Advanced Aramid Fibrous Materials:Fundamentals,Advances,and Beyond

Aramid fibers(AFs)are widely applied in many cutting-edge fields,due to their excellent comprehensive performance.Ongoing research efforts are therefore underway to expand the applicability by designing more environmentally friendly and low-cost synthesis methods,incorporating new chemical components in the skeletons or internal structures of polyamide to enhance their processability and functionality.Despite being at the forefront of scientific research,there are fewer reviews that comprehensively summarize the latest progress of AFs.This review focuses on the fundamental research of AFs since their inception and summarizes the advanced progress and applications of AFs.Firstly,the synthesis mechanism and methods of AFs and their structure-property relationship are comprehensively discussed.Subsequently,we review the recent progress in surface functionalization of AFs by using advanced micro-nanoscale modification strategies to enhance the interface properties and ultraviolet(UV)-resistance properties,and summarize the advantages and disadvantages of various modified methods.Then,applications of AF and aramid nanofiber(ANF)in various fields are discussed.Finally,the possible challenges and outlooks toward the future development of AFs are highlighted,which is expected to provide new insights for the next-generation advanced functional AF materials and facilitate the industrialization development level for high-performance AFs and their composites.

Ultra-broadband microwave absorber and high-performance pressure sensor based on aramid nanofiber,polypyrrole and nickel porous aerogel

Electronic devices have become ubiquitous in our daily lives,leading to a surge in the use of microwave absorbers and wearable sensor devices across various sectors.A prime example of this trend is the aramid nanofibers/polypyrrole/nickel(APN)aerogels,which serve dual roles as both microwave absorbers and pressure sensors.In this work,we focused on the preparation of aramid nanofibers/polypyrrole(AP15)aerogels,where the mass ratio of aramid nanofibers to pyrrole was 1:5.We employed the oxidative polymerization method for the preparation process.Following this,nickel was thermally evaporated onto the surface of the AP15 aerogels,resulting in the creation of an ultralight(9.35 mg·cm^(-3)).This aerogel exhibited a porous structure.The introduction of nickel into the aerogel aimed to enhance magnetic loss and adjust impedance matching,thereby improving electromagnetic wave absorption performance.The minimum reflection loss value achieved was-48.7 dB,and the maximum effective absorption bandwidth spanned 8.42 GHz with a thickness of 2.9 mm.These impressive metrics can be attributed to the three-dimensional network porous structure of the aerogel and perfect impedance matching.Moreover,the use of aramid nanofibers and a three-dimensional hole structure endowed the APN aerogels with good insulation,flame-retardant properties,and compression resilience.Even under a compression strain of 50%,the aerogel maintained its resilience over 500 cycles.The incorporation of polypyrrole and nickel particles further enhanced the conductivity of the aerogel.Consequently,the final APN aerogel sensor demonstrated high sensitivity(10.78 kPa-1)and thermal stability.In conclusion,the APN aerogels hold significant promise as ultra-broadband microwave absorbers and pressure sensors.

Functional–Structural Integrated Aramid Nanofiber‑based Honeycomb Materials with Ultrahigh Strength and Multi‑Functionalities

Multifunctional microwave-absorbing(MA)honeycombs are in urgent demand both in civil and military fields,while they often suffer from great limitations due to the complicated preparation process,inferior strength,and the susceptible peeling off of the absorbent coatings.Herein,we develop a straightforward strategy of assembly of aramid nanofibers(ANFs)and MXene nanosheets to honeycombs,obtaining a functional–structural integrated microwave absorption aramid honeycomb(MAAH).Benefiting from the robust and integrated cell nodes and dense network structure,the compressive strength and toughness of ANF honeycomb can reach up to 18.6 MPa and 2.0 MJ m^(−3),respectively,which is 6 times and 25 times higher than that of commercial honeycomb.More importantly,the synergistic effect of the unique three-dimensional(3D)conductive network formed by uniformly distributed MXene and the hierarchical structure of the honeycomb endow it with superior wave-absorbing performance,which exhibits a minimum reflection loss(RL_(min))of−38.5 dB at a thickness of only 1.9 mm,and covering almost the entire X-band bandwidth.Additionally,MAAH presents exceptional infrared thermal stealth,sound absorption performance,and real-time monitoring of structural integrity.Therefore,these impressive multi-functionalities of MAAH with outstanding wave-absorbing performance,ultrahigh strength,along with the straightforward and easy-toscalable and recyclable manufacturing technique,demonstrating promising perspectives of the MAAH materials in aerospace and military fields.

