Water hardness effect on the association and adsorption of cationic cellulose derivative/anionic surfactant mixtures for fabric softener application

Cationic polymer LR400 and anionic surfactant oleate produce a formulation that can potentially be used as fabric softener. To understand the hardness effect on LR400/oleate complexation and adsorption of the complexes on solid surface is crucial for the actual applications. LR400 and oleate can form associative complexes of different types in aqueous solution depending on concentration. With addition of Ca2+ ions, Ca2+ ions compete with LR400 in binding with oleate and cause precipitation of the complexes. The maximum precipitation occurs at the Ca2+/oleate molar ratio of 1:2 and addition of more Ca2+ results in redispersion of the suspension due to binding of Ca2+ ions on the complexes surface. Adsorption of LR400/oleate on silica from solutions of varied Ca2+ concentration produces adsorbed layer with different structure, composition, and frictional property. The friction coefficient (mu) of the surfaces deposited with LR400/oleate complexes shows dependence on Ca2+ concentration. The smallest mu was found at 0 mM Ca2+ while the largest mu value was found at 0.34 mM Ca2+. The frictional properties indicate well the softening performance of the LR400/oleate mixtures. The study probes into the water hardness effect on the aggregation and adsorption of the softener agents and correlates the frictional property of the surface with the softening effects. It is helpful for the development and formulation optimization of the fabric softeners.