Aramid nanofiber-functionalized graphene nanosheets for polymer reinforcement

Wide-temperature-range pressure sensing by an aramid nanofibers/reduced graphene oxide flakes composite aerogel

Aerogel-based conductive materials have emerged as a major candidate for piezoresistive pressure sensors due to their excellent mechanical and electrical performance besides light-weighted and low-cost characteristics, showing great potential for applications in electronic skins, biomedicine, robot controlling and intelligent recognition. However, it remains a grand challenge for these piezoresistive sensors to achieve a high sensitivity across a wide working temperature range. Herein, we report a highly flexible and ultra-light composite aerogel consisting of aramid nanofibers (ANFs) and reduced graphene oxide flakes (rGOFs) for application as a high-performance pressure sensing material in a wide temperature range. By controlling the orientations of pores in the composite framework, the aerogel promotes pressure transfer by aligning its conductive channels. As a result, the ANFs/rGOFs aerogel-based piezoresistive sensor exhibits a high sensitivity of up to 7.10 kPa-1, an excellent stability over 12,000 cycles, and an ultra-wide working temperature range from -196 to 200 °C. It is anticipated that the ANFs/rGOFs composite aerogel can be used as reliable sensing materials in extreme environments.

Next-generation all-organic composites: A sustainable successor to organic-inorganic hybrid materials

This Review presents an overview of all-organic nanocomposites, a sustainable alternative to organic-inorganic hybrids. All-organic nanocomposites contain nanocellulose, nanochitin, and aramid nanofibers as highly rigid reinforcing fillers. They offer superior mechanical properties and lightweight characteristics suitable for diverse applications. The Review discusses various methods for preparing the organic nanofillers, including top-down and bottom-up approaches. It highlights in situ polymerization as the preferred method for incorporating these nanomaterials into polymer matrices to achieve homogeneous filler dispersion, a crucial factor for realizing desired performance. Furthermore, the Review explores several applications of all-organic nanocomposites in diverse fields including food packaging, performance-advantaged plastics, and electronic materials. Future research directions-developing sustainable production methods, expanding biomedical applications, and enhancing resistance against heat, chemicals, and radiation of all-organic nanocomposites to permit their use in extreme environments-are explored. This Review offers insights into the potential of all-organic nanocomposites to drive sustainable growth while meeting the demand for high-performance materials across various industries.

Portable and Flexible Hydrogel Sensor for On-Site Atrazine Assay on Agricultural Products

There is growing attention focused toward the problems of ecological sustainability and food safety raised from the abuse of herbicides, which underscores the need for the development of a portable and reliable sensor for simple, rapid, and user-friendly on-site analysis of herbicide residues. Herein, a novel multifunctional hydrogel composite is explored to serve as a portable and flexible sensor for the facile and efficient analysis of atrazine (ATZ) residues. The hydrogel electrode is fabricated by doping graphite-phase carbon nitride (g-C3N4) into the aramid nanofiber reinforced poly(vinyl alcohol) hydrogel via a simple solution-casting procedure. Benefiting from the excellent electroactivity and large specific surface area of the solid nanoscale component, the prepared hydrogel sensor is capable of simple, rapid, and sensitive detection of ATZ with a detection limit down to 0.002 ng/mL and per test time less than 1 min. After combination with a smartphone-controlled portable electrochemical analyzer, the flexible sensor exhibited satisfactory analytical performance for the ATZ assay. We further demonstrated the applications of the sensor in the evaluation of the ATZ residues in real water and soil samples as well as the user-friendly on-site point-of-need detection of ATZ residues on various agricultural products. We envision that this flexible and portable sensor will open a new avenue on the development of next-generation analytical tools for herbicide monitoring in the environment and agricultural products.

Strong, Tough, and Biocompatible Poly(vinyl alcohol)-Poly(vinylpyrrolidone) Multiscale Network Hydrogels Reinforced by Aramid Nanofibers

Poly(vinyl alcohol) (PVA) hydrogels are water-rich, three-dimensional (3D) network materials that are similar to the tissue structure of living organisms. This feature gives hydrogels a wide range of potential applications, including drug delivery systems, articular cartilage regeneration, and tissue engineering. Due to the large amount of water contained in hydrogels, achieving hydrogels with comprehensive properties remains a major challenge, especially for isotropic hydrogels. This study innovatively prepares a multiscale-reinforced PVA hydrogel from molecular-level coupling to nanoscale enhancement by chemically cross-linking poly(vinylpyrrolidone) (PVP) and in situ assembled aromatic polyamide nanofibers (ANFs). The optimized ANFs-PVA-PVP (APP) hydrogels have a tensile strength of ≈9.7 MPa, an elongation at break of ≈585%, a toughness of ≈31.84 MJ/m3, a compressive strength of ≈10.6 MPa, and a high-water content of ≈80%. It is excellent among all reported PVA hydrogels and even comparable to some anisotropic hydrogels. System characterizations show that those performances are attributed to the particular multiscale load-bearing structure and multiple interactions between ANFs and PVA. Moreover, APP hydrogels exhibit excellent biocompatibility and a low friction coefficient (≈0.4). These valuable performances pave the way for broad potential in many advanced applications such as biological tissue replacement, flexible wearable devices, electronic skin, and in vivo sensors.

