High-performance Polymer Fibres Research Articles

Robust and Flame-Retardant Zylon Aerogel Fibers for Wearable Thermal Insulation and Sensing in Harsh Environment.

The exceptional lightweight, highly porous, and insulating properties of aerogel fibers make them ideal for thermal insulation. However, current aerogel fibers face limitations due to their low resistance to harsh environments and a lack of intelligent responses. Herein, a universal strategy for creating polymer aerogel fibers using crosslinked nanofiber building blocks is proposed. This approach combines controlled proton absorption gelation spinning with a heat-induced crosslinking process. As a proof-of-concept, Zylon aerogel fibers that exhibited robust thermal stability (up to 650°C), high flame retardancy (limiting oxygen index of 54.2%), and extreme chemical resistance are designed and synthesized. These fibers possess high porosity (98.6%), high breaking strength (8.6MPa), and low thermal conductivity (0.036 W m-1 K-1 ). These aerogel fibers can be knotted or woven into textiles, utilized in harsh environments (-196-400°C), and demonstrate sensitive self-powered sensing capabilities. This method of developing aerogel fibers expands the applications of high-performance polymer fibers and holds great potential for future applications in wearable smart protective fabrics.

Effect of thermally induced microstructural changes on the mechanical properties and ballistic performance of poly (p-phenylene terephthalamide) fibers

Microstructural variations have a strong influence on the load transfer capacity of the high-performance polymeric fibers, which is also reflected in their ballistic property changes. The focus of the present study is to investigate thermally induced microstructural changes and their reflection on the mechanical properties and theoretical ballistic limit of poly ( p-phenylene terephthalamide) fibers by a correlation. From the quantitative analysis of XRD, thermally induced changes in unit cell a-dimension show profound sensitivity in affecting the tenacity and modulus of the fibers. Based on the physicochemical changes in FTIR and FESEM analysis, significant surface deterioration and changes in the chemical network are observed. However, dimensional variations of the crystal structure along a-direction show a stronger influence than the chemical and morphological changes, reflecting sigmoidal responses with tenacity, modulus and theoretical V50 by correlations. As an effect of unit cell dimensional variation, changes in crystallinity are resulted and lead to the loss in theoretical ballistic limit of the fibers by following first-order kinetics. Lastly, angular separation and (200) orientation angle are determined to build a global correlation with modulus and theoretical ballistic limit for quickly decoding macro-changes in terms of micro-properties. The given correlations can help to identify crystallographic transformations upon other induction techniques and view their effect on mechanical and ballistic parameters. In addition, the given approach can be extended for different ballistic materials under any environmental conditions.

Fibers and Textiles for Personal Protective Equipment: Review of Recent Progress and Perspectives on Future Developments

This article reviews recent developments in fibers and textiles for Personal Protective Equipment (PPE) applications. Fibers are grouped into six categories: highly extensible elastomeric fibers, cellulose-based fibers, commodity synthetic fibers, high strength inorganic materials, and high performance polymer fibers. New developments with highly extensible elastomeric fibers include polyester-based elastic fibers and shape memory polyurethane. In the case of cellulose-based fibers, environmentally friendly processes and nanotechnology-enabling treatments are developed for natural fibers where attempts are made to transfer interesting attributes of the feedstock to regenerated cellulose fibers. Commodity synthetic fibers comprise polyolefins, polyester, and polyamide; they have seen recent developments in terms of surface functionalization and the formation of structures at the nanoscale. In terms of high strength inorganic materials, basalt fibers and carbonaceous materials have found increased use in PPE. Boron is also generating considerable interest for fibers and coatings. Research on high-performance polymer fibers includes further improving their short- and long-term performance, moving to the nanoscale for new functionalities, and exploring their recyclability. An additional section describes a series of special textile structures relevant to PPE involving 3D textile structures, auxetic textile structures, shear thickening fabrics, nanoporous structures, phase change materials, and some specially designed textile-based composite structures for improved protection against mechanical hazards. The article ends with some perspectives on promising avenues for further developments.

