Resorcinol‐Formalin Foam Balls Via Gelation of Emulsion Using Phase‐Transfer Catalysts

Abstract

Abstract Summary: Highly spherical (98.5%) low‐density foam balls with 1‐mm diameters were fabricated from a density‐matched emulsion consisting of a resorcinol/formalin aqueous solution and a (mineral oil and carbon tetrachloride) mixture. Phase‐transfer catalysts of carboxylic acid were utilized to induce gelation of the emulsion. The gelation process was monitored by a mechanical test. Gelation forming ball shapes happened within 20–30 min, depending on the catalysts, at room temperature. The gelation time decreased with high‐catalyst concentration. Acids with long alkyl chains did not induce gelation and no balls were obtained. The gelated balls were dried to obtain foam via an exchange of the solvent with 2‐propanol and extraction using the supercritical fluid CO 2 . The density obtained from the catalyst was 0.15–0.16 g · cm −3 . SEM images revealed surface membrane formation, which can be explained by local concentration at the interface of W/O. We observed different bulk foam cell sizes, which may depend on the catalysts and, therefore, on the different gelation rates. Structure of a highly spherical low‐density foam ball with 1‐mm diameter. magnified image Structure of a highly spherical low‐density foam ball with 1‐mm diameter.