j. Soc. Cosmet. Chem., 34, 285-300 (September/October 1983) The adsorption of long-chain amines and diamines on keratin fibers IAN W. STAPLETON, CSIRO, Division of Protein Chemistry, Parkville 3052, Victoria, Australia. Received February 24, 1983. Synopsis Adsorption isotherms of n-octyl, n-decyl, n-dodecylamine and the corresponding c•,c0-diamines on loose wool fibers have been determined as a function of pH, temperature, and added electrolytes. The equilibrium saturation levels were found to increase with increasing pH and addition of salt. The monoamines were found to have much greater affinity for the fiber than c•,c0-diamines of the same chain-length. Affinities of both series of amines increased with increasing chain-length. The influence of several anions of the lyotropic series on the extent of maximum adsorption uptake was investigated. Adsorption was found to be promoted by water-structure-breaking ions in the case of a monoamine, and lowered when the adsorbate was a diamine of the same chain length. Estimates of standard affinities (A/x ø) at 40 ø, 60 ø, and 80 ø showed that the standard enthalpy (AH ø) of sorption was zero in the case of 1-aminododecane and - 250 cal/mol in the case of 1,12-diaminododecane. The standard entropies (AS ø) of sorption for both sorbates were found to be positive over the temperature range studied. It is concluded that the sorption of amines on keratin fibers takes place over the "internal" surface, and in a manner which entails cooperative formation of an unstructured miceIlar layer around ionically bound ammonium ions. INTRODUCTION The sorptive capacity of keratin fibers for surface active agents such as detergents, wetting agents, softeners, etc., has been the subject of many physiochemical studies extending over most of this century (see 1-2 for reviews of early work). In the case of wool fibers most of the research has been concerned with anionic surfactants such as alkyl sulfates (3-4), while in the case of hair fibers most interest has been shown in the sorptive propensity of cationic surfactants (5-6). This division of emphasis is possibly a reflection of the extent of commercial application anionic products are used widely in wool production technology as wetting agents and dyeing auxiliaries, while cationic types find wide usage in hair care products as conditioning agents. A determination of the factors controlling the interaction of amines, and in particular, polyamines, with the wool fiber surface is a current research objective in this laboratory. This has come about as a consequence of recent findings relating to 285

286 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS polymer shrinkresist finishes, where it has been shown that a long-chain aliphatic aliamine or a polyamine (such as polyethyleneimine) pretreatment improves the efficiency of the applied polymer (7-8). In work carried out thus far, the pretreatment reagent has been applied by pad rolls followed by a heat fixation step. For commercial processes, however, an exhaust application would be more economical, and therefore a knowledge of the factors affecting the affinity of simple long chain ammonium ions on wool is required. An additional property of amine-treated wool which may be of greater relevance to cosmetic chemistry, is the greatly enhanced dye affinity--even at ambient temperatures. Thus hair dyeing could be facilitated by a pre-treatment which effectively incorporates a polyamine (preferably surface-active) into the hair fiber surface. As a preliminary investigation, an examination was made on the effects of increasing chain-length in alkyl monoamines on their equilibrium uptakes on the fiber, comparing these with the uptakes of c•,c0-diamines of the same chain lengths. In addition, the effects of pH, temperature, and the presence of various inorganic salts in the sorption medium were also examined. The results are presented as adsorption isotherms no attempt was made to gain information on rates of uptake. EXPERIMENTAL MATERIALS Octyl-, decyl-, and dodecylamine were obtained from commercial sources and purified by conversion to the hydrochloride salt, which was then repeatedly crystallized from chloroform/ether. Three diamines--l,8-diamino-octane, 1,10-diaminodecane, and 1,12- diaminododecane--were purchased as high purity reagents and used as such. The monoamines were made up into 0.1 34 solutions from their hydrochloride salts, and the diamines were dissolved in water containing two equivalents of HCI to the same concentration. The Merino wool used was originally in the form of greasy staples. The tips were cut off and the remainder cleaned by Soxhlet extraction with petroleum ether (400-60 ø fraction) for four hours, followed by diethyl ether for two hours. After the solvent had evaporated, the degreased wool was washed repeatedly with deionised water the wool was then squeezed dry, dried in a forced-air oven, and carded to remove vegetable matter. Finally the wool was conditioned to constant weight at 20 ø and 65% humidity. The average fiber diameter was found to be 21 microns and the moisture content 12.7%. The solution used in each sorption isotherm was prepared by adding 5 ml of electrolyte solution and the appropriate volume of 0.1 34 amine hydrochloride solution to a 20 ml volumetric flask and making up to the mark with deionized water. The electrolyte solution compositions were as follows with the pH referring to that found after equilibrium with wool: (a) pH 8:0.4 34 sodium chloride containing boric acid (0.02 34) and sodium hydroxide (0.006 34). For isotherms determined in the presence of thiocyanate, acetate, nitrate, and sulfate, the sodium chloride is replaced with the sodium salt of the appropriate anion (0.4 34). (b) pH 4: Sodium chloride (0.4 34) containing hydrochloric acid (0.016 34).