High Temperature Clay Filled Epoxy Composites
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High Temperature Clay Filled Epoxy Composites Dharmaraj Raghavan1, Joseph Ktoo Langat1, Mauro Zammarano2, and Jeffrey Gilman2 1 Department of Chemistry, Howard University, 525 College Street, Washington, DC, 20059 2 National Institute of Standards and Technology, Gaithersburg, MD, 20899
ABSTRACT The primary objective of this study is to improve the thermal stability of epoxy nanocomposites based on organo-modified clays. A 1-hexadecyl-3-(6-hydroxyhexyl)-2methylimidazolium modified montmorillonite was prepared by ionic exchange and dispersed in an epoxy resin and cured with metaphenylene diamine (m-PDA) at 110 °C for 7 h and post cured at 140 °C for 4 h. The thermal stability of the modified clay and clay filled epoxy composite was characterized via thermogravimetric analysis (TGA). The onset decomposition temperature of the imidazolium functionalized clay was 360 °C. Transmission Electron Microscopy (TEM) of the composite showed mixed morphology with predominant fraction of intercalated clay platelets in the epoxy matrix. The onset of decomposition temperature for the modified clay filled epoxy composite was found to be higher than that of pristine epoxy. INTRODUCTION During the last decade, the area of clay filled polymers has drawn much attention because of facile method of enhancing mechanical, ablation, barrier, thermal stability, and flame retardant properties of pristine thermoplastic and thermoset by addition of few weight percent of inexpensive clay filler (1-6). The property enhancements attained with these materials are commonly achieved by dispersing the alkyl ammonium functionalized clay in the polymer matrix. The thermal decomposition of alkyl ammonium ions in the functionalized clay starts at temperatures as low as 200 °C with bulk of the decomposition occurring between 200 and 500 °C (7,8). The onset of thermal decomposition for the organic modifier sets the ceiling temperature for polymer processing and/or resin curing. This is a major concern because many of the polymeric materials are processed at much higher temperature and are used in environments where they are exposed to elevated temperature for prolonged duration. The degradation of organic ammonium cations from layered silicate at elevated temperature has strong implications on the overall structure and property of nanocomposite. Ionic liquids can be used instead of alkyl ammonium salt for preparing thermally stable functionalized clay with enhanced flame retardancy (7). They can be based on cations such as imidazolium, phosphonium ions, (9). In this study, we investigate the dispersion of the imidazolium functionalized clay in the epoxy matrix and evaluate the thermal properties of clay filled epoxy nanocomposites. EXPERIMENTAL METHODOLOGY Preparation of Imidazolium functionalized clay Figure 1 shows the structural representation of 1-hexadecyl-3-(6-hydroxyhexyl)-2-methyl imidazolium chloride. The imidazolium salt was synthesized by reacting 2-methyl imidazole with sodium hydride and bromohexadecane to form 1-hexadecyl-2-methy
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