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.

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.

Statistical Constitutive Equation of Aramid Fiber Bundles

Tensile impact tests of aramid (Twaron) fiber bundles were carried om under high strain rates with a wide range of 0. 01/s～1000/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.

Simultaneously enhanced interfacial shear strength and tensile strength of heterocyclic aramid fiber by graphene oxide

Heterocyclic aramid fibers,a typical kind of high-performance fibers,have been widely used in aerospace and protection fields because of their excellent mechanical properties.However,the application of heterocyclic aramid fibers as a reinforcement is hindered by the weak interfacial combination with matrix materials,especially epoxy.Traditional strategies enhancing the interfacial shear strength(IFSS)usually decrease the tensile strength.Therefore,simultaneous enhancement of both mechanical properties remains a challenge.Herein,we report a novel heterocyclic aramid fiber with high interfacial shear strength(49.3 MPa)and tensile strength(6.27 GPa),in which 4,4′-diamino-2′-chlorobenzanilide(DABA-Cl)and a small amount of graphene oxide(GO)are introduced through in-situ polymerization.Hydrogen bonds andπ–πinteraction between GO and polymer chains trigger the enhancement in crystallinity,orientation,and lateral interaction of the fibers,thus improving the tensile strength and interfacial shear strength of the fibers.Moreover,the interfacial interaction between fiber and epoxy is enhanced due to the improvement of the surface polarity of the fibers caused by DABA-Cl.Therefore,a method to improve both tensile strength and interfacial shear strength of heterocyclic aramid fibers was found by introducing GO and DABA-Cl,which may provide guidance for the design and preparation of other high-performance fibers.

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.

Validity of Amontons's law for run-in short-cut aramid fiber reinforced elastomers:The effect of epoxy coated fibers

Friction between two contacting surfaces is studied extensively.One of the k n o w n friction theories is Amontons,law which states that the friction force is proportional to the normal force.However,Amontons7 law has been found to be invalid for elastomers.In the present study,the validity of Amontons7 law for short-cut aramid fiber reinforced elastomers is studied.Two types of fillers are used to reinforce the elastomers,namely highly dispersible silica and short-cut aramid fibers.Short-cut aramid fibers with two different surface treatments are used,namely non-reactive fibers with standard oily finish(SF-fibers)and fibers treated with an epoxy coating(EF-fibers).A pin-on-disc tribometer is used to investigate the frictional behavior of the composites in sliding contact with a granite counter surface.The results show that,after the run-in phase,Amontons,law is valid for those composites that are reinforced by short-cut aramid fibers(without reinforcing filler,i.e.,silica)if the contact pressure is below a threshold value.However,once the contact pressure exceeds this threshold value,Amontons'law will be invalid.The threshold contact pressure of the composites containing EF-fibers is higher than of the composites containing SF-fibers.The composites that are reinforced by silica and short-cut aramid fibers do not follow Amontons7 law.

Paper‑like Polyphenylene Sulfide/Aramid Fiber Electrode with Excellent Areal Capacitance and Flame‑Retardant Performance

In this paper,an aramid chopped fiber,so-called(ACF)/polyphenylene sulfide(PPS)composite,containing multi-walled carbon nanotubes(MWCNT),and in situ polymerized polypyrrole(PPy)was designed and fabricated,to be applied as a paper based electrode.The ACF/PPS/MWCNT-PPy electrode features highly porous paper-like structure with excel-lent electrochemical activity,rendering it a high areal capacitance of~3205 mF cm^(-2) at a current density of 5 mA cm^(-2).After 5000 charge-discharge cycles,the areal capacitance still maintains 93%and 70%at high current densities of 20 and 80 mA cm^(-2),respectively.Moreover,the ACF/PPS/MWCNT-PPy electrode displays over 50%the areal capacitance and maintains it's mechanical stability after annealing at 300℃.The UL-94 test reveals that the highest V-0 flame-retardant performance can be achieved.All these results suggest that the ACF/PPS/MWCNT-PPy composite is a promising material to be used as electrode for supercapacitor with high energy-storage capability and noninflammability.

沉析纤维尺寸和含量对间位芳纶纸性能的影响

使用不同目数的筛网对自制的Z沉析纤维进行筛分,将得到的不同尺寸的沉析纤维与间位芳纶短切纤维按一定质量比配抄成纸,制备间位芳纶纸;通过红外光谱、X射线衍射、扫描电镜及热失重、动态滤水分析对自制的Z沉析纤维的化学结构、热性能、动态滤水性能进行表征,并与进口的J沉析纤维对比;研究了沉析纤维的尺寸和含量对间位芳纶纸性能的影响。结果表明:Z沉析纤维与J沉析纤维均为膜状结构,化学结构基本一致,动态滤水性能及热性能相当;经30目或50目的筛网筛分后的沉析纤维可以与短切纤维更好地抱合,间位芳纶纸的抗张强度、断裂伸长率、撕裂度、击穿强度均达到较大值;间位芳纶纸的撕裂度随沉析纤维含量的增加逐渐降低,间位芳纶纸的抗张强度、断裂伸长率、击穿强度随沉析纤维含量的增加呈现先增后降的变化趋势,当沉析纤维质量分数为55%时,间位芳纶纸的抗张强度、断裂伸长率、击穿强度均达到最大值,分别为3.0 kN/m、5.50%、18.7 kV/mm。

