【作者】 李文华；

【导师】 陈小华；

【作者基本信息】 湖南大学 ， 材料物理与化学， 2008， 博士

【摘要】 碳纳米管独特的结构和优异的性能,已引起人们利用它们制备纳米复合材料的极大兴趣。然而,CNTs表面呈化学惰性,使其在聚合物基体中的分散性差,与基体材料难以形成牢固结合,从而限制了其应用范围。要发挥碳纳米管改性复合材料的先进性,必须在界面结构及性质设计的基础上,对碳纳米管进行有效的修饰。本论文首先对碳纳米管进行表面修饰处理,制备得到了6种功能化碳纳米管;在此基础上,选择聚丙烯(PP)作为基体材料,利用这6种功能化的碳纳米管对其进行改性,制备得到了多种碳纳米管/聚丙烯复合材料,研究了改性前后复合材料的力学、热学及电学等性能。研究具有基础性和前瞻性,具有广泛的应用前景。首先,利用氢氧化钠对碳纳米管进行修饰,得到了羟基化碳纳米管(HO-CNTs);在此基础上,利用甲醛的亲电性,对碳纳米管进行修饰处理得到了羟甲基碳纳米管(HOCH2-CNTs)。进一步使HO-CNTs和HOCH2-CNTs分别与MAH发生酯化反应,制备得到接枝了MAH的羟基碳纳米管(MAH-CNTs)和接枝了MAH的羟甲基碳纳米管(MAH-OCH2-CNTs)。结果显示:通过氢氧化钠和甲醛对碳纳米管的修饰,在其表面引入了一定数量的羟基和羟甲基;与MAH反应后,羟基消失,MAH通过酯基被引入到了碳纳米管的表面;四种修饰方法均未改变CNTs的骨架结构,这对于发挥CNTs的优良力学性能非常重要;同时,被修饰过的CNTs在有机溶剂中有较好的溶解性,为下一步利用溶剂法制备CNTs/PP复合材料打下了基础。其次,利用HO-CNTs和MAH-CNTs两种修饰碳纳米管,根据MAH与PP复合顺序的先后,采用溶液法分别制备了CNTs/MAH/PP、MAH-CNTs/PP及CNTs/MAH-PP复合材料,研究了修饰CNTs含量对复合材料性能的影响。利用HOCH2-CNTs和MAH-OCH2-CNTs,根据MAH加入与否以及与PP复合顺序的先后,分别制备了HOCH2-CNTs/PP、MAH-OCH2-CNTs/PP、HOCH2-CNTs/MAH/PP和HOCH2-CNTs/MAH-PP复合材料,并研究了HOCH2-CNTs或MAH-OCH2-CNTs含量与复合材料性能的影响之间的关系。对复合材料进行的形貌、结晶行为、界面连接和性能测试显示:经过修饰的碳纳米管( HO-CNTs、MAH-CNTs、HOCH2-CNTs和MAH-OCH2-CNTs)均匀分散于聚丙烯基体中,并且修饰过的CNTs被聚丙烯均匀包覆,两者相容性良好,碳纳米管和聚丙烯通过MAH形成了共价连接;修饰过的碳纳米管对聚丙烯具有较强的异相成核作用,有效的减小了聚丙烯球晶尺寸,但并未改变PP的晶型;复合材料的力学、热学性能均优于纯PP和直接混合CNTs/PP;其体积电阻率随着CNTs含量的增加均表现出先缓慢减小而后迅速减小的变化趋势。对比研究发现:在初始原料均为HO-CNTs、MAH、PP的情况下,HO-CNTs先与MAH复合所合成的MAH-CNTs/PP复合材料具有比其他复合方式所制备的复合材料更优异的性能。在初始原料均为HOCH2-CNTs、MAH、PP的情况下,先使HOCH2-CNTs与MAH复合所制备的MAH-OCH2-CNTs/PP具有比其他复合方式所制备HOCH2-CNTs/MAH/PP和HOCH2-CNTs/MAH-PP较优异的性能。第三,利用碳纳米管表面大稠环芳烃结构极强的自由基捕捉能力,使甲基丙烯酸丁酯在碳纳米管表面发生接枝聚合,得到了聚甲基丙烯酸丁酯接枝碳纳米管(PBMA-CNTs)。结果表明:经过修饰处理,CNTs表面成功接上了PBMA,且修饰处理过程不会破坏CNTs本身的结构。接枝在碳纳米管上的PBMA有效地提高了其在有机溶剂(二甲苯)中的分散稳定性。第四,利用上述得到的PBMA-CNTs制备了PBMA-CNTs/PP复合材料,并考察了不同的CNTs和BMA配比对复合材料性能的影响。结果显示:当CNTs:BMA=1:100时,复合材料呈串晶纤维状, CNTs充当了串晶中心轴;当CNTs:BMA=5:100时,复合材料呈网孔膜状, CNTs被包覆于这些网孔中。在PBMA-CNTs/PP复合材料中, PBMA-CNTs与PP之间存在较强的吸附作用。PBMA-CNTs对PP的异相成核作用没有单独使用CNTs作用明显,这主要是因为PBMA的疏水性与PP更为匹配,容易缠绕而起不到成核作用。用CNTs:BMA=1:100的PBMA-CNTs所制备的PBMA-CNTs/PP复合材料与用CNTs:BMA=5:100的PBMA-CNTs相比,具有更好的力学性能,这与其串晶纤维结构有着紧密的联系。用两种不同CNTs与BMA配比所制备的PBMA-CNTs/PP复合材料都具有比纯PP优异的热稳定性。当CNTs:BMA=5:100时,复合材料的热稳定性达到最佳。第五,利用接枝了MAH的PP( MAH-PP)作为基体材料,制备了PBMA-CNTs/MAH-PP复合材料。利用不同配比PBMA-CNTs所制备的PBMA-CNTs/MAH-PP复合材料的形貌有很大的不同。CNTs:BMA=1:100的PBMA-CNTs/MAH-PP复合材料呈网孔球状;而CNTs:BMA=5:100的复合材料呈互穿网络结构,且CNTs在基体中定向排列。由于CNTs与BMA的配比不同,每根CNTs上接枝的PBMA数量也不同;当PBMA-CNTs与MAH-PP复合时,PBMA接枝量少的CNTs更易于与MAH形成化学键合,而使得CNTs受到PBMA与PP两个大分子的拽拉、牵制作用,趋向于被拉直。而对于CNTs:BMA=1:100的复合材料,因CNTs表面接枝了太多的PBMA,使得CNTs趋向于弯曲缠绕,因而复合材料形成了网孔球状。在PBMA-CNTs/MAH-PP复合材料中,通过CNTs和MAH之间的酯化反应,使得CNTs和PP通过MAH形成了化学连接。利用不同配比的PBMA-CNTs所制备的PBMA-CNTs/MAH-PP复合材料的力学和热学性能均好于纯PP。更多还原