Physico-chemical and antifungal studies of spun cotton thread reinforced cellulose film

This study examines cellulose films reinforced with spun cotton thread and their antifungal properties. The morphology and structure of the cellulose film are analyzed using various techniques, including X-ray Diffraction (XRD), Fourier Transform Infrared (FT-IR) Spectroscopy, Field Emission Scanning Electron Microscope (FE-SEM), Atomic Force Microscope (AFM), UV-Visible Spectroscopy (UV-Vis), Thermogravimetric Analysis (TGA), and Differential Scanning Calorimetry (DSC). The XRD pattern confirms the crystalline nature of the spun cotton-reinforced cellulose film. UV absorption analysis shows activity in the UV region of the optical spectrum. The reinforced cellulose film shows a band gap of 4.7 eV by employing the Wood and Tauc equation. FTIR spectroscopy confirms the film's structural formation. Morphological analysis reveals a random distribution of numerous pore structures on the material's surface. Thermalgravimetric Analysis indicates the material's stability at elevated temperatures, suggesting versatile applications. The film also exhibits antifungal activity against Candida albicans. This research highlights the potential of reinforced cellulose film in various applications, such as food and non-food packaging, offering enhanced UV protection and strength for heavy goods transport. The study emphasizes the multifunctional properties of the material, showcasing its promising role as a polymer in various practical applications.

Cellulose nanocrystal functionalized aramid nanofiber reinforced epoxy nanocomposites with high strength and toughness

The mechanical properties of polymer nanocomposites can be improved by incorporating various types of nanofillers. The hybridization of nanofillers through covalent linkages between nanofillers with different dimensions and morphology can further increase the properties of nanocomposites. In this work, aramid nanofibers (ANFs) are modified using chlorinated cellulose nanocrystals (CNCs) and functionalized with 3-glycidoxypropyltrimethoxysilane to improve the chemical and mechanical interaction in an epoxy matrix. The integration of CNC functionalized ANFs (fACs) in the epoxy matrix simultaneously improves Young's modulus, tensile strength, fracture properties, and viscoelastic properties. The test results show that 1.5 wt% fAC reinforced epoxy nanocomposites improve Young's modulus and tensile strength by 15.1% and 10.1%, respectively, and also exhibit 2.5 times higher fracture toughness compared to the reference epoxy resin. Moreover, the glass transition temperature and storage modulus are found to increase when fACs are incorporated. Thus, this study demonstrates that the enhanced chemical and mechanical interaction by the CNC functionalization on the ANFs can further improve the static and dynamic mechanical properties of polymer nanocomposites.

Aramid Nanofiber/XNBR Nanocomposite with High Mechanical, Thermal, and Electrical Performance

Aramid nanofibers (ANFs) were successfully produced by deprotonation of Kevlar fiber followed by grafting epichlorohydrin in dimethyl sulfoxide solution. The ANFs were then incorporated into carboxylated acrylonitrile butadiene rubber (XNBR) by means of latex blending, followed by vulcanization. The interaction between ANFs and XNBR, and the effects of ANFs on the mechanical strength, dielectric properties, and thermal stability of ANF/XNBR nanocomposites were investigated. The results revealed that hydrogen bonding and covalent bonding interactions existed between ANFs and the XNBR matrix and played a critical role in the reinforcement of ANFs to XNBR nanocomposites. After adding 5 phr (parts per hundred rubber) of ANFs, the XNBR nanocomposite exhibited a significant improvement in mechanical properties, namely a 182% increase in tensile strength and a 101% increase in tear strength. In addition, the dielectric constant and thermal properties of ANF/XNBR also increased dramatically. ANFs may thus make an ideal candidate for high-performance rubber materials.

Aramid Nanofibers/Reduced Graphene Oxide Composite Electrodes with High Mechanical Properties

In this work, aramid nanofibers (ANFs)/reduced graphene oxide (ANFs/RGO) film electrodes were prepared by vacuum-assisted filtration, followed by hydroiodic acid reduction. Compared with thermal reduced ANFs/RGO, these as-prepared film electrodes exhibit a combination of mechanical and electrochemical properties with a tensile strength of 184.5 MPa and a volumetric specific capacitance of 134.4 F/cm³ at a current density of 0.125 mA/cm², respectively. In addition, the film electrodes also show a superior cycle life with 94.6% capacitance retention after 5000 cycles. This kind of free-standing film electrode may have huge potential for flexible energy-storage devices.