间位芳纶的结构与耐酸碱性能研究

通过X射线衍射仪和红外光谱仪分别对间位芳纶的晶体聚集态结构和大分子结构进行表征,利用场发射扫描电镜观察其表面形貌,使用热重/差示扫描量热同步热分析仪测试其热学性能,并对酸碱处理后的纤维力学性能进行表征。结果表明:间位芳纶的结晶度为46.24%,晶区轴取向指数为0.8494;间位芳纶表面粗糙,内部大分子链中存在苯环结构;间位芳纶具有良好的耐热性能,在292℃的高温内无任何损伤;间位芳纶具有一定的耐强酸强碱腐蚀能力,在85℃下分别经体积分数小于等于20%的硫酸溶液及质量分数小于等于20%的氢氧化钠溶液处理,处理后其断裂强度均保持在原来的90%以上。

芳纶纤维的发展现状及应用

总结了芳纶纤维的性能、改性研究、染色印花性能研究发展现状,以及芳纶纤维在金属化、体育运动、柔性防刺防弹材料、航空航天材料等的应用及研究情况。

冻融循环作用下芳纶纤维增强混凝土力学性能研究

芳纶纤维具有纤维含量高、密度小、韧性大等特点,对提升混凝土材料的力学性能有着巨大的潜力。以芳纶纤维为原料,对冻融循环作用下不同纤维体积掺量(1%、2%、4%)及纤维长径比(200、400、600)的芳纶纤维增强混凝土(AFRC)力学性能进行试验研究,得到了AFRC的抗压强度和抗拉强度。试验结果表明,随着冻融循环次数的增加,混凝土的抗压强度和抗拉强度均有所降低。在循环60次时,AFRC抗压强度和抗拉强度均降低50%左右。AFRC抗压强度随纤维体积掺量的增加而降低,随纤维长径比的增加而增加,抗拉强度基本保持不变。此外,基于试验数据建立了芳纶纤维增强混凝土抗压强度及抗拉强度的预测与转换模型。

提升杂环芳纶复合性能的研究进展

杂环芳纶是指主链中含有芳杂环(通常为苯并咪唑)的一类对位芳纶,其具有轻质、高强高模、高耐热、耐溶剂等优异性能。相比典型的芳纶Ⅱ纤维,杂环芳纶具有更加优异的力学性能,目前在我国的航空航天和防弹防护等领域得到了实际的应用。然而,与其他有机纤维类似,杂环芳纶由于表面惰性,其与树脂的复合性能相对较低,限制了其在先进复合材料领域的应用。本文从杂环芳纶表面改性和结构设计两方面出发,总结近年来提高杂环芳纶复合性能的设计思路、技术手段和研究成果,展望其在先进复合材料应用领域的发展趋势,为有机纤维的界面设计及改善界面粘接性提供帮助和参考。

芳纶纤维增强复合材料转子的有限元分析

转子是机械转动部件中的一种,存在于电动机、水轮机、风力发电机、飞轮储能系统等各种机电设备中。在飞轮储能系统中,转子的材料、形状等关键因素都会对系统的性能产生影响。文中以提高飞轮储能系统转子的转速为出发点,建立了复合材料转子的数字化模型,并且对芳纶纤维复合材料转子开展了有限元分析,确定了复合材料层数变化、过盈量变化等对轮毂和轮缘的径向应力、周向应力及转速的影响。数值模拟结果为芳纶纤维增强树脂基复合材料在复合材料飞轮中的应用提供了参考。

基于分子动力学的芳纶/功能化碳纳米管复合材料体系热力学性能模拟

对位芳纶绝缘纸以其优异的介电性能、力学性能在电气绝缘领域得到广泛应用。为探究不同功能化碳纳米管与对位芳纶共掺的复合材料热力学性能,该文通过分子动力学模拟方法建立了对位芳纶分子体系模型、未功能化碳纳米管以及分别接枝羟基、羧基和氨基官能团的芳纶/功能化碳纳米管复合体系模型。在Materials Studio和LAMMPS中计算了复合材料热导率、玻璃化转变温度、力学性能、结构参数及相对介电常数。结果表明,芳纶复合材料体系各项性能均有不同幅度提升。芳纶/羧基化碳纳米管(PPTA/CNT—COOH)的热导率较掺杂前提升了75.4%,玻璃化转变温度提升了43.29 K。芳纶/羟基化碳纳米管(PPTA/CNT—OH)和芳纶/氨基化碳纳米管(PPTA/CNT—NH2)的热导率依次提升70.2%和63.2%。在力学性能上,复合材料比掺杂前的弹性模量平均增强30%以上,剪切模量增强15%以上。通过计算体系结构参数,从均方位移、自由体积占比、氢键数量与结合强度等分子层面阐释了材料性能增强的内在机理,最终发现PPTA/CNT—COOH在热力学性能上较其他掺杂体系提升最为明显,且碳纳米管的掺入未对材料介电常数引起较大改变,所得结果可为对位芳纶复合绝缘材料的掺杂设计、性能调控提供理论支持。

