论文标题:碳纳米管/低密度聚乙烯/聚苯乙烯导电复合材料的制备及性能研究
Preparation and Properties of Conductive Composites of Carbon Nanotube/Low Density Polyethylene/Polystyrene
论文作者
论文导师 张清华,论文学位 硕士,论文专业 材料加工工程
论文单位 东华大学,点击次数 56,论文页数 82页File Size4647K
2007-12-01论文免费下载 http://paper.dic123.com/lunwen_4938437/
carbon nanotubes;; conductive composite;; low density polyethylene;; polystyrene;; percolation threshold
填充型导电高分子材料已广泛应用于电子、能源、化工、宇航等领域,被认为是最有发展前景的导电高分子材料之一。自从1991年Iijima发现碳纳米管以来,由于其所具有的电学、力学等性能,受到了广泛的关注,是材料领域最前沿的研究领域之一,碳纳米管/聚合物导电复合材料的研究取得了很大的进展。 本文以聚苯乙烯(PS)和低密度聚乙烯(LDPE)为基体,以多壁碳纳米管(MWNT)为导电填料,采用熔融共混加工技术,制备了一系列的导电复合材料,对复合材料的形态、结构与性能进行了系统的研究。主要开展了以下几个方面的研究工作: 1.对两相MWNT/PS和MWNT/LDPE导电复合材料及三相MWNT/LDPE/PS复合材料的电学性能进行了研究。研究结果表明,三者均表现出很好的导电性能;但他们的导电渗滤行为有明显差别,两相体系的渗滤阈值分别为6wt%和8wt%的MWNT含量,当LDPE/PS的组成为50/50时,多相体系的渗滤阈值仅为4wt%。对复合材料的PTC效应的研究发现,多相复合材料的PTC效应与LDPE的变化有关,且与MWNT/LDPE的PTC行为类似。 2.使用光学显微镜和SEM对复合材料的形貌观察表明,MWNT选择性的分布于LDPE相中,且LDPE与PS在很大的组成范围内形成双连续相结构,从而有利于形成导电的"双重渗滤",降低多相复合体系的渗滤阈值,改善材料的力学和可加工性能。 3.动态流变的研究表明,多相复合材料的复数粘度、损耗模量、储能模量都随MWNT含量的变化出现相同的变化趋势。在低频区,当MWNT含量低于3wt%时,复合材料的流变行为对频率有一定的依赖性,随MWNT含量的增大,高于3wt%后,复合材料的流变行为对频率不敏感,出现类固体行为;"第二平台"的出现表明,MWNT在材料中形成了网络结构。动态流变对相分离的研究表明,MWNT的加入,使得复合材料的相分离温度降低,复合材料的相分离趋势加强。 4.MWNT/LDPE/PS多相导电复合体系表现出不同的流变渗滤行为和导电渗滤行为,流变阈值3wt%,而导电阈值4wt%,这主要因为导电和流变出现渗滤阈值所要求的MWNT之间的间距有所不同。 5.对复合材料的结晶性能的研究表明,MWNT/LDPE和MWNT/LDPE/PS的结晶和熔融行为相似,一定程度上说明了MWNT选择性的分布于LDPE相中。MWNT的加入对于LDPE的晶型没有明显影响,但是结晶度降低,结晶速度变慢。 6.多相复合材料的力学性能随MWNT含量的增加而提高。
Conductive polymer composites have been extensively used in many fields,such as electronic,energy and chemical engineering.The discovery of carbon nanotubes (CNTs)by Iijima in 1991 has brought a widespread research because of their unique electronic,mechanical and other properties.The application of carbon nanotube as conductive filler in polymer composites has been paid attention. In this thesis,A series of ternary and binary conductive polymer composites of polystyrene(PS),the low density polyethylene(LDPE)and multi-walled carbon nanotube(MWNT)were prepared by melt-mixing method.The work is summarized as following: 1.The conductive properties of the binary composites of MWNT/PS and MWNTT/LDPE,as well as the ternary one of MWNT/LDPE/PS,were prepared via melt processing.The electrical percolation thresholds of MWNT/LDPE and MWNT/PS are 8 wt%and 6 wt%of MWNT loadings,respectively.whereas,the ternary multiphase of MWNT/LDPE/PS with a composition of LDPE/PS(50/50) exhibits a low electrical percolation,being 4 wt%MWNT loading.The positive temperature coefficient(PTC)effect of ternary conductive composites is similar to MWNT/LDPE,which is related to the LDPE domain"s transition. 2.Optical microscope and scanning electron microscope(SEM)were employed to observe the morphology of the conducive composites and the distribution of the carbon nanotubes in composites.As a result,the matrix polymers of LDPE and PS form co-continuous phases in polymer blends,and the carbon nanotubes preferably locate in LDPE phase and produce electrically conductive path.The formed "double percolation threshold" results in the decrease of the loading of conducting fillers,and the mechanical properties and processability of the multi-phase composites are thus improved. 3.The measurement of dynamic rheology shows that the multiphase composites exhibit a very strong shear thinning effect.At low frequencies,the rheological behavior of the composites gives an obvious dependence of frequency for <3.0 wt% MWNT.At high frequencies,the fraction of MWNT has a slight influence on the rheological behavior of the composites.The results indicate a solid-like behavior formed in the composites,which suggests the formation of a nanotube network. Moreover,the addition of MWNT in the multiphase composite leads to the phase-separate temperature shifting to low temperature. 4.The multiphase composites of MWNT/LDPE/PS exhibits a difference between rheological percolation and electrical percolation,being 3%and 4%loadings of the carbon nanotubes,respectively.We understand this difference in terms of the nanotube distance required for electrical conduction,as compared to the distance for impeding polymer motion. 5.DSC was used to analyze the crystallization and to study crystalline kinetics of the ternary composites.The spectra and data indicate that the crystallization and melt behavior of MWNT/LDPE/PS is similar to MWNT/LDPE,revealing MWNT selectively located in LDPE domain.The addition of MWNT does not change the crystal form of LDPE;whereas,crystallization rate and crystallinity of the multiphase composites decrease due to LDPE molecular chain movement hindered by MWNT during crystallization. 6.The addition of MWNT improves mechanical properties of the multiphase composites,resulting in the increase of tensile strength.
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