The Joule Heating Effect of a Foldable and Cuttable Sheet Made of SWCNT/ANF Composite

A foldable and cuttable sheet heater was fabricated using single-walled carbon nanotubes (SWCNTs) and aramid nanofibers (ANFs). SWCNTs are particularly well suited for Joule heating based on their high thermal stability, electrical properties, high current density, and aspect ratio. When the SWCNT/ANF composite reaches a high temperature during Joule heating, ANFs will endure this temperature due to their impressive thermal stability, derived from aramid fibers. With the aim of achieving a synergistic effect between the SWCNTs and ANFs, 0-100 wt% SWCNT/ANF composite sheets were fabricated by tip-type sonication and vacuum filtration. After assessing the thermal stability and electrical properties of the composite sheets, the Joule heating effect was analyzed. TGA showed that our sheet had high thermal stability in an air condition up to around 500 °C. The electrical conductivity of the composite sheet was improved as the amount of SWCNT added rose to 790.0 and 747.5 S/cm in the 75 and 100_SWCNTs/ANF, respectively. The maximum heating temperature, up to 280 °C, reached by Joule heating was measured as a function of SWCNT content and input voltage, and the relationship among SWCNT content, input voltage, heating temperature, and electric power was described. Mechanical properties were also measured in a temperature range similar to the heating temperature of 300 °C reached by Joule heating. Ultimately, we obtained a foldable and cuttable composite sheet with a stretchable structure, capable of being molded into a variety of shapes. This energy-efficient material can potentially be employed in any device in which a heater is required to deliver high temperatures.

Mechanically Robust and Elastic Graphene/Aramid Nanofiber/Polyaniline Nanotube Aerogels for Pressure Sensors

The preparation of graphene-based aerogels with excellent mechanical strength, elasticity, and compressibility is still a challenge. Herein, we demonstrate a robust, elastic, and lightweight graphene/aramid nanofiber/polyaniline nanotube (rGO/ANF/PANIT) aerogel that is prepared by mixing graphene oxide (GO), ANF, and PANIT dispersions, followed by thermal treatment at 90 °C, freeze-drying, and a low-temperature annealing process. The PANIT bonds the graphene sheets tightly, benefitting the formation of composite gels. The ANF tightly interconnects the graphene sheets and further reinforces the composite network framework significantly, hence endowing rGO/ANF/PANIT composite aerogels with robust mechanical property. The prepared aerogels present a low density of ∼12 mg cm^-3, high conductivity, good resilience, and high compressibility. The rGO/ANF/PANIT aerogels as pressure sensors exhibit a high sensitivity of 1.73 kPa^-1, low detection limit (40 Pa), wide detection range, and excellent compressive cycle stability, highlighting the promising applications in pressure-sensitive electrical devices, including medical health detection, wearable electronics, and intelligent packaging fields.

Mechanically Strong Electrically Insulated Nanopapers with High UV Resistance Derived from Aramid Nanofibers and Cellulose Nanofibrils

Aramid nanofibers (ANFs) have great potential for civil and military applications due to their remarkable mechanical modulus, excellent chemical reliability, and superior thermostability. Unfortunately, the weak combination of neighboring ANFs limits the mechanical properties of ANF-based materials owing to their inherent rigidity and chemical inertness. Herein, high-performance nanopapers are fabricated by introducing a tiny amount of cellulose nanofibrils (CNFs) to serve as reinforcing blocks via vacuum filtration. As a result of the formation of nanosized building blocks and hydrogen-bonding interaction of CNFs, the resultant ANF/CNF nanopaper yields a record-high tensile strength (406.43 ± 16.93 MPa) and toughness (86.13 ± 5.22 MJ m^-3), which are 1.8 and 4.3 times higher than those of the pure ANF nanopaper, respectively. When normalized by weight, the specific tensile strength of the nanopaper is as high as 307.90 MPa·g^-1·cm³, which is even significantly superior to that of titanium alloys (257 MPa·g^-1·cm³). The ANF/CNF nanopaper also possesses excellent dielectric strength (53.42 kV mm^-1), superior UV-shielding performance (≥99.999% absorption for ultraviolet radiation), and a favorable thermostability (T_onset = 530 °C). This study proposes a new design strategy for developing ultrathin ANF-based nanopapers combined with high reliability and thermostability for application in high-end electrical insulation fields, such as 5G communication, wearable electronics, and artificial intelligence.

Ultrafast formation of ANFs with kinetic advantage and new insight into the mechanism

Aramid nanofibers (ANFs) have important applications in many fields, including electrical insulation and battery separators. However, a few limitations seriously restrict the application of ANFs currently, such as low preparation efficiency and the unclear preparation mechanism. To overcome these limitations, the present work proposes a new view-point from the perspective of reaction kinetics. The preparation efficiency was proven to essentially rely on the effective c(OH-). With a simple pre-treatment, a kinetic advantage was created and the preparation time of ANFs was reduced from multiple hours to 10 minutes, which was a considerable step towards practical applications. Moreover, the resultant ANF membranes still exhibited excellent properties in terms of mechanical strength (tensile strength > 160 MPa), thermal stability, light transmittance, and electrical insulation (above 90 kV mm-1). This work not only presents an ultrafast method to produce ANFs but also provides new insights into the mechanism that will benefit the subsequent development of ANF-based materials.

