Influence of surface modification of magnesium hydroxide on the processingand mechanical properties of composites of magnesium hydroxide and an ethylene vinyl acetate copolymer

Magnesium hydroxide is of increasing interest as an environmentally friendl y flame retardant filler for ethylene vinyl acetate (EVA) copolymers which are widely used in cable applications. In this paper, magnesium hydroxide ( Premier Periclase DP393) was used at a flame retardant loading of 60% w/w i n an EVA copolymer with a vinyl acetate content of 18% (molar). The particu lar modifiers used in this study were stearic acid (converted to ammonium s tearate (AS)) and gamma-aminopropyltriethoxysilane (aPS). The effect of sur face-treated magnesium hydroxide on the processing, mechanical and the flam e retardant properties were determined, together with characterisation of t he interaction between filler and polymer. These studies have shown that, r elative to the untreated filler, use of AS coating leads to a decrease in t ensile strength to a limiting value at monolayer coverage, but an increase in elongation at break, which reaches a maximum at monolayer coverage. Howe ver, the APS treatment enhanced both tensile strength and elongation: relat ive to untreated filler, when used at levels in excess of monolayer. Charac terisation studies suggest that this effect was related to the silane treat ment promoting increased filler-matrix adhesion, and at levels greater than monolayer, promoting formation of a thick interphase and possible crosslin king of the bull; matrix.