The Research Of Technology On Raising The Decomposition Temperature Of Flame-retardant Grade Aluminum Hydroxide

Aluminium hydroxide is a fine flame retardant, and it can be used for flameretardance, smoke suppression and filling. It is non-toxic, non-volatile and can besynergized with other flame retardants. While aluminium hydroxide has a lowdecomposition temperarure, which limits its usage range. So, the research oftechnology on raising the thermal stability of aluminium hydroxide is of greatimportance. This paper mainly studied the effects of different surfacemodifications on the thermal stability of aluminum hydroxide, and primarilyanlysised the mechanism of raising thermal stability, meanwhile a novlealuminum salt with better thermal stability was prepared at atmospheric pressure,the main conclutions of the paper are as follows:(1) The thermal stability of the aluminum hydroxide can be improved by drysurface modification with phosphoric acid. While the mass rate of phosphoric acidto the aluminum hydroxide is 5wt%, the concentration of the modifacation agentis 0.2g/ml, milling time is 10min, the initial loss temperature of crystal water inmodified aluminum hydroxide rises from 192℃to 208℃, but the modifiedaluminum hydroxide has a larger particle size and bad agglomerate, the oilabsorption turns to be 74ml castor oil per 100g aluminum hydroxide from theoriginal of 44ml castor oil per 100g aluminum hydroxide.(2) The initial loss temperature of modified aluminum hydroxide withpolyacrylic acid can be up to 200℃, and the oil absorption is 41ml castor oil per100g aluminum hydroxide, which is less than that of the original; When modifiedwith the mixture of phosphoric acid and polyacrylic acid(mass ratio 1:1), theproduct's decomposition temperature can be 203℃, and its particle size and oilabsorption are smaller than those of modified with phosphoric acid.(3) It is found that the the initial decomposition temperature of aluminumhydroxide modified with ammonium dihydrogen phosphate(MAP) can up to 205℃when wet modification process employed, the favourate condition is:temperature of 90℃, mixing time of 90min, MAP addition (MAP/ATH) of 5wt%,the ratio of liquid to solid of 5, the final pH value in the modifying solution of6.0～6.5. The research shows the particle size of modified powder agglomerateds alittle, and the oil absorption increases a little, it is 51ml castor oil per 100g aluminum hydroxide.(4) A novel modifying agent PNC was exploited, the modified particle withthis modifying agent has the same thermal stability as the aluminum hydroxidemodified with MAP, and agglomerateds decreases, meanwhile the oil absorptionis 41ml castor oil per 100g aluminum hydroxide, which is less than the originalaluminum hydroxide.(5) The mechanism of surface modification improving the thermal stabilityof aluminum hydroxide was analyzed from the views of dynamics andthermodynamics. The mechanism of surface modification improving the thermalstability of aluminum hydroxide, according to dynamics, is that water moleculeproduces when the modified aluminum hydroxide decomposes has to get over notonly the obstruction of AlOOH, but also the obstruction of coating generated insurface modification; according to thermodynamics, because of the coating, theconcentration of water molecule on the surface of aluminum hydroxide kernelincreases so that the equilibrium vapor pressure increases, accordingly thedecomposition temperature rises.(6) An aluminum salt (contains hydroxy aluminum oxalate and partlydecomposed alnminum hydroxide) with higher thermal stability was prepared atatmospheric pressure, and the result shows, the product has a decompositiontemperature of 231℃, the decalescence of the decomposition of 1981kJ/kg, theseall indicate that the product may be used as flame retardant in the future.