Enhanced air filtration performances by coating aramid nanofibres on a melt-blown nonwoven

Nanofibre membranes with a small diameter and a large specific surface area are widely used in the filtration field due to their small pore size and high porosity. To date, aramid nanofibres (ANFs) have received extensive research interest because of their high stiffness and excellent temperature resistance. However, the preparation of ANFs usually takes a long time, which greatly hampers the practical application of these fibres. Herein, we report the preparation of ANFs by a modified deprotonation method at elevated temperature. Owing to the increase of temperature, the preparation cycle of ANFs was shortened to 8 hours. The resulting ANF dispersion was further coated on a polypropylene melt-blown nonwoven to form a composite nonwoven filter. With the submicron porous structure, the filtration efficiency, pressure drop and quality factor of the filter were 95.61%, 38.22 Pa and 0.082 Pa^-1, respectively. Compared to the pristine nonwoven, the filtration, mechanical, and heat insulation properties of the composite filter were also significantly improved. This work may offer a simple and efficient way for enhancing the air filtration performances of current filters.

Transparent cellulose/aramid nanofibers films with improved mechanical and ultraviolet shielding performance from waste cotton textiles by in-situ fabrication

Cellulose films with biodegradability and intrinsically antistatic property have many applications. However, conventional cellulose films show poor toughness and UV-shielding property, and the major sources are high-grade cotton linter or wood pulp. Herein, by using low-cost waste cotton textiles as the raw materials, we successfully fabricated transparent cellulose/aramid nanofibers (ANFs) films, in which in-situ retained ANFs had a diameter of 20-30 nm and a length of several micrometers. Because ANFs and cellulose chains formed strong hydrogen bonding interactions, the tensile strength and elongation of the resultant cellulose/ANFs film with 1.0 wt% ANFs could reach 54.4 MPa and 15.8%, respectively, increased by 63.4% and 154% compared to those of pure cellulose film (33.3 MPa and 6.2%). Meanwhile, the cellulose/ANFs films show excellent UV-shielding properties and irradiation stability. Hence, the novel cellulose/ANFs films with improved mechanical and UV-shielding performance were in-situ prepared leading to enhance the valorization of waste cotton textiles.

Polyvinyl alcohol-mediated splitting of Kevlar fibers and superior mechanical performances of the subsequently assembled nanopapers

In this work, a composite of aramid nanofibers (ANFs) and polyvinyl alcohol (PVA) was prepared by PVA-assisted splitting of macro Kevlar fibers, which assures the uniform wrapping of PVA chains on the surface of ANFs, thus leading to an enhanced interfacial bonding strength between ANFs and PVA. The morphological characterizations manifest the enhanced diameters of the ANFs after PVA wrapping. The subsequently assembled ANFs/PVA paper shows a strength of 283.25 MPa and a toughness of 32.41 MJ m^-3, which are increased by 57% and 152% compared to the pure ANF paper, respectively. The superior mechanical properties are attributed to the strong interfacial bonding strength, enhanced hydrogen bonding interactions, the densification of the materials, and curved fracture paths. Meanwhile, the ANFs/PVA paper also shows robust UV shielding and visible transparency properties, as well as excellent environmental stabilities, especially at high and low temperatures.

Mechanically strong multifunctional three-dimensional crosslinked aramid nanofiber/reduced holey graphene oxide and aramid nanofiber/reduced holey graphene oxide/polyaniline hydrogels and derived films

To endow high mechanical strength and thermal stability aramid nanofibers (ANF) with novel functionality will lead to great applications. Herein, a strategy to generate covalent bonds among components towards obtaining uniform ANF/reduced holey graphene oxide (ANF/rHGO) and ANF/rHGO/polyaniline (ANF/rHGO/PANI) hydrogels with high mechanical properties is proposed through solvent exchange gelation and subsequent hydrothermal treatment. The as-prepared ANF/rHGO and ANF/rHGO/PANI hydrogels demonstrate excellent recoverability at high compressive strength of 20.2 and 13.8 kPa with a strain of 34.4% and 30.6%, respectively, compared to a recoverability of 92.5% at a strain of ∼20% for ANF hydrogels. Moreover, ANF/rHGO and ANF/rHGO/PANI aerogels possess fast and high oil absorption capacity of 38.9-64.1 g g^-1 and 24.5-44.0 g g^-1, respectively. ANF/rHGO and ANF/rHGO/PANI films obtained after vacuum-drying exhibit a high tensile strength of 121.4 and 95.5 MPa, respectively. Additionally, ANF/rHGO/PANI thin films present good selective absorption of visible light by controlling the doping level of PANI. ANF/rHGO/PANI aerogel films prepared by freeze-drying are assembled into flexible solid-state symmetric supercapacitors and deliver a favorable specific capacitance of 200 F g^-1, a desirable capacitance retention of 98.9% after 2500 mechanical bending cycles and an approximately 100% capacitance retention even after keeping tensile force for 15 h. The as-prepared hydrogels, aerogels and derived films with such excellent performances are promising for applications in oil pollution removal, optical filters and flexible load-bearing energy storage devices.