Compressive testing of thermoset composites reinforced with high-performance polymer fibres

High-performance polymer fibres offer promising tensile and physical properties but are rarely used in structural composite applications due to their poor compressive performance. To better understand their performance inside a composite, unidirectional thermoset composites made with three types of polymer fibres were tested in shear-loaded compression. The results confirmed the poor compressive performance of the composites despite good fibre alignment, low porosity, and decent interfacial adhesion. Showing that the fibres collapse rather than microbuckle proves that intrinsic fibre behaviour in compression is the key culprit. The developed finite element model predicted that the short gauge lengths required to avoid buckling lead to significant strain concentrations due to the grips. This causes the test to underestimate the compressive modulus and potentially the rest of the compressive stress in the stress–strain diagram.

The translaminar fracture toughness of high-performance polymer fibre composites and their carbon fibre hybrids

The translaminar fracture toughness is a key property that governs the damage tolerance and notch sensitivity of fibre-reinforced composites. Compact tension tests were performed to investigate the translaminar fracture toughness of composites reinforced with three types of high-performance polymer fibres: polyarylate (PAR), polybenzobisoxazole (PBO) and aramid fibre. A carbon fibre composite was used as the reference system. The propagation translaminar fracture toughnesses of the PAR and PBO fibre composites were 492 kJ/m2 and 547 kJ/m2, respectively. These are among the highest translaminar fracture toughness values recorded in the literature. It was hypothesized that the fibrillation of the fibres upon failure was an important energy dissipating mechanism alongside pull-outs that were much longer than for carbon fibre. Replacing a small strip of a carbon fibre ply by a strip of PAR or PBO fibres successfully reinforced the material by locally arresting crack growth. By contrast, the performance of the aramid fibre composites and their hybrids with carbon fibre was lacklustre. The results presented in this work can be used to further improve the safety of composite parts by optimising the design for damage tolerance while also reducing the weight of the parts.

Carbonene Materials Modified High-Performance Polymer Fibers: Preparation, Properties, and Applications

Carbonene Materials Modified High-Performance Polymer Fibers: Preparation, Properties, and Applications

Spinning conditions affect structure and properties of Nephila spider silk

Raman spectroscopy is used to elucidate the effect of spinning conditions upon the structure and mechanical properties of silk spun by Nephila spiders from the major ampullate gland. Silk fibers produced under natural spinning conditions with spinning rates between 2 and 20 mm s−1 differed in microstructure and mechanical properties from fibers produced either more slowly or more rapidly. The data support the “uniform strain” hypothesis that the reinforcing units in spider silk fibers are subjected to the same strain as the fiber, to optimize the toughness. In contrast, in the case of synthetic high-performance polymer fibers, the both units and the fiber experience uniform stress, which maximizes stiffness. The comparison of Nephila major and minor ampullate silks opens an intriguing window into dragline silk evolution and the first evidence of significant differences between the two silks providing possibilities for further testing of hypotheses concerning the uniform strain versus uniform stress models.Impact statementIt is well established that the microstructure and mechanical properties of engineering materials are controlled by the conditions employed to both synthesize and process them. Herein, we demonstrate that the situation is similar for a natural material, namely spider silk. We show that for a spider that normally produces silk at a reeling speed of between 2 and 20 mm s−1, silk produced at speeds outside this natural processing window has a different microstructure that leads to inferior tensile properties. Moreover, we also show that the silk has a generic microstructure that is optimized to respond mechanically to deformation such that the crystals in the fibers are deformed under conditions of uniform strain. This is different from high-performance synthetic polymer fibers where the microstructure is optimized such that crystals within the fibers are subjected to uniform stress.Graphic abstract

Calcia-doped ceria hybrid coating functionalized PBO fibers with excellent UV resistance and improved interfacial compatibility with cyanate ester resins

