Tagawa Yumiko

Cleaning power of different surfactants was investigated using a model detergent system consisting of a PET film and stearic acid. Surfactants used were alcohol ethoxylates (AE, C12) and methyl ester ethoxylates (MEE, C12) with different ethylene oxide (EO) chain lengths. For comparison with these nonionic surfactants, anionic surfactant, sodium alkyl sulfate (AS, C12), was chosen. After depositing stearic acid, the PET film was cleaned in aqueous surfactant solutions by applying stirring as a mechanical action for soil removal. The amounts of stearic acid deposited on the PET film before and after the cleaning were obtained by binary processing of microscopic images of the PET film surface, from which the removal efficiency was calculated. The surface tension gamma and the contact angle on the PET film theta of the surfactant solution were measured by the pendant drop and the sessile drop method, respectively. For the nonionic surfactants, critical micelle concentration, cmc, and gamma and theta above cmc decreased with decreasing EO chain length. The removal efficiency of stearic acid increased with increasing surfactant concentration and further increase in the removal above cmc was observed in the cases of AE and MEE with EO chain length of 10. The removal efficiencies obtained in all systems had good relation with both gamma and theta, indicating that the penetration of the surfactant solution between stearic acid and the PET film in the contact zone was a dominant factor in the soil removal in the present system.

The soil removal behavior from poly(ethylene terephthalate) (PET) films was investigated using a microscopic image analysis system. Carbon black or stearic acid as a model soil was deposited onto a PET film. The PET film was cleaned in various aqueous and non-aqueous solutions by applying stirring or frequency-modulated ultrasound as a mechanical action of soil removal. The amounts of soil deposited on the PET film before and after cleaning were obtained via binary processing of microscopic images, from which the removal efficiency was calculated. Most of the carbon black was deposited on the PET film as submicron aggregates and ultrasound removed them efficiently in a short time, even for relatively smaller aggregates. The removal efficiencies with stirring were less than ca. 10% in all solutions, whereas the removal using ultrasound had high efficiencies that exceeded 80% in the surfactant-free systems. In the case of stearic acid, the removal efficiency with stirring was below 30% in the aqueous solutions, although stearic acid was removed completely in ethanol and n-decane. For ultrasonic cleaning, the removal efficiencies of stearic acid in aqueous solutions became 2-3 times as large as those with the stirring action. To improve soil release in aqueous solutions, the PET film was treated by the dry processing using an atmospheric pressure plasma jet (APPJ) equipment. The wettability and the surface free energy of the PET film were found to increase due to surface oxidation via the APPJ treatment, which resulted in enhanced removal of carbon black and stearic acid in any aqueous solutions. © 2013 by Japan Oil Chemists' Society.