Polymer-based Fiber Research Articles

Numerical Modelling of Thermally Bonded Nonwovens: Continuous and Discontinuous Approaches

Nonwoven fabrics are web structures of randomly-oriented fibres, bonded by means of mechanical, thermal or chemical techniques. This paper focuses on nonwovens manufactured with polymer-based fibres and bonded thermally. During thermal bonding of such fibres, as a hot calender with an engraved pattern contacts the fibre web, bond spots are formed by melting of the polymer material. As a result of this bonding process, a pattern of bond points connected with randomly oriented polymer-based fibres form the nonwoven web. Due to their manufacturing-induced composite microstructure and random orientation of fibres, nonwovens demonstrate a complex mechanical behaviour. Two distinct modelling approaches were introduced to simulate the non-trivial mechanical response of thermally bonded nonwovens based on their planar density. The first modelling approach was developed to simulate the mechanical behaviour of high-density nonwovens, and the respective fabric was modelled with shell elements with thicknesses identical to those of the bond points and the fibre matrix having distinct anisotropic mechanical properties. Random orientation of individual fibres was introduced into the model in terms of the orientation distribution function in order to determine the material’s anisotropy. The second modelling approach was introduced to simulate low-density nonwovens, and it treated the nonwoven media as a structure composed of fibres acting as truss links between bond points.

Electrospun poly(lithium 2-acrylamido-2-methylpropanesulfonic acid) fiber-based polymer electrolytes for lithium-ion batteries

Novel single-ion conducting polymer electrolytes based on electrospun poly(lithium 2-acrylamido-2-methylpropanesulfonic acid) (PAMPSLi) membranes were prepared for lithium-ion batteries. The preparation started with the synthesis of polymeric lithium salt PAMPSLi by free-radical polymerization of 2-acrylamido-2-methylpropanesulfonic acid, followed by ion-exchange of H+ with Li+. Then, the electrospun PAMPSLi membranes were prepared by electrospinning technology, and the resultant PAMPSLi fiber-based polymer electrolytes were fabricated by immersing the electrospun membranes into a plasticizer composed of ethylene carbonate and dimethyl carbonate. PAMPSLi exhibited high thermal stability and its decomposition did not occur until 304°C. The specific surface area of the electrospun PAMPSLi membranes was raised from 9.9 m2/g to 19.5 m2/g by varying the solvent composition of polymer solutions. The ionic conductivity of the resultant PAMPSLi fiber-based polymer electrolytes at 20°C increased from 0.815 × 10−5 S/cm to 2.12 × 10−5 S/cm with the increase of the specific surface area. The polymer electrolytes exhibited good dimensional stability and electrochemical stability up to 4.4 V vs. Li+/Li. These results show that the PAMPSLi fiber-based polymer electrolytes are promising materials for lithium-ion batteries. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Liquid crystal main-chain polymers for high-performance fibre applications

The chemistry and physics of high-performance fibre spinning based on main-chain liquid crystal polymer (MCLCP) solutions and melts is discussed, which is the largest industrial application of liquid crystal technology. The high modulus and strength of liquid crystal polymer-based high-performance fibres is due to the exceptionally high orientational order that can be achieved, reaching values of 0.95 and higher. Together with the chemistry that ensures strong intermolecular interactions, often based on hydrogen bonding, it is possible to make fibres with unusual mechanical and thermal properties. The modulus and strength of such fibres can reach values at about 50–75% of the theoretical limit. Within materials science high-performance fibres are especially interesting, as they are one of the few systems where the material properties can be successfully predicted based on molecular models for the orientational order together with rather simple assumptions on the effect of flow on the director alignment. The most studied MCLCP systems for high-performance fibre spinning PPTA/H2SO4, cellulose/phosphoric acid, PIPD(M5)/PPA and melt-spun VectranTM are discussed.

