The Preparation Of Modified Ultrafine Magnesium Hydroxide Flame Retardant

As a kind of halogen-free and environmentally friendly flame retardant, ultrafinemagnesium hydroxide has become one of the most promising inorganic flame retardantsdue to its efficient, non-toxic, smoke-free and pollution-free characteristics. However, themagnesium hydroxide flame retardant in China has the problems of uniform particle sizedistribution, high cost and small production, so in order to prepare a high performanceultrafine magnesium hydroxide flame retardant, the exploration of a modification methodwhich is cost-effective and can reach continuous production is quite significant. In thisstudy, ultrafine magnesium hydroxide flame retardants with the characteristics of highpurity, dispersion well, small particle size and no uniform distribution size, good flameretardant performance were prepared, by the methods of direct precipitation and highgravity precipitation respectively, using six water magnesium chloride and sodiumhydroxide as materials, polyvinyl alcohol, fatty alcohol ethoxylates and acetaminophen assurface modifiers.The effects of polyvinyl alcohol, fatty alcohol ethoxylates and acetaminophen thedosage on separation characters of ultrafine magnesium hydroxide were investigated byexaming the sedimentation and filtration performance of Mg（OH）₂slurry, and the dosage ofsurface modifiers was optimized.The results showed that by addition of3.0%polyvinylalcohol,5.0%fatty alcohol ethoxylates,2.0%acetaminophen dosage, the prepared ultrafinemagnesium hydroxide flame retardants slurry have the maximum natural sedimentation rate,minimum filter cake specific resistance and the best dispersion performance.The modified and unmodified magnesium hydroxide flame retardants prepared with the methods of direct precipitation and high gravity precipitation were characterized byXRD,TEM and laser particle size analyzer.Results indicated that the modified ultrafinemagnesium hydroxide flame retardants have the properties of well dispersion, smallerparticle size, narrow particle size distribution, and high crystallinity. The properties ofMg（OH）₂flame retardants using high gravity precipitation method with and without surfacemodifierscould bothachieve better performance levels, and the improvement of theproperties with surface modifiers was small due to the residence time was too short, whichindicated a better mechanical modification effectionof the rotating packed bed.Tests of all samples usingthe magnesium hydroxide industrial standards prove thatmost of the samples are qualified products between class Ⅱ andⅠ, except that the purityof samples preparated by High gravity precipitation was slightly lower, which indicated thatthe addition of the selected three kinds of surface modifiers by online modification methoddid not introduce impurities, and the composition ratio of the synthesized ultrafinemagnesium hydroxide flame retardants was not affected.When polypropylene （PP） were added to30%of modified and unmodified ultrafinemagnesium hydroxide flame retardant syntheticd by direct precipitation method and highgravity method respectively, the limit oxygen index （LOI） of PP/Mg（OH）₂compositesystem increased from17.5to28.4、29.3respectively, which conform to the requirements ofthe industry for more than27.0, and was higher than the composite system added the sameamount of commercial magnesium hydroxide whose LOI value was24.3; and themechanical properties were deteriorated withthe tensile strength reducing by10.41%and9.14%, elongation at break decrease of19.57%and17.95%. As a contrast, the compositesystem with30%of commercial Mg （OH）2was deteriorated with the tensile strengthreducing by39.27%, elongation at break decrease of28.68%. The experiment proved that the prepared modified and unmodified ultrafine Mg（OH）₂powder products using twopreparation methods have good flame retardant properties, preferable compatibility with thepolypropylene, and little effect on its mechanical properties.