Synthesis Of Spherical Magnesium Hydroxide, Phosphorus- Silicon Modification And Its Application On Flame Ratarded On EVA

Magnesium hydroxide(MH) has become a focus of research and application of new inorganic halogen- free flame retardant in the world, because of its multiple advantages including flame retardancy, smoke suppression, excellent thermal stability and friendly to environment in use. But, due to its low flame retardant efficiency, magnesium hydroxide has a maximal addition in flame retardant applications. At the same time, it can worsen the mechanical behavior of polymer materials. Now, it is a research hotspot all over the world that is to improve the hydrophilic properties of the magnesium hydroxide, which will improve the compatibility with polymer materials, and reduce the addition of magnesium hydroxide. In this thesis, a reverse precipitation method is used to make the flower-shaped spherical magnesium hydroxide, 9,10-dihydro-9-oxa-10-phospha phenanthrene-10-oxide(DOPO) and γ- glycidoxypropyl trimethoxysilane(K H560) as the phosphorus source and silicon source were used to modify magnesium hydroxide with a P-Si synergistic effect. While improving the dispersion of magnesium hydroxide in the polymer matrix, it also improved the flame retardant properties of the material.This thesis is divided into three parts:Part I: Spherical flower- like magnesium hydroxide was prepared by reverse titration method with seven hydrated magnesium sulfate and ammonia. The influence of concentration of ammonia and magnesium sulfate, the stirring time, settling time, the temperature and dropping rate on the morphology and particle size of the magnesium hydroxide particle were investigated. The product was characterized by scanning electron microscope(SEM) to investigate the morphology and particle size. X-ray Diffraction(XRD)、 Fourier infrared spectrum(FTIR)verified its chemical structure. Results showed that the optimal conditions for the synthesis of magnesium hydroxide: concentration of ammonia 5wt%, magnesium sulfate concentration 1mol/L, temperature 20 oC, stirring time 10 min,settling time 1h, dropping rate 3m L/min. With the increase of initial concentration of the reactants, morphology of magnesium hydroxide changed into a spherical shape, continued to increase the concentration, the spherical contour beco mes blurred, and the particle size with the increasing concentration of reactants ranged smaller from lager; stirring time increases, magnesium hydroxide morphology changed to rules, the particle size also decreased; certain aging time was in favor of magnesium hydroxide transition from metastable structure to steady-state; the too low and too high reaction temperature didn’t conducive to the growth of the spherical magnesium hydroxide; dropped slower, more regular appearance of magnesium hydroxide appeared, the particle size would smal er.Magnesium hydroxide microspheres particle size showed an overall decreased first and then increased to the rules, minimum up to 500 nm, but due to reunite again, most of the microsphere particle diameter was about 1-3 μm.Part II: KH560 and DOPO were used to synthesiz the modified magnesium hydroxide(MHDK). The structur was characterized by transform infrared spectroscopy(FTIR), X-ray diffraction(XRD). FTIR showed P-Ar, P-O-Ph, and Si-O-Mg appeared in MHDK, and the number of-OH group was decreased. XRD data showed that MHDK did not change the crystalline structure of MH, DOPO and KH560 was just grafted to the surface of MH. Contact angle experiments showed that MHDK contact angle increase from 8.31 o to 35.96 o, and hydrophobic improved. Thermogravimetric analysis showed that the thermal stability of MHDK improved, through residual rate can calculate the volume of MHDK grafted which was about 3%. The starting decomposition temperature of MHDK increased 20 oC higher than MH.Part III: Adding MH and MHDK to the EVA, MH/EVA and MHDK/EVA composite materials were prepared. Limiting oxygen index(LOI) results showed that the MHDK can significantly improve the flame retardance, the limiting oxygen index of 50wt% MHDK/EVA increased from 28% to 29.2%, thermogravimetric analysis showed the material added MHDK improved the thermal stability and the initial thermal decomposition temperature of 50wt%MHDK/EVA increased 25 oC and carbon residue rate increased 1.4%. Carbon residue of the material was analyzed by FTIR and SEM. The results showed that after the combustion, the char residues remained P, Si. Phosphorus carbon residue promoted materials into carbon. At the same time, due to the increase of MHDK, there appeared plenty of holes in the carbon residue, the external smooth, the thickness of the remnant carbon increased, and these led to the heat insulation and the suppression of the harmful gas spillover. Tensile test results showed that the tensile strength of MHDK/EVA and the elongation became higher, which indicated that the compatibility of MHDK and EVA increased.The surface polarity of MHDK improved, the flame retardant property of MHDK improved, and the limiting oxygen index was 1% higher than that of MH At the same time, the compatibility of MHDK with material improved, and the mechanical proper ties of the materials improved.