Modelling of detergency performance for some technical nonionic surfactants

The detergency behaviour towards nonpolar soil was modelled for seven technical nonionic surfactant as a function of surfactant concentration, washing time and washing temperature. The detergency experiments were carried out according to a central composite circumscribed statistical experimental design. Second order polynomial functions were used for the modelling. It was possible to establish good models for all surfactants except one. For three of the surfactants the models predicted a detergency maximum. The detergency effects of these surfactants were examined at the variable settings predicted to give maximum detergency. The results obtained were in good agreement with predictions. The surfactant concentration giving maximum detergency is not directly linked to the c. m. c. The temperature for maximum detergency corresponds to the cloud point of the washing solution with the surfactant concentration giving maximum detergency. The cloud point has to be determined with the soil present. This indicates that a microemulsion has to be present to obtain maximum nonpolar soil removal.