【作者】 张海龙；

【导师】 徐樑华；

【作者基本信息】 北京化工大学 ， 材料科学与工程， 2010， 博士

【摘要】 碳纳米管(CNT)是纳米管状材料,独特的结构使其具有优异的力学、电学和磁学性能等,在复合材料中受到广泛的关注。丙烯腈聚合物(PAN)是高性能碳纤维的主要前驱体。用碳纳米管改性丙烯腈聚合物,将有可能获得特殊性能的碳纤维。本论文对碳纳米管表面进行修饰,将其引入到丙烯腈聚合物中,围绕PAN分子结构的形成及演变的规律,研究了碳纳米管表面官能团特性对丙烯腈聚合物化学结构、纤维成纤过程中聚集态结构、以及对聚丙烯腈大分子链热氧化环化行为的影响规律。通过系统的实验和理论分析,进一步丰富了碳纳米管／丙烯腈聚合物体系的学术内涵,为持续的科学技术研究奠定了良好的基础。对纯化的碳纳米管进行酸化和胺化修饰,分别得到表面含羧基、羟基官能团(Acid-CNT)和含胺基官能团的碳纳米管(Amid-CNT)。采用红外光谱、X射线光电子能谱(XPS)、拉曼光谱和透射电子显微镜对改性后的碳纳米管进行了表征。结果表明：原始的碳纳米管纯化后,去除了其内的金属催化剂和无定型碳等杂质。红外光谱分析表明：双氧水修饰后的碳纳米管,其表面接枝上了羧基和羟基官能团。XPS测得其表面氧元素的相对含量较原始碳纳米管增加。Acid-CNT酰氯化和胺化后,碳纳米管的表面含有胺基官能团,XPS测得其表面含有氮元素。以水相沉淀原位聚合的方法制得了碳纳米管／丙烯腈(共)聚合物复合材料,用自由基溶液聚合制得了碳纳米管／聚丙烯腈复合纺丝液。采用湿法纺丝技术得到不同牵伸倍数的复合纤维。研究了碳纳米管表面官能团特性对丙烯腈(共)聚合物化学结构的影响。红外光谱分析结果表明：碳纳米管表面不同的官能团对丙烯腈均聚物(PAN)分子链上氰基的水解有一定的影响,使Acid-CNT/PAN复合材料中氰基的含量增加,而Amid-CNT/PAN复合材料中含有更多的酯基。对于丙烯腈共聚物(PANIA), Acid-CNT表面的羟基与PANIA分子链上的羧基发生相互反应,生成了酯基,使复合材料中羧基的相对含量减少；Amid-CNT表面的胺基与PANIA分子链上的羧基发生化学反应也使复合材料中羧基的相对含量减少。通过扫描电镜分析得知：原位聚合后得到的复合材料,碳纳米管分散比较均匀。通过拉曼光谱分析得知：Amid-CNT与丙烯腈(共)聚合物之间的相互作用强于Acid-CNT/丙烯腈(共)聚合物。研究了碳纳米管表面官能团特性对复合材料聚集态结构的影响。对于丙烯腈均聚物,CNT的加入降低了复合材料的结晶度,却提高了复合材料的晶粒尺寸。对于丙烯腈共聚物,CNT的加入使复合材料的结晶度和晶粒尺寸均增加。在PANIA成纤过程中,CNT的加入使复合纤维的结晶度降低。随着牵伸倍数的增加,复合纤维与PANIA纤维之间结晶度的差值变大。对于凝固丝,复合纤维比PANIA纤维有较大的晶粒尺寸；而对于一牵丝和原丝,复合纤维比PANIA纤维的晶粒尺寸小。Amid-CNT对晶粒尺寸的影响较Acid-CNT大。碳纳米管在复合纤维中的取向随着牵伸倍数的增加而增大,复合纤维中晶区的取向较PANIA纤维低,而其氰基的取向较PANIA纤维高。通过子午扫描得知,Amid-CNT复合原丝中含有螺旋型构象,而PANIA原丝中只有锯齿型构象。丙烯腈聚合物在热处理过程中发生复杂的化学反应,分别采用红外光谱、差式扫描量热仪和扫描电子显微镜研究了碳纳米管表面的不同官能团对此过程的影响。对于丙烯腈均聚物,空气气氛下,Amid-CNT/PAN复合材料比其具有更低的起始放热温度和环化放热温度。对于丙烯腈共聚物,空气气氛下,Acid-CNT/PANIA复合材料的放热量比其低,而Amid-CNT/PANIA复合材料的放热量比其高。碳纳米管的加入降低了丙烯腈(共)聚合物的玻璃化转变温度。在丙烯腈聚合物成纤过程中,空气气氛下,Amid-CNT/PANIA复合纤维比PANIA纤维具有低的起始放热温度和环化放热温度,以及低的放热量。在空气中,经过相同热处理条件的纤维,Amid-CNT/PANIA复合纤维具有较高的相对环化率和密度。对于热处理后纤维的放热效应,空气气氛下,Acid-CNT/PANIA复合纤维的放热量比PANIA纤维高,而Amid-CNT/PANIA复合纤维的放热量比PANIA纤维低。通过扫描电镜分析分析得知,热处理后的复合纤维断面比PANIA更加不规整。通过非等温DSC方法研究了碳纳米管表面官能团特性对PANIA纤维热化学反应动力学的影响。结果表明：在氮气气氛下,碳纳米管的加入使复合纤维的环化反应活化能提高,其中Acid-CNT/PANIA复合纤维的活化能为177.62KJ/mol,Amid-CNT/PANIA复合纤维的活化能为158.30KJ/mol,而PANIA纤维的活化能为156.45KJ/mol。在空气气氛下,PANIA纤维、Acid-CNT/PANIA复合纤维和Amid-CNT/PANIA复合纤维的环化反应活化能分别为211.18KJ/mo、200.39KJ/mol和149.76KJ/mol,而氧化反应的活化能分别为136.74KJ/mo、140.63KJ/mol和143.58KJ/mol。碳纳米管的加入对PANIA热化学反应的反应级数影响不是很大,均近似为一级反应。更多还原

【Abstract】 Carbon nanotubes (CNT) are the nano-tube materials with the remarkable mechanical properties, electrical properties and magnetic properties owing to the unique structure. So the CNT in the composite was focused by many researchers. Acrylonitrile polymer (PAN) is the main precursor for manufacturing the high strength carbon fiber. The addition of CNT into the PAN polymer would obtain the excellent properties for the carbon fiber. In this paper the CNT was modified by different methods, and then was added into the PAN matrix. According to the formation and evolving of the PAN molecular structure, the CNT with different function groups on the chemical structure of acrylonitrile polymer, the aggregation structure of acrylonitrile polymer during spinning, the heat chemical reaction for the acrylonitrile polymer were studied, respectively. Through the systemic experiment and theoretical