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.

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.

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.

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.

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.

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.

THE MASS TRANSFER BEHAVIORS OF FE(Ⅲ), CO(Ⅱ) AND NI(Ⅱ) IN SULFURIC ACID WITH CYANEX302 BY USINGMICROPOROUS HOLLOW FIBER

In this paper the mass transfer behaviors of Fe(Ⅲ), Co(Ⅱ) and Ni(Ⅱ) with Cyanex302(bis(2,4,4- trimethylpentyl)monothiophosphinic acid) from sulfate medium by using hollow fiber membrane in counter-currently circulating operation were studied. The effect of acidity in aqueous solution and the extractant concentration on the mass transfer coefficient (Kw) was discussed. The reaction mechanism of membrane extraction was considered as a false one series reaCtion and the rate controlling step was membrane resistance. When the value of Kw arrived at 1.0 × 10-6 m/s, △pH:CoFe equaled tO 6.225, and △pH:NiFe was bigger than △p HCoFe.

石墨烯、碳纳米管改性芳纶Ⅱ及芳纶Ⅲ的研究进展

简要介绍了芳纶Ⅱ及芳纶Ⅲ的制备方法及性能提升途径,重点综述了石墨烯、碳纳米管改性芳纶Ⅱ及芳纶Ⅲ的研究进展。石墨烯、碳纳米管的引入能有效提升芳纶Ⅱ及芳纶Ⅲ的力学、电学、热学及抗紫外性能,并对其未来发展做出展望。

芳纶Ⅲ纤维增强复合材料老化测试方法研究

芳纶Ⅲ纤维增强复合材料在航空航天、军事及个体防护装备等领域中应用广泛,在使用和贮存过程中材料会受到温度、水、化学物质及紫外线等因素的影响,这些影响因素会不同程度地导致材料性能的劣变,甚至会导致其丧失原本的功能。采用热老化实验箱、温度冲击实验箱和氙灯老化实验箱对芳纶Ⅲ纤维增强复合材料进行人工加速老化实验,以模拟材料在应用场景中受到环境条件的影响。结果表明,在芳纶Ⅲ纤维增强复合材料人工加速老化实验中,应根据材料的实际应用场景选择合适的老化时间、温度、湿度、辐照度等条件,适当延长老化时间可以提高测试结果的稳定性;而老化后的芳纶Ⅲ纤维增强复合材料进行16 h以上的状态调节时间可以减少测试结果的分散性;通过氙灯老化实验,发现树脂基体力学性能受到温度的影响相对较大,而芳纶Ⅲ纤维对光和水分更敏感。通过分析不同老化测试条件对芳纶Ⅲ纤维复合材料测试结果的影响,为科学合理选择相应的老化测试方法提供依据。

成型过程中的芳纶Ⅲ纤维聚集态结构衍变

通过电子强伸仪、广角X射线衍射仪(WAXD)、声速取向仪及扫描电镜(SEM)等测试仪器,分析探讨了芳纶Ⅲ树脂、原丝、成品丝的力学性能与聚集态结构的差异,并与生产工艺相联系。讨论了芳纶Ⅲ纤维成型过程中聚集态结构衍变过程,探讨了芳纶Ⅲ具有优异力学性能的根本原因。通过X射线衍射分析,发现芳纶Ⅲ树脂本身是非晶态,在原丝纺制阶段结晶也进行得不完善且结晶度低,但经过热处理后成品丝具有较高的结晶度且晶粒变大,但晶面间距保持不变;取向度测试表明,芳纶Ⅲ纤维在原丝阶段就有较高的取向度,经热处理后取向度有所提高;SEM测试表明,芳纶Ⅲ成品丝比原丝的结构均一致密,从而反映了热处理工艺在芳纶Ⅲ纤维生产过程中的重要性。

芳纶Ⅲ纤维拉伸性能的实验研究

测试了芳纶Ⅲ纤维的拉伸性能等，并与F-12和Kevlar-49纤维进行了对比。对由芳纶Ⅲ纤维与环氧树脂基体复合成型的单向纤维增强环形试样，测试了其拉伸强度、弹性模量和层间剪切强度，结果表明：芳纶Ⅲ纤维单向纤维复合材料的拉伸强度和弹性模量与F-12纤维相当，分别比Keylar-49纤维要高出约25．7％和24．7％；但早期的芳纶Ⅲ纤维与环氧树脂基体的界面结合性较差，层间剪切强度仅为32．0～35．2MPa。

芳纶Ⅲ纤维及其混杂碳纤维复合材料的压缩性能研究

对比研究了芳纶Ⅲ纤维复合材料、芳纶Ⅲ纤维/T800碳纤维混杂复合材料、T800碳纤维复合材料单向板压缩性能,以及三种状态下缠绕的150 mm容器轴压性能。结果表明:混杂复合材料压缩强度和模量随混杂比(VCF)的增大而增加,当VCF为28.5%时,混杂复合材料单向板压缩强度比芳纶Ⅲ纤维复合材料提高57%,压缩模量提高20.9%;混杂复合材料150mm容器(VCF=46%)轴压破坏载荷达到138.6 k N,比芳纶Ⅲ纤维复合材料150 mm容器的轴压破坏载荷提高18.5%,但仍为混杂负效应。

