Mats and fabrics for electromagnetic interference shielding

Fabrics (with continuous electrically conductive fibers) are more effective than mats (with discontinuous conductive fibers) for electromagnetic interference shielding. Conductive fibers in the form of metal-coated polymer fibers or metal-coated carbon fibers are more effective than those in the form of bare carbon fibers. The highest shielding effectiveness of 53 dB at 1.0 GHz was attained by a metal-coated polymer fabric. The shielding is due mainly to reflection. A higher shielding effectiveness correlates with a higher reflectivity and a lower electrical resistivity. Both shielding effectiveness and reflectivity decrease with increasing frequency from 300 kHz to 1.5 GHz. The shielding effectiveness increases with thickness, as shown for bare carbon fiber mats. A nickel-coated carbon fiber mat of areal weight 9 g/m² is similar to a bare carbon fiber mat of areal weight 17 g/m² in shielding effectiveness.     

Mechanical properties,morphology, and flame retardance of glass fiber-reinforced polyamide-toughened novolac-type phenolic resin

The mechanical properties (tensile, flexural modulus, and impact strength) and the flame retardance of glass fiber-reinforced novolac-type phenolic resin modified with polyamide (PA-6, PA-66) were investigated. Results show that polyamide improves the mechanical properties of composites, especially for the impact strength up to 1.5-fold which shows a maximum value at 7 wt % of polyamide content. The interface between the matrix and glass fiber is increased due to the hydrogen-bonding function present in the polyamide chain. This modified phenolic composite shows excellent flame retardance, that is, UL-94, V-0, and LOI is higher than 55. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 881–887, 1999     

影响塑料排水板处理效果的因素

从塑料排水板的等效直径、井阻作用、涂抹作用及砂垫层的作用几个方面,总结了国内外学者认为这些因素对塑料排水板处理效果产生影响的观点和看法。     

两种改善富营养化湖泊水质的生物膜技术比较

用三个长宽高各为1.0m×1.0m×1.2m的水缸,装15cm的底泥和85cm的富营养化污水,来模拟水/底泥系统。分别在两个水缸中布设软性填料和自制人工水草来改善水质,另一水缸做空白对照。结果表明:在同投影面积下,布设人工水草比布设软性填料提高水体透明度的速度快;布设软性填料和人工水草在第36d时,CODMn分别降低89.63%、92.90%;TN分别降低93.45%、94.97%;NH3-N分别降低65.10%、70.15%;两者对TP都有一定影响。总体效果而言,人工水草处理效果优于软性填料。     

微机发变组整套保护误动原因分析

介绍了某型微机发变组保护装置因执行反措不彻底而发生硬件故障导致整套保护误动跳闸的情况,分析了事故发生的原因,提出了整改措施。     

玻纤毡增强聚丙烯复合材料的增容及力学性能

通过玻璃纤维(GF)毡与双螺杆挤出相容剂改性聚丙烯(PP)膜的多层叠合,以熔融浸渍法制得PP基GF毡增强热塑性塑料(GMT)复合材料,研究了相容剂PP接枝马来酸酐(PP-g-MAH)和PP接枝丙烯酸(PP-g-AA)的用量(为PP基体质量的百分数)及其复配改性,以及相容剂改性PP基体分布和毡体种类对GMT力学性能的影响。结果表明,PPg-MAH可明显提高GMT的拉伸与弯曲性能,但降低了冲击性能;PP-g-AA可明显提高GMT的冲击性能,但不利于拉伸与弯曲性能的提高,只有当PP-g-AA用量超过5%后,拉伸性能才有所提升。在PP-g-MAH用量为3%的条件下,将其与不同用量的PP-g-AA进行复配改性没有对GMT力学性能产生协同作用。在各相容剂用量相近(3%~3.5%)的情况下,与相容剂复配改性GMT相比,以两层PP-g-AA改性PP为芯层、PP-g-MAH改性PP为上下表面层作为改性基体分布时,GMT拉伸与弯曲强度分别提高17%和27%、缺口冲击强度提高48%;而以两层PP-g-MAH改性PP为芯层、PP-g-AA改性PP为上下表面层作为改性基体分布时,在不损失强度与刚性的同时,缺口冲击强度提高了88%。采用连续GF毡的GMT力学性能比采用短切GF毡的GMT高,尤其是缺口冲击强度提高了89.6%。     

