High-performance Polymer Fibres Research Articles

Tensile properties of carbon nanotube fibres described by the fibrillar crystallite model

This work presents a model that successfully describes the tensile properties of macroscopic fibres of carbon nanotubes (CNTs). The core idea is to treat such a fibre as a network of CNT bundles, similar to the structure of high-performance polymer fibres, with tensile properties defined by the CNT bundle orientation distribution function (ODF), shear modulus and shear strength. Synchrotron small-angle X-ray scattering measurements on individual fibres are used to determine the initial ODF and its evolution during in-situ tensile testing. This enables prediction of tensile modulus, strength and fracture envelope, with remarkable agreement with experimental data for fibres produced in-house with different constituent CNTs and for different draw ratios, as well as with literature data. The parameters extracted from the model include: CNT bundle shear strength, shear modulus and tensile strength. These are in agreement with data for commercial high-performance fibres, although high compared with values for single-crystal graphite and short individual CNTs. The manuscript also discusses the unusually high fracture energy of CNT fibres and exceptionally high figure of merit for ballistic protection. The model predicts that small improvements in orientation would lead to superior ballistic peformance than any synthetic high-peformance fiber, with values of strain wave velocity (U1/3) exceeding 1000m/s.

Hyperelastic modelling of yarn structures for dynamic applications

Dry fabrics comprised of high performance polymeric fibers have been widely used as protection layers in structures submitted to high velocity impacts (HVI). Their outstanding impact energy dissipation ability combined with an high strength-to-weight ratio make them a preferable choice in different applications such as bullet vests or blade containment systems over standard materials. Among the different approaches adopted to study these structures numerical methods assume a central role. Thanks to their reduced costs and the related possibility of evaluating the effects of single phenomena, they are often used to predict the structure ballistic limits or to study the physical events which occur during the penetration. Among the different strategies adopted to model a fabric, mesoscopic models have been largely adopted by different authors. These models assume the yarns as a continuum body while the fabric geometry is explicitly described. Nowadays yarn material models are universally assumed to be linear elastic and orthotropic. This modelling approach mostly focuses on the longitudinal behaviour of the yarn, however fiber-scale analyses and experimental results shows the importance of three-dimensional stress state on the ballistic limit. In order to obtain a three-dimensional description of the yarn strain state during the impact, a novel hyperelastic model for yarn structures here is developed. In a first step, fiber-level preliminary analyses have been performed to obtain the effective behaviour of these structure under the projectile collision. In the second step, the hyperelastic model has been implemented and identified thanks to microscopic elementary tests. Finally, a continuum model of the yarn have been performed. First results show the relevance of the hyperelastic model compared to the fiber-level observation and enhance the limit of the classical linear elastic material model.

Tensile behavior of high-strength strain-hardening cement-based composites (HS-SHCC) made with high-performance polyethylene, aramid and PBO fibers

The article at hand presents an investigation of the tensile behavior of high-strength strain-hardening cement-based composites (HS-SHCC) made with four different types of dispersed high-performance polymer fibers. In particular, high-density polyethylene (HDPE), poly(p-phenylene-terephthalamide) (aramid), as-spun poly(p-phenylene-2,6-benzobisoxazole) (PBO) and high-modulus PBO fibers were examined in respect of their reinforcing effect in a high-strength, finely grained, cementitious matrix. Besides the tension experiments at the composite level, single fiber pullout tests were performed for a micromechanical characterization of each composite material. Furthermore, contact-angle measurements and microscopic investigations were carried out to assess the fibers' ability to be wetted and to explain their interaction with the cementitious matrix.

Preparation of poly (tetrafluoroethylene) nanofiber film by electro-blown spinning method

As a kind of high-performance fiber, PTFE fiber has been widely used in many fields because of its unique characteristics. In this study, pure PTFE nanofiber film was prepared effectively through electro-blown spinning (EBS) under dual forces of high speed air flow and static electric method followed by a thermal treatment process. The effects of PTFE/PVA ratio, the amount of boric acid (BA), air pressure, applied voltage and sintered temperature were discussed to obtain the PTFE nanofibers with different diameters, and the film had been characterized by SEM, TG, XRD and XPS, respectively. The results showed that pure PTFE nanofiber film with good morphology could be large scale prepared through the EBS process. Moreover, this novel EBS method may realize the industrialized production of high performance polymer fibers.

Solventless High Throughput Manufacturing of Poly(butylene terephthalate) Nanofibers.