The adsorption of aromatic macromolecules on graphene with entropy-tailored behavior and its utilization in exfoliating graphite

Aromatic macromolecules tend to form a compact conformation after physically adsorbed on graphene and it brings about great entropy loss for physisorption, due to the strong interaction between aromatic macromolecules and graphene. However, previous researches have validated the availability of aromatic macromolecules to stabilize graphene based on physisorption. In order to clarify the underlying mechanism of this physisorption process on graphene, a series of aromatic polyamide copolymers are used as models in this research. Apart from their adsorbed conformations on graphene, the conformations of these copolymers as the free states in diluted solutions are taken into consideration. Although these copolymers present the fully extended conformation on graphene, their conformations in diluted solutions vary largely with the copolymer composition. It is verified that the copolymer with smaller conformational change could have the better stabilization effectiveness for graphene, rather than the one having stronger interaction with graphene. Therefore, the entropy-tailored behavior for the adsorption of aromatic macromolecules on graphene is put forward. Based on this mechanism, the chemical structure of aromatic polyamide is optimized and furthermore it is utilized to directly exfoliate natural graphite flakes. Eventually, high-quality graphene nanosheets with a large dimension and low defects are obtained. Moreover, its exfoliating effectiveness is superior to those of the commonly used exfoliating agents nowadays.

Aramid nanofibers reinforced polyvinyl alcohol/tannic acid hydrogel with improved mechanical and antibacterial properties for potential application as wound dressing

The poor mechanical properties and the lack of antibacterial ability of hydrogels limit their applications as wound dressing. In this work, a novel and high strength polyvinyl alcohol (PVA)/tannic acid (TA) hydrogel with aramid nanofibers (ANFs) as the reinforcement was successfully fabricated. The surface composition and microstructure of the hydrogel were characterized by fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The mechanical properties, water content and swelling behaviors, as well as the antibacterial abilities and biocompatibility of the prepared hydrogel were systematically analyzed as well. The results indicated that the prepared hydrogel showed excellent mechanical properties. The tensile strength and elongation of the prepared hydrogel can respectively reach 2.06 MPa and 950% owing to the formation of the multiple H bonds among PVA, ANFs and TA. What's more, PVA/ANFs/TA (PAT) hydrogel possessed shape memory and broad-spectrum antibacterial properties against S. aureus, E. coli and P. aeruginosa (100% antibacterial rate) at the concentration of 12 mg/mL. PAT hydrogels also had low cytotoxicity, affirming its potential application as wound dressing.

Thermal Mechanical Properties of Graphene Nano-Composites with Kevlar-Nomex Copolymer: A Comparison of the Physical and Chemical Interactions

This paper reports the preparation of Kevlar-Nomex copolymer nano-composites with exfoliated pristine and functionalized graphene sheets (Grs). The graphene oxide (GrO) platelets were amidized by the reaction of amine-terminated aramid (Ar) with the functional groups present on the GrO surface to prepare the nano-composites films with different loadings of GrO. Chemical changes involved during the oxidation and subsequent amidation were monitored by Raman, FTIR and XP spectroscopic analyses. Morphology of the composite films was studied by atomic force and scanning electron microscopies. Viscoelastic properties of the hybrid films were studied for their glass transition temperature (Tg) and storage modulus by dynamical mechanical thermal analysis (DMTA). A higher shift in glass transition temperature was obtained by chemically binding the aramid copolymer chains on the functionalized Gr sheets. The increase in tensile strength and modulus at various loadings of GrO are compared with the composites using pristine Gr. The effect of interfacial interactions between the matrix chains and the reinforcement on the properties of these hybrids have been explained.

Graphene-Incorporated Natural Fiber Polymer Composites: A First Overview

A novel class of graphene-based materials incorporated into natural lignocellulosic fiber (NLF) polymer composites is surging since 2011. The present overview is the first attempt to compile achievements regarding this novel class of composites both in terms of technical and scientific researches as well as development of innovative products. A brief description of the graphene nature and its recent isolation from graphite is initially presented together with the processing of its main derivatives. In particular, graphene-based materials, such as nanographene (NG), exfoliated graphene/graphite nanoplatelet (GNP), graphene oxide (GO) and reduced graphene oxide (rGO), as well as other carbon-based nanomaterials, such as carbon nanotube (CNT), are effectively being incorporated into NLF composites. Their disclosed superior mechanical, thermal, electrical, and ballistic properties are discussed in specific publications. Interfacial shear strength of 575 MPa and tensile strength of 379 MPa were attained in 1 wt % GO-jute fiber and 0.75 wt % jute fiber, respectively, epoxy composites. Moreover, a Young’s modulus of 44.4 GPa was reported for 0.75 wt % GO-jute fiber composite. An important point of interest concerning this incorporation is the fact that the amphiphilic character of graphene allows a better way to enhance the interfacial adhesion between hydrophilic NLF and hydrophobic polymer matrix. As indicated in this overview, two basic incorporation strategies have so far been adopted. In the first, NG, GNP, GO, rGO and CNT are used as hybrid filler together with NLF to reinforce polymer composites. The second one starts with GO or rGO as a coating to functionalize molecular bonding with NLF, which is then added into a polymeric matrix. Both strategies are contributing to develop innovative products for energy storage, drug release, biosensor, functional electronic clothes, medical implants, and armor for ballistic protection. As such, this first overview intends to provide a critical assessment of a surging class of composite materials and unveil successful development associated with graphene incorporated NLF polymer composites.

