【作者】 张琴；

【导师】 傅强；

【作者基本信息】 四川大学 ， 高分子材料， 2002， 博士

【摘要】 熔体插层法制备聚合物／层状硅酸盐纳米复合材料作为一种新的制备方法已经得到广泛的应用，该过程的一些理想化模型和理论也得到了深入的研究。但是，由于大分子插层的特殊性，理想化的模型一方面需要实验进行验证；另一方面由于对插层过程的简化，还不能解释一些实验现象，比如纳米复合材料的形成过程、剥离机理等。纳米复合材料的形成与分散不仅与层状硅酸盐的化学改性、两者之间的相互作用、是否加入相容剂有关，而且与加工条件与过程密切相关。层状硅酸盐的分散形态直接影响聚合物纳米复合材料的性能，对于聚合物纳米复合材料的分散形态与性能之间的关系也缺乏深入的研究。为了进一步理解熔体插层过程，探索纳米复合材料的形成过程、剥离机理、形态与性能等基本理论问题，本文在前人工作的基础上，以熔体插层法制备聚丙烯／蒙脱土纳米复合材料作为研究对象，对该体系的熔体插层过程及其影响因素、蒙脱土的分散形态与性能的关系、纳米复合材料的形态结构进行了深入的研究。 本文首先在热力学分析的基础上，通过WAXD和SEM对聚丙烯／蒙脱土纳米复合材料的形成过程和剥离机理进行研究。分别研究了混合时间、混合设备、加工工艺对纳米复合材料的形成的影响，由此提出纳米复合材料形成和剥离的模型，并对其影响因素进行了讨论。研究发现，熔体插层在1分钟内已经发生，混合时间的延长只能增加剥离部分蒙脱土的含量，使插层过程更加完善。但是更长的熔融共混时间无助于进一步的剥离，长时间的熔融共混会导致蒙脱土片层的重新集聚。纳米复合材料的最终形态依赖于聚合物与蒙脱土之间的相互作 四川大学博土学位论文用、相容剂的用量、加工过程所受到的剪切作用、熔体插层时间、熔体插层温度以及聚合物熔体的粘度。 因为聚丙烯的非极性特点，很难通过熔体插层制备完全剥离的纳米复合材料，总是形成部分插层、部分剥离的结构。只有完全剥离的纳米复合材料才能表现出最好的增强效果，因此如何得到完全剥离的聚丙烯纳米复合材料是目前研究的重点。为了进一步提高蒙脱土的剥离和分散，我们引入动态剪切场进一步控制材料的剥离和取向程度。通过 Zd．WAXD研究蒙脱土和聚丙烯的不同的－取向形态，用WAXD、SEM和TEM研究蒙脱土在聚丙烯基体中的分散行为。“研究发现，动态保压产生的剪切场有利于蒙脱土片层在聚丙烯基体中的进一步的剥离和分散。蒙脱土的含量越高，剪切引起的分散效果越明显。通过动态剪切还可以研究聚合物在硅酸盐片层之间的受限情况。只有当聚丙烯和蒙脱土之间存在很好的相互作用时，蒙脱土片层明显限制聚丙烯分子链在外力作用下的取向，使聚丙烯分子链的取向度降低。剥离的蒙脱土对聚丙烯分子链运动的限制作用更大。 目前，熔体插层纳米复合材料的研究集中于制备方法、形态表征、以及性－＿能研究方面，但是对于层状硅酸盐的分散形态与力学性能的关系却未见报道。本文在用WAXD、SEM和TEM对蒙脱土在聚丙烯中的分散行为进行全面表征的基础上，讨论了蒙脱土的分散情况对纳米复合材料的增强效果的影响，探索聚丙烯／蒙脱土纳米复合材料的性能提高幅度不大的原因；以及蒙脱土片层的取向对纳米复合材料性能的影响。研究发现，蒙脱土片层的解离程度和蒙脱土片层的取向是影响纳米复合材料的性能的两个关键因素。研究还发现，在蒙脱土的含量较低时，聚丙烯／蒙脱土纳米复合材料能够达到同时增强、增韧的效果。 本文采用PLM、WAXD、SAXS对纳米复合材料中聚丙烯的结晶结构从球晶的尺寸到晶片厚度进行了全面的研究，系统地讨论了蒙脱土片层的加入对聚丙烯的形态结构的影响。蒙脱土片层在聚丙烯的结晶过程中起到了有效的成核作用。由于纳米级分散的蒙脱士片层与聚丙烯有很好的相互作用，对聚丙烯的结晶起阻碍作用，使晶片厚度和结晶度降低，对无定形区的影响很小。蒙脱土的分散尺寸越小、分散越均匀，对结晶的影响更明显。 本文还通过DSC对聚丙烯／蒙脱土纳米复合材料的等温结晶动力学和非等温结晶行为进行研究。由于剥离的蒙脱土片层具有更好的成核作用，蒙脱土的 四川大学博土学位论文 含量为 IWt％的纳米复合材料的结晶速率最快。聚丙烯及其纳米复合材料在等温 结晶过程中基本上满足Avrami方程，结晶活化能明显降低。聚丙烯／蒙脱土纳 米复合材料的结晶温度增加，熔融温度和结晶度有一定的降低。 本论文的特色和创新性主襄表现在以下几个方面： 1．我们采用扫描电子显微镜（SEM）、广角X－射线衍射（WAXD）和透射电镜 （TEM）相结合，从宏观到微观的不同层次上研究蒙脱土片层在聚合物基体 中的分散情况。首次对不同混合时间、不同混合设备以及加工工艺进行研究， 由此提出纳米复合材料的形成过程和剥离机理。特别是发现了蒙脱土的插层 和剥离过程在1分钟内就已经发生，而且时间的增加会导?更多还原