Computation of mechanical anisotropy in thermally bonded bicomponent fibre nonwovens

Having a unique microstructure composed of randomly-oriented polymer-based fibres, nonwovens exhibit complex deformation characteristics. The most prominent one is the mechanical anisotropy leading to their direction-dependent deformation behaviour. This paper focuses on mechanical anisotropy of thermally bonded bicomponent fibre nonwovens with polymer-based bicomponent core/sheath fibres. A relation between mechanical anisotropy of these nonwovens and random orientation of their fibres is developed in this study. Random orientation of individual fibres is quantified in terms of the orientation distribution function (ODF) in order to determine the material’s anisotropy. The ODF is obtained by analysing the data acquired with scanning electron microscopy or X-ray micro-computed tomography using digital image processing techniques based on the Hough transform. A numerical tool is developed to perform this analysis and determine the anisotropic parameters in order to define direction-dependency of the structure’s mechanical properties. Finally, anisotropic parameters of various nonwovens computed with the introduced numerical approach are compared with those obtained from tensile tests applied in machine and cross directions of nonwovens.

Soft capacitor fibers for electronic textiles

A highly flexible, conductive polymer-based fiber with high electric capacitance is reported. The fiber is fabricated using fiber drawing method, where a multimaterial macroscopic preform is drawn into a submillimeter capacitor microstructured fiber. A typical measured capacitance per unit length of our fibers is 60–100 nF/m which is about 3 orders magnitude higher than that of a coaxial cable of a comparable diameter. The fiber has a transverse resistivity of 5 kΩ m. Softness, lightweight, absence of liquid electrolyte, and ease of scalability to large production volumes make the fibers interesting for various smart textile applications.

Soft capacitor fibers using conductive polymers for electronic textiles

A novel, highly flexible, conductive polymer-based fiber with high electric capacitance isreported. In its cross section the fiber features a periodic sequence of hundreds of conductiveand isolating plastic layers positioned around metallic electrodes. The fiber is fabricatedusing the fiber drawing method, where a multi-material macroscopic preform is drawn intoa sub-millimeter capacitor fiber in a single fabrication step. Several kilometers of fibers canbe obtained from a single preform with fiber diameters ranging between 500 and1000 µm. A typical measured capacitance of our fibers is60–100 nF m−1 and it is independent of the fiber diameter. Analysis of the fiber frequency response showsthat in its simplest interrogation mode the capacitor fiber has a transverse resistance of5 kΩ m L−1, which is inversely proportional to the fiber lengthL and is independent of the fiber diameter. Softness of the fiber materials, the absence ofliquid electrolyte in the fiber structure, ease of scalability to large productionvolumes and high capacitance of our fibers make them interesting for varioussmart textile applications ranging from distributed sensing to energy storage.

Molecular Dynamics Simulation of Double-Walled Carbon Nanotube Vibrations: Comparison With Continuum Elastic Theories

ABSTRACTDouble-walled carbon nanotubes (DWNTs) are expected to be useful as elements in improving conventional polymer-based fibers and films. An extensive molecular dynamics simulation and continuum analyses are carried out to estimate the influence of matrix stiffness and the intertube radial displacements on free vibration of an individual DWNT. The effects of nanotube length and chirality are also taken into account. The continuum analyses are based on both Euler-Bernoulli and Timoshenko beam theories which considers shear deformation and rotary inertia and for both concentric and non-concentric assumptions considering intertube radial displacements and the related internal degrees of freedom. New intertube resonant frequencies are calculated. Detailed results are demonstrated for the dependence of resonant frequencies on the matrix stiffness. The results indicate that internal radial displacement and surrounding matrix stiffness could substantially affect resonant frequencies especially for longer doublewalled carbon nanotubes of larger innermost radius at higher resonant frequencies, and thus the latter does not keep the otherwise concentric structure at ultrahigh frequencies.