High Modulus, Thermally Stable, and Self-Extinguishing Aramid Nanofiber Separators

Mechanically and thermally robust separators offer an alternative approach for preventing battery failure under extreme conditions such as high loads and temperatures. However, the trade-off between electrochemical performance and mechanical and thermal stability remains an ongoing challenge. Here, we investigate aramid nanofiber (ANF) separators that possess high moduli and self-extinguishing characteristics. The ANF separators are formed from the dissolution of bulk Kevlar fibers and their subsequent vacuum-assisted self-assembly. Thermogravimetric analysis shows a high 5 wt % decomposition temperature of 447 °C, which is over ∼175 °C higher than commercial Celgard separators. The ANF separator also possesses a high Young's modulus of 8.8 GPa, which is ∼1000% higher than commercial separators. Even when dry or when soaked in battery electrolyte, the ANF separators self-extinguish upon exposure to flame, whereas commercial separators melt or drip. We show that these features, although adventitious, present a trade-off with electrochemical performance in which a lithium nickel manganse cobalt (NMC) oxide-based battery possessed a reduced capacity of 123.4 mA h g^-1. Considering the separator holistically, we propose that the ANF separator shows an excellent balance of the combined properties of high modulus, flame-resistance, thermal stability, and electrochemical stability and might be suitable for extreme environment applications with further testing.

Development in Additive Methods in Aramid Fiber Surface Modification to Increase Fiber-Matrix Adhesion: A Review

This review article highlights and summarizes the recent developments in the field of surface modification methods for aramid fibers. Special focus is on methods that create a multifunctional fiber surface by incorporating nanostructures and enabling mechanical interlocking. To give a complete picture of adhesion promotion with aramids, the specific questions related to the challenges in aramid-matrix bonding are also shortly presented. The main discussion of the surface modification approaches is divided into sections according to how material is added to the fiber surface; (1) coating, (2) grafting and (3) growing. To provide a comprehensive view of the most recent developments in the field, other methods with similar outcomes, are also shortly reviewed. To conclude, future trends and insights are discussed.

Comparison of Nanoarchitecture to Porous Media Diffusion Models in Reduced Graphene Oxide/Aramid Nanofiber Electrodes for Supercapacitors

Structural electrodes made of reduced graphene oxide (rGO) and aramid nanofiber (ANF) are promising candidates for future structural supercapacitors. In this study, the influence of nanoarchitecture on the effective ionic diffusivity, porosity, and tortuosity in rGO/ANF structural electrodes is investigated through multiphysics computational modeling. Two specific nanoarchitectures, namely, "house of cards" and "layered" structures, are evaluated. The results obtained from nanoarchitecture computational modeling are compared to the porous media approach and show that the widely used porous electrode theories, such as Bruggeman or Millington-Quirk relations, overestimate the effective diffusion coefficient. Also, the results from nanoarchitecture modeling are validated with experimental measurements obtained from electrochemical impedance spectroscopy and cyclic voltammetry. The effective diffusion coefficients obtained from nanoarchitectural modeling show better agreement with experimental measurements. Evaluation of microscopic properties such as porosity, tortuosity, and effective diffusivity through both experiment and simulation is essential to understand the material behavior and to improve its performance.

Aramid Nanofiber Templated In Situ SNAr Polymerization for Maximizing the Performance of All-Organic Nanocomposites

The performance limits of conventional super engineering plastics with inorganic nanofillers are surpassed by all-organic nanocomposites prepared via in situ S_NAr polymerization of polysulfone (PSU) in the presence of a highly dispersed aramid nanofiber (ANF) solution. The latter is directly used, bypassing the energy-consuming, nanostructure-damaging workup process. Using only a 0.15 wt % nanofiller, the all-organic nanocomposite shows an ultimate tensile strength 1.6× higher and 3.4× tougher than neat PSU and its blending counterpart due to the mutually interactive filler and maximally homogenized matrix. The exceptional toughness of the ANF/PSU nanocomposite originates from the grafted PSU on the surface of ANF; it drives stress-delocalized deformation, as revealed by stress-absorbable viscoelastic behavior and ductile elongation of materials. This material is a promising candidate for use as a filler-interactive, high-performance nanocomposite.

Highly flexible and mechanically strong polyaniline nanostructure @ aramid nanofiber films for free-standing supercapacitor electrodes

A key challenge for the fabrication of flexible electrochemical capacitors is to prepare robust electrode materials with excellent integration of high specific capacitances and superior mechanical properties. Aramid nanofibers (ANFs) are emerging candidates for constructing flexible electrode materials due to their superior mechanical properties. However, the present ANF based electrode materials are generally designed by mixing ANFs with electrochemically active components, which results in an unfavorable trade-off in mechanical and electrochemical properties. In this work, we reported flexible, mechanically strong, and free-standing supercapacitor electrodes based on polyaniline (PANI) nanostructure functionalized ANF films for the first time. The flexible PANI@ANF film electrodes achieved an efficient combination of mechanical and electrochemical performance in a single platform with a specific capacitance of 441.0 F g^-1 at a current density of 1 A g^-1 and a tensile strength of 233.3 MPa, respectively. This kind of free-standing electrode material may have great potential in the development of flexible energy-storage devices. Furthermore, we anticipate that this study may provide insight into the functionalization of aramid nanofiber-based materials for structural energy and power systems with high mechanical performance.

