Ceramifiable polymer composites for fire protection application
Creators: name: Al-Hassany, Zynab
Publisher: name: RMIT University
Year: 2024

description: This thesis presents an investigation of a combination of several different mineral fillers in a polymeric matrix. Each mineral component imparted specific charring characteristics to the composite, and the combinations investigated formed residues ranging from soft and powdery to strong and dense. The decomposition mechanism and interactions of these compounds were studied. <br><br>The aim of this study was to investigate the inorganic components that have multifunctional ability for fire retardance and ceramic formation. One of the objectives was to develop composites with optimum selection of fillers where the thermal and oxidative removal of the polymer increased the ceramic strength. Several filler combinations offered fire retardance combined with ceramification and this was found to be enhanced by specific compound formation between the fillers. <br><br>FR polymer composites were prepared by dispersion of filler particles in aqueous polymer emulsions. The resulting composites were analysed before and after furnace heating regimes to explore the filler interactions and strength development over the critical transitional stage. The thermal degradation reaction mechanisms of individual FR fillers and inorganic minerals have been investigated using thermogravimetry (TGA). Magnesium hydroxide (MH) and aluminium hydroxide (ATH), talc and mica underwent dehydroxylation reactions that were initiated at different temperatures. The metal hydroxides formed thermally stable inorganic residues magnesium oxide (MgO) and aluminium oxide (Al2O3). The TGA results showed that ATH had lower thermal stability compared with MH. Talc, being a layered magnesium silicate, had a minor amount of water loss due to dehydroxylation, however it functioned by providing structure and platelet morphology for barrier performance through limiting gas diffusion and heat conduction. CaCO3 decomposed at high temperature with the release of carbon dioxide (CO2) and calcium oxide (CaO). Decomposition of mica formed mullite. Zinc borate and APP were used for their char enhancing properties. Zinc borate underwent several changes during decomposition; dehydroxylation leading to an amorphous structure before crystallising and further melting at elevated temperature. APP decomposition showed elimination of ammonia and water leading to the transformation of linear crystalline APP to crosslinked polyphosphoric acid (ultraphosphate). <br><br>The binary combination of the pure inorganic fillers, ATH and/or CaCO3, had the potential to improve the FR action of APP. The combination showed interactions that had an impact on increasing the char yield and improving the insulation properties of the char. APP:ATH or CaCO3 mixtures on heating led to the formation of thermally stable aluminium phosphate and/or calcium phosphate respectively. <br><br>Ternary combinations of the pure inorganic fillers such as APP:ATH:CaCO3 produced residues that were found to be tricalcium phosphate alumina (Al2O3•Ca3(PO4)3). The presence of mica in the composite (APP:CaCO3:mica) caused a shift in the mass loss steps to higher decomposition temperatures more than the other inorganic fillers due to the formation of calcium phosphate silicate (Ca5(PO4)2•SiO4). <br><br>The thermal decomposition of emulsion based poly(vinyl acetate) (PVAc) and butyl acrylate methyl methacrylate co-polymer (BAMMA) have been investigated using TGA. The degradation of PVAc led to the elimination of acetic acid, followed by a smaller mass loss from scission of the polymer back-bone.<br><br>