【作者】 翟滢皓；

【导师】 张勇； 任文坛；

【作者基本信息】 上海交通大学 ， 材料学， 2013， 博士

【摘要】 现代社会的发展带来了越来越严重的电磁辐射和电磁污染的问题。吸波材料能够吸收微波的能量，减少反射，可以广泛地应用在抗电子干扰、电磁兼容、安全信息保密、人体安全防护等许多方面。理想的吸波材料应该具有吸收强、频段宽、质量轻等特点。传统的磁性吸波材料的比重较大，且填充量大，其在一些领域中的应用受到限制。碳材料具有优异的导电和介电性能、低密度以及耐腐蚀的优点，低用量填充复合材料就可以获得高的电磁波衰减系数，碳材料在吸波材料领域日益受到重视。橡胶为基体的吸波材料除了能有效耗散微波能量之外，还因其柔软、易剪裁、粘附性好的特点，容易布置用作结构复杂器件或腔体内部的吸波层。本论文选用氢化丁腈橡胶（HNBR）为基体，以多壁碳纳米管（MWCNT）等碳填料以及稀土化合物等作为吸波剂制备了高性能的吸波材料，研究了碳填料和稀土化合物的种类及其复配对于吸波性能的影响，探索了控制复合材料相形态和填料的分布状态以提高材料吸波性能的方法。首先研究了导电炭黑（CCB）、碳纤维（CF）和MWCNT填充HNBR复合材料的电磁特性和吸波性能。在相同的填料用量下，HNBR/MWCNT复合材料具有更高的电导率以及复介电常数实部和虚部。复合材料的复介电常数与填料用量间的关系可以采用Maxwell–Garnett模型描述。HNBR/MWCNT复合材料具有最好的吸波性能，当MWCNT用量为10phr时反射率最低，达到49:3dB。HNBR/CCB和HNBR/CF复合材料分别在填料用量为15phr和30phr时有较好的吸波性能，反射率分别为13:1dB和7:1dB。将MWCNT和CF与磁性填料羰基铁粉（CIP）复合填充HNBR制备了吸波材料。MWCNT和CF能够显著提升HNBR/CIP复合材料的复介电常数实部和虚部以及介电损耗，提高复合材料的吸波性能，降低匹配频率并拓宽吸收频段。通过水合肼原位还原氧化石墨烯的方法，将石墨烯与CIP复合填充HNBR，制备了HNBR/CIP/还原氧化石墨烯（rGO）复合材料。rGO以剥离的状态分散在复合材料中，提高了HNBR/CIP复合材料的复介电常数虚部和介电损耗，改善吸波性能。通过氧化镧（La2O3）和丙烯酸的原位反应，制备了稀土化合物改性HNBR复合材料。用红外光谱仪、X射线衍射仪、扫描电子显微镜等表征了制备过程中的原位反应，La2O3在原位反应之后转化为丙烯酸镧，硫化后成为纳米颗粒，且粒径分布变窄。原位生成的丙烯酸镧能够显著补强HNBR，并提高HNBR的玻璃化转变温度。进一步用多种稀土化合物制备了不同稀土丙烯酸盐改性的HNBR/MWCNT复合材料，研究了原位生成的丙烯酸盐对于复合材料介电性能、吸波性能、力学性能的影响。轻稀土元素（Nd、Sm、Eu）的丙烯酸盐聚合物在HNBR基体中以大尺寸的聚集体存在，而重稀土元素（Gd、Tb、Dy、Ho、Er、Tm、Yb、Lu）的丙烯酸盐聚合物在HNBR基体中均匀分散为细小的纳米颗粒。重稀土元素的丙烯酸盐能够提高复合材料的复介电常数的实部和虚部以及介电损耗，延长介电松弛时间，对于提高HNBR/MWCNT的吸波性能有协效作用，其中Dy、Gd、Tm、Lu等稀土元素的效果最为显著。轻稀土元素的丙烯酸盐对于HNBR/MWCNT复合材料的吸波性能影响很小。通过氢氧化锂和丙烯酸的原位反应制备了HNBR/丙烯酸锂（LiAA）复合材料，研究了其导电性能、介电性能和吸波性能。原位生成的LiAA在HNBR中均匀分散，能够有效地提高HNBR的拉伸强度和定伸应力。复合材料吸收水分后使复合材料的电导率提高5个数量级，加入氯化镧和氯化铈等稀土氯化物（RECl3）后复合材料的电导率进一步提高。HNBR/LiAA/RECl3复合材料吸水之后，其复介电常数的实部和虚部以及介电损耗提高，介电松弛时间变短，吸波性能提高。以不相容的HNBR和乙丙橡胶（EPR）共混物作为吸波材料基体，通过分段共混的方法将MWCNT和CIP选择性地分散到HNBR和EPR中。通过调整基体中HNBR和EPR的比例，可以得到不同填料分布状态的复合材料。研究了微观相形态对于复合材料的电磁特性、吸波性能、力学性能等的影响。当HNBR为连续相，即MWCNT在基体中呈连续分布时，HNBR/EPR/MWCNT/CIP复合材料具有最高的复介电常数虚部和介电损耗，吸波性能最好，反射率可达56:8dB，优于单一HNBR作为基体的HNBR/MWCNT/CIP复合材料。当EPR为连续相时，HNBR/EPR/MWCNT/CIP复合材料的吸收频宽最大，达到5.5GHz。以聚氯乙烯（PVC）和预交联粉末丁腈橡胶（P-NBR）为基体、MWCNT为吸波剂，制备了不同MWCNT含量以及分散状态的PVC/MWCNT复合材料。研究了MWCNT的分散状态对于复合材料的导电性能、介电性能、吸波性能的影响。MWCNT用量在4phr或以上时，MWCNT非均匀分散的PVC/P-NBR/MWCNT复合材料具有更高的电导率、复介电常数虚部和介电损耗，其吸波性能优于MWCNT更多还原

【Abstract】 The development of modern society is bringing increasing problems of electromag-netic radiation and pollution. Microwave absorbing materials (MAM) dissipating inci-dent microwave energy, are widely used in electromagnetic interference, electromag-netic compatibility, information security and human body protection applications. Highabsorption, broad absorption bandwidth and lightweight are the requirement of high per-formance MAM. Most magnetic absorbing materials have the disadvantage of relativelyhigh density and high fller loading, which would restrict their usage. Carbon fllers haveexcellent