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| 說明 | 287 p |
| 附註 | Source: Dissertation Abstracts International, Volume: 67-10, Section: B, page: 5898 |
| Adviser: Lawrence T. Drzal |
| Thesis (Ph.D.)--Michigan State University, 2006 |
| The focus of this research is to investigate the interactions between exfoliated graphite nanoplatelets (graphene sheets ∼10nm thickness, ∼1 um diameter), a new nanomaterial developed by Drzal's group, with polyolefin based thermoplastics. The goal is: (i) to fabricate exfoliated graphite nanoplatelet (xGnP) polypropylene nanocomposites and determine properties and (ii) to elucidate the fundamental interfacial (i.e. adhesion and dispersion), processing and property mechanisms in polyolefin thermoplastics |
| This research provides an understanding about how the fabrication method and processing conditions used, which were optimized using factorial design of experiments, affect the properties of these xGnP/PP nanocomposites and therefore can lead to materials with desired properties. A significant development is a new compounding method, i.e., premixing of xGnP and PP powder in isopropyl alcohol using sonication to disperse the xGnP by coating individual PP powder particles. The premixing method is more effective than the solution method widely used, in terms of lowering the percolation threshold of thermoplastic nanocomposites, and enhancing the probability that the large platelet morphology of xGnP can be preserved in the final composite. The feasibility of using xGnP-PP nanocomposites was investigated by evaluating the properties of this system and comparing the xGnP-PP with composites made with commercial available reinforcements |
| It was found that xGnP can be used at very low concentrations as a nucleating agent for the beta-form of PP crystals which have higher impact strength and toughness compared to the most common occurring beta-form. The aspect ratio and concentration of xGnP combined with the crystallization conditions can also affect the population and size distribution of PP spherulites, which were found to nucleate and grow on the xGnP surface, are closely related to the mechanical and barrier properties |
| In addition, the crystal structure of the polymer was also found to affect the percolation threshold. The presence of many small spherulites nucleated by the xGnP disrupts the continuous network formed by the conductive particles and thus increases the percolation threshold. Other factors such as the shape and aspect ratio of the conductive filler, its morphology, distribution and orientation which affect the percolation threshold and conductivity of composites were also explored and evaluated |
| The morphological investigation of the PP nanocomposites indicated the presence of particle agglomerates and poor dispersion especially in the case of high aspect ratio xGnP and clays. The plateau observed at the flexural strength-xGnP loading curve points toward weak adhesion along the xGnPP-PP interface. The problem of agglomeration was partially solved by using the premixing compounding method. Oxidation of xGnP followed by silane treatment was employed to address the weak adhesion problem. As a result, this crystallization study provides a fundamental understanding of how the xGnP affects the crystallization behavior of PP and allows fabrication of xGnP-PP nanocomposites with engineered crystal structure |
| School code: 0128 |
| 主題 | Engineering, Chemical |
| Engineering, Materials Science |
| 0542 |
| 0794 |
| ISBN/ISSN | 9780542907234 |
