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Effect of graphitic carbon nanomodifiers on the electromagnetic shielding effectiveness of linear low density polyethylene nanocomposites.

机译：石墨碳纳米改性剂对线性低密度聚乙烯纳米复合材料电磁屏蔽效能的影响。

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摘要

Conductive polymer composites have become alternative materials for providing electromagnetic and electrostatic shielding where metals are not suitable. In this study, the effect of crystallinity, morphology, concentration and orientation of carbon nanomodifiers on shielding provided by their polyethylene-based composites has been investigated relative to their transport properties.;First, the electrical properties and EM SE of composites consisting of heat-treated carbon nanofibers (PyrografRTM-III PR-19 CNF) in a linear low density polyethylene (LLDPE) matrix were assessed. Heat treatment (HT) of CNF at 2500°C significantly improved their graphitic crystallinity and intrinsic transport properties, thereby increasing the EM SE of the nanocomposites. Although the strain-to-failure was about one-third that of pure LLDPE, the absolute value of 180+/-98% indicates a significant retention of ductility.;Second, the influence of the morphology of carbon modifiers on the electrical, thermal and mechanical properties of their composites was investigated. Four heat-treated carbon modifiers were investigated: PR-19 HT carbon nanofibers, multi-walled carbon nanotubes (MWNT HT), helical multi-walled carbon nanotubes (HCNT HT), and pitch-based P-55 carbon fibers (CF). MWHT HT, with the highest aspect ratio, led to the largest composite electrical and thermal conductivities (34 S/m, 1 W/m.K) and EM SE (~24 dB). In contrast, HCNT HT, due to their coiled shape and low aspect ratio, led to a non-percolating microstructure in the composites, which produced poor EM SE (<1 dB). Nonetheless, HCNT HT composites displayed the highest ductility (~250%) and flexibility, which is probably owed to the matrix-modifier mechanical bonding (interlocking) provided by the helical morphology.;Using the carbon modifiers that previously led to the best EM SE (i.e., PR-19 HT and MWNT HT), the influence of composite electrical properties on the plane-wave EM SE in the VHF-UHF bands was studied further. Both graphitic nanomodifiers were dispersed in LLDPE matrix to produce a nominally random in-plane modifier orientation. For a concentration of 10 vol% nanomodifiers, EM SE values of 22 dB and 24 dB were obtained for PR-19 HT and MWNT HT nanocomposites (2.5-mm thick), respectively. At a high concentration of 40 vol%, EM SE values as high as 68 dB and 55 dB were respectively attained. Because such nanocomposites possess only moderate electrical conductivity, a model for generally-lossy materials was used to predict the plane-wave EM SE and its components. Based on the material properties of the nanocomposites, the predicted values of EM SE were found to be consistent with the experimental values.;Finally, the electrical conductivity and EM SE of nanocomposites that contained 10 vol% of oriented graphitic nanomodifiers (PR-19 HT and MWNT HT) in LLDPE are reported. Micro-filament spinning was used to generate flow-induced orientation of the carbon nanomodifiers. Consequently, the conductivity of the resulting nanocomposites exhibited anisotropy. Thus, the in-plane conductivity in the longitudinal direction (PR-19 HT comp.: ~0.02 S/m; MWNT HT comp.: ~3 S/m) was at least an order of magnitude higher than that along the transverse direction. As measured with a rectangular waveguide (WR510, 1.45-2.2 GHz), the PR-19 HT and MWNT HT oriented nanocomposites (1-mm thick) displayed EM SE values of 0.7+/-0.4 dB and 3.0+/-0.8 dB, respectively, when the nanomodifiers were transversely oriented with the polarized electric field. In contrast, when the orientation of the nanomodifiers was parallel with the field, values of 3.2+/-1.0 dB and 9.0+/-1.0 dB were obtained, respectively. Therefore, as a result of this anisotropy, as analyzed by polarized electromagnetic waves, the composites displayed anisotropic shielding. (Abstract shortened by UMI.).
机译：导电聚合物复合材料已成为金属不适合使用时提供电磁和静电屏蔽的替代材料。在这项研究中，研究了碳纳米改性剂的结晶度，形态，浓度和取向对它们基于聚乙烯的复合材料提供的屏蔽性能的影响。相对于它们的传输性能。;首先，由热组成的复合材料的电性能和EM SE评估了线性低密度聚乙烯（LLDPE）基质中处理过的碳纳米纤维（PyrografRTM-III PR-19 CNF）。 CNF在2500°C的热处理（HT）显着改善了它们的石墨结晶度和本征传输特性，从而提高了纳米复合材料的EM SE。尽管断裂应变约为纯LLDPE的三分之一，但绝对值180 +/- 98％表示塑性显着保留;其次，碳改性剂的形态对电，热的影响并对其复合材料的力学性能进行了研究。研究了四种热处理的碳改性剂：PR-19 HT碳纳米纤维，多壁碳纳米管（MWNT HT），螺旋多壁碳纳米管（HCNT HT）和沥青基P-55碳纤维（CF）。具有最高纵横比的MWHT HT导致最大的复合电导率和热导率（34 S / m，1 W / m.K）和EM SE（〜24 dB）。相反，HCNT HT由于其盘绕形状和低长宽比，导致复合材料中的非渗流微观结构，从而产生较差的EM SE（<1 dB）。尽管如此，HCNT HT复合材料仍显示出最高的延展性（〜250％）和柔韧性，这可能归因于螺旋形貌提供的基体-改性剂机械键合（互锁）;使用以前导致最佳EM SE的碳改性剂（即PR-19 HT和MWNT HT），进一步研究了复合电学特性对VHF-UHF频带中的平面波EM SE的影响。两种石墨纳米改性剂均分散在LLDPE基质中，以产生名义上随机的面内改性剂方向。对于浓度为10 vol％的纳米改性剂，PR-19 HT和MWNT HT纳米复合材料（2.5毫米厚）的EM SE值分别为22 dB和24 dB。在40vol％的高浓度下，EM SE值分别达到68dB和55dB。由于此类纳米复合材料仅具有中等电导率，因此使用了一般损耗材料的模型来预测平面波EM SE及其成分。根据纳米复合材料的材料性能，发现EM SE的预测值与实验值一致;最后，纳米复合材料的电导率和EM SE含量为10 vol％的定向石墨纳米改性剂（PR-19 HT以及LLDPE中的MWNT HT）。使用微丝纺丝来产生碳纳米改性剂的流动诱导取向。因此，所得纳米复合材料的电导率表现出各向异性。因此，纵向的平面内电导率（PR-19 HT补偿：〜0.02 S / m； MWNT HT补偿：〜3 S / m）至少比横向方向高一个数量级。 。用矩形波导（WR510，1.45-2.2 GHz）测量时，PR-19 HT和MWNT HT取向纳米复合材料（1毫米厚）显示的EM SE值为0.7 +/- 0.4 dB和3.0 +/- 0.8 dB，当纳米改性剂通过极化电场横向取向时相反，当纳米改性剂的取向与电场平行时，分别获得3.2 +/- 1.0dB和9.0 +/- 1.0dB的值。因此，作为这种各向异性的结果，如通过极化电磁波分析的，该复合材料显示出各向异性屏蔽。 （摘要由UMI缩短。）。

著录项

  • 作者

    Villacorta Hernandez, Byron S.;

  • 作者单位

    Clemson University.;

  • 授予单位 Clemson University.;
  • 学科 Engineering Chemical.;Engineering Materials Science.
  • 学位 Ph.D.
  • 年度 2013
  • 页码 231 p.
  • 总页数 231
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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