Studies of Soiling and Detergency
Authors: Fort Tomlinson , Billica H.R. , Grindstaff T.H. 
Published: March 2007

A study was made of the desorption of a carbon-14 labeled fatty acid, fatty alcohol, hydrocarbon, and triglyceride from cellulose. nylon, polyethylene terephthalate (PET), and tetrafluoroethylenehexafluoropropylene (TFEP) copolymer surfaces into aqueous solutions of typical cationic, anionic. and nonionic detergents. Use of the polymers 'in film form as end windows of a Geiger cqunter allowed continuous monitoring of the amount of sorbed radioactive material, and hence of desorption kinetics, under a wide variety of wash conditions. Results of the experiments were used to elucidate the nature of the sorbed material and the mechanisms of detergency.

Average rates of desorption of the four soils increased in the order: hydrocarbon < triglyceride < fatty alcohol < fatty acid. The fraction of sorbate removed in a given time seemed to be independent of the amount of material initially present on the surface. The rate of detergency of a given constituent of a soil mixture was increased by the presence of other relutively easily removed constituents and decreased by the presence of other relatively difficulty removable constituents.

Relative rate of removal of a given soil from the four polymeric substrates depended on both the temperature and the detergent. Thus. at 20°C, removal became faster in the order TFEP ≃ PET ≃ nylon << cellulose. At 60°C, with the cationic and anionic detergents, soil removal rate increased in the order PET < TFEP < nylon < cellulose. With the nonionic detergent at this same temperature, ease of cleanability increased in the order TFEP < cellulose < PET < nylon.

Iligh temperatures increased the rate of detergency of all sorbed species tested. High temperatures also increased the rate of thermally induced diffusion of sorbate into the interior of the polymers, where it was inaccessible to the detergent. Most complete soil removal was not, therefore, always achieved by the hottest detergent solutions. Of the three detergents tested, the nonionic was by far the most' effective soil remover from the hydrophobic polymer substrates which it washed cleaner than it did cellulose. The cationic was intermediate and the anionic poorest. On cellulose the order was anionic> nonionic > cationic. Effectiveness of all three detergents increased with concentration to amounts greater than the critical micelle concentration.

Carboxylate soaps were slightly superior to the synthetic anionic detergent, but much inferior to the nonionic detergent, as fatty soil removers from PET.

Agitation in the detergent solution had a larger effect on soil removal at 60° than at 20°. It was more important for detergency from the hydrophobic polymers than from cellulose.

An excellent correlation was established between soil removal from polyethylene terephthalate film and fabric surfaces. The rate of detergency was determined by the kinetics of rolling up, penetration, and mechanical dislodgment of the soil by the detergent solutions.

Optimum conditions for soil removal from cellulose were not the same as optimum conditions for soil removal from the other polymers. However, detergents mid wash temperatures, etc., were found which would wash both natural and synthetic polymer surfaces clean. Combination of these improved laundry systems with efficient optical brighteners should do much to reduce use discoloration of all fabrics sent to home and commercial laundries.