氨气等离子体改性处理芳纶Ⅲ表面的研究

以氨气为反应气体,对芳纶Ⅲ进行等离子体表面改性处理,研究了等离子体处理时间和处理功率对纤维表面性能的影响;采用X射线光电子能谱、场发射扫描电镜、接触角和微脱粘实验等测试方法对改性前后纤维表面元素组成、形貌、润湿能力以及界面粘结强度进行表征。结果表明:芳纶Ⅲ经过氨气等离子体改性后,表面含氮极性基团的含量增加,粗糙程度增大,润湿能力得到明显的改善;当氨气等离子体处理时间为15 min,功率为100 W时,芳纶Ⅲ与环氧树脂的界面粘结强度从处理前的12.9 MPa提高到18.2 MPa,与水的接触角由处理前的71.4°下降到46.8°。

基体性能对芳纶Ⅲ纤维复合材料力学性能的影响

设计了三种环氧树脂基体,研究了基体性能对芳纶Ⅲ纤维复合材料力学性能的影响,对比分析了不同韧性的两种复合材料层间剪切破坏过程的声发射特性参数。结果表明:设计的R1、R2、R3三种树脂基体其韧性为R1>R2>R3;芳纶Ⅲ纤维复合材料层间剪切强度分别为49 MPa、44.8 MPa、40.1 MPa,层间剪切性能随树脂基体韧性的增加而增大;声发射实验表明,基体韧性增加,复合材料急剧损伤得到延迟,声发射事件数明显减少。

空气等离子体处理芳纶Ⅲ的性能研究

比较了国产芳纶Ⅲ与芳纶1414以及进口Twaron纤维的表面性能;采用空气等离子体处理技术对芳纶Ⅲ的表面进行改性,研究了空气等离子体处理工艺条件以及处理前后芳纶Ⅲ的结构与性能的变化。结果表明:国产芳纶Ⅲ的表面存在不均匀的浅沟槽,比芳纶1414和Twaron纤维表面粗糙,其表面浸润性较差,但却优于芳纶1414和Twaron纤维;空气等离子体处理芳纶Ⅲ的最佳条件为放电功率65 W,空气放电气压2 000 Pa,处理时间11 min,在此条件下处理的芳纶Ⅲ表面接触角由未处理时的55.8°降至41.5°,纤维的浸润性能得到改善,而其力学性能和大分子结构不受影响。

芳纶Ⅲ与Kevlar-49纤维组成、结构与力学性能的对比

通过红外光谱和元素分析对芳纶Ⅲ和Kevlar-49纤维的进行对比研究得出,芳纶Ⅲ纤维中存在含氮的芳杂环结构,并结合X射线衍射方法分析芳纶Ⅲ和Kevlar-49纤维的晶体结构,其中芳纶Ⅲ纤维的结晶度为30.44%,明显低于Kevlar-49。芳纶Ⅲ力学性能优于Kevlar-49,其拉伸强度、弹性模量和断裂延伸率分别为4250MPa、139MPa和3.2%。

新型国产芳纶Ⅲ纤维的性能实验研究

测试了7批次新型国产芳纶Ⅲ纤维的复丝拉伸性能，且采用第07批次的芳纶Ⅲ纤维进行缠绕制作了NOL环试样和Ф150mm试验容器。实验结果表明，第04批、06挑、07批芳纶Ⅲ纤维复丝强度平均值达到4535MPa以上，弹性模量大于139GPa，这些性能与Armos（2A）纤维相当，断裂延伸率较Armos（2A）纤维低，约为2．9％-3．3％。芳纶Ⅲ纤维单向复合材料的拉伸性能也与Armos（2A）纤维相当，但层间剪切强度较Armos（2A）纤维低很多，Ф150mm国产芳纶Ⅲ纤维试验容器性能有高有低，表明芳纶Ⅲ纤维的成型工艺性差，线密度太低且不均匀，另外与树脂浸润性差，层间剪切强度低，有待于进一步优化成型工艺参数。

等离子体处理的时效性对芳Ⅲ/双马复合材料耐湿热性能的影响

目的考察等离子体处理前后及其时效性对芳Ⅲ/双马复合材料弯曲强度、界面性能及耐湿热性能的影响。方法用低温射频耦合等离子体处理芳纶纤维表面,分别将未处理的、等离子体刚处理过的和等离子体处理后在空气中放置三天后的纤维通过溶液预浸渍工艺制备芳Ⅲ/双马复合材料预浸料,再经过高温模压成形技术制备芳Ⅲ/双马复合材料单向板。采用万能材料试验机对水煮前后复合材料的弯曲强度和层间剪切强度进行测试,利用扫描电子显微镜对复合材料层间剪切破坏形貌进行观察。结果等离子体处理后,复合材料的吸水率由未处理时的0.51%下降到0.33%,复合材料层间剪切强度由49.4 MPa提高到62.9 MPa。等离子体处理时效后复合材料的吸水率增加到0.69%,复合材料的层间剪切强度下降到56.0 MPa。结论等离子体处理提高了复合材料界面性能,但等离子体处理的时效后,复合材料的界面性能及其耐湿热性能有所下降。等离子体处理及时效性对复合材料的弯曲强度和耐湿热性能变化不大。

酸碱处理条件下芳纶Ⅲ的强伸性能研究

探讨酸碱环境下国产芳纶Ⅲ纤维的强伸性能变化情况。测试分析了国产芳纶Ⅲ纤维原样及其在酸碱处理条件下的强伸性能,并与对位芳纶进行了对比。结果表明:芳纶Ⅲ纤维的断裂强度几乎是对位芳纶的1.5倍,模量也高于对位芳纶。在强酸溶液处理下,其大分子结构中的酰胺键会出现水解现象,但仍表现出较好的耐酸性;在碱溶液处理下,国产芳纶Ⅲ纤维表现出极佳的耐碱腐蚀性能。认为:芳纶Ⅲ纤维适用于高强高模、且有一定耐酸碱腐蚀性要求的场合,是一种较好的过滤材料。