| Mg(OH)2 is an environment-friendly inorganic flame retardant with high thermal decomposition temperature and no toxic and harmful gases.It is widely used in coatings,plastics,rubber fields to improve the flame retardancy of polymer materials.However,Mg(OH)2is a kind of additive flame retardant with high filling content,which usually has negative impact on the mechanical properties of polymer materials.What's more,the solution to the problem of high content of Mg(OH)2 mainly depends on the control of the morphology and size of Mg(OH)2 particles and the surface modification technology.Therefore,the purpose of this study is to prepare hexagonal Mg(OH)2 with main exposed(001)crystal plane and good flame retardant performance,and to modify the surface of the prepared Mg(OH)2 by chemical coating and grafting polymerization,and to apply it to the flame retardant rubber composite to investigate the mechanical properties and flame retardant properties.It mainly includes the following research contents:Using MgCl2 and NH3·H2O as raw materials,the hexagonal flake Mg(OH)2 was prepared by hydrothermal method.The effects of reactant concentration,structure directing agent,hydrothermal temperature,hydrothermal reaction time,PEG with different molecular weight and its addition amount on the crystal growth of hexagonal flake Mg(OH)2 were studied,and the crystallization process and morphology evolution of Mg(OH)2 were analyzed.The results show that when the concentration of magnesium chloride was 1 mol/L,that of ammonia was 13.33 mol/L,PEG-8000 with 3%theoretical yield of Mg(OH)2 was added,hexagonal flake Mg(OH)2with regular morphology and main exposed(001)crystal plane was obtained at 120?for 12 h.In the hydrothermal process,PEG molecular chains preferentially were adsorbed on the(001)crystal surface of Mg(OH)2small grains,and then assembled them into large and regular hexagonal flakes with low polarity.The surface of hexagonal flake Mg(OH)2 was modified by chemical coating and grafting polymerization.Using sodium oleate to modify the surface of Mg(OH)2 and investigate the effect of chemical coating modification temperature,time and modifier amount on the modification effect;The grafting polymerization of MMA on the surface of Mg(OH)2 modified by sodium oleate was carried out to optimize the experimental conditions and determine the mechanism of grafting polymerization.The optimization condition of modification with sodium oleate added 3%of Mg(OH)2 mass,at 65?for 3h;The The optimization condition of grafting polymerization of MMA on the surface of Mg(OH)2 was the amount of sodium oleate 5%of the mass of Mg(OH)2,the amount of monomer twice that of Mg(OH)2,the amount of dispersant PVP 20%of the mass of monomer,and the initiator AIBN 1%of the mass of monomer.The mechanism of surface modification of Mg(OH)2 is that during the modification of Mg(OH)2 by sodium oleate,C17H33COO-in aqueous solution was chemically adsorbed on the surface of hexagonal flaky Mg(OH)2,and hydrophobic long-chain alkanes are exposed on the outside,then the polarity Mg(OH)2 was changed from hydrophilic to hydrophobic;Sodium oleate modification introduces unsaturated bonds(-C=C-)on the surface of Mg(OH)2,then under the action of the initiator AIBN,the unsaturated double bond is opened and polymerized with the MMA monomer to realize the grafting of PMMA on Mg(OH)2.Since the polarity of PMMA was higher than that of sodium oleate,the hydrophobicity of Mg(OH)2 was further improved after grafting polymerization.Modified hexagonal flakes Mg(OH)2was used to replace for Al(OH)3 in the core paste formula of PVG flame retardant conveyor belt.With the increase of the amount of Mg(OH)2,the viscosity,hardness,tensile strength and elongation at break of the core paste increased gradually.The mechanical properties and flame retardancy of the product obtained by substituting 2%modified Mg(OH)2 for 9%Al(OH)3 in the core paste formula of PVG flame retardant conveyor belt were improved.The composite flame-retardant rubbers were prepared at the condition of keeping other flame-retardant components unchanged and using modified hexagonal flakes Mg(OH)2 to replace for Al(OH)3 part of the flame retardant.The results showed that the properties of rubber prepared with Al(OH)3 and modified Mg(OH)2 are better than the national standard;the mechanical properties and flame retardant properties of rubbers prepared with modified Mg(OH)2 are better than those of Al(OH)3,the composite flame-retardant rubber prepared by sodium oleate modified Mg(OH)2 has excellent mechanical properties,and that prepared by graft polymerization modified Mg(OH)2 has excellent flame-retardant properties. |
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