Nanofibers possess high surface area to volume ratios and are particularly attractive for a variety of applications including tissue regeneration, drug delivery, fiber-reinforced composites, filtration, and protective clothing. Though the production of nanofibers from common thermoplastic polymers is relatively well-demonstrated, processing constraints have limited high throughput manufacturing of nanofibers from high performance polymers. This has in turn limited broad technological exploitation of polymer nanofibers in areas such as hot chemical filtration or high-performance lightweight composites for aerospace and defense applications. We report here that nanofibers can be produced in a solventless high throughput process from polymers such as poly(butylene terephthalate) (PBT) using a newly developed technology termed "Forcespinning" that employs centrifugal force to attenuate fibers. Our investigations also show that these nanofibers have a high crystallinity and enhanced molecular orientation which is important for realizing desirable physical and chemical properties of many high-performance polymer fibers.

Surface modification of high-performance polymeric fibers by an oxygen plasma. A comparative study of poly( p-phenylene terephthalamide) and poly( p-phenylene benzobisoxazole)

Poly( p-phenylene terephthalamide) (PPTA) and poly( p-phenylene benzobisoxazole) (PBO) fibers were exposed to an oxygen plasma under equivalent conditions. The resulting changes in the surface properties of PPTA and PBO were comparatively investigated using inverse gas chromatography (IGC) and atomic force microscopy (AFM). Both non-polar ( n-alkanes) and polar probes of different acid–base characteristics were used in IGC adsorption experiments. Following plasma exposure, size-exclusion phenomena, probably associated to the formation of pores (nanoroughness), were detected with the largest n-alkanes (C 9 and C 10). From the adsorption of polar probes, an increase in the number or strength of the acidic and basic sites present at the fiber surfaces following plasma treatment was detected. The effects of the oxygen plasma treatments were similar for PPTA and PBO. In both cases, oxygen plasma introduces polar groups onto the surfaces, involving an increase in the degree of surface nanoroughness. AFM measurements evidenced substantial changes in the surface morphology at the nanometer scale, especially after plasma exposure for a long time. For the PBO fibers, the outermost layer – contaminant substances – was removed thanks to the plasma treatment, which indicates that this agent had a surface cleaning effect.

High velocity impact and armour design

Improving combat survivability is the most important aspect of military technology. Hence the development of new lightweight armour systems is a key requirement. A large number of new high performance polymer fibres have been developed in recent years, which include Aramid fibres, polyethylene fibres and polypropylene fibres, amongst others, and have been applied to soft armour systems. To gain a fundamental understanding of which fibre type is the best for a specific application requires the development of techniques which can span all length scales. It has been widely recognised that multiscale modelling, which encompasses the full range of length and time scales, will be an important factor in the future design and testing of novel materials, and their application to armour design. In the present paper a new material damage model suitable for the simulation of impact on thin laminated panels fabricated from high performance fibres is implemented into the commercial ls-dyna ® finite element code. The new material model links the mesoscale behaviour of the individual fibres to the macroscale behaviour within a conventional shell finite ele- ment. The implemented model is used in a parametric high velocity study to illustrate the applicability of the model to the design of thin armour panels.

Modelling on-axis microdiffraction to investigate crystallographic texture within high-performance polymer fibres

Radial crystallographic texture in high-performance polymeric fibres is a common structural feature. Quite why such preferred orientation should exist and how it impacts upon the mechanical properties of the fibre is still not fully understood. This study reports the use of a modelling approach to investigate radial texture in the poly(p-phenylene benzobisoxazole) fibre type. The model allows azimuthal scattering profiles to be calculated corresponding to an on-axis microdiffraction geometry. The results show that, in order to model experimental data successfully, an offset is required between theaunit-cell axis and the fibre radial direction. The origin of this offset is tentatively attributed to solvent outflow during coagulation, which aligns the planar molecular chains. Meanwhile, textural differences between different fibre types can be explained by processing differences.

Raman and IR micro-analysis of high performance polymer fibres tested in traction and compression

The analysis of the (nano)structure and texture of polymer fibres (polyamides 66, Bombyx mori and spider silks) by Raman (IR) microscopy/metry, in particular after deuteration and isotopic H/D dilution, is applied so as to differentiate between crystalline and amorphous macromolecules. Bonding is very similar in the two cases but a broader distribution of conformations is observed for the amorphous macromolecules, in agreement with the para-crystal model. These conclusions are then used to discuss the modifications induced by the application of a tensile or compressive stress, including the effects of fatigue. Detailed attention is paid to water and the inter-chain coupling for which the importance of hydrogen bonding is reconsidered. The significant role of the “amorphous” bonds in the process of fracture/fatigue is shown. The approach is extended to the analysis of silks.