High numerical aperture polymer microstructured fiber with three super-wavelength bridges

The transmission properties of a novel high numerical aperture polymer-based fiber are detailed. The proposed fiber features a large core (520 μm) suspended in air by three bridges of ∼3 μm thickness. Unlike existing high NA fibers featuring a large number of subwavelength supports, the bridge size in our fiber is not subwavelength. However, as there are only three such bridges and the core diameter is large, our fiber still confines light efficiently in the inner core. We then detail a modified cutback measurement procedure to study fiber transmission loss. We report an extra ∼ 5d B m −1 leakage loss from the core through the bridges in addition to the core material absorption loss. We then present a numerical aperture measurement procedure for relatively short fiber pieces guiding in the non-equilibrium mode distribution regime. An NA of over 0.60 was demonstrated for fiber pieces smaller than 30 cm and was shown to decrease gradually for longer fibers. Furthermore, even for fibers as long as 80 cm a relatively high NA of over 0.3 was observed. Finally, we have demonstrated high NA operation of such fibers when the fiber tip was inserted into a highly diffusive aqueous environment (milk). We have also demonstrated a much higher light collection efficiency of our fibers compared to that of a simple rod-in-the-liquid fiber of identical diameter. We believe that the proposed fiber has a strong potential for short range evanescent sensing and light collection applications due to the fiber’s simple fabrication methodology, wide unobstructed air channels, relatively low loss and high NA.

Review of Glass and Polymer Multimode Fibers Used in a Wimedia Ultrawideband MB-OFDM Radio Over Fiber System

In this paper, we have exhibited the potential of the glass- and polymer-based multimode fibers to be used in a radio over fiber (ROF) system in order to extend the indoor coverage of the Wimedia multiband orthogonal frequency division multiplexing (MB-OFDM) ultrawideband (UWB) standard. After the design of a test setup operating at 850 nm, we have performed the physical characterization of the ROF system especially the mask test compliance, the error vector magnitude (EVM), or the relative constellation error (RCE) variation as a function of the system parameters [radio frequency (RF) power, optical attenuation, fiber length, laser bias current]. The transmission performance of both 200 and 480 Mb/s Wimedia signals is demonstrated through a 100 m link length of glass- and polymer-based multimode fibers: transmission penalties are quantified by RCE with values under the standard requirements. Two different behaviors depending on the core material of the fiber have been identified in this study.

Synthesis and characterization of short Grewia optiva fiber‐based polymer composites

AbstractNatural fibers, such as Flax, Sisal, Hibiscus Sabdariffa, and Grewia optiva (GO) possess good reinforcing capability when properly compounded with polymers. These fibers are relatively inexpensive, easily available from renewable resources, and possess favorable values of specific strength and specific modulus. The mechanical performance of natural fiber‐reinforced polymers (FRPs) is often limited owing to a weak fiber‐ matrix interface. In contrast, urea–formaldehyde (UF) resins are well known to have a strong adhesion to most cellulose‐containing materials. This article deals with the synthesis of short G. optiva fiber‐reinforced UF polymer matrix‐based composites. G. optiva fiber‐reinforced UF composites processed by compression molding have been studied by evaluating their mechanical, physical, and chemical properties. This work reveals that mechanical properties such as: tensile strength, compressive strength, flexural strength, and wear resistance of the UF matrix increase up to 30% fiber loading and then decreases for higher loading when fibers are incorporated into the polymer matrix. Morphological and thermal studies of the matrix, fiber, and short FRP composites have also been carried out. The swelling, moisture absorbance, chemical resistance, and water uptake behavior of these composites have also been carried out at different intervals. The results obtained lay emphasis on the utilization of these fibers, as potential reinforcing materials in bio‐based polymer composites. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers

Carbon nanotube-reinforced composites: frequency analysis theories based on the matrix stiffness