【Abstract】 Since their discovery, carbon nanotubes (CNTs) have attracted enormous attention due to their unique structure, remarkable mechanical properties and potential applications. Specially, CNTs are an ideal candidate in polymer composites. However, to achieve maximum enhanced properties as reinforced additives, there are two fundamental issues needed to be addressed. They are related to the poor dispersion and chemical inertia of CNTs. Thus, it is necessary to decorate or coat CNTs to strengthen reinforced effects. In this dissertation, the research work ranging from decorating CNTs to modifying polypropylene (PP) with those decorated CNTs has been carried out. Moreover, the mechanical, thermal and electronic properties of modified composites were investigated.Firstly, decoration to CNTs was carried out by using sodium hydroxide (NaOH). The resulted product (HO-CNTs) was then methyloated using eletrophilicity of formaldehyde. Subsequently, maleic anhydride (MAH) was grafted onto the HO-CNTs and methyloated CNTs (HOCH2-CNTs) via esterification. The IR results showed that a certain amount of -OH and -CH2OH groups have been introduced onto the surface of CNT, then the -OH groups were replaced by ester groups after the HO-CNTs and HOCH2-CNTs were grafted by MAH. The four process of decoration did not destroy the structure of CNTs. Moreover, the twining degree of CNT was reduced and the dispersion of CNTs in organic solvent was enhanced, which open a convenient door for other chemists in further research.Secondly, the HO-CNTs and MAH-CNTs were used to fabricate CNTs/MAH/PP, MAH-CNTs/PP and CNTs/MAH-PP composites through solution blending, respectively. Also HOCH2-CNTs/PP, MAH-OCH2-CNTs/PP, HOCH2-CNTs/MAH/PP and HOCH2-CNTs/MAH-PP were prepared by using HOCH2-CNTs and MAH-OCH2-CNTs. The investigation showed that the decorated CNTs (HO-CNTs, MAH-CNTs, HOCH2-CNTs and MAH-OCH2-CNTs)were not only homogeneous dispersed in PP matrix, but also uniformly wrapped by PP. It is indicated that the decorated surface of CNTs benefit the dispersion of CNTs in PP. In addition, the decoration to CNTs improved the compatibility between the CNTs and PP, resulting in stronger interfacial adhesion. The IR results showed that there was covalently linkage between PP and CNTs via MAH grafting. This strong interfacial bonding between PP and CNTs by MAH grafting was beneficial for load-transfer processes between nanotubes and matrix.The crystallization behavior of composites was investigated. It is found that decorated CNTs had strong