China’s plastic flame retardant material is mainly based on decabromodiphenyl ether, but decabromodiphenyl ether in combustion will produce toxic carcinogenic polybrominated dibenzofuran and other substances, and make it some countries to resist the use of. Therefore, flame-retardant materials also develop towards the direction of high efficiency, low toxicity and low smoke. It is necessary to develop nontoxic flame retardant with excellent performance. Inorganic materials used as flame retardants include Mg(OH)2, AL(OH)3, Sb2O3, etc. These inorganic flame retardants not only have flame retardancy effect in the synthetic materials, but also inhibit the production of smoke and hydrogen chloride. It is widely used because of its non-toxic and non-corrosive nature. Especially magnesium hydroxide, because of its excellent flame retardant performance and effect and widely favored, it is mainly used in polypropylene, polyvinyl chloride and resin and other polymer materials flame retardant, and used in the treatment of lead wastewater, is an environmentally friendly product, its market prospects.Using industrial magnesium chloride as raw material, the preparation process of nanometer magnesium hydroxide was studied, and the preparation method and process conditions of nanometer magnesium hydroxide flame retardant were analyzed.
1. 1 test materials
Low temperature synthesis of magnesium hydroxide by ammonia process is based on the reaction between industrial grade magnesium hydroxide and the precipitator ammonia (with surfactant added). The reaction equation is as follows:
MgCL2 + 2 2 nh4cl nh3 · H2O + Mg (OH) 2
The raw material magnesium chloride (hexahydrate magnesium chloride) used in this study was provided by a chemical enterprise in hubei province. The chemical analysis results of its main components are shown in table 1. Other reagents used are analytically pure.
1. 2. Flame retardant characteristics of magnesium hydroxide
According to the Differential Thermal Analysis curve of tga-dta (Thennpgravimetric Analysis Differential Thermal Analysis) (figure 1), the non-toxic, flame retardant and smoke-suppression magnesium hydroxide with high Thermal stability starts to decompose at about 340℃ :
MgO style of Mg (OH) 2 + H2O_Q, decomposition rate is highest at 430 ℃, 490 ℃ when the end of decomposition, the thermal decomposition process produces water vapor and refractory MgO style only, do not produce corrosive gas, decomposition heat absorption capacity is 0.77 KJ/g, (44.8 KJ/mol), and high thermal stability and good smoke abatement effect, its degradation characteristics of smoke abatement in the solid region is better than calcium carbonate and aluminum hydroxide flame retardant.
1. 3 Test equipment and process flow
The experimental device for synthesis of magnesium hydroxide from low-temperature ammonia water is shown in figure 3, including the reactor with agitator, the ammonia container with constant temperature water bath and the low-cost device (mixed with surfactant). The function of constant temperature water bath is to keep the temperature of solution in the reactor basically at a certain value. The process flow of the experimental study is shown in figure 4. The low-temperature synthesis adopts the method of continuous feeding, that is, ammonia water is added into magnesium chloride solution for reaction at a certain speed.
2. 1 Effect of reaction temperature on particle size and morphology of magnesium hydroxide
When the initial concentration of magnesium ions was 1.0 ~ 1.2mol/L, the concentration ratio of magnesium ions to hydroxide ions was 1:1.7, and the reaction time was 60min, the relationship between particle size of magnesium hydroxide and temperature was shown in table 2 under different temperature conditions. The influence of reaction temperature on particle size of magnesium hydroxide is shown in figure 5. As can be seen from figure 5, the particle size of magnesium hydroxide particles increases as the reaction temperature increases, and decreases when the temperature exceeds 80℃. Through electron microscope analysis, it was found that with the rise of reaction temperature, the particle size distribution was uniform at 75℃ and formed a flake structure.
2. Effect of initial concentration of magnesium ion on particle size and morphology of magnesium hydroxide When the concentration ratio of magnesium ion and hydroxide ion is 1:1.7, the reaction temperature is 70 ~ 80℃, and the reaction time is 60min, the influence of the initial concentration of magnesium ion on the particle size of magnesium hydroxide is shown in figure 6.With the increase of the initial concentration of magnesium ions in the solution, the particle size of producing nano magnesium hydroxide gradually decreased, from 45nm to 30nm. When the initial concentration of magnesium ion is 1.05mol/L, about 35nm flake and uniform particle size can be obtained to obtain nanometer magnesium hydroxide.
2. 3 Effect of reaction time on particle size and morphology of magnesium hydroxide
When the reaction temperature is 70 ~ 80℃, the magnesium ion concentration is 1.0 ~ 1.2mol/L, and the material mass ratio of Mg2+ and OH- is 1:1.7, the influence of the reaction time on the particle size of magnesium hydroxide is shown in figure 7, and the data is shown in table 4. The results show that the reaction between magnesium chloride and ammonia is very fast, and the whole reaction can be completed in an instant. With the extension of reaction time, the particle size of magnesium hydroxide decreased gradually. However, the results show that the reaction time is too short, and most of the magnesium hydroxide exists in the amorphous state. The reaction takes some time to form a complete magnesium hydroxide crystal.
2 .4 Effect of surfactant on particle size and morphology of magnesium hydroxide
The purpose of adding surfactant in the experiment is to change the surface properties of magnesium hydroxide particles, effectively reduce the agglomeration of magnesium hydroxide particles, and improve the morphology of magnesium hydroxide particles. The results show that the particle size of magnesium hydroxide decreases first and then increases with the increase of surfactant concentration.
conclusion: The following conclusions can be drawn from the synthesis of nano magnesium hydroxide flame retardant by ammonia method at low temperature: 1) adding surfactant can prepare nano magnesium hydroxide flame retardant at low temperature. The appropriate process conditions are: reaction temperature (70 ~ 80℃), reaction time (60min), initial concentration of magnesium ions (1.0 ~ 1.2mol/L), ammonia concentration (3 ~ 3.2mol/L), surfactant concentration (3%) and concentration ratio of magnesium ions to hydroxide ions (1:1.7). 2) shorten the process of hydrothermal synthesis of magnesium hydroxide and reduce the reaction conditions. The mean particle size of magnesium hydroxide flame retardant was 35nm