Strong and versatile carbon nanotubes are finding new applications in improving conventional polymer-based fibers and films. This paper studies the influence of matrix stiffness and the intertube radial displacements on free vibration of an individual double-walled carbon nanotube (DWNT). For this, a double elastic beam model is presented for frequency analysis in a DWNT embedded in an elastic matrix. The analysis is based on both Euler–Bernoulli and Timoshenko beam theories which considers shear deformation and rotary inertia and for both concentric and non-concentric assumptions considering intertube radial displacements and the related internal degrees of freedom. New intertube resonant frequencies and the associated non-coaxial vibrational modes are calculated. Detailed results are demonstrated for the dependence of resonant frequencies and mode shapes on the matrix stiffness. The results indicate that internal radial displacement and surrounding matrix stiffness could substantially affect resonant frequencies especially for longer double-walled carbon nanotubes of larger innermost radius at higher resonant frequencies, and thus the latter does not keep the otherwise concentric structure at ultrahigh frequencies. Therefore, depending on the matrix stiffness, for carbon nanotubes reinforced composites, different analysis techniques should be used while the aspect ratio of carbon nanotubes has a little effect on the analysis theory which should be selected.

Effect of Flame Retardant on Mechanical Properties and Flammability of Sisal/PP Composites

Due to environmental reasons and their acceptable mechanical properties, natural fiber based polymer composites have been increasingly used in various applications, e.g. housing materials, automotive parts. However, their low thermal resistance and fire behavior limit the use of these materials. In this work, magnesium hydroxide (Mg(OH)2), as a flame retardant, was incorporated into sisal/polypropylene composites. Ratio of sisal fiber to Mg(OH)2 in each composite sample was varied. Maleic anhydride grafted polypropylene (MAPP) was also used to improve the interface of polypropylene and fillers. Flammability and thermal behavior of the composites were examined using a horizontal burning test and thermo gravimetric analyzer, respectively. Morphology and mechanical properties of the composites were also investigated.

Specialty High Performance Coatings for Optical Fiber Applications via Perfluorocyclobutyl (PFCB) Aryl Ether Polymers

AbstractThere is a growing need for optical fiber coatings that can sustain higher temperatures than present materials permit. To date, polyimides are used predominantly but they generally are difficult to process and usually require multiple depositions to achieve the desired film thickness. Perfluorocyclobutyl (PFCB) aryl ether polymers have demonstrated much success as processable and amorphous fluoropolymers,[1] with particular emphasis on high performance optical applications.[2] This work discusses recent efforts into perfluorocyclobutyl aryl ether polymer-based optical fiber coatings.[3] A series of silica-based optical fibers were drawn with differing PFCB polymer coatings compositions and molecular weights on a Heathway draw tower. Results include a more than doubled usage temperature of coating (decomposition temperatures (Td) in nitrogen and air were above 450 °C) without affecting fiber mechanical properties and comparable isothermal stability to conventional coatings, except with a >150 °C higher temperature. Preliminary results of the first successful coating of optical fibers by PFCB polymers will be presented herein, as well as future endeavors.

Characterization of Electrospun PVdF Fiber-Based Polymer Electrolytes

Porous PVdF fiber-based membranes with a three-dimensional network structure, high porosity, large electrolyte solution uptake, and adequate mechanical properties were prepared by an electrospinning technique using various mixed-solvent compositions with poly(vinylidene fluoride) (PVdF). Their physical properties, including surface morphology, average fiber diameter, pore size, and electrolyte solution uptake, strongly depended on the composition of the polymer solution used for electrospinning. From X-ray diffraction and FT-Raman data, we found the PVdF membranes to have mixed-crystal structure sof Form II (α-type) and Form III (γ-type). Electrospun PVdF fiber-based polymer electrolytes were prepared by immersing porous PVdF membranes into 1 M LiPF6 electrolyte solutions. On the basis of FT-Raman data of the PVdF fiber-based polymer electrolytes, it was shown that ethylene carbonate molecules mainly participated in the solvation of the lithium salt. Moreover, with the exception of diethyl carbonate, thes...

Optical Properties of Electrospun Nanofibers of Conducting Polymer-Based Blends

Conducting polymers were electrospun into fibers with other spinnable polymers. The optical properties of the electrospun fibers were characterized in comparison with spin-cast thin films. The electrospun conducting polymer-based fibers with different fiber diameters of 100 nm and 1 microm were prepared. Aligned nanofibers were prepared using a rotating disc collector in order to induce molecular orientation in the electrospun fibers. The effect of electrospinning processes on the optical properties was discussed in terms of fiber diameter and molecular orientation.

