Author: Lam, Chun-ki
Title: Improvement of the mechanical properties of polymer-based materials using layered silicates for product development
Degree: Ph.D.
Year: 2007
Subject: Hong Kong Polytechnic University -- Dissertations
Polymeric composites
Nanostructured materials
New products
Department: Department of Mechanical Engineering
Pages: xi, 128, [25] leaves : ill. ; 30 cm.
Language: English
Abstract: Recently, nonoclay/epoxy composites (NCs) have attracted much attention by researchers from different fields. Many studies have reported that the mechanical properties of epoxy can be improved with only mixing a small amount of nanoclay (3-5 wt.%). Polymer and advance composite industries can highly benefit from such achievements both economically and practically. From recent researches, it was reported that the degree of exfoliations of nanoclay platelets in epoxy is extremely important for altering the mechanical properties of the NCs. Due to an increase of interfacial bonding surface area of exfoliated nanoclay platelets, the bonding strength as well as stress transferability between nanoclays and epoxy therefore increase, which result in improving the overall mechanical properties of the NCs. Nevertheless, purely exfoliated nanoclay platelet structures can only be found in carefully controlled laboratory environments. It is difficult to achieve through traditional manufacturing processes, such as, extrusion and injection moldings. Non-uniform pressure distribution in mixtures is always the major cause of agglomerations of nanoclays during the manufacturing process. Many studies have reported that agglomerations of particles decrease the total kinetic energy in a two-phase mixture. Therefore, the movements of particles decrease and they adhere to each other to form larger molecules that consist of many single particles, which are called clusters. The agglomerating phenomenon in particles explains the cause of formation of nanoclay clusters which intercalated structures in the NCs. Hence, there is a need to have an indepth study on the effects of the inclusion of intercalated nanoclay in the NCs in order to suit the real engineering applications.
In this project, the mechanical properties of the NCs with intercalated nanoclay clusters (hereafter called "nanoclay clusters") are studied in detail. With the X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray(EDX) materials characterizations, the co-relation of the size and shape of the nanoclay clusters found in the NCs with different manufacturing parameters are investigated. Vickers micro-hardness, wear resistance and creep test are conducted on NC samples for the visualization of the mechanical properties by the reinforcements of nanoclay clusters. Nucleation of nanoclay clusters in the NCs is explained by the nucleation theory while the distribution of nanoclay clusters in the NCs is examined by nanoindentation. Mathematical models are proposed to facilitate the estimation of the mechanical properties of the NCs with different amount of nanoclay clusters. The importance of the thermo-mixing process during production of the NCs is analyzed from the Flory’s principle. Creep mechanism of the NCs with intercalated nanoclay clusters is also studied by nanoindentation and a modified model with the aid of the Kelvin-Voigt model. From the various mechanical property tests and mathematical models, maximal mechanical properties were found at 4 wt.% of nanoclays in the NCs. With the analysis in this project, the principle of the formation of nanoclay clusters and the mechanical properties of NCs with nanoclay clusters are interpreted in detail that have not been studied elsewhere previously.
Rights: All rights reserved
Access: open access

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