Poly(p-phenylene-2,6-benzobisoxazole) (PBO) fibers display weak outdoor stability and reliability due to their poor UV resistance and chemically inert surface. In this work, calcia-doped ceria (Ce0.8Ca0.2O1.8) nanoparticles was fabricated via chemical co-precipitation method, and the novel Ce0.8Ca0.2O1.8/P(S-co-BCB-co-MMA) organic–inorganic hybrid coating was then designed and prepared for surface functionalization of PBO fibers (PBO@P-Ce0.8Ca0.2O1.8). Organic-inorganic hybrid coating presents high surface roughness and excellent UV resistance. When the concentration of Ce0.8Ca0.2O1.8 nanoparticles with the particle size of about 50 nm is 0.6 wt%, PBO@P-Ce0.8Ca0.2O1.8–3 fibers (sample 4, 0.6 wt%) present the best interfacial bonding strength with modified bisphenol A cyanate (BADCy) resins, the single fiber pull-out strength between sample 4 and modified BADCy resins reaches the maximum value of 4.6 MPa, 48.4% higher than that of pristine PBO fibers (sample 0, 3.1 MPa). Meanwhile, the tensile strength of sample 4 after 288 h UV aging is increased from 1.4 GPa (PBO fibers) to 4.1 GPa. Overall, functionalized PBO fibers in this work demonstrate higher surface activity, excellent UV resistance and improved interfacial bonding strength with modified BADCy resins, which provides a new idea for functionalizing the surface activity and UV resistance of high-performance polymer fibers.

Moisture absorption characteristics and effects on mechanical properties of Kolon/epoxy composites

Para-aramid fibers (Kolon) are high performance polymeric fibers characterized by their high tenacity and impact resistance. They are used for the soft body armor structures in ballistics. In this study, the testing specimens were made from multilayered Kolon fabrics impregnated with epoxy resin where silicon carbide (SiC) microparticles or SiC nanofibers were added as reinforcement. The laminated composite samples were fabricated by hot compression and curing of epoxy resin.The tensile and impact strengths of the untreated specimens were compared with the ones that underwent water absorption in duration of 72 h (immersion or humidity) followed by desorption. The immersion of the specimens in water and exposure to high humidity (70%) were performed according to the ISO 62 standard while the tensile test was carried out in accordance with the ASTM D 3039 standard. In the end, the tensile test simulation of the laminated composite by using software Abaqus® was accomplished.

On the low reinforcing efficiency of carbon nanotubes in high-performance polymer fibres

Driven by the exceptionally high mechanical properties of carbon nanotubes (CNTs), over the years an extensive research effort has been devoted to the reinforcement of high-performance polymer fibres with CNTs. However, to date, improvements in the strength of these fibres have been rather modest even for relatively high CNT contents. After a brief review of CNT reinforced polymer fibres, here, analytical and numerical finite element models will be used to show that these experimental findings are to be expected based on the intrinsic mechanical properties of these polymer fibres and CNTs, their aspect ratio and interfacial characteristics. Results show that for realistic CNT contents and aspect ratios, the extraordinary strength of CNTs cannot be easily fully exploited in high-performance polymer fibres like Dyneema®or Kevlar®. Even if CNTs are perfectly aligned, bonded and dispersed, the low intrinsic shear strength of these highly anisotropic polymer fibres limits effective stress transfer and nanotube reinforcement.

Nanoindentation on peeled high-performance polymeric fibers reveals failure mechanisms

High-performance fibers are key to many structural and lightweight applications as they are the main reinforcing components of continuous fiber-reinforced composites and fabrics. These fibers are drawn from synthetic polymers such as poly(p-phenylene terephthalamide) (PpPTA) or ultrahigh-molecular-weight polyethylene (UHMWPE). During the drawing process, highly oriented and crystalline nanofibrils of 10–50 nm width form and assemble into larger bundles of 100–500 nm width, thereby creating a hierarchical microstructure. Although it is known that hierarchy generally improves the properties of materials, its role in the failure of synthetic fibers has not been studied. In particular, measuring properties at the intermediate submicrometric scale is challenging. To better understand the role of this organization in the mechanical performance of fibers, the research groups of Yuris Dzenis at the University of Nebraska–Lincoln and Kenneth Strawhecker at the US Army Research Laboratory have taken up the challenge and studied the mechanical interactions between the bundles. Their results were published in ACS Applied Materials and Interfaces (doi:10.1021/acsami.9b23459).

