Engineering all-aromatic polyamide surface from hydrophilic to superhydrophobic and the accelerated strategy

Being a new kind of nanomaterials, aromatic polyamide nanofibers (ANF) have been much highlighted in recent studies. We here demonstrate an isopropyl alcohol (IPA) accelerated chemical cleavage on poly (p-phenylene terephthalamide) chopped fibers, which provides an efficient preparation method of ANF. The comprehensive study on the processes accelerated by different alcohols revealed that the preparation time of ANF in the mixed medium of dimethyl sulfoxide (DMSO)-alcohol (20:1 in volume) was shorten to 45 min and 75 min for methanol (ethanol) and isopropanol, respectively. However, the nanofibers prepared in DMSO-IPA exhibited the minimum in axial and radial dimensions, providing the finest and most uniform diameter of 16 nm. The corresponding ANF films through vacuum assisted filtration also showed the highest tensile strength of 150 MPa, in comparison with those of the ANF films prepared using other alcohols, which were about 110 MPa. Furthermore, ANF/silicon hybrid films were prepared by the ionic ring-opening reaction followed by the alkoxysilane condensation and nanoparticle fabrication. By changing the organo functional groups in the alkoxysilane, the surface of the films were adjustable in a wide contact angle range from 56° (hydrophilic) to 150° (superhydrophobic), suggesting the amendable interfacial properties potential applicable to composite fabrication with most of the resin matrix.     

Sustainability-guided life-cycle design and assessment for bio-based composite foams: Integrate flame retardancy/lightweight in usage and energy utilization after service

Sustainable development strategy has aroused a great interest in biomass resources as alternative raw materials. A kind of biomass-derived poly(butylene succinate) (PBS), has been developed as porous foams to reduce resource exhaustion and meet lightweight demands. For fire-safety in-service, graphene oxide (GO) was functionalized by 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) to combine flame-retardant elements and heat-barrier function. Hence, a very low loading level of P-containing GO as only 5 wt% could reduce peak heat release rate (pHRR) and total heat release (THR) of PBS-based foams by 58.5% and 22.3%, respectively. Meanwhile, N-/P-doped mesoporous char with a specific surface area of 136 m²/g, which derived from combustion of flame-retardant foaming PBS, contributes to a potential of energy storage applications in the capacitor or the anode of Li-ion battery with long-term stability. Overall, the sustainability of bio-based polyester could integrate lightweight of foaming, and be extended to utilization after use via facile combustion inspired by flame-retardancy design.     

Fabrication of phytic acid embellished kaolinite and its effect on the flame retardancy and thermal stability of ethylene vinyl acetate composites

A modified kaolinite by grafting with phytic acid (PA-g-Kaol) is fabricated, and it was introduced into ethylene vinyl acetate (EVA) with intumescent flame retardancy (IFR) together to improve the flame retardancy of EVA composites. The results show the limiting oxygen index value of EVA/ (18.0 wt% IFR)/ (2.0 wt% PA-g-Kaol) is 30.8%. Meanwhile, there is only one dripping produced in the vertical burning test. What's more, the flame-retardant mechanism is demonstrated by TG-IR, real-time-IR and GC–MS analysis. The results indicate that some pyrolytic products of IFR and PA-g-Kaol, like ammonia and phosphoric acid, catalyze the crosslinking of EVA and flame retardant, the resultant compact char protects the substrate from further burning.     

Spatial distribution of silica fillers in phase-separated rubber blends investigated by three-dimensional elemental mapping

The distribution of nano-sized silica in binary rubber blends is characterized by scanning transmission electron microscopy (STEM) tomography combined with energy dispersive X-ray spectrometry (EDX). 3D distribution of silica is visualized by STEM-EDX tomography with the tilt-series of silicon elemental maps, while the phase-separated morphologies of polyisoprene rubber (IR) and styrene-butadiene rubber (SBR) are visualized by STEM-tomography in high-angle-annular-dark field (HAADF) mode. The combination of STEM-EDX and STEM-HAADF tomography enables us to determine the distribution of silica between the two rubber phases quantitatively even with high contents of silica up to 70 phr (weight parts per hundred rubber). It is found that silica is preferentially distributed in the SBR phase, but it is also distributed in the IR phase when the IR fraction in the total rubber components is higher than 40 wt%. The preferential distribution of silica in the SBR phase improves the dispersion of the IR domains. This is the first use of this technique for a multicomponent polymer system, showing the advantage to characterize the complicated multicomponent polymer composite morphologies.     

