Jay C. Harris

Effect of cotton substrate characteristics upon surfactant adsorption

It is shown that the reported differences in anionic surfactant adsorption on cotton can be largely attributed to the presence of variable amounts of natural wax on the fiber surface. High adsorption values with peaks near critical micelle concentration (cmc) result from surfactant adsorption on the wax surface. Wax-free surfaces fail either to show the same high maxima or the same relative magnitude of adsorption. At surfactant cmc the adsorption relationship for waxy cotton (millimoles/g. of cotton) cationic: nonionic: anionic was roughly 66 to 17 to 74. For dewaxed cotton, this became 40 to 10 to nil.Confirming the findings of others, no adsorption by cotton of sodium tripolyphosphate occurs either with waxy or wax-free cotton. Also addition of tripolyphosphate decreased the adsorption of several anionic surfactants.At concentrations greater than cmc and at sufficiently-high solution temperature, anionic surfactants can solubilize cotton wax, leaving a less waxy substrate upon which adsorption is then reduced.

Correlation between critical micelle concentration, fatty soil removal, and solubilization

Using two model soil-detergent systems (hard substrate/triglyceride; cotton/fat, mineral oil, graphite) it was shown that soil removal begins at, or near, critical micelle concentration (eme), confirming the work of other investigators with different systems. Maximum detergency occurs at concentrations considerably in excess of cmc, varying some 6 to 10 times cmc for different surfactants. An equation for soil removal showed excellent fit of experimental values for both detergency systems.Direct correlation between cmc, solubilization (of several materials), and soil removal was demonstrated. Marked differences between surfactant type and solubilization of triglycerides were found. The nonionic surfactants were excellent solubilizers for triolein correlating with their effective soil removal. Neither sodium oleate nor sodium tripolyphosphate effectively solubilized the triglyceride but both are effective soil removers, suggesting that their soil removal mechanism differs from the nonionics, possibly as an emulsification or displacement mechanism. Solubilization of triglyceride occurs most effectively considerably in excess of cmc.

Electrical Forces Affecting Soil and Substrate in the Detergency Process—Zeta Potential:

Electrokinetic forces are of considerable importance in the mechanism of soil removal and redeposition. One electrokinetic measurement is that of the difference in potential between the immovable layer attached to the surface of a solid phase (soil or substrate) and the movable part of the diffuse layer in the body of the detergent liquid, and is termed zeta potential. Correlations have been obtained which indicate that, in a de tergent system, it is desirable that the zeta potentials of soil particles and substrate become nearly equal to reduce attractive forces tending to cause them to adhere. The effect of surfactants and electrolytes upon the zeta potential of soils and sub strates has been collated, permitting an estimate of the areas in need of further elucida tion. Cited are available correlations between zeta potential and suspension values, critical micelle concentration, and detergency values.

Removal of fatty soil from glass. Electrolyte detergent-builder effect

SummaryThe mechanism of radio-tagged tristearin removal from a glass substrate by sodium tripolyphosphate is primarily one of preferential displacement. Tristearin removal by STP appears to be a competition for primary polar adsorption sites: being the more polar, STP displaces the soil. Continuous soil films are more slowly removed than spotty soil films because initially fewer accessible adsorption sites are available for displacement attack by STP. It is believed that emulsification of these heavy films occurs initially by the ‘stripping” or preferential displacement by STP of the adsorbed monolayer at a site, followed by a rolling up of coherent soil along with the desorbed monolayer, resulting in a degree of emulsification.In addition to its sequestrant water-softening action, previously considered its main function, and its detersive effectiveness, another very important feature has been discovered. Tripolyphosphate (and sequestrant type of anion) adsorbs on a glass surface and reduces the tenacity of subsequent fatty resoiling. This may account to a considerable degree for the demonstratedly high practical cleansing effectiveness of the compound.Adsorption of STP is not by a base exchange mechanism for quartz also displays the same effect as glass. It seems apprarent that the same type of adsorption sites exists on both glass and quartz surfaces though those on quartz suggest either a stronger adsorption of a higher energy level or a larger number of adsorption sites.These data demonstrate the relatively high detersive efficiency of the polyphosphates for this soil/substrate system. Sodium metasilicate and sodium carbonate fall considerably lower in soil-removal value.

Solubilization—A micellar phenomenon

SummaryThe ability of dilute surfactant solutions to solubilize water-insoluble substances to form stable systems is termed solubilization. Reviewed are the mechanism, methods for measurement, and temperature effect. Discussed in detail are surfactant structure and solubilizates, and the principles of solubilization involved. The application of solubilization to detergency operations is discussed broadly.It is concluded that solubilization is a minor, difficultly measurable factor in the large majority of aqueous cleaning operations.