Constructing mainstay-body structure in heterocyclic aramid fiber to simultaneously improve tensile strength and toughness

High-performance polymer fibers have broad applications in composites due to high strength and excellent toughness. However, the enhancement in tensile strength often results in a decrease in elongation at break, and simultaneous increase of strength and toughness is still challenging for aramid fiber. Herein, an effective method based on relaxation time theory is proposed to simultaneously enhance the tensile strength and elongation at break for heterocyclic aramid fiber. Ultra-high molecular weight heterocyclic aramid (HMPBIA) was added in the heterocyclic aramid (PBIA) spinning dope to prepare fibers. The structure evolution of fiber is studied in detail combining with experiment and simulation. Results of Molecular Dynamics simulations prove that HMPBIA acts as a role of mainstay by maintaining straight chain conformation in highly oriented fibers. This unique mainstay-body structure weaken slippage between molecular chains when the fiber is subject to tension. Further characterizations by small angle X-ray scattering (SAXS) and scanning electron microscope (SEM) confirm the formation of mainstay-body structure in the fiber, which improves tensile strength and elongation at break by 17.7% and 16.7%, respectively.

Liquid crystalline polymers: Discovery, development, and the future

Liquid crystalline polymers (LCPs) have drawn much interest because of their superior properties and widespread applications in high-performance polymer fibers, optics, energy storage, shape memory, surface modification, data storage, actuator, etc. LCPs can self-assemble into various liquid crystalline (LC) phases, such as nematic, smectic, columnar, and cholesteric phases. The self-assembling structures of LCPs can be influenced by architectures and chemical structures of the polymer backbone, mesogenic unit, flexible spacer, surrounding alkyl tail, etc. In the last decades, the structure-property relationships of LCPs have been researched extensively. In this perspective, the history, self-assembly, and applications of main-chain, side-chain, mesogen-jacketed, dendronized, main-chain/side-chain, and crosslinked LCPs are briefly reviewed. Finally, the future direction of research on LCPs is also discussed.

High Perfomance Fiber- Kevlar the Super Tough Fiber

In today’s fast growing market, apart from general apparel clothing, some special applications are expected from textile fibers. Such fibers are used specifically for protective clothing and thus require certain high performance properties. This generation of fibers has been recently developed in the 20th century and are called high performance fibers. A class of these fibers have very high tenacity and high modulus which are used in applications such as bullet proof jackets, whereas another class of fibers would have high thermal or chemical resistance which can be used as flame resistant fabrics etc. High performance fibers include polymeric fibers such as aramids, aromatic copolyesters, extended chain flexible polyolefin etc.; carbon fiber; glass fibers; ceramic fibers and metallic fibers. High performance polymeric fibers being used for high mechanical properties should be highly oriented, linear aliphatic or aromatic molecules since flexible chains would give low melting polymers and thus low thermal resistance. On the other hand, carbon fibers are planar graphite structures with outstanding mechanical properties. Inorganic fibers have a three dimensional structure compared to a one dimensional and two dimensional structure of polymeric materials and carbon fibers respectively. They have very good mechanical properties but are brittle and have the highest thermal resistance. However, carbon fibers as well as inorganic fibers (except glass fibers) are very expensive. In the following sections, particularly, polymeric fibers would be discussed in detail. Although in the past there were some research works had done and papers also been published, but this paper just simplifies the things as well as highlight some superb features of the Kevlar fiber. However this is not a research article rather than a review article.

