Modifications of High-Oriented Magnesium Hydroxide and Its Applications in Ethylene-Vinylacetate Copolymer
The light calcined powder(mainly composed of MgO)obtained from magnesite calcination was used as the raw material,and ammonium nitrate solution was used as the mother liquor for ammonia evaporation.The ammonia evaporation conditions were changed to improve the ammonia conversion rates.Layered highly-oriented Mg(OH)2 was synthesized by using the ammonia circulation method.During the ammonia distillation process,the effects of the initial molality of ammonium nitrate(CNH4NO3),ammonia temperature,and the ratios of amounts of substance between ammonia and magnesium on the ammonia conversion rates were studied.To modify the prepared Mg(OH)2,the silane coupling agents[ethylene trimethoxysilane(HD-171)and ethylene trimethoxysilane(β-Methoxyethoxy silane(HD-172)]were used as the surface modifiers.The HD-171-and HD-172-modified Mg(OH)2 additives were added to ethylene-vinylacetate copolymer(EVA).The tensile properties and flame retardancy of the composite materials were characterized.The results show that,temperature and the ratios of amounts of substance between ammonia and magnesium are the key factors affecting the leaching rate of magnesium ions in the ammonia distillation reaction.The Mg(OH)2 product with a purity of 99.98%,a particle size of 1.3 μm,and a high orientation of hexagonal flakes[I(001)/I(101)=1.3,where I is the diffraction peak intensity of the crystal plane]was successfully prepared.By comparing the oil absorption values of Mg(OH)2 before and after modification,the modification effect of modifier HD-171 on Mg(OH)2 is the best when the reaction temperature is 75℃,the mass fraction of modifier HD-171 is 4%,and the reaction time is 60 min.The modification effect of modifier HD-172 on Mg(OH)2 is the best when the reaction temperature is 85℃,the mass fraction of modifier HD-172 is 4%,and the reaction time is 60 min.When the additive mass fractions of composite materials are 70%,compared with the unmodified Mg(OH)2/EVA composites,the tensile strengths of HD-171-and HD-172-modified Mg(OH)2/EVA composite materials respectively increase by 4.05 MPa and 2.53 MPa,and the oxygen index values respectively increase by 2.6%and 1.1%.These results indicate that HD-171-and HD-172-modified Mg(OH)2 could effectively improve the flame retardancy and tensile properties of EVA.
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