Effects of surface characteristics of F-12 polymeric fibers on the mechanical properties of F-12/epoxy composites

The effects of the surface properties and skin-core structure of F-12 high-performance polymeric fibers on the mechanical properties of F-12 fiber-reinforced epoxy composite were investigated. Atomic force microscopy, scanning electron microscopy and X-ray photoemission spectroscopy were employed to characterize the microstructure and surface-elemental analysis of the F-12 fiber. Mechanical properties of the composite, such as interfacial shear strength, interlaminar shear strength, flexural modulus and flexural strength were tested. The results clearly show the skin-core structure and surface properties of F-12 fiber have great effects on the water absorption rate and mechanical performances of the composites.

Rigid‐rod polymeric fibers

AbstractThis paper traces the historical development of high temperature resistant rigid‐rod polymers. Synthesis, fiber processing, structure, properties, and applications of poly(p‐phenylene benzobisoxazole) (PBO) fibers have been discussed. After nearly 20 years of development in the United States and Japan, PBO fiber was commercialized with the trade name Zylon® in 1998. Properties of this fiber have been compared with the properties of poly(ethylene terephthalate) (PET), thermotropic polyester (Vectran®), extended chain polyethylene (Spectra®), p‐aramid (Kevlar®), m‐aramid (Nomex®), aramid copolymer (Technora®), polyimide (PBI), steel, and the experimental high compressive strength rigid‐rod polymeric fiber (PIPD, M5). PBO is currently the highest tensile modulus, highest tensile strength, and most thermally stable commercial polymeric fiber. However, PBO has low axial compressive strength and poor resistance to ultraviolet and visible radiation. The fiber also looses tensile strength in hot and humid environment. In the coming decades, further improvements in tensile strength (10–20 GPa range), compressive strength, and radiation resistance are expected in polymeric fibers. Incorporation of carbon nanotubes is expected to result in the development of next generation high performance polymeric fibers. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 100: 791–802, 2006

Crystalline and amorphous deformation of process-controlled cellulose-II fibres

Raman spectroscopy has been used as a tool to monitor the microdeformation of a range of process-controlled fibres with different orientations. The mechanical properties of the fibres are shown to be related to the orientation parameter (〈sin 2 θ〉), and that by using the particular fibre spinning process ( N-methylmorpholine N-oxide (NMMO)/cellulose), a plateau is reached, beyond which no improvements can be made. Clear shifts in the 1095 cm −1 Raman band towards a lower wavenumber are observed upon the application of external tensile deformation, which are thought to relate to the molecular deformation of the cellulose chain. It is found that relationships are determinable between the rate of band shift with respect to strain of the 1095 cm −1 Raman band and the orientation parameter. For the first time, a modified series model is related to the molecular deformation as revealed by Raman spectroscopy, and that the data for these fibres is consistent with a structure with a dominant amorphous fraction. Other high modulus cellulose fibres are shown to behave more like high performance polymer fibres such as poly( p-phenylene benzobisoxazole) (PBO) and poly( p-phenylene terephtalamide) (PPTA). The need, if high performance variants of these fibres are to be developed, to improve the microstructure of NMMO–cellulose fibres is discussed.

Raman spectroscopy - a technique to assess the residual stress in fiber-reinforced polymeric insulation materials

Fiber reinforced polymeric insulation materials are composite insulating materials that are made from high-performance polymeric insulation material and high-performance fibers. This makes reinforcement of fiber-reinforced polymeric insulation material of interest in many structural insulation applications subject to high voltage or ultra high voltage environment. In this paper, the effect of residual stresses on the electrical insulation integrity is first summarized followed by the description of the laser Raman spectroscopy technique for the assessment of the residual stress in high-performance fiber reinforced polymeric insulation. The present investigation is concerned with the use of the laser Raman spectroscopy to analyze the residual stresses in a Twaron/spl reg/-type aromatic polyamide (aramid) fibers/Araldite/spl reg/ epoxy resin system.

Compressive behaviour of rigid rod polymer fibres and their adhesion to composite matrixes

The deformation behaviour of the new high performance polymer fibres, poly(p-phenylene benzobisoxazole) (PBO) and polypyridobisimidazole (PIPD) and their adhesion to an epoxy composite matrix have been investigated. Both fibres give well defined Raman spectra, and the deformation micromechanics of PBO and PIPD single fibres and composites were studied from stress induced Raman band shifts. Single fibre stress-strain curves were determined in both tension and compression, thus providing an estimate of the compressive strength of these fibres. It was found that the PIPD fibre has a higher compressive strength (~1 GPa) than PBO (~0·3 GPa) and other high performance polymer fibres, because hydrogen bond formation is possible between PIPD molecules. It has been shown that when PBO and PIPD fibres are incorporated into an epoxy resin matrix, the resulting composites show very different interfacial failure mechanisms. The fibre strain distribution in the PBO-epoxy composites follows that predicted by the full bonding, shear lag model at low matrix strains, but deviations occur at higher matrix strains due to debonding at the fibre/matrix interface. For PIPD-epoxy composites, however, no debonding was observed before fibre fragmentation, indicating better adhesion than for PBO as a result of reactive groups on the PIPD fibre surface.