electrical conductivity and dielectric properties, low density, as well as corro-sion resistance, are getting more and more attention in the research of MAM. Because ofitsadvantagesofsoftness, cohesivenessandeasytotailorintocertainshape, rubberbasedMAM can be used as the absorbing layer of devices with complex structures or inner sur-facesofcavities. Inthisthesis,hydrogenatedacrylonitrile–butadienerubber(HNBR)wasblended with multi-walled carbon nanotubes (MWCNT) and rare earth (RE) compoundsto prepare high performance MAM. Dependence of the type of carbon fllers, rare earthcompounds and their combinations on the microwave absorbing properties was studied.The effect of phase morphology in polymer matrix and fller dispersion on enhancing themicrowave absorbing properties was also investigated.Conductivecarbonblack(CCB),carbonfber(CF)andMWCNTwereblendedwithHNBR to prepare MAM, and their electromagnetic characteristics and microwave ab-sorbing properties were studied. HNBR/MWCNT composites had higher electrical con-ductivity, real part and imaginary part of complex permittivity than HNBR/CCB andHNBR/CF composites at a given fller loading. The relationship between permittivity of the composites and their fller loading can be described using the Maxwell–Garnettmodel. HNBR/MWCNTcompositeshadthebestmicrowaveabsorbingpropertiesamongthethreekindsofcomposites,HNBR/MWCNT(100/10)compositehadthelowestrefec-tion loss of49:3dB, while HNBR/CCB (100/15) and HNBR/CF (100/30) compositeshad the refection losses of13:1dB and7:1dB, respectively.MWCNT and CF were added into HNBR/carbonyl iron powder (CIP) compositesto prepare MAM. MWCNT and CF can signifcantly increase the complex permittivityand dielectric loss of HNBR/CIP composites. The HNBR/CIP/carbon fller compositeshad lower refection loss, lower matching frequency and broader absorption bandwidththan the HNBR/CIP composites. HNBR/CIP/reduced graphene oxide (rGO) compositeswere prepared by in situ reducing graphene oxide using hydrazine, and rGO was exfoli-ated in HNBR matrix. HNBR/CIP/rGO composite had higher imaginary part of complexpermittivity and dielectric loss than that of HNBR/CIP composite, and the microwaveabsorbing properties of HNBR/CIP composite could be improved.Rare earth modifed HNBR composites were prepared by in situ reactions betweenlanthanum oxide (La2O3) and acrylic acid (AA). The in situ reactions were traced usinginfraredspectra, X-raydiffractionanalysisandscanningelectronmicroscopy. La2O3wasconverted to lanthanum acrylate (La(AA)3) after the in situ reactions, and became nano-size particles with narrower size distribution after vulcanization. The La(AA)3couldreinforce HNBR remarkably and increase the glass transition temperature of HNBR aswell. Different kinds