Design, Synthesis And Flame Retardant Properties Of Layered Mg-Al Hydroxides

Layered Magnesium-Aluminium (Mg-Al) hydroxides are layered compounds with unique oxygen octahedral sheets. Because of their composition and structure characteristics, Mg-Al based hydroxides have excellent flame retardant and smoke-suppression properties. They have been extensively investigated and used in flame retarded polymeric materials. However, the compatibility of the layered Mg-Al hydroxides (particularly brucite) and polymer matrix is very poor because of their hydrophilicity. In addition, their fatal disadvantages are low flame-retardant efficiency and thus high filler contents (possibly higher than 60% w/w) are required to obtain satisfactory fire properties of composites materials, which lead the mechanical and processing properties of materials to drop down sharply. Ultrafine surface-modification of layered brucite powder is investigated as starting point. On this basis, the reduction of filler contents or improvement on flame retardant and mechanical properties of composite materials are studied through complex synergism between modified brucite and whisker, element adjustment and the design of the structure of layered hydroxides.The results are listed below:1. The ultrafine surface-modified brucite powders was prepared by mechano-chemical method with the planetary high-energy ball mill using 325 mesh brucite powders as starting materials. The kinetic equation of ball milling of brucite was established and milling process parameters was optimized. The granularity and the modification effect of powder were investigated by laser particle size analysis, SEM, XRD, viscosity measurement and contact angle measurement. The results indicated that the D90 of the surface-modified samples reduced from 32.75μm to 1.26μm. The ultrafine powders had a uniform morphology and retain the original crystal structures. The contact angle result of the modified powders increased to 131 degrees when the added amount of stearic acid was 2 percent of powder mass. The brucite/polyester composites were prepared by adding untreated and the ultrafine surface-modified brucite powders into the unsaturated polyester resin. At the same content of brucite, peak of heat release rate of the brucite/polyester composites with untreated and the ultrafine surface-modified brucite were 194.9 kW/m2 and 183.7 kW/m2 respectively. 2. The synthesis and synergistic flame retardant effect on modified brucite of NaAl(OH)2CO3 whiskers were studied. The regular and well-dispersed NaAl(OH)2CO3 whiskers were successfully synthesized via facile hydrothermal route using aluminium isopropoxide and NaHCO3. The effects of reactants and reaction temperature on the structure and morphology of NaAl(OH)2CO3 whiskers were investigated. Based on complex synergism, the novel halogen-free flame retardant system composed of NaAl(OH)2CO3 and brucite was used for flame retarded ethylene vinyl acetate(EVA). The thermal and fire properties of flame retarded EVA system were evaluated by TGA, LOI and UL-94 test. The LOI value of 32 and the UL-94 V-0 grade of the composites were attained by adding 5wt% NaAl(OH)2CO3 and 45wt% modified brucite. The LOI value of 27 and the failed UL-94 test of the composite were attained by only adding 50wt% modified brucite. Meanwhile, the tensile strength and elongation at break of the composite were increased 9%,64% respectively.3. The synthesis and flame retardant properties of MgAlFe-CO3 LDHs were studied. MgAlFe-CO3 LDHs were synthesized by urea hydrothermal method. The effects of reactants concentration, urea/(Al3++Fe3+) molar ratio, time and reaction temperature on the structure and morphology of the samples were investigated. The EVA composites with different flame retardant formulations were prepared by melt blending. The results showed that the the interaction of different elements at the molecular level was benefit for the increasing of flame retardant properties. Compared with the composites samples with brucite and MgAl-C03 respectively at the same filler content, LOI value of 33 of the composites with MgAlFe-CO3 were attained and LOI value of 27 and 27.8 of the composites with brucite and MgAl-C03 respectively were attained. The composite with MgAlFe-CO3 had the lowest CO release than that of the comparision samples.4. The synthesis and flame retardant properties of znic hydroxy benzoate(ZHB) with LHS structure were studied. Based on the compatibility of benzoic acid and polystyrene(PS), ZHB samples were synthesized by hydrothermal reaction. The PS/ZHB nanocomposites were prepared by the bulk polymerization of styrene in the presence of ZHB. The PS/ZHB composites were characterized by X-ray diffraction (XRD), infrared spectroscopy, transmission electron microscopy (TEM). The dispersion of ZHB in the matrix and the effect of ZHB loading on the thermal properties of PS were discussed. The ZHB compound had a basal spacing of 1.46nm while brucite and MgAlFe-CO3 LDHs had basal spacing 0.48nm and 0.79nm respectively. The exfoliated-intercalated structures of nanocomposite were observed from XRD and TEM results. When the 10wt% weight loss was selected as a comparison point, the thermal decomposition temperature of PS/ZHB nanocomposites with 1% ZHB was 25℃ higher than that of pure PS.