【作者】 王博；

【导师】 郑昌佶；

【作者基本信息】 哈尔滨理工大学 ， 电气工程， 2023， 硕士

【摘要】 随着纳米技术的发展,纳米SiO₂颗粒掺杂改性聚乙烯使得聚乙烯的介电性能和力学性能都有一个质的飞跃。纳米SiO₂颗粒在复合材料中的分散性对其宏观介电性能有重要影响,然而,纳米颗粒在LDPE基体中不能均匀的分散,容易引起大颗粒的团聚是纳米复合材料制备的重要难题。本文利用电子万能拉力机对制备好的纳米复合材料进行超拉伸处理,获得了具有不同分散性的SiO₂/LDPE纳米复合材料,并对其进行了结构表征和直流电学性能测试,研究了超拉伸对LDPE及SiO₂/LDPE复合材料的微观结构和直流介电性能的影响。研究结果表明,超拉伸处理会改善纳米SiO₂的团聚,使SiO₂颗粒在LDPE中可以均匀分散。同时,超拉伸会在某种程度上破坏聚合物和纳米复合材料的晶体结构,从而导致结晶规整性的破坏,从而对材料的整体性能产生负面影响。变温空间电荷测试结果表明,超拉伸会使得SiO₂/LDPE在高温下仍具备优良的空间电荷抑制能力,SiO₂/LDPE复合材料的空间电荷积累受抑制的主要原因是SiO₂与LDPE间的界面区。分析SiO₂/LDPE复合材料超拉伸后空间电荷抑制能力提高的原因是SiO₂颗粒分散性提升,界面区比例增加,深陷阱密度增加。对SiO₂/LDPE纳米复合材料进行了电导电流测试,发现其比LDPE低很多,超拉伸的SiO₂/LDPE在高温下的电导特性优于LDPE,超拉伸产生的结构劣化并未显著劣化纳米复合材料的电导特性。对SiO₂/LDPE复合材料的电导率数据运用COMSOL软件结合直流电缆模型进行电场仿真,结果表明,SiO₂/LDPE复合材料引入的深陷阱导致电导活化能增加,电场发生畸变,但经超拉伸处理后电场畸变得到抑制。TSC测试结果表明,超拉伸处理的SiO₂/LDPE复合材料并未出现新的电流峰,LDPE和SiO₂/LDPE对应的电流峰面积增加,温度微降。击穿强度测试的分析中可看出,超拉伸导致的分子链结构和结晶结构的缺陷是击穿强度降低的主要原因,对LDPE基体的劣化作用导致其击穿场强降低,纳米SiO₂的掺杂引入的深陷阱可使复合材料在高温下保持较高击穿强度。本文的研究证实,复合材料的超拉伸处理尽管会带来分子链的断裂、缠结等缺陷以及结晶结构的破坏,但超拉伸可以有效提高LDPE基体中纳米颗粒的分散性,改善纳米粒子的团聚问题,对复合材料的介电性能产生有着积极影响。更多还原

【Abstract】 With the development of nanotechnology,the doping of nano-SiO₂particles to modify polyethylene has led to a qualitative leap in the dielectric and mechanical properties of polyethylene.The dispersion of nano-SiO₂particles in the composites has an important influence on their macroscopic dielectric properties,however,the inability of nano-particles to be uniformly dispersed in the LDPE matrix and the tendency to cause agglomeration of large particles are important challenges in the preparation of nano-composites.In this paper,the prepared nanocomposites were subjected to overstretching treatment using an electronic universal tensile machine to obtain SiO₂/LDPE nanocomposites with different dispersions,and their structural characterization and DC electrical properties were tested to investigate the effects of overstretching on the microstructure and DC dielectric properties of LDPE and SiO₂/LDPE composites.The results show that the hyperstretching treatment will improve the agglomeration of SiO₂nanoparticles,so that the SiO₂particles can be uniformly dispersed in the LDPE.At the same time,hyperstretching will to some extent disrupt the crystal structure of the polymer and nanocomposites,thus leading to a disruption of the crystalline regularity and thus negatively affecting the overall properties of the material.The results of variable temperature space charge tests show that hyperextension causes SiO₂/LDPE to have excellent space charge suppression even at high temperatures and that the main reason for the suppressed space charge accumulation in SiO₂/LDPE composites is the interfacial region between SiO₂and LDPE.The analysis of the improved space charge suppression ability of SiO₂/LDPE composites after superstretching is due to the improved dispersion of SiO₂particles,the increased proportion of interfacial zone and the increased deep trap density.The conductivity currents of the SiO₂/LDPE nanocomposites were tested and found to be much lower than those of LDPE.The conductivity properties of the superstretched SiO₂/LDPE were better than those of LDPE at high temperatures,and the structural degradation resulting from superstretching did not significantly degrade the conductivity properties of the nanocomposites.The conductivity data of the SiO₂/LDPE composites were simulated using COMSOL software in combination with a DC cable model,and the results showed that the deep trap introduced into the SiO₂/LDPE composites led to an increase in conductivity activation energy and distortion of the electric field,but the electric field distortion was suppressed after the superstretching treatment.composites did not show new current peaks,the area of the corresponding current peaks for LDPE and SiO₂/LDPE increased and the temperature decreased slightly.The analysis of the breakdown strength tests shows that the defects in the molecular chain structure and crystalline structure caused by the hyperextension are the main reasons for the reduction in breakdown strength,the degradation of the LDPE matrix leads to a reduction in its breakdown field strength,and the deep traps introduced by the doping of nano-SiO₂allow the composites to maintain a high breakdown strength at high temperatures.The study confirms that the superstretching of composites can effectively improve the dispersion of nanoparticles in the LDPE matrix,improve the agglomeration of nanoparticles and have a positive impact on the dielectric properties of the composites,despite the defects such as molecular chain breakage and entanglement as well as the destruction of the crystalline structure.更多还原