Effect of Washing Conditions on Cleaning Action of Linear Alkylbenzene Sulfonate in Hard Water

Abstract

The effects of water hardness on textile detergency in aqueous linear dodecylbenzene sulfonate (LAS) solutions were examined under various washing conditions. Plain-woven and towel cotton fabrics and plain-woven polyester fabric were soiled with a mixture of carbon black/oleic acid. The soiled fabrics were shake-washed in the LAS solution together with the original unsoiled fabrics. Surface reflectance measurements revealed that the soil removal and redeposition decreased and increased, respectively, with increasing water hardness. The identity of the mineral species (calcium or magnesium ions) in the hard water had no notable effect on the detergency. The addition of significant amounts of extra LAS did not fully compensate the reduction in detergency in hard water. Addition of softening agents and an alkali builder to the hard water limited the reduction in detergency, but the detergency was still lower than that in the absence of hardness salts. Moreover, a high wash temperature and repeated rinse procedure did not prevent the reduction in detergency in hard water. Finally, a washing test was carried out in hard water under the conditions considered to be effective for improving the detergent quality in hard water, based on the experimental results. The LAS detergency toward the cotton fabrics under these conditions was still poorer than that in the absence of hardness salts. We concluded that using soft wash water is the best choice for maximizing the cleaning power of detergents.