Super-Tough and Environmentally Stable Aramid Nanofiber@MXene Coaxial Fibers with Outstanding Electromagnetic Interference Shielding Efficiency

Although electrically conductive and hydrophilic MXene sheets are promising for multifunctional fibers and electronic textiles,it is still a challenge to simultaneously enhance both conductivity and mechanical properties of MXene fibers because of the high rigidity of MXene sheets and insufficient inter-sheet interactions.Herein,we demonstrate a core-shell wet-spinning methodology for fabricating highly conductive,super-tough,ultra-strong,and environmentally stable Ti_(3)C_(2)T_(x) MXene-based core-shell fibers with conductive MXene cores and tough aramid nanofiber(ANF)shells.The highly orientated and low-defect structure endows the ANF@MXene core-shell fiber with supertoughness of~48.1 MJ m^(-3),high strength of~502.9 MPa,and high conductivity of~3.0×10^(5)S m^(-1).The super-tough and conductive ANF@MXene fibers can be woven into textiles,exhibiting an excellent electromagnetic interference(EMI)shielding efficiency of 83.4 dB at a small thickness of 213μm.Importantly,the protection of the ANF shells provides the fibers with satisfactory cyclic stability under dynamic stretching and bending,and excellent resistance to acid,alkali,seawater,cryogenic and high temperatures,and fire.The oxidation resistance of the fibers is demonstrated by their wellmaintained EMI shielding performances.The multifunctional core-shell fibers would be highly promising in the fields of EMI shielding textiles,wearable electronics and aerospace.

Statistical Tensile Strength for High Strain Rate of Aramid and UHMWPE Fibers

Dynamic tensile impact properties of aramid (Technora) and UHMWPE (DC851) fiber bundles were studied at two high strain rates by means of reflecting type Split Hopkinson Bar, and stress-strain curves of fiber yarns at different strain rates were obtained. Experimental results show that the initial elastic modulus, failure strength and unstable strain of aramid fiber yarns are strain rate insensitive, whereas the initial elastic modulus and unstable strain of UHMWPE fiber yarns are strain rate sensitive. A fiber-bundle statistical constitutive equation was used to describe the tensile behavior of aramid and UHMWPE fiber bundles at high strain rates. The good consistency between the simulated results and experimental data indicates that the modified double Weibull function can represent the tensile strength distribution of aramid and UHMWPE fibers and the method of extracting Weibull parameters from fiber bundles stress-strain data is valid.

Self-Exfoliation of Flake Graphite for Bioinspired Compositing with Aramid Nanofiber toward Integration of Mechanical and Thermoconductive Properties

Flexible yet highly thermoconductive materials are essential for the development of next-generation flexible electronic devices.Herein,we report a bioinspired nanostructured film with the integration of large ductility and high thermal conductivity based on self-exfoliated pristine graphene and three-dimensional aramid nanofiber network.A self-grinding strategy to directly exfoliate flake graphite into few-layer and few-defect pristine graphene is successfully developed through mutual shear friction between graphite particles,generating largely enhanced yield and productivity in comparison to normal liquid-based exfoliation strategies,such as ultrasonication,high-shear mixing and ball milling.Inspired by nacre,a new bioinspired layered structural design model containing three-dimensional nanofiber network is proposed and implemented with an interconnected aramid nanofiber network and high-loading graphene nanosheets by a developed continuous assembly strategy of sol-gel-film transformation.It is revealed that the bioinspired film not only exhibits nacre-like ductile deformation behavior by releasing the hidden length of curved aramid nanofibers,but also possesses good thermal transport ability by directionally conducting heat along pristine graphene nanosheets.

