Experimental Studies on Adsorption of Surfactants Onto Cellulosic Surface and its relevance to Detergency

Abstract

The adsorption of anionic - sodium dodecylbenzenesulfonate (NaDBS), cationic – cetyl trimethyl ammonium bromide (CTAB) and nonionic - Triton X-100 (TX-100) surfactants under different conditions on cellulose-water interface are investigated. The adsorption isotherms in general, show four different regimes for the three types of surfactant, such as anionic, cationic and nonionic with some differences. Two important phenomena reflected in the adsorption isotherms are the steep enhancement in the extent of adsorption due to hemimicellization below the critical micellar concentration (CMC) and the reduction in the extent of adsorption above the CMC. The adsorption isotherm for NaDBS shows a maximum at CMC and beyond CMC it shows a decrease in the extent of adsorption. However, for TX-100 and CTAB, hemimicellization occurs with steep enhancement below CMC and the adsorption isotherm levels off without showing a maximum. Adsorption of anionic surfactant, NaDBS gets enhanced in presence of monovalent (K+) or bivalent (Ca++) cation while for nonionic surfactant, TX-100 there is no such enhancement in adsorption in presence of salt. An analysis of adsorption data indicates approximately 25% of the sites are hydrophobic in nature and the rest 75% of sites are hydrophilic in nature and negatively charged. The detergency experiments are conducted to correlate the adsorption of surfactant on cellulose water interface to the removal of particulate and composite soil (particulate and oily) from cotton. Two different soiled cotton, terrace and WFK-10D show the maximum in detergency similar to maximum in adsorption isotherm. Adsorption of NaDBS on cellulose surface is enhanced with increasing ionic strength, but the effect of ionic strength in particulate soil detergency is reverse.