Cotton fabrics soiled with fatty acids or bovine serum albumin were washed with LAS, sodium oleate, SDS, AOS, and the influence of water hardness on the detergency was investigated.
The apparent removal efficiency of fatty acids extracted by diethylether did not decrease with higher water hardness, contrary to the decreasing tendency of removal efficiency of albumin. This unexpected behavior could be considered that calcium salts of fatty acids remained in fabric were not extracted by diethylether.
The corrected value of soil removal efficiency obtained by taking the formation of calcium salt of fatty acids into consideration from the difference of adhering calcium amount between in scoured fabric and in soiled one after washing, decreased with increase of water hardness, and corresponded to the lowering of concentration of free surfactant residue. Exceptionally, corrected removal efficiency of fatty acids washed with AOS had negative values, and this fact was considered to be the characteristic adhesion mechanism of calcium in AOS washing water.
