Mechanism and performance of solid non-particulate soil (waxy solid) removal from fabrics

Abstract

Methyl palmitate or palmictic acid methyl ester was used as both a model solid fat and an oily soil was removed from cotton and polyester above and below the melting point. Surfactants studied were extended surfactants (C12,13-4PO-SO4Na , C12,14-10PO-2EO-SO4Na and C12,14-16PO-2EO-SO4Na), alcohol ethoxylate (EO9), sodium dodecyl sulfate (SDS), methyl ester sulfonate (MES), methyl ester ethoxylate (MEE), and mixed surfactants between extended surfactant (C12,13-4PO-SO4Na) and sodium mono- and dimethyl naphthalene sulfonate (SMDNS). Above the melting point (~30 ºC) of methyl palmitate, the maximum oily soil removal was found to correlate well with the lowest dynamic interfacial tension (IFT) with increasing washing temperature and salinity. Therefore, roll-up of liquid soil is an important mechanism. Below the melting point, the detergency efficiency was high corresponding to the low contact angles (indicating high wettability) of the wash solution on the methyl palmitate surface for all studied surfactants. The solidified methyl palmitate was dislodged from fabric surface and dispersed in the wash solution as small solid particles by surfactant penetration resulting from wetting the surface rather than solubilization. Therefore, surfactant and salinity improves wetting, dispersion stability, and decreases detached particle size. Unlike particulate soil, electrostatics is not the primary driving force for solid non-particulate soil detergency.