【作者】 刘玉兰；

【导师】 王延相；

【作者基本信息】 山东大学 ， 材料学， 2011， 硕士

【摘要】 利用原位聚合和溶液共混的方式制备出了聚丙烯腈基碳纳米管复合材料。使用傅立叶变换红外光谱仪(FTIR)、热重分析仪(TG)、扫描电镜(SEM)、透射电镜(TEM)、R/SCC同轴圆柱体流变仪、X-射线衍射仪(XRD)、差示扫描热量仪(DSC)等测试方法研究了碳纳米管纯化前后的结构与性能的变化,并且利用以上分析手段研究了碳纳米管对聚丙烯腈基碳纳米管复合材料的结构和性能的影响,利用Fluke 1508型绝缘电阻测试仪测试复合薄膜的表面电阻率研究发现,利用浓硝酸在常温下可以很好的除去碳纳米管(CNTs)中的杂质,同时在没有破坏碳纳米管本身优良的长径比结构的前提下接枝上COOH、OH基团。同时对碳纳米管在不同溶剂中的溶解程度进行了研究,结果表明,碳纳米管在DMAc中分散性最好,碳纳米管在不同溶剂中分散性为：DMAc>DMSO>DMF。对原位聚合法制备的复合材料进行了转化率及结构形态的研究,结果表明：碳纳米管对复合材料的转化率产生影响,随着碳纳米管含量的增加,反应转化率逐渐升高,但当含量高于0.3%时聚合反应的转化率开始下降；通过对制得的复合材料进行FTIR、DSC、XRD测试可以看出,PAN可以有效的接枝到碳纳米管上使聚合粉料的预氧化温度提前,放热量和放热速率均降低,这有效的避免了预氧化过程中的集中放热；碳纳米管使其结晶程度也有所减弱,但并没有改变聚合物的结晶晶型,只是有序度改变了；对复合薄膜的断面进行SEM观察,结果表明,PAN基复合材料的导电性能明显提高,碳纳米管的单根分散为增强复合材料提供了可能。通过溶液共混法制备复合溶液并对其流变性能进行了研究。结果表明,在低剪切速率下,随着碳纳米管含量的增加,复合溶液的表观粘度出现减小趋势,但当其含量超过0.5%时,复合溶液表观粘度又出现增大趋势,这证实了纳米粒子在含量较低时,增稠作用只有在较高剪切速率下才能体现出来；并且在碳纳米管含量较低时,随着测试温度的升高,溶液表观粘度的减小趋势减弱,说明此时溶液粘度对温度表现的敏感；随着碳纳米管含量的进一步提高,溶液的粘度逐渐增大,结构化程度提高,物理稳定性变差,可纺性难度增大,但整体变化不大,其对剪切速率的变得敏感。对复合材料进行了DSC测试可以看出,溶液共混同样可以改善复合材料的热性能,减少复合材料集中放热的可能；通过XRD测试表明,预氧化后复合材料的结晶峰由2θ≈17°转移到20≈25°附近,这是代表材料芳构化结构的峰,说明复合材料在较低的预氧化温度下就完成了很好的环化而纯PAN在该处的峰则不十分明显。两种材料经400℃低温碳化后,在10°～40°之间均产生了一个肩峰,说明在400℃下材料均已完成环化作用,二者的不同只是体现为材料有序区与无序区分布的不同。对材料进行FTIR、TEM研究表明,碳纳米管在复合薄膜中主要以物理结合形式存在,但在预氧化阶段对环化有促进作用,C≡N和CH2等一些主要吸收特征峰逐渐减弱并消失,而C=C和C=N基团的伸缩振动峰逐渐出现并增强,同时复合薄膜中的C≡N降低量明显高于纯PAN的。当碳纳米管的含量达到2%时,复合薄膜的环化率达到70.41%,而纯PAN环化率仅为20.24%,碳化阶段碳纳米管对材料的影响不大；碳纳米管在复合材料中部分呈单根分散状态,但也有很多团聚结构存在对复合薄膜的表面电阻率的研究表明,当碳纳米管含量达到5%时,复合薄膜的表面电阻率由大于104MΩ迅速变为5.74 MΩ,但碳纳米管含量再增加时电阻率变化不大,说明碳纳米管一旦在薄膜材料中形成网络结构,材料的导电性能就迅速增强。更多还原

【Abstract】 In this paper polyacrylonitrile (PAN)-based carbon nanotubes (CNTs) composite were produced by insitu polymerization and solution blending. Effects of CNTs content on the structure and the performance of composite were studied. The structure and proformance of CNTs before and after treated with structures and properties of composite were observed, which were characterized by Fourier transform infrared spectroscopy (FTIR), Raman spectra (LRS), X-ray diffraction (XRD), thermal gravimetric analysis (TG), differential scanning calorimetry (DSC), R/SCC coaxial cylinder rheometer, scanning electron microscopy (SEM) and transmission electron microscopy(TEM). The surface resistivity of composite film was tested by using Fluke 1508 type insulation resistance tester.It has been found that we can remove the impurities of CNTs by using nitric acid (65%) in room temperature very well, and can graft-COOH,-OH group onto the CNTs whitout disrupting the excellent length-diameter ratio stucture of CNTs. The dispersion for CNTs in different solvent was tested as follows:dimethylacetamide (DMAc)>dimethylsulphoxide (DMSO)>dimethyl formamide (DMF) in room temperature.Composites which produced by insitu polymerization were studied and found some phenomenon as follows:with the increase of the content of CNTs, the reactions conversion increased gradually, but when the content reached to 0.3%, the conversion began to decline; at the same time, the preoxidation temperature of polymer was in advance because of CNTs, and alleviated the exothermic reaction, all of which would improve the peoperty of PAN; in some extent, it hindered polymer crystallization, but the structure and crystal of polymer could change.The investigation on the composites solution rheology showed that the viscosity reduces fristly and then increases with the CNTs content increases, which was produced by solution blending. Solution viscosity became lower when the CNTs content achieved 0.5%, but in high shear rate this phenomenon disappeared, this indicated that thickening role can be reflected with low content of CNTs. The viscosity and the structure viscous index became higher, the Non-Newtonian index was smaller and the physical stability was worse while the content of CNTs was higher. The solution was temperature-sensitive with the low content of CNTs but was tended to be shearing-sensitive with the higher one.The analysis of DSC、XRD showed that the carbon nanotubes could improve the thermal properties of composite materials, and alleviated the exothermic reaction. During the preoxidation process the position of crystallization of composite was varied from 20≈16°to 29≈25°, which suggested the structure of aromatization appear; in addition, they produced a shoulder peak at about 20≈10°～40°in carbonization stage, the cyclization was completed, it had different distribution of the order and the disorder region.The analysis of FTIR showed that during the preoxidation process the stretching vibrations of nitrile (C≡N) and the methane group (CH2) decreased and nearly disappeared such as C=C and C=N during the preoxidation process(255℃), which represented the ladder structure appeared and became stronger gradually. At the same time the dope of C=N group in composite film decreased quickly than that the formed pure PAN, and the cycilzation rate of film increased from 20.24% to 70.41%, when the content of CNTs was 2%, however, the effect of CNTs was not basically discovered in carbonization stage (400℃). On one hand, the part of carbon nanotubes in the composites was in a single dispersion state, on the other hand, the aggregate structure of the carbon nanotubes was found.When the content of CNTs reached to 5%. the surface resistivity of composite film reduced to 5.74 MΩfrom> 104 MΩquickly, and it has a little change with the content of CNTs increase.更多还原