced by carbon fiber dimensions. In fact, smooth muscle cell, fibroblast, and chondrocyte adhesion decreased with an increase in either carbon nanofiber surface energy or simultaneous change in carbon nanofiber chemistry. To determine properties that selectively enhanced osteoblast adhesion, similar cell adhesion assays were performed on polymer (specifically, poly-lactic-co-glycolic; PLGA) casts of carbon fiber compacts previously tested. Compared to PLGA casts of conventional carbon fibers, results provided the first evidence of enhanced select osteoblast adhesion on PLGA casts of nanophase carbon fibers. The summation of these results demonstrate that due to a high degree of nanometer surface roughness, carbon fibers with nanometer dimensions may be optimal materials to selectively increase osteoblast adhesion necessary for successful orthopedic/dental implant applications.

Fiber-based Optical Parametric Amplifiers and Their Applications

Abstract: The theoretical fundamentals of fiber-based optical parametric amplifiers(OPA) are reviewed,and their applications are discussed in this paper.In the end the future research aspects are expected.

Hybrid fiber reinforced concrete (HyFRC): fiber synergy in high strength matrices

Abstract: In most cases, fiber reinforced concrete (FRC) contains only one type of fiber. The use of two or more types of fibers in a suitable combination may potentially not only improve the overall properties of concrete, but may also result in performance synergy. The combining of fibers, often called hybridization, is investigated in this paper for a very high strength matrix of an average compressive strength of 85 MPa. Control, single, two-fiber and three-fiber hybrid composites were cast using different fiber types such as macro and micro-fibers of steel, polypropylene and carbon. Flexural toughness tests were performed and results were extensively analyzed to identify synergy, if any, associated with various fiber combinations. Based on various analysis schemes, the paper identifies fiber combinations that demonstrate maximum synergy in terms of flexural toughness.

Continuous carbon nanotube composite fibers: properties, potential applications, and problems

Abstract: Using solution spinning, which involves an intermediate gel-state, we obtained exceptionally strong carbon nanotube fibers that are tougher than either spider silk or any fiber used for mechanical reinforcement. We use these fibers to make 100 micron diameter supercapacitors and electronic textiles. Per weight, the energy needed to break these fibers is about 4× higher than spider dragline silk and 20× higher than steel wire. This article describes this advance, comparisons with the prior art, potential applications, and present barriers for large volume applications.