Evaluation of Surface State of Magnesium Hydroxide as Flame Retarder by Potentiometric Titration Method

Abstract

Magnesium hydroxide powder for flame retarder of plastics must have hydrophobic property for providing good dispersion state during mixing the powder and plastics having hydrophobic property. In order to evaluate the character as a flame retarder of magnesium hydroxide powders treated with stearic acid and a silane coupling reagent, potentiometric titrations were done for dispersions consisting of the powder and aqueous solution of LiClO₄ and TritonX-100 as a wetting agent. The acid-base reaction was Mg(OH)₂ + 2HNO₃ → Mg(NO₃)₂ + 2H₂O which proceeded for the powder without the surface treatment reagents in the pH range between 10 and 10.5. The titration curves obtained for the powders with the reagents shifted to the pH reagion below 10 due to inhibition of the reaction by the reagents at the powder surface. The shifting degree was greater with increase in the amounts of the reagents at the surface. The powders yielding greater shifting, viz., serious reaction inhibition were found to be excellent flame retarder, which can be easily compounded with ethylene-ethylacrylate copolymer as a covering plastic for electric wire under lower torque of mixing machine to provide composites having better characteristics on elongation, tensile strength and electrical resistance per unit volume as the physical poroperties. The potentiometric titration method used was found to be very useful for evaluation of the magnesium hydroxide powder for flame retarder.