Vacuum Extraction of Caustic Soda Solution from Fabrics Containing Cotton: Impact on Mercerization

Abstract

The vacuum extraction of aqueous NaOH solutions from fabrics containing cotton was studied on a laboratory scale. Removing the NaOH solution by vacuum was less effective than water removal because of the chemical combination of NaOH with the cellulose and the greater water retention of the swollen cotton fibers. Because cotton preferentially absorbs NaOH, the extracted solution was always more dilute than that in the initial bath. Thus, because of the substantivity of NaOH for cotton fibers, vacuum extraction increased the concentration of the solution retained by the material, and the extracted solution was more dilute. The water content of cotton fabrics after extraction increased by about 25% when they were mercerized, washed, neutralized, and then vacuumed again. This was a consequence of increased water absorption by the swollen fibers and not of lower air permeability decreasing the efficiency of ex traction. Vacuum extraction of wet fabrics prior to simple padding eliminated exchange of the water with the bath solution. The use of vacuum extraction in mercerization is outlined.