heterogeneous nucleation in the composites, and the crystal grain of PP containing CNTs was effectively controlled. Owing to the uniform dispersion of CNTs and covalent adhesion between PP and CNTs, the mechanical strength and the thermal stability of the composites were higher than that for neat PP and the CNTs/PP (with the same CNTs content) composite. Their volume electrical resistivities were decreased slowly primarily and then decreased sharply with continuous increasing the decorated CNTs content.Thirdly, butyl methacrylate (BMA) was polymerized from CNTs surface to form PBMA-grafted CNTs composite (PBMA-CNTs) by using the strong radical trapping capacity of polycondensed aromatic rings of CNTs surface. The results showed that PBMA was grafted onto the surface of CNTs and the structure of CNTs was not destroyed by the process of functionalization. The dispersion of PBMA-CNTs in organic solvent was much enhanced by the introduction of PBMA. The application of CNTs will be expanded owing to the better solubilization of PBMA-CNTs.Fourthly, the preparation of PBMA-CNTs/PP composite was carried out using PBMA-CNTs. The influence of the ratio of CNTs and BMA on the structure and property of PBMA-CNTs/PP composite was investigated. The results showed that when the ratio of CNTs and BMA was 1:100, one-dimensional CNTs were periodically decorated with PP lamellae crystals and the CNTs acted as shish-kebab axis, resulting in nano-hybrid shish-kebab (NHSK) structures. The PBMA-CNTs composite was shown as latticed membrane and the CNTs were embedded in the lattice membrane when the ratio of CNTs and BMA reached 5:100. When CNTs:BMA=1:100, PBMA-CNTs/PP had better mechanical strength than those of CNTs:BMA=5:100. Whether CNTs:BMA=1:100 or CNTs:BMA=5:100, the thermal stability of PBMA-CNTs/PP was higher than neat PP.Finally, using PBMA-CNTs and MAH-grafted PP (MAH-PP), we prepared PBMA-CNTs /MAH-PP composite. The morphology of PBMA-CNTs/MAH-PP composite depended on the ratio of CNTs and BMA. When CNTs:BMA=1:100, the PBMA-CNTs/MAH-PP composite was shown as latticed sphere. When the ratio reached 5:100, CNTs in PBMA-CNTs/MAH-PP composite appeared as alignment and the dispersion of CNTs was comparative uniform. An interpenetrating networks (IPN) framework was formed due to the cross-link of PP on the aligned CNTs. In PBMA-CNTs/MAH-PP composite, there was covalently linkage of CNTs with PP via MAH. Based on the uniform dispersion and covalently linkage, the mechanical and thermal property of PBMA-CNTs/MAH-PP composite was enhanced.更多还原