C-N Coupling Reactions on Graphene with Aromatic Macromolecules and the Spatial Conformation of Grafted Macromolecules

The fabrication of advanced graphene-based nanocomposites with high-performance polymers requires covalent modification of graphene with aromatic macromolecules. Herein, C-N coupling reactions between fluorinated graphene (FG) and aromatic polyamides containing the benzimidazole moiety are successfully achieved. The optimized conditions are presented based on the nucleophilic behavior of the C-N coupling reaction on graphene. Different from the C-N coupling reaction between two small aromatic molecules, the conformation of grafted aromatic polyamide after reaction changes from torsional to paralleled alignment on graphene with the molecular length increment. Non-covalent interactions between graphene and aromatic polyamides result in this conformational change owing to the extended π systems of graphene and aromatic polyamides, and the synergistic effect of covalent and non-covalent interactions is put forward. As a consequence, graphene dispersibility is greatly enhanced in the solution of aromatic polyamide.

Aramid Nanomaterials of Various Morphologies: Preparation and Mechanical Property Enhancement

Aramid nanofibers (ANFs) are a novel type of promising nanoscale building blocks for high-performance nanocomposites. Conventionally, ANFs are used to composite with polymers containing polar groups such as –OH and –NH₂ since those polymers can interact with the amide groups in ANFs through polar-polar interaction such as hydrogen bonding. In this study, ANFs were derivatized with non-polar alkyl groups including ethyl, octyl and dodecyl groups and used as a performance-enhancing additive to polyvinyl chloride (PVC) with weak polarity. Interestingly, it was observed that the morphologies of the resulting alkyl-derivatized aramid nanomaterials (R-ANMs) varied significantly including nanofibers, nanobranches, nanosheets, and nanospheres, all of which depended on the degree of substitution (DS) and the chain length of the alkyl group. As an additive, R-ANMs improved the Young's modulus, toughness and yield strength of the PVC films. This study proves the concept that ANFs can be used to composite weakly polar or non-polar polymers.

Stronger aramids through molecular design and nanoprocessing

We describe how to build ultrastrong polymeric nanofilms through a combination of molecular design and nanostructuration.

Aramid nanofiber-reinforced three-dimensional graphene hydrogels for supercapacitor electrodes

HYPOTHESIS

Self-assembled graphene hydrogels are notable in the field of electrochemical energy storage for their unique combination of excellent specific surface area, high porosity, and electrically conductive continuous network. However, graphene hydrogels suffer from poor mechanical integrity compared to layered architectures like graphene buckypapers, limiting their applications in practical devices. We propose the use of high strength, Kevlar®-derived polymeric nanofillers, aramid nanofibers (ANFs) as structural fillers to enhance graphene hydrogel's shear modulus in the context of multifunctional (mechanical and electrochemical) architectures.

EXPERIMENTS

Graphene hydrogels are fabricated using sol-gel self-assembly of graphene oxide (GO) nanosheets in presence of ammonium hydroxide. Colloidal dispersion of ANFs and GO are integrated using a novel combination of solvent exchange and dialysis approach to fabricate GO-ANF hydrogels with 0-15 wt.% of ANFs loading (dry weight basis). Shear modulus and electrochemical properties of resulting hydrogel composites are evaluated using rheology and symmetric supercapacitor cell.

FINDINGS

The addition of 2 wt.% ANFs resulted in an 80% improvement in shear modulus compared to neat graphene hydrogel. Addition of ANFs resulted in gradual reduction of specific capacitance, with the specific capacitance of 190 F/g for neat graphene hydrogel, reducing to 128 F/g for an ANF loading of 15 wt.% (dry weight basis). This work shows the broader concept that adding high-strength nanofibers to a nanomaterial gel can add reinforcement provided that the gelation process itself is not disrupted.

Effect of Graphene Oxide Coating on Natural Fiber Composite for Multilayered Ballistic Armor

Composites with sustainable natural fibers are currently experiencing remarkably diversified applications, including in engineering industries, owing to their lower cost and density as well as ease in processing. Among the natural fibers, the fiber extracted from the leaves of the Amazonian curaua plant (Ananas erectifolius) is a promising strong candidate to replace synthetic fibers, such as aramid (Kevlar™), in multilayered armor system (MAS) intended for ballistic protection against level III high velocity ammunition. Another remarkable material, the graphene oxide is attracting considerable attention for its properties, especially as coating to improve the interfacial adhesion in polymer composites. Thus, the present work investigates the performance of graphene oxide coated curaua fiber (GOCF) reinforced epoxy composite, as a front ceramic MAS second layer in ballistic test against level III 7.62 mm ammunition. Not only GOCF composite with 30 vol% fibers attended the standard ballistic requirement with 27.4 ± 0.3 mm of indentation comparable performance to Kevlar™ 24 ± 7 mm with same thickness, but also remained intact, which was not the case of non-coated curaua fiber similar composite. Mechanisms of ceramic fragments capture, curaua fibrils separation, curaua fiber pullout, composite delamination, curaua fiber braking, and epoxy matrix rupture were for the first time discussed as a favorable combination in a MAS second layer to effectively dissipate the projectile impact energy.

