| 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...
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