| Mg(OH)2 is a favorable halogen-free flame retardant for the PP,PA and POM, etc, for the special properties of smoke suppression, high thermal stabilization(decompose temperature was from 340℃to 490℃) and low toxicity. When Mg(OH)2 was used as flame retardant, different kind of polymers have different demands for the particle size,morphology and surface properties. In this thesis, effect of different preparation conditions including injection methods, reaction temperature, dispersant, on the morphology of Mg(OH)2 were firstly investigated through one-step hydrothermal treatment, then, the methods for controlling the particle size were obtained and the factor in the hydrothermal treatment and surface modification was studied,the results were that:Width(diameter of hexagonal phase) and thickness of Mg(OH)2 is strongly effected by the reaction temperarure , the ratio of width to thickness is decreased first, then increased with the increasing of temperature, and it got its min value between 100℃-120℃; In ordinal-injection pitrocess, width increased all along ,but thickness got its mix value at 100℃; In reverse-injection process ,width is decreased first, then increased, it got its min value at 100℃, but thickness tend to increasing.According to the anlysis of ordinal-injection,reverse-injection,double-injection methods,the partical size of Mg(OH)2 was obviously effeced by different injection processes. In ordinal-injection pitrocess, the partical size is biggest but with polarization(big crystal blended with small crystal),In reverse-injection process,it is smallest and distribute concentratly . In double-injection process,it is between the two others.The crystal growth driving force Sd, is put farward to describe the super- saturation in different injection processes. The correlation between particle size and changeable of Sd will get the result when Sd<0, nucleation of crystal was dominance; Sd>0, growth was dominance. The nucleation and growth velocity of Mg(OH)2 would be controlled through the controlling of the Sd in different injection processes and variety of size was obtained.Hydrothermal treatment was used to improve the crystallinity of Mg(OH)2 using water,ethanol and urea as media. The results showed that the use of the concentrated carbamide in hydrothermal media, the increase of temperature is favorable for the enhancement of the width and thickness, and concentration increasing is good for the uniform of crystallinity.At last, the surface coating was used to modify Mg(OH)2, It was found that surface properties promote obviously , The mixed anion and anion surfactant (such as stearic and oleic acid sodium) could bring better effect than individually. The optimical amount of surfactant : Tween-20 or Span-80 is 5%, stearic acid sodium or oleic acid sodium is 8%. |
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