Timesaving, High-Efficiency Approaches To Fabricate Aramid Nanofibers

Aramid nanofibers (ANFs) have become promising nanoscale building blocks due to their extraordinary performance. However, there are numerous challenges related to the preparation of ANFs, such as the lengthy preparation cycle (7-10 days), low preparation concentration (0.2 wt %), and high difficulty in quantitatively judging the end point of the deprotonation reaction. Herein, we report three time-saving and high-efficiency strategies (fibrillation, ultrasonication, and proton donor-assisted deprotonation) to prepare ANFs with excellent performance. The fiber micromorphology during the deprotonation and protonation recovery processes was first investigated. Then the end point of the deprotonation reaction was detected by Raman spectra and the cationic demand of the ANF/DMSO system. Finally, the size, preparation cycle, and performance of the corresponding ANFs and ANF films fabricated by different approaches were investigated in detail. The results showed that proton donor-assisted deprotonation significantly shortened the traditional preparation cycle from 7 days to 4 h, and is the most efficient method reported thus far. It is noteworthy that a high concentration of ANFs (4.0 wt %) could also be achieved within 12 h. Interestingly, the fabricated ANFs exhibit rigid morphology and a small diameter with a narrow size distribution (10.7 ± 1.0 nm). The resultant ANF film displays desired characteristics of high strength and toughness. The work offers a timesaving, feasible and effective strategy to realize the large-scale production for ANFs, which will facilitate the application of ANFs in the production of advanced nanomaterials.

Nanoporous aramid nanofibre separators for nonaqueous redox flow batteries

Redox flow batteries are attractive for large-scale energy storage due to a combination of high theoretical efficiencies and decoupled power and energy storage capacities. Efforts to significantly increase energy densities by using nonaqueous electrolytes have been impeded by separators with low selectivities. Here, we report nanoporous separators based on aramid nanofibres, which are assembled using a scalable, low cost, spin-assisted layer-by-layer technique. The multilayer structure yields 5 ± 0.5 nm pores, enabling nanofiltration with high selectivity. Further, surface modifications using polyelectrolytes result in enhanced performance. In vanadium acetylacetonate/acetonitrile-based electrolytes, the coated separator exhibits permeabilities an order of magnitude lower and ionic conductivities five times higher than those of a commercial separator. In addition, the coated separators exhibit exceptional stability, showing minimal degradation after more than 100 h of cycling. The low permeability translates into high coulombic efficiency in flow cell charge/discharge experiments performed at cycle times relevant for large-scale applications (5 h).

Nonaqueous redox flow batteries may offer high energy and power densities, but development of separators is key for optimization. Here the authors achieve high coulombic efficiency with a nanoporous aramid nanofibres-based separator with low permeability, high ion conductivity, and exceptional stability.

Exfoliation and dispersion of boron nitride nanosheets to enhance ordinary Portland cement paste

Exfoliation and dispersion of boron nitride nanosheets (BNNSs) is the key to achieving desired reinforcing effects for ordinary Portland cement (OPC). Few studies exist, however, of the dispersion of BNNSs in a cement-induced alkaline environment and their effect on the mechanical properties of normal OPC paste. In this study, protocols were developed to prepare BNNS-reinforced OPC paste. Ultrasonication was used to exfoliate BNNSs from h-BN in water based suspensions. The addition of surfactants in the suspension was found to hinder the exfoliation of the BNNSs. The surfactants were, however, found to be essential for the dispersion of the BNNSs in pore solution. Among the three surfactants used in this study, polycarboxylate based superplasticizer was most suitable as it maintained over 40% of the BNNSs stable in the pore solution for 4 hours and increased the hydration flow peak over 20%. Atomic force microscopy results indicated that the thickness of the BNNSs was mostly under 10 nm. With the addition of 0.003 wt% BNNSs, the compressive and tensile strengths of the cement were increased by 13% and 8%, respectively. Besides the nucleation effect as indicated by hydration heat, pore structure refinement and chemical bonding were also found as the main reinforcing mechanisms of BNNSs in OPC matrix.

Graphene-assisted fabrication of poly(ε-caprolactone)-based nanocomposites with high mechanical properties and self-healing functionality

A fast NIR light-induced self-healing PCL nanocomposite with superior mechanical properties was achieved by tailoring the cyclic mechanical annealing process.

Benzimidazole-containing aramid nanofiber for naked-eye detection of heavy metal ions

The rapid detection of heavy metal ions in wastewater has received significant attention in modern society.