【作者】 喻冬秀；

【导师】 杨卓如；

【作者基本信息】 华南理工大学 ， 化学工程， 2007， 博士

【摘要】 短碳纤维具备有高强度、高模量、质轻、良好的导电性能,以及独特的长径比特征,而备受电磁屏蔽工作者的青睐,但应用于电磁屏蔽涂料存在分散稳定差、电磁特性达不到要求等缺点,采用复合技术来改善其性能成为近年来研究热点之一。本论文从物理学和材料学的观点出发,提出了导电聚合物包覆短碳纤维的模型,运用复合等效电磁参数理论,推导了纤维状复合材料的等效电磁参数方程,制备了改性短碳纤维,并把改性短碳纤维应用于丙烯酸酯涂料制备出多涂层功能型电磁屏蔽材料。本文的研究结果为扩大短碳纤维的应用提供了理论指导和技术支持,同时也为同类型材料设计提供了新的思路和实验依据。从复合材料的电磁性能和物理化学等基础理论出发,设计了导电聚苯胺包覆短碳纤维模型、导电聚苯胺/磁性物质包覆短碳纤维模型,指导短碳纤维的表面性能和电磁性能的改善,为本研究提供理论指导。结合氧化法和原位聚合法,引入超声分散技术,制备了分散稳定性较好并具有良好电磁性能的聚苯胺包覆短碳纤维(PAOSCF)。考察了nAPS/AN、MHCl、反应温度以及反应时间等因素对包覆层的致密性、完整性和PAOSCF的电性能的影响。研究发现:这些因素的影响大小为:nAPS/AN >反应温度>MHCl>反应时间,在nAPS/AN为1.5,MHCl为1.0mol/L,反应温度为10℃±3℃,反应时间为12小时条件下,可得到电阻率为0.084Ω˙cm,且包覆层较均匀、致密的PAOSCF。聚苯胺包覆层较好的改善了其分散稳定性。采用XPS对PAOSCF进行元素分析,发现导电聚苯胺与氧化处理后短碳纤维表面的含氧官能团发生了化学键合作用,生成了新的CO-N键,验证了导电聚苯胺包覆短碳纤维的设计模型。采用微波矢量网络测量仪测量了PAOSCF的电磁性能,结果发现:聚苯胺包覆提高了短碳纤维复介电常数的实部和虚部,有利于对电磁波的吸收损耗,但对复磁导率没有影响,因为导电聚苯胺为电损耗性材料。添加磁性物质,采用原位聚合法,制备了导电导磁改性短碳纤维。采用EDS和XPS对导电聚苯胺/磁性物质在短碳纤维表面的包覆机理分析,发现导电聚苯胺与磁性物质之间形成了Fe…O-C-键的键合作用,通过这种键合作用导电聚苯胺把磁性物质包裹在里面,然后与短碳纤维表面的含氧官能团形成新的CO-N键,包覆在短碳纤维的表面,形成包覆层完整、致密的改性短碳纤维。验证了导电聚苯胺/磁性物质包覆短碳纤维的设计思想。采用微波矢量网络测量仪测量了导电导磁短碳纤维的电磁性能。结果表明:磁性物质的引入提高了材料的复磁导率,从而提高了其磁性损耗;但磁性物质破坏了导电聚苯胺的结构和导电通路的连续性,致使材料的介电性能有所下降。针对屏蔽涂层导电而致的短路等缺点,探索性的提出制备不导电聚苯胺包覆的短碳纤维,研究发现表面不导电的改性短碳纤维对电磁波具有一定的衰减损耗,且体现出弱磁损耗特性。本文完成了频率f<2GHz下改性短碳纤维体系从成分、结构到屏蔽性能的计算机辅助设计,为评估复合填料应用于涂料的屏蔽性能提供了新的思想。把改性短碳纤维应用于涂料体系,制备了多涂层屏蔽功能材料。实验表明:采用聚苯胺以及聚苯胺/磁性物质包覆改性短碳纤维可提高材料的吸收损耗,符合新型屏蔽材料的发展方向。更多还原

