【作者】 李侃社；

【导师】 王琪；

【作者基本信息】 四川大学 ， 材料学， 2002， 博士

【摘要】 本文建立了磨盘碾磨固相剪切纳米复合新技术(S~3C)，实现了鳞片石墨(FG)和膨胀石墨(EP)的层间滑移、片层剥离和与聚丙烯(PP)的纳米复合，成功制备了系列PP/石墨导电、导热纳米复合材料；系统研究了影响石墨片层剥离和与PP纳米复合的因素和机理，以及磨盘碾磨剪切力场和石墨受限环境对PP微观结构的影响；系统研究了PP/石墨纳米复合材料的导电性能和逾渗规律，论述了导电机理和影响导电性能的因素；研究了PP/石墨复合材料的导热性能和导热机理，分析了影响聚合物复合材料导热性能的因素，提出了预测导热系数的理论模型，发展了复合材料导电、导热理论；研究了PP/石墨复合材料的力学性能，获得了兼具优良导电、导热和良好力学性能的PP/石墨复合材料。取得了以下主要研究成果： 1．建立了磨盘碾磨固相剪切纳米复合技术(S~3C)，实现石墨的层间剥离和与PP的纳米复合，成功制备了系列PP/石墨导电、导热纳米复合材料。 利用层状无机物(如石墨)的弱层间结构和聚合物的粘弹性特点，在磨盘碾磨剪切力场作用下，通过摩擦和拉伸形变错位、挤压嵌合、拉伸滑移、剪切剥离与粉碎和混合分散等过程，实现层状无机物层间剥离和与聚合物的纳米复合。 研究结果表明，磨盘碾磨剪切力场实现石墨的层间剥离及与PP的纳米复合是分阶段完成的，是碾磨过程产生的摩擦、挤压、拉伸和剪切应力及物料螺旋运动过程综合作用的结果。通过控制碾磨条件可分别制备插层型或剥离型纳米复合材料。 2．磨盘碾磨剪切力场使PP分子链断裂，相对分子质量减小，石墨的导热和润滑性能抑制PP的降解和粉碎，使PP/YEP250(膨胀石墨250倍)复合粉磨盘碾磨固相剪切复合技术及导电导热PP/石墨纳米复合材料的制备与性能体中，PP分子运动活性提高，结晶能力增强，为PP在熔融加工中进一步向己剥离的石墨片层间扩散，形成纳米复合结构创造了条件。磨盘碾磨剪切力场导致石墨的微晶尺寸减小;PP的晶面间距增大，微晶尺寸减小，结晶度下降，这些变化在受热或加工成型过程中可以得到部分恢复。 石墨片层的受限空间影响i一PP/YEP25O复合材料中PP结晶行为，进入石墨片层间的PP分子一部分择优取向，形成沿(040)晶面法线方向择优生长的a一晶，另一部分相对分子质量较小、运动活性较高的PP分子则受到石墨片层的挤压和限制而转化为Y-晶，在i一PP厅EP250复合材料中，Y-晶相对含童达34.8%。 3.S3c技术是制备聚合物/石墨导电复合材料的有效途径，可以大幅度降低复合体系的导电逾渗闭值，在低填充量实现聚合物复合材料高电导性。与熔体共棍相比，PPIYEP250复合体系中，导电逾渗阅值由4.3 voL%降低到0.55vol.%，在石墨含量为4.2voL%时，电导率提高10个数量级。PPINFG(撰状石墨)复合体系中，石墨含量为9.0 vol.%时，电导率增加6个数量极。 TEM分析结果表明，S3C技术所得PP/膨胀石墨复合材料具有纳米插层复合结构，通过石墨纳米片层的相互搭接形成导电网络，PP与石墨片层相互嵌入形成附聚体，构成点一键复合逾渗模式，其导电规律符合经修正的统计逾渗模型。 实验结果和理论分析表明，聚合物复合材料的导电性能是导电通道、隧道效应和场致发射三种导电机理共同作用的结果。在PP/石墨纳米复合材料中，具有很大径厚比的石墨片层相互搭接可形成导电通路;石墨片层与聚合物基体形成的插层纳米复合结构，构成点一键一面复合配位模式的导电多面体，使石墨粒子的有效半径延伸，导电电荷不再局域于某一粒子，而在导电多面体间跃迁，从而形成隧道电流，所以具有极低的导电逾渗闭值Vc和极高的临界维度指数b，对PP/YEP25O复合材料，Vc为O.55voL%，相应的维度指数b为12.8。 4.石墨与PP复合可大幅度提高PP的导热性能和耐热性能，在PP/YEP35复合体系中，当石墨含量为17voL%时，可使PP的导热系数提高2.4倍达到0.78w/m .K，在PP/Y EP250复合体系中，当石墨含量为4.2vol.%时，导热系数提高1.6倍。通过S3C技术制备的HDPE/FG复合材料，当石墨含量为30voL%时，导热系数达到2.oZw/m .K，是HnPE的5倍。s3e制备的PP/ YEP25o(石墨含量2.2vol.%)复合材料的热分解温度比简单熔体共混法提高10℃以上，比PP提高19℃。四川大学博士学位论文 基体和填料的导热性能以及二者的复合方式是影响聚合物填充复合材料导热性能的重要因素，提高插层型/平行并联复合模式在复合体系中出现的几率P是提高导热性能的关键，研究结果表明，S3c技术可有效提高P，从而提高复合体系的导热性能。 建立了预测导热系数的理论模型。该模型可描述PP/石墨和HDPE/石墨复合材料的导热规律，并能较好地拟合文献报道的天然橡胶(NR)/石墨、N侧不锈钢纤维、N侧碳纤维复合材料的导热系数与填料体积分数之间的关系，并可成功解释N侧石墨复合材料与N侧碳纤维复合材料导热系数的差别。 5.提出了利用S3c技术制备的聚丙烯/石墨复合粉体，增强、增韧聚丙烯的技术路线，建立了聚合物/无机填料复合粉体增强增韧聚合物新技术。在赋予PP良好导电和导热功能的同时，又实更多还原