Investigation of the mechanical and ballistic properties of hybrid carbon/aramid woven laminates

High-performance ballistic fibers,such as aramid fiber and ultra-high-molecular-weight polyethylene(UHMWPE),are commonly used in anti-ballistic structures due to their low density,high tensile strength and high specific modulus.However,their low modulus in the thickness direction and insufficient shear strength limits their application in certain ballistic structure.In contrast,carbon fiber reinforced epoxy resin matrix composites(CFRP)have the characteristics of high modulus in the thickness direction and high shear resistance.However,carbon fibers are rarely used and applied for protection purposes.A hybridization with aramid fiber reinforced epoxy resin matrix composites(AFRP)and CFRP has the potential to improve the stiffness and the ballistic property of the typical ballistic fiber composites.The hybrid effects on the flexural property and ballistic performance of the hybrid CFRP/AFRP laminates were investigated.Through conducting mechanical property tests and ballistic tests,two sets of reliable simulation parameters for AFRP and CFRP were established using LS-DYNA software,respectively.The experimental results suggested that by increasing the content of CFRP that the flexural properties of hybrid CFRP/AFRP laminates were enhanced.The ballistic tests'results and the simulation illustrated that the specific energy absorption by the perforation method of CFRP achieved 77.7%of AFRP.When CFRP was on the striking face,the shear resistance of the laminates and the resistance force to the projectiles was promoted at the initial penetration stage.The proportion of fiber tensile failures in the AFRP layers was also enhanced with the addition of CFRP during the penetration process.These improvements resulted in the ballistic performance of hybrid CFRP/AFRP laminates was better than AFRP when the CFRP content was 20 wt%and 30 wt%.

Behavior of Aramid Fiber/Ultrahigh Molecular Weight Polyethylene Fiber Hybrid Composites under Charpy Impact and Ballistic Impact

The aramid fiber礥HMWPE (ultrahigh molecular weight polyethylene) fiber hybrid composites (AF礑F) were ma-nufactured. By Charpy impact, the low velocity impact behavior of AF礑F composite was studied. And the high velocity impact behavior under ballistic impact was also investigated. The influence of hybrid ratio on the performances of low and high velocity impact was analyzed, and hybrid structures with good impact properties under low velocity impact and high velocity were optimized. For Charpy impact, the maximal impact load increased with the accretion of the AF layers for AF礑F hybrid composites. The total impact power was reduced with the decrease of DF layers and the delamination can result in the increase of total impact power. For ballistic impact, the DF ballistic performance was better than that of the AF and the hybrid ratio had a crucial influence. The failure morphology of AF礑F hybrid composite under Charpy impact and ballistic impact was analyzed. The AF礑F hybrid composites in suitable hybrid ratio could attain better performance than AF or DF composites.

Analysis and Control of Surface Delamination Defects During Milling of Orthogonal Aramid Fiber‑Reinforced Composites Laminates

The aramid fiber-reinforced composites(AFRC)can increase the durability of corresponding applications such as aerospace,automobile and other large structural parts,due to the improvement in hardness,heat build-up,wear properties and green environmental protection.However,because of its complex multiphase structure and unique heterogeneity and anisotropy,the poor compression fatigue resistance and the incident surface fibrillation are inevitable.To improve the assembly precision of AFRC,mechanical processing is necessary to meet the dimensional accuracy.This paper focuses on the influence of contour milling parameters on delamination defects during milling of AFRC laminates.A series of milling experiments are conducted and two different kinds of delamination defects including tearing delamination and uncut-off delamination are investigated.A computing method and model based on brittle fracture for the two different types of delamination are established.The results can be used for explaining the mechanism and regularity of delamination defects.The control strategy of delamination defects and evaluation method of finished surface integrity are further discussed.The results are meaningful to optimize cutting parameters,and provide a clear understanding of surface defects control.

