Water hardness control by detergent builders

Abstract

Commercial detergent additives to control water hardness are of three main types, sequestrant, precipitant or ion-exchange builders. These builders lower the free hardness ion (Ca⁺², Mg⁺²) concentration in a wash system by different mechanisms. An electrometric experimental method was used to evaluate the relative water hardness control performances of different builder-types under conditions closely simulating those of detergent’s end-use. Experimental data for the following builders are presented: EDTA, NTA, STPP, PAA, CMOS, Na-Citrate, Na₂CO₃ and type A zeolite. It is shown that the relative rankings of the various builders in water hardness control differ significantly with differences in use level concentration of the builder (0.005–0.100 gm per 100 ml). The application of the method to the selection of optimum molecular weight range of the newly emerging class of organic polymeric detergent builders like sodium polyacrylates (Na-PAA) (M_w=2000−220,000) also is discussed.