Spider-net within the N6, PVA and PU electrospun nanofiber mats using salt addition: Novel strategy in the electrospinning process

Electrospun nanofibers are promising candidates in the nanotechnological applications due to the advantages of the nanofibrous morphology. Therefore, many attempts were reported to modify the electrospun mats to gain more beneficial properties. In the present study, we are introducing a strategy to synthesize electrospun polymeric nanofiber mats containing spider-net binding the main nanofibers. Addition with long stirring time of a metallic salt having tendency to ionize rather than formation of sol–gel in the host polymer solution reveals to synthesize a spider-net within the electrospun nanofibers of the utilized polymer. Nylon6, polyurethane and poly(vinyl alcohol) have been utilized; NaCl, KBr, CaCl₂ and H₂PtCl₆ have been added to the polymeric solutions. In the case of nylon6 and poly(vinyl alcohol), addition of the inorganic salts resulted in the formation of multi-layers spider-network within the electrospun nanofibers mats. The synthesized spider-nets were almost independent on the nature of the salt; the optimum salt concentration was 1.5 wt%. The metallic acid led to form trivial spider-nets within both of nylon6 and poly(vinyl alcohol) nanofibers. In a case of polyurethane, few spider-nets were formed after salt addition due to the low polarity of the utilized solvents. According to TEM analysis, the synthesized spider-net consisted of joints; the later issued from the main nanofibers at Taylor's cone zone. The spider-net improved the mechanical properties and the wetability of the nylon6 nanofiber mats, accordingly a mat having amphiphilic feature has been prepared.     

静电纺丝法纺制聚乳酸纳米纤维无纺毡

采用静电纺丝法制备了生物降解聚乳酸(PLLA)纳米纤维无纺毡。分析了纺丝液浓度、电压、接收距离、挤出速度等因素对纤维形态的影响。结果表明:纺丝液的浓度和挤出速度对纤维直径的影响较为明显,溶液挤出速度增大,所得纤维微孔含量及尺寸也增大;适当的电压和接收距离有利于收集无液滴纤维;随着纤维直径的减小,无纺毡的孔径呈减小趋势。在PLLA质量分数为5．7％、挤出速度0．8 mL／h、接受距离 15．5 cm、电压8 kV的静电纺丝条件下,可制备纤维直径为200-400 nm的PLLA纳米纤维无纺毡。     

高速明渠流条件下高性能加筋草皮抗侵蚀特性研究

现有针对高性能加筋草皮的抗侵蚀性能研究,大多建立在大规模试验基础上,重点研究允许冲刷流速和表面切应力。为了研究高速明渠水流条件下高性能加筋草皮侵蚀过程,对天然草皮和3种高性能加筋草皮共48个样品进行培植,并布置在高速明渠流的倾斜水槽中,通过不同坡度和流量分别进行间断和不间断冲刷试验,分析流速、流量和侵蚀量的关系。结果表明,间断和不间断冲刷的侵蚀速率有明显差异,说明初始冲刷引起了高性能加筋草皮的大部分侵蚀。样本侵蚀过程显示侵蚀速率随侵蚀量的增加而降低,证明明渠高速水流作用下加筋草皮存在“侵蚀上限”特征。此外,还讨论了流量和生态加筋网结构对侵蚀过程的影响,并尝试拟合了平均侵蚀速率与水流表面流速的关系。     

Treatment of Mine Water by a Microbial Mat: Bench-scale Experiments

Abstract.   We investigated the treatment of acid mine drainage (AMD) by a blue-green algae-microbial consortium and substrate (containing powdered goat manure, wood chips, and soil) in 1 m³ bench scale biological treatment test cells. The microbial mat resulted from the interaction of bacteria and filamentous blue-green algae (predominantly Oscillatoria spp). The experiments were carried out for different water column heights, and were evaluated for 24, 48, 72, 96, and 168 hours of retention. Within 24 hours of retention, the pH increased from 2.93 to 6.78 as net alkalinity went from -125 mg/L to 197 mg/L as CaCO₃. Turbidity decreased by 33–54%, sulphate decreased by 23–29%, and hardness decreased by 19 to 26%. We also observed that: 95% of the Fe, 79–97% of the Cu, 84–86% of the Zn, 88% of the Pb, 59–83% of the Co, 22–62% of the Ni, and 28–45% of the Mn were removed. A blue-green algae/microbial mat consortium may be a cost–effective treatment technique for removing metals from AMD.