Dynamic Sorption of Semistable Foams by Fabrics

Abstract

Foam is an effective medium for chemical treatment of fabrics at low wet pickup, due to the expanded volume and large internal surface area of the foam bubbles. For a high speed continuous process combining foam application and dissipation steps, foam of limited stability, with high shear susceptibility and dynamic sorption rate is needed. Such semistable foams require delivery of uniformly aged foam to the fabric under positive hydrostatic pressure and precise control of the foam-fabric contact time to achieve uniform distribution in the substrate. For these reasons, semistable foams cannot be applied uniformly by conventional coating methods using a doctor blade and foam bank of variable dimensions. Conversely, stable foams applied by coating methods lack the rapid dynamic sorption rate needed for high speed single- step application.

A mechanism of high speed foam application is proposed, whereby the breaking foam is distributed through the fabric via yam interstices under hydrostatic pressure, and the broken foam liquor wets the interfiber pores driven by interfacial forces. Wetting rates are calculated using typical FFT process operating conditions and cotton fabric geometric parameter estimates. The results indicate that through-fabric wet- out is completed during the interval when the fabric is over the applicator slot. The wetting of interfiber pores is predicted to be slower than through-fabric wetting, but rapid enough to be completed at the applicator. The comparatively rapid wetting rates of yam and fiber surfaces with respect to fiber swelling rates is postulated to make possible the uniform semistable foam application of finishing chemicals to hydrophilic fiber substrates at pickup levels substantially below their moisture ab sorption capacity.