analysis, the academic contents were enriched by the CNT/acrylonitrile polymer, which laid a solid foundation for the continuous scientific and technological research. The purified CNT was modified by hydrogen peroxide and triethylenetetramine to obtain the carboxylic acid and hydroxyl group on the surface of CNT (Acid-CNT) and the amide-groups on the surface of CNT (Amid-CNT), respectively. The modified CNT were characterized by Fourier transform infrared spectrum (FTIR), X-ray photoelectron spectroscopy (XPS), Raman spectrum and Transmission electron microscopy (TEM). The results showed that the metal catalyst and amorphous carbon in the pristine CNT disappeared after purification. The results from the FTIR spectrum showed that the surface of CNT contained the carboxylic acid and hydroxyl groups after modification by hydrogen peroxide. The content of oxygen element on the surface of CNT was increased through XPS analysis. After modification by thionyl chloride and triethylenetetramine for the Acid-CNT, the amide-groups were grafted onto the surface of CNT. The surface of Amid-CNT have new element-nitrogen element by XPS analysis.The different function CNT/acrylonitrile (co-)polymer composite were synthesized by aqueous deposition in situ polymerization. The composite spinning solutions were prepared by radical solution polymerization, and the different drafting composite fibers were obtained by wet spinning method. The Effects of functional CNT on the chemical structure for the acrylonitrile (co-)polymer were studied. The results from the FTIR spectrum showed that the hydrolysis of nitrile groups for the PAN homopolymer was affected by the different functional groups on the surface of CNT. The Acid-CNT/PAN composite have more nitrile groups than PAN homopolymer, and the Amid-CNT/PAN composite have more ester groups. For the acrylonitrile copolymer (PANIA), the hydroxyl groups on the surface of Acid-CNT had reacted with the carboxylic acid groups on the molecular chain of PANIA polymer and formed the ester groups, which made the Acid-CNT/PANIA composite having lower relative content of carboxylic acid groups than the PANIA polymer. The amide-groups on the surface of Amid-CNT had reacted with the carboxylic acid groups on the molecular chain of PANIA polymer, which made the Amid-CNT/PANIA composite having lower relative content of carboxylic acid groups than the PANIA polymer. After in situ polymerization, the CNT could be homogeneously dispersed into composite by Scanning electron microscopy (SEM) analysis. The interfacial interaction between the Amid-CNT and acrylonitrile (co-)polymer composite was stronger than that of the Acid-CNT/acrylonitrile (co-)polymer composite by Raman spectrum analysis.The effects of functional CNT on the aggregation structure were studied. For the PAN homopolymer, the addition of CNT decreased the degree of crystallization, and improved the size of crystalline for the composite. For the PANIA polymer, the addition of CNT increased the degree of crystallization and the size of crystalline for the composite, respectively. The CNT/PANIA