Wetting and absorbency of nonionic surfactant solutions on cotton fabrics

The effects of changing aqueous solution properties by nonionic surfactants on the wetting and absorbency in cotton fabrics are reported. A range of solution properties were produced by mixing and diluting two nonionic surfactants, i.e., sorbitan monolaurate (Span 20) and polyoxyethylene(20) sorbitan monolaurate (Tween 20). Desizing and alkaline scouring were employed to produce hydrophobic and hydrophilic cotton fabrics. The molecular areas at water/air interface of individual surfactant molecules, derived from Gibbs adsorption equation, are 19.4 and 60.3 Å2 for Span 20 and Tween 20, respectively. Span 20 has lower surface tension at critical micelle concentration (CMC) and small molecular area, indicating it is more efficient in lowering the surface tension and effective in adsorption than Tween 20. The wetting properties of hydrophobic cotton fabrics are greatly improved by addition of nonionic surfactants in the aqueous systems. The cosine contact angles (θ) of aqueous liquid increased with decreasing liquid surface tension (γ). The amount of aqueous liquid retained in the pore structure of cotton fabric also increased with decreasing γ until the concentration of surfactants approached CMC. In diluted surfactant systems, aqueous liquid retention dramatically increase near CMC, even though the increases in cos θʹs were relatively small. The existence of micelles in a nonionic solution is important for the retention of the aqueous solution in the fabrics. The aqueous retention (W) in cotton fabrics is positively related to its wetting behavior (cos θ) and negatively related to the liquid γ. The critical surface tension of the unscoured cotton fabric, estimated from dilutions of Tween 20, is found to be 28.0 dyn cm−1.