Preparation And Flame Retardancy Of Nanocrystalline Rare Earth-containing Layered Double Hydroxides

Layered Double Hydroxides (LDHs), which can be also called as Hydrotalcite (HT), are a class of layered materials, showing that especial physicochemical properties can be obtained by changing the nature of the metal cations. LDHs are applied to polymer, which show non-toxic, smoke-suppressing and environmentally friendly and so on. Therefore, LDHs have attracted an increasing attention in halogen-free flame retardant (HFFR) additives. Because rare earth elements have special electronic structure, which has a broad application as luminescent, catalytic, magnetic materials, etc. Rare-earth elements modified LDHs and corresponding mesoporous mixed oxides should also be vaster applications. In the dissertation, a series of LDHs were prepared by microwave irradiation with low cost, simple process, short crystallization time and fewer reports in the previous literatures. The thus synthesized samples were applied in the polymers, such as polypropylene (PP) and ethylene vinyl acetate (EVA), the doping impact of rare earth and other transition metals upon retardant properties of LDHs was investigated. Some new and valuable research achievements are described in the dissertation.A series of LDHs with cerium and lanthanum were prepared by low saturation co-precipitation and microwave-assisted method in the crystallization of the samples. The crystalline structure of LDHs were characterized by XRD and IR, Zn-Al-Ce-LDHs [(n(Zn2+)/ n(Al3+)=3, n(Ce3+)/n(Al3+)=1/2)] had LDHs structure with high crystalline and single crystal phase. The thus synthesized sample was applied to PP, the flame retardancy in PP was studied by the technique of limiting oxygen index (LOI). When the Zn-Al-Ce-LDHs content was 10%, the LOI of PP was elevated from 17.4% to 22%, and LOI increased with further increase in adding levels, indicating a linear relationship with the amount of addition. When the content of Zn-Al-Ce-LDHs was 50%, the LOI of PP could reach 28%, which showed that Zn-Al-Ce-LDHs could effectively improve the flame retardant property of the composite materials.The thermal stability of LDHs/PP composite materials was studied by adopting different types of LDHs with similar amount of addition to the composite materials. The results showed that Zn-Al-Ce-LDHs could effectively delay thermal degradation of the composite materials at the low temperature range, while the char residue of Zn-Al-Ce-LDHs/PP was significantly more than that of Mg-Al-LDHs/PP and Mg-Al-Ce-LDHs/PP at the high temperature range, which revealed that Zn-Al-Ce-LDHs effectively could promot char formation of the composite materials. Moreover, it could be found the thermal stability and char residue of the composite materials showed a linear relationship with the amounts of addition Zn-Al-Ce-LDHs.Zn-Al-Ce-LDHs/EVA composite material was prepared by melt compounding and its property of flame retardancy was conducted by LOI and cone calorimeter (CONE). The results showed that there was no obvious enhancement of flame retardant property of the composite material when the amount of Zn-Al-Ce-LDHs was less than 40%, however, the flame retardant property of the composite material remarkably increased when Zn-Al-Ce-LDHs content exceeded 40%. At the same time, the heat and smoke emission rates of the composite material decreased with increase in the addition of Zn-Al-Ce-LDHs, which implyed that Zn-Al-Ce-LDHs had a significant inhibiting function on the combustion and fuming of EVA materials. The results of thermogravimetric analysis (TGA) showed that Zn-Al-Ce-LDHs could effectively delay the thermal degradation of EVA material and promote its char formation. It could be also found that the thermal stability of the composite material was a linear relationship with the amount of addition Zn-Al-Ce-LDHs. In a word, the Zn-Al-Ce-LDHs could reduce heat release rate, effectively delay and inhibit the smoke release rate and promote the thermal stability of EVA.