【作者】 冯江涛；

【导师】 蔡伟；

【作者基本信息】 哈尔滨工业大学 ， 材料物理与化学， 2009， 博士

【摘要】 本文采用混酸处理、表面活性剂修饰和表面接枝三种方法对碳纳米管进行表面修饰,以纯态碳纳米管和经不同表面修饰的碳纳米管为增强体,利用溶剂蒸发法制备碳纳米管/聚乳酸复合材料,采用红外吸收光谱、拉曼光谱、X射线衍射仪、偏光显微镜、扫描电镜、透射电镜、热重分析仪、差示扫描量热分析仪及拉伸试验研究了经不同方法修饰的碳纳米管表面形貌和结构以及复合材料的链结构、聚集态结构、力学性能、热性能和降解行为,揭示了碳纳米管表面修饰对其聚乳酸基复合材料结构和性能的影响规律和机制。研究发现,修饰方法对碳纳米管的表面形貌和结构有显著影响。经混酸(硝酸、硝酸/硫酸、硝酸/双氧水和王水)处理后,碳纳米管表面形成羧基官能团并受到一定的损伤,其中经硝酸/双氧水混酸处理的碳纳米管表面损伤较小,可在去离子水中长时间分散而不沉降;采用共混法,通过π-π非共价键的作用,在碳纳米管表面形成均匀的十二烷基苯磺酸钠包覆层,该方法形成的复合物可在三氯甲烷中形成稳定的分散液。利用原位开环聚合法在Fe3O4涂覆的碳纳米管(磁性碳纳米管)表面形成分布均匀、结合牢固和接枝率可控的聚乳酸包覆层,其接枝机理为引发剂在磁性碳纳米管表面形成醇锡化合物,该化合物亲核攻击丙交酯,形成“引发剂-配体”中间产物,该中间产物重复攻击丙交酯实现链增长;具有超顺磁性的聚乳酸接枝磁性碳纳米管不但可均匀分散在三氯甲烷溶剂中,而且在外加磁场作用下实现定向排列。碳纳米管/聚乳酸复合材料结构研究表明,纯态碳纳米管和经表面修饰后碳纳米管的加入对聚乳酸链结构的规整性构型和结晶相的晶体结构无明显影响,但对聚乳酸中结晶相的晶体形态和光学性质影响较大,其中纯态碳纳米管、羧基化碳纳米管和聚乳酸接枝磁性碳纳米管导致球晶尺寸变小,光学性质由纯态聚乳酸时的负光性变为混合光性,十二烷基苯磺酸钠修饰碳纳米管抑制了球晶的形成。试验结果表明,纯态碳纳米管和经混酸处理的碳纳米管在聚乳酸中分散性差,界面结合较弱,没有起到增强体的作用;十二烷基苯磺酸钠的包覆和聚乳酸的接枝改善了碳纳米管在聚乳酸中的分散性,碳纳米管与聚乳酸基体形成较强的界面结合,提高了强度,其中聚乳酸接枝磁性碳纳米管/聚乳酸复合材料的强度提高尤为明显,当聚乳酸接枝磁性碳纳米管含量为3wt%时,断裂强度增幅可达67%。降解试验结果表明,碳纳米管表面修饰对其聚乳酸基复合材料的降解行为有显著影响,在模拟体液中降解56天后,按照质量损失率由大到小的顺序,依次为纯态碳纳米管/聚乳酸复合材料、羧基化碳纳米管/聚乳酸复合材料、十二烷基苯磺酸钠修饰碳纳米管/聚乳酸复合材料、聚乳酸接枝磁性碳纳米管/聚乳酸复合材料。更多还原

【Abstract】 The surface of MWCNTs are modified by way of mixing acids refluxing, surfactant modification and polymer grafting. The composites combined with poly(L-lacitde)(PLLA) and reinforcing fillers, pristine MWCNTs and modified MWCNTs, are fabricated by the solution casting method. The morphologies and structures of modified MWCNTs are studied by FT-IR, Raman, SEM, TEM and TGA. The chain structure, aggregation structure of the composites are analized by FT-IR, XRD and PM. The mechanical properties, thermal properties and biodegradable behavior of the composites are investigated by tensile testing, DSC, FT-IR and SEM. The effects and mechanism of modified MWCNTs to the structure and properties of PLLA based composites are revealed.It is shown that the morphology and structure of MWCNTs are affected remarkably by the different modification methods. Carboxylated groups and some defects are formed on the surface of MWCNTs after refluxing in the mixing acids(HNO3/H2SO4, HNO3/H2O2, HNO3 and HNO3/HCl). Compared to MWCNTs treated by other acids, the surface of MWCNTs treated by HNO3/H2O2 acids have less defects and MWCNTs treated by HNO3/H2O2 acids suspend in deionized water for longer time. Homogeneous sodium lauryl benzenesulfate(SDBS) layers are formed on the surface of MWCNTs by mixing method throughπ-πnoncovalend bond, which make MWCNTs suspend stably in the chloroform. Homogeneous PLLA grafted layers are formed on the surface of Fe3O4 coated MWCNTs(mMWCNTs) by means of in situ ring-opening polymerization of lactide, which are bonded to mMWCNTs firmly. The amount of grafted PLLA are controllable. The mechanism of PLLA grafted to the surface of mMWCNTs is that firstly, a compound is formed on the surface of mMWCNTs after the initiator reacts with mMWCNTs, and then the“initiator-ligand”intermediate products are obtained when the compound reacts with lactide by way of nucleophilic attack, finally, the procedure aboved repeats, leading to polymer chain propagation. PLLA grafted mMWCNTs(mMWCNTs-g-PLLA) exhibit superparamagnetic behavior and suspend stably in the chloroform, which also are aligned under an extra magnetic field.Study on the structure of composites comprising of PLLA and MWCNTs shows that the effect of pristine MWCNTs and modified MWCNTs to the chain structure and crystalline structure of PLLA is not obvious. But, compared to pure PLLA, the size of spherulite become smaller and the mixed spherulite are formed for pristine MWCNTs/PLLA, MWCNTs-COOH/PLLA and mMWCNTs-g-PLLA/PLLA composites. The formation of spherulite is prevented by SDBS/MWCNTs for SDBS/MWCNTs/PLLA composites.The tensile properties of MWCNTs/PLLA composite are investigated. It is found that pristine MWCNTs and MWCNTs treated by acids(MWCNTs-COOH) cause the tensile strength of composites decreased because aggregation of MWCNTs and MWCNTs-COOH happens and there are weak interfacial adhesion between MWCNTs, MWCNTs-COOH and PLLA matrix. The SDBS layers and grafting PLLA improve the dispersion of MWCNTs in PLLA matrix and strengthen the interfacial adhesion between MWCNTs and PLLA, resulting the tensile strength of SDBS/MWCNTs/PLLA and mMWCNTs-g-PLLA/PLLA composites increased. In contrast to SDBS/MWCNTs/PLLA composites, the enhancement ratio of tensile strength of mMWCNTs-g-PLLA/PLLA composites is much higher, which reaches 67% at 3wt% mMWCNTs-g-PLLA content.The biodegradable behavior of MWCNTs/PLLA composites is investigated. The results show that different modified surface of MWCNTs affect the biodegradable behavior of PLLA distinctly after the composites degradate in PBS solution for 56 days. The mass loss ratio of composites is as followed in high to low sequence: pristine MWCNT/PLLA, MWCNTs-COOH/PLLA, SDBS/MWCNTs/PLLA and mMWCNTs-g-PLLA/PLLA composites.更多还原