紫外辐照对芳纶纤维结构与性能的影响

在空气中对芳纶纤维进行紫外辐照,研究紫外辐照对芳纶纤维结构变化、热稳定性能、结晶性能、表面微观形貌以及拉伸性能的影响。采用傅里叶变换红外光谱仪(FTIR)、热重分析仪(TG)表征分析了芳纶纤维紫外辐照前后化学结构、热稳定性的变化。采用扫描电子显微镜(SEM)、原子力显微镜(AFM)和X射线广角衍射仪(XRD)分别观察芳纶纤维紫外辐照前后的表面形貌和晶体结构转变。最后采用单丝强力仪等对样品力学性能进行表征。FTIR结果表明,经过紫外辐照后纤维表面出现新的含氧化合物。SEM和AFM观察结果显示,紫外辐照后纤维表面变得粗糙,并出现沟壑,且随辐照时间增加,粗糙度增加。XRD结果表明,紫外辐照对芳纶纤维晶体结构影响较小。拉伸性能结构显示随着紫外辐照时间的增加,芳纶纤维的单丝抗拉强度出现下降。芳纶纤维经紫外辐照后,表面化学活性提高,粗糙度增加,这将有效改善芳纶纤维与复合基体之间的界面黏合性,增强界面作用力,这对于解决高性能纤维自身难以编织以及复合强度不佳的瓶颈问题具有重要意义,为进一步拓宽芳纶纤维在高防护服饰、防护鞋面等需要增强界面黏合的复合材料领域方面的应用提供参考。

芳纶防弹复合材料的影响因素分析研究

芳纶防弹复合材料的影响因素较多,本文主要对芳纶展开宽度、纤维布形态、胶粘剂使用年限、上胶工艺以及拉伸强度等影响因素进行分析,并对相应靶片进行了防弹性能测试,分析结果并给出结论:纤维展开的宽度为2.5 mm±0.5 mm时,纤维布形态为UD时,防弹效果较好;胶粘剂满足标准使用期限8年的老化速度,防弹效果没有变化;采取浸胶方式的上胶工艺、控制纤维损伤程度在4%以下时靶片的防弹性能最优。本研究可为芳纶防弹复合材料从业人员提供参考。

芳纶短纤维对天然橡胶胶料性能的影响

基于轮胎胎面胶配方,研究芳纶短纤维用量和长度对天然橡胶(NR)胶料性能的影响。结果表明:当芳纶短纤维长度为3 mm时,芳纶短纤维用量为2份的胶料的Payne效应最弱,硫化胶的拉伸强度最大,定伸应力和撕裂强度较大,耐磨性能和抗湿滑性能最好;当芳纶短纤维用量为2份时,芳纶短纤维长度为2 mm的胶料的Payne效应最弱,硫化胶的定伸应力和拉伸强度最大,芳纶短纤维长度为3 mm的硫化胶的定伸应力和拉伸强度较大,撕裂强度最大,综合性能最好。

芳纶纤维对EPDM基阻燃材料性能的影响

选用三元乙丙橡胶(EPDM)为基体,考察芳纶纤维(AF)用量以及磷酸、γ-氨丙基三乙氧基硅烷(KH550)改性芳纶纤维(AF-P-Si)对EPDM基复合材料性能的影响。结果表明,当AF用量为1~5份(质量份,下同)时,EPDM混炼胶焦烧时间变化不大;超过3份时,硫化程度增加。随着AF用量增加,硫化胶的拉伸强度、拉断伸长率降低,硬度、撕裂强度、耐磨性和热氧老化性能逐渐提高,尤其3份和5份AF补强的EPDM硫化胶的100%定伸应力明显提高。改性后AF-P-Si的添加有利于提高硬度、拉伸强度、断裂伸长率和撕裂强度。锥型量热仪数据表明,3份和5份AF添加的EPDM硫化胶表现出较高的火灾行为指数(FPI),而AF-P-Si则表现出更佳的阻燃效果。

芳纶短纤维长度对天然橡胶/溶聚丁苯橡胶并用胶性能的影响

研究芳纶短纤维长度对天然橡胶(NR)/溶聚丁苯橡胶(SSBR)并用胶性能的影响。结果表明:随着芳纶短纤维长度的增大,NR/SSBR并用胶的交联密度和储能模量增大,填料网络化程度增大,填料分散性变差;加入长度为1 mm的芳纶短纤维时,NR/SSBR并用胶的拉伸强度较大,耐磨性能较差;加入长度为3 mm的芳纶短纤维时,NR/SSBR并用胶的邵尔A型硬度、100%定伸应力和撕裂强度较大,DIN磨耗量较小。