Effects of the molecular structure from pitch fractions on the properties of pitch-based electrospun nanofibers

Mesophase pitch was separated into different pitch fractions to investigate the effect of pitch fractions on the properties of their nanofibers prepared by electrospinning. The evolution of different pitch fractions-derived nanofibers during stabilization and carbonization were explored, and the properties of the resultant carbon nanofibers (CNFs) as electrode materials for supercapacitor were compared. Results indicated that the hexane insoluble-toluene soluble (HI-TS) and toluene insoluble-tetrahydrofuran (THF) soluble (TI-THFS) fractions had good spinnability due to their narrow molecular weight distribution. Moreover, compared with HI-TS and THF insoluble (THFI), TI-THFS consisted of appropriate aromaticity and branched alkyl groups which promoted the stabilization and carbonization behaviors of its nanofibers, resulting in maintaining ideal fiber morphology of TI-THFS-derived nanofiber due to the mitigation of their exothermic reactions. Meanwhile, the TI-THFS-derived CNFs presented the highest surface area of 543 m² g⁻¹ and exhibited an excellent specific capacitance of 167 F g⁻¹ at 0.5 A g⁻¹ in 6 M KOH electrolyte.     

晶须增韧EVA/PE⁃LD/ATH复合材料的阻燃性能研究

制备了晶须增韧乙烯-乙酸乙烯酯共聚物/低密度聚乙烯/氢氧化铝（EVA/PE-LD/ATH）复合材料,通过扫描电子显微镜（SEM）、热重分析仪（TG）、氧指数仪、锥形量热仪（CCT）、万能拉力机和高阻计等对添加不同晶须的EVA/PE-LD/ATH复合材料的微观结构、阻燃性能、力学性能和电学性能进行了表征。结果表明,ATH颗粒在复合材料中未出现明显团聚,复合材料中晶须呈交错分布并与基体界面结合致密;晶须对复合材料阻燃性能的提高源于晶须热解产物网络状骨架对炭层的增强作用;碱式硫酸镁晶须（MHSH）、硼酸铝晶须（ABW）和硫酸钙晶须（CSW）添加质量比为13.5∶6.75∶6.75的复合材料的800 ℃质量保留率为32.7 %,极限氧指数为26.8 %,热释放速率峰值为364.4 kW/m²,总热释放量为20.8 MJ/m²,总烟释放量为187.2 m²/m²,阻燃性能相对最优;MHSH具有降低复合材料热释放速率峰值、总烟释放量和增强复合材料拉伸强度的作用,而CSW能够延迟点燃时间,减弱出现轰燃的趋势,但增大了总烟释放量,同时,CSW还具有提高复合材料断裂伸长率的增韧作用;混合晶须对复合材料拉伸强度、邵氏硬度和电绝缘性能的影响有限。     

含能材料锥形双螺杆安全混合径向间隙的研究

以锥形双螺杆挤出机挤出段、过渡体和挤出机头为研究对象,基于Polyflow非等温稳态和瞬态的有限元模拟,对不同径向间隙下流场中各场量分布情况和变化曲线进行分析,研究含能材料在挤出段、过渡体和挤出机头流道中的安全和混合问题。从安全和混合效果两方面考虑,建立了综合评价方法,优选径向间隙。结果表明,最大剪切速率、最高剪切应力和最高黏性耗散热均在挤出段流道入口附近,最高压力在挤出段流道出口处,最高温度在机头处;锥形双螺杆的混合效果随着间隙的增加而增加;在径向间隙为0.5 mm时,流道的安全性能最差,径向间隙为1 mm时,流道的安全性能最好。     

基于相变蓄热技术的高过载配电变压器研制与应用

本文中作者提出了一种基于相变蓄热技术的高过载变压器,采用石蜡蓄热方式显著提升其抗过载发热能力,并通过试验验证了其实用价值。     

变压器绕组初始缺陷对辐向稳定性的影响

本文中笔者仿真分析了撑条分布状态、绕组偏心、导线绕制紧密程度三种初始缺陷对绕组辐向稳定性的影响.     

PWF转子秤在入窑给料系统中的应用

介绍了PWF转子秤的结构组成及工作原理,采用PWF转子秤代替原有冲板流量秤进行生料喂料计量,解决了计量稳定性差、误差大、易冲料以及易受干扰等问题,运行稳定,操作简便,使用效果较好