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for the continued support and guidance in all the time of research and writing of this thesis. I would also like to thank Dr. Sundarajan V. Madihally and Dr. Jindal Shah for sharing their valuable and insightful thoughts and comments, which helped me to complete this project. My sincere thanks also goes to Prof. Robert Agnew, who helped me use the equipment of cone calorimeter, and Logan C. Hatanaka and Lubna Ahmed from Texas A&M University, who helped make the test specimens. I also appreciate the help and suggestions from my group mates, Qingtong Liu, Beibei Wang, and Hang Yi. Last but not the least, I am thankful to my parents and my sister for their love and patience throughout writing this thesis and my life in general, which always motivates and inspires me to overcome any obstacles.

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The effect of polymer cross-linkages on thermal degradation of silica/poly (methyl methacrylate) (PMMA) nanocomposites is investigated using a single novel nanoparticle. Nanosilica surface treated with KH570, an organic surface treatment capable of free-radical polymerisation, was used to cross-link PMMA via an in situ method. Scanning electron microscopy was used to characterise nanosilica before use, while X-ray diffraction confirmed silica was well dispersed in PMMA. Thermogravimetric analysis (TGA) results showed that thermal degradation of silica cross-linked nanocomposites was significantly stabilised compared to PMMA, with a 30% reduction in the peak mass loss rate. Kinetic studies revealed the degradation of nanocomposites in this work abide by first-order kinetics, with an increase in the degradation activation energy of approximately 100 kJ mol −1 . This is nearly double the improvement compared to conventional PMMA-silica nanocomposites in literature, showing dramatic enhancements to thermal stability. Analysis of high-temperature residuals from TGA tests suggest that cross-linked silica have increased char yields when compared with both PMMA and traditional silica nanocomposites. Cone Calorimetry results showed the materials in this work have reduced heat release rates compared to PMMA and traditional silica-PMMA nanocomposites.

Using an in-situ polymerization method, poly (methyl methacrylate) (PMMA) cross-linked by trimethylolpropane triacrylate (TMPTA) was embedded with nanosilica, aluminum oxide, or modified montmorillonite to produce various crosslinked nanocomposites. The same three nanofillers were also embedded into PMMA without TMPTA cross-linkages to quantify the effect of TMPTA cross-linkages on the thermal stability and char yield of nanocomposites. Data from Thermogravimetric Analysis (TGA) and Derivative Thermogravimetric Analysis (DTG) were used to show that cross-linking and nanofiller content act synergistically to improve the thermal stability of PMMA, increasing the onset of degradation by nearly 100°C. The increase in thermal stability was attributed to the elimination of low temperature end initiated polymer unzipping by TMPTA cross-linkages and simultaneous stabilization of remaining degradation reactions due to nanofiller content. Char formed during a fire accumulates on the surface of the nanocomposite, forming a barrier that protects any unburned material below the surface. The DTG data showed nanocomposites containing 1wt% silica in PMMA cross-linked by TMPTA produced 14.1% char residues, while nanocomposites without TMPTA cross-linkages required five times the mass of nanofiller to achieve similar yields.

Polymeric nanocomposites have gained attention over the past few decades for their enhanced thermal stability and degradation. However, the reactions involved in a polymer nanocomposite can vary significantly from system to system, making it necessary to investigate novel nanofillers in search for more effective materials. Nanocomposites comprised of alpha-zirconium phosphate (ZrP) nanosheets in poly (methyl methacrylate) (PMMA) were prepared with a wide range of nanoparticle loadings (0, 5, 10, and 30 wt.% ZrP in PMMA). The ZrP nanocomposites were characterized using UV-visible spectroscopy (UV-vis), x-ray diffraction (XRD), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Nanocomposites were well dispersed and optically transparent as shown by XRD and UV-vis. However in the UV region, transparent ZrP nanocomposites possessed excellent UV scattering properties, significantly reducing the transmittance of UV-light, while remaining transparent to the visual spectrum. Thermal stability studies using TGA and DTG showed the peak mass loss rate (PMLR) was reduced by 10% and simultaneously shifted to higher temperatures by 41 °C. Since the nanocomposites in this work cover such a large range of ZrP loadings, large amounts of high-temperature residuals were encountered after TGA studies, indicating that the high loading ZrP nanocomposites are largely noncombustible. In addition, DSC studies showed that ZrP content does affect the glass transition temperature, but not enough to limit the application in which ZrP nanocomposites could be used. These results point to ZrP nanocomposites being useful as polymer replacements, behaving like polymers until the event of a fire, in which case they are largely noncombustible.