Uptake of Clays by Cotton1

Abstract

Cotton swatches were treated with dispersions of sodium and calcium montmorit lonite and kaolinite. The amount of clay taken up by the fabric or retained after washing with water was studied as a function of clay concentration, number of wash cycles, and stirring speed. Fabrics treated with sodium montmorillonite dispersions of different concentrations seemed to reach a saturation uptake of 0.32% clay at very low clay concentrations. An apparent saturation limit of 0.75% clay was obtained for calcium montmorittonite only at higher concentrations, and no saturation was observed for kaolinite. Cotton swatches treated with sodium montmorillonite dispersions and given suc cessive wash cycles attained the constant clay content of 0.13% ± 0.01% after the third wash cycle. This level of tenaciously retained clay was independent of concentration. rate of stirring, and temperature. It was not increased by introducing carhoxytic acid groups into the cellulose in the H⁺, Na⁺, Ca⁺⁺ or Fe⁺⁺⁺ form. The ash of fabric treated with sodium montmorillonite was a shrunken replica of the fabric, preserving microscopic details faithfully. These facts and comparison of the specific surface areas of cotton and sodium montmorillonite indicate that cotton was completely covered with a clay layer having an average depth of 3-4 laniellae of 9.5 A each. Owing to the fact that primary particles in sodium montmorillonite dis persions are packets averaging 3-4 lamellae, the depth of coverage was greater than single lamellae. The ash of fabric treated with kaolinite retained the bare outline of the weave because kaolinite did hot cover the fibrils with a coherent layer. Successive wash cycles gradually reduced the kaolinite level of the fabric, following first-order kinetics. Cal cium montmorillonite was intermediate between sodium montmorillonite and kaolinite : the ashes preserved the microscopic details of the fabric structure, but a constant clay level was only attained by fabric treated with dilute dispersions and after many wash cycles. The difference between sodium montmorillonite and kaolinite results from the fact that montmorillonite breaks up into very thin flakes in water and has a much higher specific surface area than kaolinite. Moreover, the thinner montmorillonite flakes mold themselves to the cellulose fibrils and establish a much more intimate contact than the less Hexible kaolinite.