Preparation of Reinforcing Fillers from Japanese Acid Clays with Lime and by Calcination. I. Availability of Raw Materials for Preparing Hard Clay and the Properties of Products

Abstract

Abstract Reinforcing fillers for elastomers were prepared from three representative specimens of Japanese acid clay by treatment with hydrated lime (CaO 10%), subsequent calcination (600°C, 1.5 hr), and mechanical disintegration. Physicochemical properties of the products such as hygroscopicity, pH, diphenylguanidine (DPG) adsorption, specific gravity, and bulk density were determined in comparison with those of raw materials. Morphological and structural features were investigated by means of electron microscopy, X-ray diffraction, infrared and far infrared spectroscopy, DTA, and TGA. The reinforcing effects on SBR-1502 were compared with those of Dixie Clay and Silene EF. The following results were obtained. (1) Acid clays containing montmorillonite and α-cristo-balite as principal constituents are suitable for the preparation of the fillers, but not the clay containing halloysite mineral as a major component in the randomly mixed-layers of kaolinite and montmorillonite with no excess silica. (2) Irreversible contraction as well as the formation of calcium silicates took place in montmorillonite minerals. Calcium silicate is formed in two states, one covering the surface of montmorillonite minerals and the other being set free. This gives rise to remarkable changes in adsorptivity, pH, swelling, bulk density, and specific gravity. Thus it becomes possible to use acid clays as reinforcing fillers. Hygroscopicity and the pH could be made about the same as those of Silene EF. The DPG adsorption capacities could be reduced as low as that of Dixie Clay. The products thus obtained greatly increased in bulk density and exhibited an average property of Dixie Clay and Silene EF in reinforcing SBR-1502.