Narrow Diameter Carbon Nanotubes (CNTs) for Polymer Composite Reinforcement

Strong and versatile carbon nanotubes are finding new applications in improving conventional polymer-based fibers. Nanotube-reinforced composites could ultimately provide the foundation for a new class of strong and lightweight fibers with properties such as electrical and thermal conductivity unavailable in current fibers. A recent research has discovered that the best type of nanotube for polymer composite reinforcement is the small diameter multiwalled nanotubes (MWNTs). Here, a catalytic technique has been developed to produce narrow diameter bulk multiwalled carbon nanotubes of less than 38 nm. Structural characterizations including scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), thermo gravimetric analysis (TGA) and Raman spectroscopy conducted on CNTs grown on three different catalysts, namely iron, cobalt and nickel have indicated that the catalyst used affects their sizes and crystallinity. Results showed that the smallest CNTs could be obtained by catalytic growth on Ni catalyst. The study has proven that with the skillful use of catalyst, a range of narrow sized nanotubes could be produced, providing the material needed to investigate the optimum diameter for the best mechanical reinforcement of polymer composites.

Optically reconfigurable azobenzene polymer-based fiber Bragg filter

Optically writable, thermally erasable surface relief gratings in thin Disperse Red 1 polymethyl methacrylate azopolymer films were used to demonstrate an arbitrarily reconfigurable fiber Bragg filter. Gratings were optically written on azopolymer-coated side-polished fiber blocks, and a write-erase-write cycle was demonstrated. Finite difference time domain simulations reveal that this optically reconfigurable device concept can be optimized in a silicon-on-insulator waveguide platform.

Polymer microresonator strain sensors

A new class of fiber-based polymer microresonator strain sensors is analyzed and demonstrated. The flexible sensors are fabricated using a liftoff process and are based on the distortion of the microring by strain and the subsequent shift of the resonant wavelength. For the demonstration, a controlled strain was achieved by flexing the sensor. The measured sensitivity at 1310 nm, 0.32 /spl times/ 10/sup -3/ nm//spl mu//spl epsiv/, is in good agreement with the predictions.

Deformation studies of single rigid-rod polymer-based fibres. Part 1. Determination of crystal modulus

This series of papers covers several aspects related to the influence of external stresses on the crystalline microstructure of rigid-rod polymer-based fibres. For the study, the main three fibres of this type have been selected, namely poly( p-phenylenebenzobisoxazole) (PBO fibres), poly( p-phenylenebenzobisthiazole) (PBT or PBZT fibres) and the novel poly{2,6-diimidazo[4,5- b:4′-5′- e]pyridinylene-1,4(2,5-dihydroxy)phenylene} (PIPD or M5 fibres). Synchrotron radiation was employed to record high-quality wide-angle X-ray scattering patterns from single fibres. The present paper deals mainly with the evaluation of lattice strain along the fibre axis ( c-)direction. Crystal moduli of the different fibres were calculated from the variation with stress of the lattice strain determined from the shift of the major meridional (00 l) reflections. This procedure rendered values of approximately 440 GPa for the crystal modulus of PIPD and PBO fibres, and 350 GPa for the PBT one. The difference between these two values was explained in terms of specific molecular conformation of the monomers in the unit cell. Discrepancies between the crystal and macroscopic (calculated from tensile tests) moduli are due to imperfections generated during the manufacture of the fibres.

Nanotube–polymer adhesion: a mechanics approach

The interfacial shear strength in single-wall nanotube–polymer composites is calculated using a traditional force balance approach, modified for a hollow tube, and the effect of varying some of the model parameters is examined and discussed. It is shown that high values of the interfacial shear strength (compared to those in current advanced fiber-based polymer composites) are in principle attainable. Defects in the hexagonal structure of a nanotube, which technically is a `perfect' material, are expected to strongly reduce its strength and the model predicts that, as a consequence, a large variability should be experimentally observed in either the interfacial strength or the critical length of apparently identical nanotubes.