of rare earth acrylates modifed HNBR/MWCNT composites wereprepared,andtheirdielectric,microwaveabsorbingandmechanicalpropertieswerestud-ied. The acrylates of light rare earth elements (Nd, Sm, Eu) formed large aggregates inHNBR matrix, while the acrylates of heavy rare earth elements (Gd, Tb, Dy, Ho, Er,Tm, Yb, Lu) were dispersed in HNBR matrix as fne particles. The acrylates of heavyrare earth elements could increase the complex permittivity, dielectric loss and dielectricrelaxation time, improve the microwave absorbing properties of HNBR/MWCNT com-posites, while the acrylates of light rare earth elements had little effect on the microwaveabsorbing properties of HNBR/MWCNT composite.HNBR/lithium acrylate (LiAA) composites were prepare using in situ reactions be-tween lithium hydroxide and AA. The in situ prepared LiAA was uniformly dispersedin HNBR matrix, and signifcantly increased the tensile strength and modulus of HNBR.The electrical conductivity of HNBR/LiAA increased by fve orders of magnitude af- ter water absorption, and increased even further by adding lanthanum chloride (LaCl3)or cerium chloride (CeCl3). The HNBR/LiAA/RECl3composites after water absorptionhad higher complex permittivity and dielectric loss, longer dielectric relaxation time, aswell as improved microwave absorbing properties than the composites without water ab-sorption.Immiscible HNBR and ethylene–propylene rubber (EPR) blends were used as thematrix for MAM, and MWCNT and CIP were selectively dispersed in HNBR and EPR,respectively. Composites with different fller distribution could be obtained by changingHNBR/EPR ratio. The infuence of phase morphology on the electromagnetic charac-teristics, microwave absorbing and mechanical properties of the composites was investi-gated. WhileHNBRformedcontinuousphase,theHNBR/EPR/MWCNT/CIPcompositehad the highest imaginary part of complex permittivity, dielectric loss, and the best mi-crowave absorbing properties. It had the refection loss of56:8dB, lower than thatof HNBR/MWCNT/CIP composite with HNBR as the only matrix. While EPR formedcontinuousphase, theHNBR/EPR/MWCNT/CIPcompositehadwidestabsorptionband-width of5.5GHz.Polyvinyl chloride (PVC) and crosslinked acrylonitrile–butadiene rubber powder(P-NBR) were used as MAM matrix to prepare PVC/MWCNT composites with differentMWCNTloadinganddispersionstate. TheeffectofMWCNTdispersionontheelectricalconductivity, dielectric, microwave absorbing properties of MWCNT composites was in-vestigated. WhentheMWCNTloadingwashigherthan4phr,thePVC/P-NBR/MWCNTcomposites with nonuniformly dispersed MWCNT, had higher electrical conductivity,imaginary part of complex permittivity, dielectric loss, and better microwave absorbingproperties than PVC/MWCNT composites.更多还原