Four kinds of magnesium hydroxide (Mg(OH) 2 ) with different particle sizes are chosen and mixed with ethylene vinyl acetate copolymer (EVA) to investigate the effect of particle size on the flame retardancy of composites, which is evaluated by limiting oxygen index (LOI) testing, horizontal fire testing, and cone calorimeter. When Mg(OH) 2 filling level changes from 35 to 70 wt %, the composites filled with nano-Mg(OH) 2 do not always possess the best flame retardancy, and among the composites filled with micro-Mg(OH) 2 , the composites filled with 800 mesh Mg(OH) 2 show the best flame retardancy; however, the composites filled with 1250 mesh presents the worst one. So the effect of particle size on the flame retardancy of microMg(OH) 2 -filled EVA is not linear as expected. All the differences are thought to result from both particle size effect and distributive dispersion level of Mg(OH) 2 . To prepare the composites with better mechanical properties and flame retardancy, authors suggested that Mg(OH) 2 of smaller size should be chosen as flame retardant, and good dispersion of Mg(OH) 2 particles also should be assured.

In this article, FTIR spectra and ESEM images were employed to evaluate the effect of stearic acid surface modification of Mg(OH) 2 . As a result, the absorbing peak intensity of organic group on Mg(OH) 2 increased with the coating amount of stearic acid increasing and there was no socalled surface saturation as expected. The results indicated stearic acid surface treatment of Mg(OH) 2 belonged to the acid-base reaction between stearic acid and Mg(OH) 2 , and it would not stop until Mg(OH) 2 was reacted completely. In addition, stearic acid surface treatment of Mg(OH) 2 had remarkable influence on the properties of ethylene vinyl acetate/Mg(OH) 2 composites. With the increasing coating amount of stearic acid, the composites had decreased tensile strength, increased elongation at break, and deteriorated flame retardancy, compared with the composites filled with the uncoated Mg(OH) 2 . However, stearic acid surface treatment of Mg(OH) 2 benefited processing ability of composites, and the composites had better processing ability as the coating amount of stearic acid increased.

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