【Abstract】 In recent years short carbon fibers (SCF) have been received increasing attention, due to their high strength and modulus, good conductivity and low density which makes them suitable for light-weight shielding materials. However, there are two obvious weaknesses in the electromagnetic shielding coatings filled with SCF, the poor dispersion stability of SCF in coatings and the lower electromagnetic characteristic of SCF materials difficult to reach the application demands of new shielding materials. One of the effective methods to improve the performances is the material composite technology. In this dissertation, several coated models were proposed to fabricate composite materials to improve the dispersion stability and electromagnetic of modified SCF based on the electromagnetic, materials science theory and effective electromagnetic parameters theory of the composite materials. The effective electromagnetic equations were deduced based on the theory of the composite materials effective mediums. Multilayer electromagnetic shielding materials were prepared by the modified SCF. The research results afford theory and technology guidance, meanwhile it may give a new design method and experiment base for the same composite materials.From physics and materials science point of view, models of conducting polyaniline-coated SCF and conducting polyaniline and magnetic materials-coated SCF were proposed to improve the performance of SCF. The effective parameters equations about the fiber composites were educed. Theoretic base was afforded to this dissertation.According to single layer coated effective electromagnetic parameters theory and the conducting polymer coated SCF model, the conducting polyaniline-coated SCF (PAOSCF) was prepared. Conducting polyaniline was polymerized by in-situ polymerization and subsequent deprotonation on the surface of oxidized SCF. The effect of nAPS/AN, hydrochloric acid concentration, reaction temperature and reaction time on the structure and electric properties of polyaniline-coated SCF were studied. It was found that use of ultrasonic dispersion improved the rate of reaction and decreased the polymerization time. In the experiment condition of the dissertation, when the nAPS/AN 1.5, hydrochloric acid concentration 1.0mol/L, reaction temperature 10℃±3℃, and reaction time 12h,the PAOSCF with 0.084?˙cm surface resistance, good adhesion and compact coated layer were obtained. XPS element analysis of PAOSCF is shown that PANI bonded on the surface of oxidized SCF with–CO-N- chemical bonds, which is consistent with the design model of polyaniline-coated SCF. It was also found that polyaniline coated layer can enhance the complex permittivity of PAOSCF, propitious to increasing absorption loss. However, the complex permeability is 1-0j, because conducting polyaniline is electrical loss material.According to complex composite effective electromagnetic parameter theory, the conducting polyaniline and magnetic powders coated SCF were prepared. The mechanism of the conducting polyaniline and magnetic powder coating on oxidized SCF was studied by EDS and XPS. The results indicated that the Fe…O-C- chemical bonds were formed between polyaniline and magnetic powder, the polyaniline coated magnetic powder formed a conducting and magnetic layer on the surface of oxidized SCF with–CO-N- chemical bonds, which is consistent with the design model of conducting polyaniline and magnetic -coated SCF. The complex permittivity and complex permeability of conducting polyaniline and magnetic -coated SCF was studied. The results showed that magnetic powders can improve complex permeability, and improve magnetic loss of modified SCF, but the dielectric performance of modified SCF is decreased because magnetic powder may break the structure of conducting polyaniline and the gateway of electron.Non-conducting polyaniline coated SCF (NPASF) was studied and exploited to meet the especial demand of shielding materials for protecting the electronic equipments which do not form short circuit on the surface. The results showed that NPASCF with low magnetic loss took on electromagnetic wave attenuation characteristic.Finally, the analysis of the component, structure to CAD of shielding performance of the modified SCF system f<2GHz was completed in the dissertation. This CAD method may give a new method to evaluate the shielding effect of composite fillers applied in coating. The modified SCF coatings were prepared. The results of the shielding effectiveness showed that the modified SCF system can improve the absorption loss, according with the development direction of new shielding materials.更多还原