【Abstract】 Polymer melt intercalation is a more versatile approach to make polymer layered silicate nanocomposites, which has been most widely investigated in recent years. The thermodynamics and kinetics theories involved in polymer melt intercalation have also been intensively reported. However, most of the theoretic simulations are too ideal to describe the formation of polymer melt intercalation. The formation mechanism of polymer nanocomposites is the key to the development of nanocomposite. The final properties of the fabricated articles depend on mainly the exfoliation and dispersion of the platelets. In this work, Polypropylene (PP) /montmorillonite (MMT) nanocomposite made by melt intercalation was chosen to study the melt intercalation process, exfoliation mechanism, morphology and properties of polymer nanocomposites.First, The formation process and exfoliation mechanism were investigated by WAXD and SEM. Based on the results from melt compounding time, temperature, shear force, a model of nanocomposites formation and exfoliation was proposed. At the same time, influences factor in nanocomposite formation were also discussed. We found that the melt intercalation process has occured in one minute and MMT layers may aggregate as the increasing of the compounding time. The final structure of nanocomposites depends on the interaction between polymer and silicate, the contentof compatibilizer, shear force, compounding time, melt temperature and polymer melt viscosity.In order to improve the dispersion of MMT in PP matrix, the prepared PP/MMT nanocomposites via direct melt intercalation were further subject to oscillating stress achieved by dynamic packing injection molding. Shear induced morphological changes were investigated by WAXD, SEM and TEM, as well as Instron. The original nanocomposites possess a partly intercalated and partly exfoliated morphology. A transformation of intercalated structure into exfoliated structure was found after shearing, and more homogeneous dispersion of MMT in PP matrix was obtained. On the other hand, the orientation of PP chains in PP/MMT nanocomposites becomes very difficult under external shear force, which indicates that the molecular motion of PP chain intercalated between MMT layers is highly confined.Most of articles on polymer nanocomposites focus on the importance of the chemistry used to modify the surface of the clay, usually montmorillonite(MMT) and characterization of the nano-scale structure obtained. The role and importance of processing was also discussed recently. However, few papers concerning the correlation between morphology of MMT and mechanical properties were reported. In order to better understand the tensile behavior of PP/ Montmorillonite(MMT) nanocomposites, and further improve the reinforcement efficiency, we prepared the PP nanocomposites via direct melt intercalation using conventional twin-screw extrusion. The macroscopic and microscopic dispersion of MMT in PP matrix was verified by XRD and TEM, combined with SEM. While the tensile property was obtained by video-controlled tensile set-up, which gives true stress-strain curve. The orientation of silicates platelets and the degree of exfoliation are two key factors to determine the reinforcement efficiency. The other properties of nanocomposites are also discussed.The crystal morphologies were investigated by PLM, WAXD, and SAXS. It is found that exfoliation MMT layers can serve as the nucleating agent, which speed up the crystallization rate of the nanocomposites and also causes the decreasing of crystal size. The melting point and lamellar of PP nanocomposite were found decreased, compared with the pure PP, which is an indication of a strong interaction between PP and MMT. In this case, it can be considered that PP crystallizes in a confined space.更多还原