Physico-chemical studies on the application of insecticides to sheep fleece. III—the action of micellar solutions of cationic wetting agents on fleece†

The reaction of natural fleece with wetting agents changes sharply at a critical concentration near that for micelle formation in solution. This paper describes the behaviour of cationic wetting agents at concentrations below this critical value. Measurements of the apparent removal from aqueous solution (termed the ‘inactivation’) of cetylpyridinium chloride by samples of Scotch Blackface fleece over periods of time show that such inactivation is considerable, even after one minute. The inactivation has been determined from decrease in the interfacial activity of the solution after contact with the fleece. The high inactivation observed is due to grease and suint on the wool; inactivation by the cleaned fibres is relatively slight. Suint influences the interfacial activity of the solution by co-precipitation between the long-chain suint anions and the cetyl cations, and also by the introduction of inorganic salts. High adsorption, with some absorption, occurs at the grease surface. Consideration is given to the mutual interference between these two effects. The inactivation is directly proportional to concentration up to 0.0025M. and the isotherm is almost independent of grease and suint content of the fleece; reasons for this, and possible implications, are discussed.