Deformation studies of thermotropic aromatic copolyesters using NIR Raman spectroscopy

Near infrared (NIR) Raman spectroscopy has been used to investigate the deformation behaviour of highly oriented fibres and tapes made from thermotropic aromatic copolyesters. It has been found that a number of Raman bands of thermotropic aromatic copolyesters show linear shifts towards lower wavenumbers with stress and strain following tensile deformation. The strain and stress dependencies of the 1600cm−1 band due to stretching of the p-phenyl ring, have been studied in detail and discussed in relation to values reported for high-performance aromatic polymer fibres. The behaviour has been discussed in terms of the microstructure of the thermotropic aromatic copolyester materials compared with that of other highly-oriented aromatic polymer fibres.

Molecular deformation in spider dragline silk subjected to stress

It is demonstrated that well-defined Raman spectra can be obtained from the dragline silk of the spider Nephila edulis, and that the Raman bands also shift when the silk fibre is subject to mechanical deformation. This indicates that the protein molecules in the spider silk fibre undergo direct molecular deformation when the fibre is stretched. Hence, we demonstrate that the deformation behaviour of this natural polymer fibre is similar to that of high-performance synthetic polymer fibres.

Tensile and compressive deformation of polypyridobisimidazole (PIPD)-based `M5' rigid-rod polymer fibres

The tensile and compressive deformation behaviour of a new type of heterocyclic rigid-rod polymer fibre, polypyridobisimidazole `PIPD' or `M5', produced by the spinning of liquid-crystalline solutions, have been studied. The Young's moduli and tensile strengths for the two different PIPD or M5 fibres have been determined to be greater than 300 GPa and 4 GPa, respectively. Molecular deformation in the fibres has been monitored using Raman spectroscopy and it has been shown that the peak positions of the Raman bands in the fibres are sensitive to the application of mechanical stress and strain. This has enabled a detailed study of molecular deformation to be undertaken for both tensile and compressive deformation. Full tensile-compression stress–strain curves have been derived and the compressive modulus and compressive strength of the PIPD fibres have been determined to be greater than 300 GPa and up to 1 GPa, respectively, which are both considerably higher than values for other high-performance polymer fibres. The potential use of PIPD fibres as reinforcing fibres in high-performance composites is discussed.

Metallized polymer fibers as leadwires and intrafascicular microelectrodes

We have developed a process for producing fine, very flexible microwires suitable for use as small signal leadwires or nerve electrodes. The process incorporates metallization of high-performance monofilament polymer fibers to yield electrically conductive fibers with greatly improved flexibility over solid metal wires of similar strength. The metallization layers are produced by serial vacuum deposition of a 0.3 μm thick coating of three metals, titanium-tungsten (Ti/W), gold (Au), and platinum (Pt), onto monofilament, poly- p-phenyl-terephthalate aramid fibers (Kevlar ®). The metallized fibers are then insulated with an approx. 1 μm thick layer of silicone elastomer. The result is a microlead with high electrical conductivity (linear resistance = 30 Ω/cm), desirable interfacial properties, excellent mechanical stability and extremely high flexibility. These physical characteristics are appropriate for application as signal leadwires or recording/stimulating electrodes where small size and high flexibility are paramount. In this paper we report on the electrical and mechanical properties of these metallized fibers and demonstrate their use as intrafascicular electrodes for recording multi-unit neural activity in feline peripheral nerves.

Comments on “axial X-ray scattering on high performance polymeric fibers”

Comments on “axial X-ray scattering on high performance polymeric fibers”

Compressive behavior of materials: Part II. High performance fibers

The primary focus of this paper is on the axial compression behavior of high performance polymeric and carbon fibers. Seven test methods used for determining the compressive strength of single fibers have been reviewed. Various micromechanical models proposed in the literature to understand the compressive failure in single filaments and in other anisotropic systems have been discussed and analyzed. The results of various approaches to influence the compressive strength of polymeric fibers have been summarized. Possible reasons for the variation in the compressive strength of pitch and PAN-based carbon fibers have also been addressed.