Atmospheric air dielectric barrier discharge excited by nanosecond pulse and AC used for improving the hydrophilicity of aramid fibers

In this paper, a long line-shape dielectric barrier discharge excited by a nanosecond pulse and AC is generated in atmospheric air for the purpose of discussing the uniformity, stability and ability of aramid fiber treatment. The discharge images, waveforms of current and voltage,optical emission spectra, and gas temperatures of both discharges are compared. It is found that nanosecond pulsed discharge has a more uniform discharge morphology, higher energy efficiency and lower gas temperature, which indicates that nanosecond pulsed discharge is more suitable for surface modification. To reduce the water contact angle from 96° to about 60°, the energy cost is only about 1/7 compared with AC discharge. Scanning electron microscopy,Fourier transform infrared spectroscopy and x-ray photoelectron spectroscopy are employed to understand the mechanisms of hydrophilicity improvement.

Plasma-induced graft polymerization on the surface of aramid fabrics with improved omniphobicity and washing durability

Durable superomniphobic surfaces are desirable for their practical applications,including selfcleaning,non-fouling,protective clothing and the separation of liquids.The plasma-induced polymerization of environmentally friendly C6 from a perfluoralkyl methlacrylate copolymer emulsion,AG-E081,was performed and a durable omniphobic fabric was achieved.C6 is an ecological alternative to C8(eight CF2 groups)fluorinated compounds,and it was thereafter successfully incorporated into aramid fabric to achieve a durable superomniphobic surface.The fabric became water and oil repellent with an extremely high water contact angle of 180°.As tested by the water spray AATCC test and hydrocarbon resistance test,the as-prepared fabric gained 100°(ISO 5)and grade number 4 respectively.Furthermore,the fabrics also showed significantly improved washing durability after ten washing cycles.By scanning electron microscopy(SEM),Fourier-transform infrared spectroscopy(FTIR)and x-ray photoelectron spectroscopy(XPS)tests,it is indicated that the durable superomniphobicity can be attributed to the roughness and activation of the aramid surface by the plasma pre-treatment,which induces more adsorption and chemical graft of the C6 copolymer.

Statistical Constitutive Equation of Aramid Fiber Bundles

Tensile impact tests of aramid (Twaron) fiber bundles were carried out under high strain rates with a wide range of 0. 01/s -1 000/s by using MTS and bar-bar tensile impact apparatus. Based on the statistical constitutive model of fiber bundles, statistical constitutive equations of aramid fiber bundles are derived from statistical analysis of test data at different strain rates. Comparison between the theoretical predictions and experimental data indicates statistical constitutive equations fit well with the experimental data, and statistical constitutive equations of fiber bundles at different strain rates are valid.

Effect of the Weaving Density of Aramid Fabrics on Their Resistance to Ballistic Impacts

Two Heracron? woven fabrics, HT600-1 and HT600-2, were fabricated with different weaving densities and their resistance to ballistic impact was investigated. While HT600-1 was inherently stronger along the weft than HT600-2, the latter exhibited a higher tensile strength along the warp. Crimp values indicate that HT600-1, which possesses a relatively larger weft weaving density, induces an excess in the warp crimp ratio, thereby weakening the fabric along the warp. The dimensionless fiber property U*, which is defined as the product of the specific fiber toughness and the strain wave velocity, was calculated for each fabric. The U* values of HT600-1 were lower than those of HT600-2;U* values along the warp of HT600-1 were extremely low. These analyses show that HT600-2 exhibited improved ballistic properties over those of HT600-1. These findings further indicate the existence of an optimal weave that would minimize damage to both yarn and fabric. Establishing these optimal conditions can be crucial in implementing better ballistic properties into fabrics.

ANALYSIS AND MEASUREMENT ONRESIDUAL STRESS OF ARAMIDALUMINIUMLAMINATE

Residual stresses of the ordinarily cured and pre-stressed unidirectionallaminate are analyzed quantitatively. In order to examine the analyzing formulations,strain gages were embedded in the uni-directional aramid aluminium laminates (ordi-narily cured and pre-stressed) to determine the residual stresses in the aluminiumlayers. The calculated residual stresses are in good agreement with the experimental val-ues in the longitudinal direction. Therefore, the work in this paper can be used to calcu-late, determine and design the longitudinal residual stresses according to the manufac-ture and application demands.

