title: Effects of Water Hardness on Textile Detergency Performance in Aqueous Cleaning Systems.
abstract: The effects of water hardness on textile detergency in aqueous solutions were systematically investigated using four surfactants: sodium oleate (OLNa), linear dodecylbenzene sulfonate (LAS), sodium dodecyl sulfate (AS), and polyoxyethylene (10) dodecyl ether (AE). Water hardness was adjusted according to the standard procedure described in IEC 60734:2012. As expected, by adding hardness salts the surface tension of the OLNa solution increased. Surprisingly, the addition of hardness salts lowers the surface tension for the LAS and AS solutions. In the case of the AE solution, hardness salt did not affect the surface tension. A decrease in transmittance and foamability after adding hardness salts was observed for every anionic surfactant solution, indicating that anionic surfactants can combine with divalent ions to form insoluble precipitates. Detergency experiments were performed using cotton plain-woven and towel fabrics soiled with a carbon black and oleic acid mixture. One piece each of untreated and soiled fabric were stacked and placed horizontally in detergent solution with or without hardness salts. As a mechanical action of soil removal, the shaking of 190 spm was applied. Soil removal and redeposition due to washing were evaluated from changes in values of the Kubelka-Munk function for both fabrics. With increasing water hardness, soil removal decreased and redeposition increased. In order of decreasing detergency, the surfactants were as follows: LAS > OLNa ≈ AS > AE. The results indicate that precipitates, formed by reaction of LAS or AS with hardness salts, are strongly adsorbed on the water surface because of their hydrophobicity, but they have no detergency power. The field emission scanning electron microscopic observation and X-ray photoelectron spectroscopic analysis showed that Ca(LAS)2 precipitation clung to fiber surfaces, and remained on the surfaces after washing. Significant changes in the cotton fabric due to washing were observed in mechanical properties and water absorbency.
authors.affiliation: Faculty of Human Life and Environment, Nara Women's University.
authors.forename: Keiko
authors.initials: K
authors.lastname: Gotoh
authors.forename: Kaori
authors.initials: K
authors.lastname: Horibe
authors.forename: Yang
authors.initials: Y
authors.lastname: Mei
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Tsujisaka
mesh_terms: D001557:Benzenesulfonates; D002118:Calcium; D003902:Detergents; D057927:Hydrophobic and Hydrophilic Interactions; D008855:Microscopy, Electron, Scanning; D019301:Oleic Acid; D056951:Photoelectron Spectroscopy; D011092:Polyethylene Glycols; D012492:Salts; D012967:Sodium Dodecyl Sulfate; D012996:Solutions; D013500:Surface Tension; D013501:Surface-Active Agents; D013784:Textiles; D014867:Water / Q000737:chemistry*
chemical_list: D001557:Benzenesulfonates; D003902:Detergents; D012492:Salts; D012996:Solutions; D013501:Surface-Active Agents; C478747:polyoxyethylene-10-dodecyl ether; D014867:Water; D019301:Oleic Acid; D012967:Sodium Dodecyl Sulfate; C013173:osteum; D011092:Polyethylene Glycols; C001114:dodecylbenzenesulfonic acid; D002118:Calcium