Nanoparticle-Infused UHMWPE Layer as Multifunctional Coating for High-Performance PPTA Single Fibers

High-performance fibers made of poly-(p-phenylene terephthalamide) (PPTA) with high stiffness and high strength are widely used in body armor for protection due to their high degree of molecular chain alignment along the fiber direction. However, their poor mechanical properties in the transverse direction and low surface friction are undesirable for applications requiring resistance to ballistic impact. Here we provide a simple yet effective surface engineering strategy to improve both the transverse mechanical properties and the tribological property by coating PPTA fibers with ultra-high molecular weight polyethylene (UHMWPE) embedded with silica nanoparticles. The coated-PPTA fiber shows remarkable enhancement in transverse mechanical properties including ~127% increase of Young’s modulus, which is attributed to both the alignment of UHMWPE chains in the transverse direction and the embeded ceramic nanoparticles. Meanwhile, the surface friction of the coated fiber increases twofold as a result of the ceramic nanoparticles. In addition, the coated fibers exhibit an enhanced chemical resistance to external harsh environment. The improved transverse mechanical properties, surface frictional characteristics, and chemical resistance demonstrate that coating with UHMWPE and ceramic nanoparticles can be used as an effective approach to enhance the performance of PPTA and other high-performance polymer fibers for body armor applications.

Recycling Waste Polyester via Modification with a Renewable Fatty Acid for Enhanced Processability.

Polyethylene terephthalate (PET) waste often contains a large amount of thermally unstable contaminants and additives that negatively impacts processing. A reduced processing temperature is desired. In this work, we report using a renewably sourced tall oil fatty acid (TOFA) as a modifier for recycled PET. To that end, PET was compounded with TOFA at different concentrations and extruded at 240 °C. Phase transition behaviors characterized by thermal and dynamic mechanical analyses exhibit shifts in the melting and recrystallization temperatures of PET to lower temperatures and depression of glass transition temperature from 91 to 65 °C. Addition of TOFA also creates crystal-phase imperfection that slows recrystallization, an important processing parameter. Changes in the morphology of plasticized PET reduces and stabilizes the melt viscosity at 240 and 250 °C. Melt-spun, undrawn continuous filaments of diameter 36–46 μm made from these low-melting PET exhibit 29–38 MPa tensile strength, 2.7–2.8 GPa tensile modulus, and 20–36% elongation. These results suggest a potential path for reusing waste PET as high-performance polymeric fibers.

Liquid Crystallinity of p-Aramid/Multi-walled Carbon Nanotube Composites

A systematic study regarding the liquid crystallinity of p-Aramid and MWCNTs composite at various p-Aramid and MWCNTs concentrations in sulphuric acid was investigated and optimized by solution viscosity measurement and opalescence observation. We observed a merged liquid crystalline phase consisting of both p-Aramid and MWCNTs, and we believe this is the first study to report this combined liquid crystalline phase in one suspension. In addition to providing fundamental insights, we envision this study could be useful to those developing a strong, light, and high-performance polymeric composite fibers.

Improved quasi-static twin-fiber transverse compression of several high-performance fibers

The method of determining the quasi-static transverse compressive response of several high-performance polymer fibers was improved upon from a previous twin-fiber transverse compression setup in order to detect small initial high compliance signals while maintaining consistent diametral compression. Two fibers were laid parallel between two polished tool steel platens, and the fibers were subsequently compressed using a piezo-electric actuator at quasi-static rates. The new experimental setup ensures that the compression cycle begins when extremely small load signals are detected so that initial elastic transverse moduli may be more accurately measured. Nominal stress–strain curves were obtained for several types of high-performance fibers. The results show good agreement with previously obtained measurements. S-glass fibers exhibited a vastly different mechanical response compared to the polymer fibers.

Poly(P‐Phenylene Terephthalamide) Fibers Reinforced with Ultrathin Ceramic Coatings

The poly(p‐phenylene terephthalamide) (PPTA) fibers are engineering polymer materials with high strength and stiffness, lightweight, and outstanding fatigue characteristics. However, these materials exhibit drawbacks, namely, anisotropic mechanical strength along the tensile and compressive directions. In particular, they show low compressive strength, and mismatched thermal expansion as well as moisture uptake and oxidative stability along the axial and radial directions. Here, the authors describe a hybrid material approach by integrating ultrathin ceramic coatings (alumina or silica) onto PPTA fibers to enhance their compressive modulus by 2.5 times. In addition, these ceramic coating improve the energy absorption, thermal conductivity, and chemical stability of PPTA fibers, while their flexibility and lightweight are preserved. This strategy provides a new route for the preparation of high performance polymer fibers for advanced engineering applications.

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.