Effect of Aramid/Carbon Hybrid on the Tensile Properties of Multilayered Biaxial Weft Knitted Fabric Reinforced Composites

The effects of aramid/carbon on tensile properties of multilayered biaxial weft knitted( MBWK) fabric reinforced composites are analyzed by experiments. The tensile tests are inducted by the SHIMADZU AG-250 KNE universal material testing machine and Aramis V6 digital image correlation( DIC) technique.More specifically,the composite samples own four hybrid ratios(Na∶ Nc= 12∶ 0,8 ∶ 4,6 ∶ 6 and 4 ∶ 8). The results showed that the aramid/carbon hybrid MBWK fabric reinforced composites showed nearly linear response until reaching the maximum load and the inserting yarns distribution on the surface of MBWK fabrics reinforced composites had a great influence on the strain pattern distribution. Besides,the tensile strength,the tensile modulus and the elongation at breakage of 0° samples and 90° samples increased with the decreasing of aramid/carbon hybrid ratio. In a word,the changes of tensile strength, tensile modulus and elongation at breakage have a lot to do with the difference of aramid/carbon hybrid ratio.

Prediction of Final Velocity of Aramid Fabric-Resin Composite Laminates Subjected to Ballistic Impact

The strain rate effects of aramid fiber material, quasi-static and ballistic impact perforation of composite laminates made of aramid fabric and phenolic resin/PVB are investigated respectively by means of MTS, split Hopkinson tension bars and ballistic impact apparatus. The tensile impact experiments on aramid fiber material are performed in strain rate range from 0.01/s to 1000/s. Experimental results show that the mechanical properties of aramid fiber material are insensitive to strain rate in the range from 0. 01/s to 1 000/s. An energy model to predict final velocity of composite laminates subjected to ballistic impact is proposed on the basis of experimental data of quasi-static perforation through the targets. The predicted final velocities show good agreement with the experimental final velocity.

A Novel Preparation Method of Organic-inorganic Aramid Nanofibers (ANFs) Hybrid Membrane Using Ethanol as Proton Donor

In the work,the surface of the titanium dioxide(TiO_(2))nano particles were modified with 3-Aminopropyltriethoxysilane(KH550)first.And the ANFs were loaded with the different nano TiO_(2) assisted via the ultrasonic process.Then the organic and inorganic hybrid membrane were fabrication by vacuum assisted flocculation(VAF).Ethanol as a proton donor can realize the flocculation of ANFs.The results of the nanocomposites were characterized by Transmission electron microscope(TEM),X-ray diffraction(XRD),and scanning electron microscopy(SEM).The SEM results indicated that the agglomeration of nanoparticles on ANF were reduced obviously,Through the preparation of aramid nanofiber membrane with the proton donor of ethanol,it is observed that the interlaced network structures of the membrane surface were constructed.The result of the UV data is that the addition of nano-titanium dioxide improves the UV absorption capacity of the fiber membrane.

Effect of fibre orientations on the mechanical properties of kenaf–aramid hybrid composites for spall-liner application

This paper presents the effect of kenaf fibre orientation on the mechanical properties of kenaf–aramid hybrid composites for military vehicle's spall liner application. It was observed that the tensile strength of woven kenaf hybrid composite is almost 20.78% and 43.55% higher than that of UD and mat samples respectively. Charpy impact strength of woven kenaf composites is 19.78% and 52.07% higher than that of UD and mat kenaf hybrid composites respectively. Morphological examinations were carried out using scanning electron microscopy. The results of this study indicate that using kenaf in the form of woven structure could produce a hybrid composite material with high tensile strength and impact resistance properties.

Effects of Environment on Strengths of UHMWPE and Aramid Fiber

This paper is devoted on influences of acid-base,high and low temperature on strength of UHMWPE and aramid fiber, characterized by fracture strength, SEM's effects on fiber strength and surface morphology. It turns out to be that UHMWPE fiber has a superior acid-base, low temperature and light aging resistance property,with strength keeping above 90% in acid-base environment. Comparing with UHMWPE fiber, aramid fiber does well in mechanical properties, temperature resistant performances and alkali resistances at room temperature, with strength losing less than 10% in alkaline environment.