Surface Treatment of Inorganic Fine Particles with Phosphoric Acid Alkyl Esters

Abstract

Inorganic fine particles of calcium carbonate and magnesium hydroxide were treated with phosphoric acid alkyl esters and stearic acid as a reference by the following method: The fine particles were suspended in ethanol dissolved with the treating agent and then ethanol was evaporated. The amounts of treating agent were set between 0 to 2.1 times of the amount completely covered the particle surfaces. The adhesion states of the treating agents to the fine particles were analyzed by the contact angle to water, the sedimentation volume in cyclohexane, the solvent extraction, and melting behaviors. In all cases of magnesium hydroxide series, the treating agents were ionically bonded to the particle surface as mono-molecular layer of the agent with their alkyl chains pointing outward. In the case of treating calcium carbonate with stearic acid, stearic acid molecules were not bonded but absorbed to calcium carbonate particle surfaces with their alkyl chains pointing outward. In the case of treating calcium carbonate with phosphoric acid alkyl esters, phosphate groups were ionically bonded to the particle surfaces at the first layer and adhered on them by ionic interaction at the second and third layers, generally with alkyl chains pointing outward.