composite fiber had lower degree of crystallization than the PANIA fiber during spinning. However, the composite nascent fiber had higher size of crystalline than the PANIA nascent fiber. For the first-drafting fiber and precursor fiber, the composite had lower size of crystalline than the PANIA fiber. The Amid-CNT has bigger influence compared with the Acid-CNT on the size of crystalline during spinning. The degree of orientation for CNT in the composite fiber increased with the drafting, which made the composite having lower crystal region orientation than the PANIA fiber. But the composite had higher nitrile group orientation than the PANIA fiber. The Amid-CNT/PANIA composite precursor fiber had helical conformation, and the PANIA precursor fiber only had zigzag conformation by meridional scan analysis.The acrylonitrile (co-)polymer took place complex reactions during the processing of heat treatment. The effects of different function CNT on those evolving were characterized by FTIR spectrum, DSC and SEM images. The Amid-CNT/PAN composite had lower initiation temperature and cyclization temperature than PAN homopolymer in air atmosphere. The Acid-CNT/PANIA composite had lower evolved heat than the PANIA polymer, but the Amid-CNT/PANIA composite had higher evolved heat than the PANIA polymer in air atmosphere. Moreover, the addition of CNT decreased the glass transition temperature of acrylonitrile (co-)polymer. During the spinning, the Amid-CNT/PANIA composite fiber had lower initiation temperature, cyclization temperature and evolved heat compared with PANIA fiber in air atmosphere. After the same heat treatment in air atmosphere, the Amid-CNT/PANIA composite fiber had higher relative cyclization ratio and density compared with PANIA fiber. For the exothermic effect of the heated fiber, the Acid-CNT/PANIA composite fiber had higher evolved heat than the PANIA fiber, and the Amid-CNT/PANIA composite fiber had lower evolved heat. The break sections of composite fiber with heat treatment became irregular compared with the heated PANIA fiber by SEM image analysis.The effects of the different function CNT on the kinetics for the PANIA fiber during heat chemical reaction were studied by non-isothermal DSC methods. The results showed that addition of CNT improved the activation energy of the cyclization reaction compared with PANIA fiber in nitrogen atmosphere. The activation energy of the Acid-CNT/PANIA composite fiber, Amid-CNT/PANIA composite fiber and PANIA fiber is 177.62KJ/mol, 158.30KJ/mol and 156.45KJ/mol, respectively. In air atmosphere, the activation energy of cyclization reaction for the PANIA fiber, Acid-CNT/PANIA composite fiber and Amid-CNT/PANIA composite fiber is 211.18KJ/mol,200.39KJ/mol and 149.76KJ/mol, respectively. The activation energy of oxygen reaction for the PANIA fiber, Acid-CNT/PANIA composite fiber and Amid-CNT/PANIA composite fiber is 136.74KJ/mol,140.63KJ/mol and 143.58KJ/mol, respectively. The addition of CNT did not greatly influence the order reaction for the PANIA fiber during heat treatment, which was close to the first order reaction.更多还原