Graphene Oxide-Thermoplastic Nanocomposites: Fabrication and Properties

Polymer nanocomposites are used for a wide variety of applications. These nanocomposites can have a number of important characteristics depending on the nature of the nanomaterial, its size, volume fraction, its distribution, and interactions within the host polymer. Mechanical strength, thermal and electrical conductivity are some of these materials\u27 most focused and studied features. Besides the positive influences of the reinforcements, nanomaterials also might have some adverse impacts on the polymer matrix. These issues could arise from the aggregation of the fillers and the poor interfacial interactions of the components. Several approaches are introduced to modify the nanofillers and enhance their dispersion in polymer materials, leading to better performance of these composites. Graphene oxide (GO) is a relatively new carbonaceous material that is a good candidate for incorporation in polymers owing to its two-dimensional structure composed of sheets of sp2 bonded carbon atoms. The study presented in this dissertation is dedicated to fabricating polymer/ graphene oxide nanocomposites with added functionality without deteriorating their properties. The first part of this dissertation is devoted to preparing polypropylene (PP)/graphene oxide nanocomposites based on PP short fibers through a combination of solution and melt mixing methods. Incorporating the nanoplates into the matrix is challenging because hydrophilic GO sheets tend to aggregate in the hydrophobic polypropylene matrix. Hence, GO sheets are modified to reach a good dispersion and adhesion of the filler to the matrix. For this purpose a reactive bottle brush copolymer called poly(Oligo Ethylene Glycol iii methyl ether Methacrylate [OEGMA]- Glycidyl Methacrylate [GMA]- Lauryl Methacrylate [LMA]) containing reactive, hydrophobic, and hydrophilic parts is synthesized. This copolymer that can chemically bond to the GO sheets is developed to perform as a compatibilizer between hydrophilic GO and hydrophobic polymeric matrices. The GO nanoplates are covered with the copolymer from a water suspension. It is worth mentioning that no organic solvents are used for GO modification and deposition, and all fabrication is done using water. The chemical attachment of the copolymer chains to GO sheets is examined through different characterization methods. An extensive study on the adsorption of GO sheets on the surface of PP fibers is conducted to realize and confirm the attachment of the two components. The PP fibers covered with GO/copolymer sheets are then melt-processed to obtain the bulk PP/GO nanocomposites. The thermal and mechanical properties of the composites are characterized to examine the effect of GO and modified GO on the PP matrix. It is found that the addition of GO nanosheets does not significantly change the mechanical properties of polypropylene since the copolymer shell shields the nanomaterial inside the polymer matrix. The second part of the dissertation is focused on employing the obtained functional nanocomposites for joining polymer parts via microwave heating. The heat generated by GO due to microwave absorption causes the melting of the polymer chains in the vicinity of the nanosheets and diffusing them into each other. Composites containing modified GO sheets heat up at a higher rate than those containing neat GO. These composites are used for assembling and dissembling polymeric parts, especially 3-D printed products. The 3D iv printed parts are first mechanically investigated and compared with the similar pressed samples and then are exposed to microwave radiation. Finally, the copolymer-modified graphene oxide is used as a compatibilizer for immiscible polystyrene (PS)/polypropylene (PP) blends. The copolymer containing hydrophobic and hydrophilic side chains attached to the GO sheets and pushed them to the blend interface. The PS/PP/GO blend composites are fabricated through a combination of solution mixing and melt processing methods. GO is either premixed with PS or PP in the materials\u27 processing stage. The influence of GO modification and the mixing order on the morphological and mechanical properties of the blends is studied. Based on thermodynamical predictions and morphological observations, it can be seen that modified GO sheets tend to go to the interface of PS/PP. Also, the order of mixing influences the morphology and properties of the composites