Surface Modification of Anhydrous Borax Powders with Stearic Acid via Mechanical Dry Powder Coating

Abstract

Surface modification of anhydrous borax powders with stearic acid in the laboratory-scale planetary ball mill via mechanical dry powder coating approach was investigated. The alteration of hydrophilic surface properties of anhydrous borax with stearic acid was optimized by modifier amount and activation time. The cohesion mechanisms of powders, which processed at conditions of 0.5, 1 and 2 wt. % stearic acid amount with the function of 30, 60 and 120 minute activation time, were evaluated in terms of the solubility test, contact angle measurements, particle size distributions, and scanning electron microscopy (SEM) analysis. Results indicate that anhydrous borax surface could be switched from hydrophilic to hydrophobic with changing contact angle from wetting (17 o ) to non-wetting (99 o ). Water-insoluble amount of anhydrous borax powders, as a coating efficiency indicator, was increased from 73 % to 91 % by coating with 1 wt. % stearic acid for 60 min. Furthermore, SEM analysis results demonstrate that stearic acid was discretely coated over the anhydrous borax surface. As a conclusion, an effective mechanical dry coating processing by a one-step coating approach could be applied to obtain a modified anhydrous borax surface, which offers controlled solubility behaviour in water-based suspensions.