Hawkins, Spencer Allistor (2017-08). Hybrid Epoxy Films Containing Well-Exfoliated Multi-Walled Carbon Nanotubes and Nylon-12 with Enhanced Tensile Properties, Fracture Toughness, and Electrical Conductivity. Doctoral Dissertation.
In order to gain a more fundamental understanding of multifunctional epoxy nanocomposites, model systems containing surface functionalized multi walled carbon nanotubes (MWCNTs) and thermoplastic microparticles were fabricated and studied. Epoxies are inherently brittle and electrically insulative and therefore require the introduction of fillers with different functionalities to produce a truly multifunctional epoxy composite. The mechanical, electrical, and fracture properties of a conventional aerospace grade epoxy resin were enhanced by the addition of ZnO functionalized MWCNTs and nylon 12 (PA) microparticles. Carbon nanotubes (CNTs) are an emerging class of carbon based materials that have dominated polymer nanocomposite research in recent years due to their potential application in energy storage, electronic thin films, biotechnology, multifunctional materials, etc. The strong push for fundamental research is driven by their superior mechanical, electrical, and thermal properties. However, there are numerous problems related to processability and fabrication of nanocomposites. In order to solve these problems, which include insolubility in organic solvents and polymers and dispersability, surface functionalization is used to break up large aggregates of CNTs resulting in better dispersion and enhanced compatibility with various solvents and polymers. Traditional approaches such as chemical functionalization of the CNT surface are less commonly used due to their lacking efficiency and effectiveness at controlling the exfoliation of CNTs, which are critical to the development of tailored nanocomposites with superior mechanical and electrical behavior. Further advances in the field are required whereby a fundamental understanding of the necessary steps involved is gained. MWCNTs were decorated with ZnO quantum dots (QDs) by refluxing zinc acetate dihydrate and potassium hydroxide in the presence of pristine (P MWCNTs) or oxidized (O MWCNTs). The physical decoration of ZnO QDs on MWCNTs yielded a system of well exfoliated CNTs with little to no degradation of their material properties. PA was introduced to enhance the ductility and fracture toughness of the epoxy resin by undergoing a severe level of plastic deformation when under tensile stress with and without a pre existing crack. The glass transition and elastic modulus of epoxy tends to decrease when a large concentration of a relatively soft filler is introduced resulting in a somewhat softer material. This was not observed when ZnO/MWCNTs were introduced into the PA toughened epoxy systems, which contradicts findings currently found in the literature. The morphology and dispersion of the various fillers was unambiguously confirmed via X ray diffraction (XRD), transmission electron microscopy (TEM), UV Vis NIR spectroscopy, x ray photoelectron spectroscopy (XPS), and optical microscopy (OM). The tensile, fracture, and thermos mechanical properties of the model hybrid epoxy nanocomposites have been investigated. This dissertation has expanded the understanding of the effects of filler, and filler filler interaction on the thermal, mechanical, and fracture behavior of epoxy nanocomposites.