【Abstract】 In this paper, a novel technique for preparation of polymer nanocomposites, solid-state shear compounding (S3C) based on pan-milling has been developed, by which the electrical and thermal conductive polypropylene/graphite nanocomposites were successfully prepared. The process and mechanisms of slipping, exfoliation to layered graphite and compounding with polypropylene (PP) on nano-scale were systemically studied. The effects of shearing force field offered by pan-milling and confined environment of the exfoliated graphite on the microstructure of polypropylene, the electrical and thermal conductivities of the nanocomposites were also investigated. Based on the experimental results, a modified electrical conductive model as well as thermal conductive model for polymer-based composites was proposed. In addition, the electrical and thermal conductive PP/graphite composites prepared by S3C technology keep pretty good mechanical properties. This research develops the intercalation technique for nanocomposites, as well as pan-milling mechanochemistry, the electrical and thermal conductive theories of polymer based composites. The main outcomes are listed as follows:1. A solid-state shear compounding technology based on pan-milling (S3C) has established, by which the graphite with weakly combined structure are exfoliated and then compounded with PP at nanoscale. The obtained PP/graphite nanocomposites have greatly enhanced electrical and thermal conductivity. Their structures and properties were characterized by analysis of particle size and distribution, SEM, TEM, XRD, the electrical conductivity, the thermal conductivity and heat-decomposition temperature etc.By taking advantages of the layered inorganic fillers with a weak interaction between layers (e.g. graphite) and the special viscoelasticity of polymer, interlayer exfoliation of the filler and its nanocompounding with polymers can be realized in the shearing force field of pan-milling, through the effects such as deformation, dislocation, tension-sliding and shearing exfoliation of graphite, the tension-thinning, pulverization of PP, as well as the imbedding, mixing and dispersion of graphite flakes in PP powder etc.The results show that the interlayer exfoliation of graphite and nano-compounding with PP proceeded stepwise, caused by a combination of friction, squeezing, stretching, and shearing in three-dimension during pan-milling. In addition, the intercalated or exfoliated nanocomposites can be also prepared respectively by controlling the conditions of pan-milling.2. Scission of PP molecular chains occurs during pan-milling, leading to the decrease of its molecular weight, but the thermal conductivity and lubrication of graphite weaken this procedure. In PP/YEP250 system, the mobility of PP chains increases, advantageous to its diffusion to the exfoliated graphite layers during melt processing and form composites on nanoscale. In additional, pan-milling reduces crystallite size of both graphite and PP; increases the space between crystal faces of PP. These changes can be partly restored during processing or programmed heating.Because of the confined galleries of graphite, the PP in the nanocomposites behaves different from neat PP in crystallization. Owing to the confined orientation of the PP chains intercalated in the graphite galleries, most PP develop into a-phase crystal choosing the best orientation along normal direction of (040) crystal face, however, other PP with smaller molecular weight and mobilized molecular chains develop into y-phase crystallite due to being squeezed and confined by the surrounded graphite sheets in a narrow space, and the relative content of y-phase crystallite in homo-PP/YEP250 composites reaches 34.8 %.3. S C is an effective method to prepare polymer/graphite electrical conductive composites of low loading level and high electrical conductivity. It canremarkably decrease the percolation threshold value of the composites, showing better electrical conductivities than that of更多还原