Detergents dirt redeposition prevention

Laundry detergent may also contain polyethylene glycol, a polymer that prevents dirt from redepositing on the clothes. This function used to be the job of phosphates. Another polymer used for this purpose is carboxy methyl cellulose, which is derived from natural cellulose but is very soluble in water. 

The first important commercial builder was sodium tripol3q)hosphate, NasPsOio, first used with Tide detergent in 1947. Besides sequestering polyvalent metal ions, it prevents redeposition of dirt, buffers the solution to pH = 9 -10, kills bacteria, and controls corrosion and deposits in the lines of automatic washers. 

The function of the detergent is to remove the dirt and dust particles and other constituents of the size such as china clay from the cotton fabric. The detergent keeps the soils in dispersed or suspended form in scouring solution and prevents redeposition on the fabric. Fig. 4-10 illustrates the sequence of events of soil removal. Adventitious dirt adhere to the fabric because the oil acts as an adhesive towards it. The fabric/soil/water interfaces not soluble in water is shown in... 

CMC is used primarily in surfactants and PVP is used as bath additive. Further, CMC also forms a protective colloid with the soil and thus prevents soil redeposition on the cloth. The emulsion of oil and dirt should be stable, otherwise there will be redeposition. Ordinary soap and detergent is a good emulsifying agent. 

Antiredeposition Agent. A component in a detergent formulation that acts to help prevent redeposition of dispersed dirt or grease. Example carboxymethylcellulose. See also reference [4], Detergent. 

To formulate a good detergent, one has to understand the various processes involved Wetting, removal of dirt, liquid soiling, prevention of redeposition of dirt. 

To prevent dirt particles from redepositing on the substrate once they have been removed, they must be stabilised in the cleaning bath by colloid-chemical means. Prevention can be effected by electrical charge and/or steric barriers (see below) resulting from adsorption of the surfactant molecules from the cleaning bath both by the dirt particles and substrate. The most effective detergents for this purpose are nonionic surfactants of the poly(ethylene oxide) type. In some formulations, nonionic polymers or polyelectrolytes are added to prevent the redeposition of dirt particle (e.g. sodium carboxymethyl cellulose or other nonionic polymers). 

To be effective as a detergent, a surfactant has to fulfil a number of functions. First, it must effectively wet the fabric, so that the detergent will come into contact with the surface to be cleaned. Second, it should facilitate the removal of dirt from the fabric surface. Third, it should solubilize or disperse dirt, and help to prevent its redeposition. Figure 4.19 summarizes the action of detergent through these processes. 

---