Abstract: Several organic acid reactive comminuted minerals, which are generally used as fillers for plastics, rubber, etc., are treated with unsaturated organic acids, alone or in admixture with saturated acids, antioxidants and, alternatively, liquid agents. The surfied (surface modified) fillers thus obtained have excellent wetting and dispersion in both polar and non-polar media as exemplified by their superior packing fractions. Unsaturated acids, alone or in admixture with saturated acids, do not yield fillers stable to the effects of oxidation, both in preparation and use. It has been discovered that very low concentrations of antioxidants stabilize the surfied filler against oxidation and resulting instability. Liquid agents also have been discovered to add a new dimension to the art by cooperating with the acid surfiers (surface modifiers) to modify the interface between the filler and matrix to a greater extent than by previously available techniques.

Abstract: Low density fillers or pigments adapted for use in paints, plastics, caulks and the like are produced by dispersing particulate materials of an average equivalent spherical diameter of 0.1 to 30 micrometers in an aqueous medium containing an acid-polymerizable resin. The dispersions thus produced are formed into spheroids which are heated to polymerize the resin and evaporate water therefrom so that voids are developed within the products. In this way the particles are bonded together and the product is provided with a protective coating of polymerized resin.The products thus produced are relatively low in density and may embody various particulate materials which would be hydrated or otherwise adversely reacted with water or other constituents of the paint, plastics, or medium in which they are incorporated.