Adsorption of surface-Active Agents by Fibers

1. Clibbens, D. A., and Geake, A., Shirle y Inst. Mem. 6, 117 (1927); J. Text. Inst. 19, T77 (1928). 2. Clibbens, D. A., and Little, A. H., Shirle y Inst. Mem. 15, 25 (1936); J. Text. Inst. 27, T285 (1936). 3. Egerton, G. S., Shirley Inst. Mem. 21, 161 (1947); J. Soc. Dyers and Colourists 63, 161 (1947). 4. Egerton, G. S., Shirley Inst. Mem. 21, 176 (1947); J. Text. Inst. 39, T293 (1948). 5. Egerton, G. S., Shirley Inst. Mem. 21, 188 (1947); J. Text. Inst. 39, T305 (1948). 6. Egerton, G. S., and Guirguis, F. N. Unpublished work.

Removal of fatty soil from glass by surfactants and surfactant-builder compositions

Previous papers have reported radiotagged fatty soil removal from glass either by solvents or by aqueous solutions of sodium tripolyphosphate and other builders. This paper provies soil-removal data for aqueous systems of both pure and built surfactant compositions of the nonionic and alkylbenzene sulfonate types. In general, nonionics are the most effective detergents for the system fatty soil/glass; the 10-mole ethylene oxide adduct products show peak soil-removal. Nonionic surfactants appear most effective for soil removal when used in baths closely approaching their cloud-points. Though modification of hydrophobe by EO addition can affect cloud point, peak soil-removal effectiveness seems to be controlled by hydrophobe selection. Highest soil removal for the alkylbenzene series occurred with the longer alkyl chain (pentadecyl).Admixture of surfactant and sodium tripolyphosphate provided synergistic compositions with certain 10-EO surfactants. Building of anionics markedly improved soil removal over the pure material but seldom exceeded the removal by STP alone.

Solubilization of fatty soils by a radiotracer technique

A technique for measurement of solubilized radiotagged triolein and tristearin fatty soils is described. By using surfactant solutions under standardized conditions of temperature and agitation, the solubilized soils are removed from emulsified materials by filtration through 0.1 and 0.01 micron-pore size of filters. The radiotagged fat is recovered by solvent extraction from the clear filtrate by salting-out under centrifugal force and is measured by conventional counting technique.The nonionic alkanol- and alkylphenol-ethylene oxide (EO) adducts solubilized up to 0.058% triolein (weight percentage at 75°C.) while anionic surfactant and sodium tripolyphosphate solubilization was negligible. These findings suggest for these nonionics that solubilization is one of the main, if not the controlling factor in the mechanism of soil removal. Nonionic solubilization was at a maximum for 10 molar EO adducts and at near cloud-point temperatures.For the same surfactant more triolein than tristearin was solubilized, possibly on account of spatial considerations. For tridecanol-10 EO at 0.25% the heat of solubilization of triolein, ΔHs, was 15 kcal/mole while the heat of micellization of the adduct was 1.3 kcal/mole of adduct. Differences in the colloidal ion lengths of the micelles and their aggregation numbers may explain the differences in solubilization between the anionic and nonionic surfactants tested.

Detergent application of the measurement of critical micelle concentration

SummaryThe measurement of critical micelle concentration is discussed from the viewpoint of practical detergent application. Micelles are briefly characterized, and methods for measurement are discussed. The difficulties of measuring nonionic surfactant critical concentrations is indicated, and several applicable methods are described. The practical detergent applications of critical micelle concentration (cmc), as affected by electrolyte builder combinations, are illustrated. A concise summary of the principles governing micelle formation has been developed.

Removal of radio-tagged protein and stearic acid soil from glass

Both algal protein and stearic acid soils are removed by water alone to near a 50% level; retained soil then becomes more difficult to remove. The bonding of protein soil to glass is stronger than that of tristearin, with indications that stearic acid soil is als slightly more adherent. The shape of the protein soil removal curves lacks the sigmoid shape of the tristearin or stearic acid soils, suggesting either the absence of sharp dependence upon critical micelle concentration, or the existence of adsorption largely at an essentially single energetic level. Both these soils are generally more effectively removed by anionic surfactants than was tristearin.Sodium tripolyphosphate is quite effective for removal of both soils, but combination with surfactants failed to provide the synergistic combinations found in tristearin removal. Nevertheless surfactant soil removal was improved by STP combination.