232 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS The term "hydrophobic interaction" describes the tendency of nonpolar groups to associate in aqueous solution. This interaction results in an increased ordering of the water molecules into a quasi-crystalline structure in which there is improved hydrogen. bonding surrounding the nonpolar groups. These hydrophobic regions are disrupted in nonpolar solvents because stronger solute-solvent interactions are thermodynamically favored. Thus, a unique property of the hydrophobic bond is its dependence on water for its existence. The important practical point raised by these considerations is the utility of this type of bonding for setting hair. If the hydrophobic bonds could resist the swelling pressure generated within the keratin which is exposed to high humidity, then the set-conforma- tion would be maintained and a novel process for hair manipulation would be feasible. An investigation of the properties of S-alkylated keratin was therefore undertaken, and this report is an account of such study. II. EXPERIMENTAL ,: a. MATERIALS AND METHODS 1. Reagents.' The chemicals utilized in this study were commercially available:•ii American Chemical Society grade reagents and were used without further purification. 2. Cauc sian hair.' Brown Caucasian hair as supplied • was used w•thout cleansing. ' •:-: .:. 3. Mechanical properties.' The mechanical properties of hair were determined on table model Instron.* The fibers were mounted on plastic tabs at 2 in. guage length,•:55•:. equilibrated under the desired conditions, and stretched to break at a rate of 1 in./min.• •':.• The broken ends were conditioned at 65 per cent RH, cut off the tabs, weighed, and the denier of the tested fibers calculated. :. In some cases, the calibration technique (3) was used to follow the change in the fiber :•: performance. Intact fibers were mounted as above, equilibrated in the desired solvent, and then stretched to 30 per cent extension at a rate of 1 in./min, using the table model. • Instron. After a 24-h relaxation period in water, the calibrated fibers were given the proposed chemical treatment. The ratio of the energy required to stretch the fibers (30 per cent extension) the second time to that required initially, was expressed as the 30 .-: per cent index. 4. Amino acid anaOsis.' Hai /wool samples (•10 rag) were hydrolyzed at 105øC for :• 24 h in 6 N HC1 followed by lyophilization for removal of HCI. The hydrolyzates were :• analyzed for cystine on a Phoenix$ model M-7800 Micro Analyzer. 5. Liquid retention measurements.' The swelling of hair was determined by the liquid retention technique as described by Valco and Barnett (4). This involved measuring. *De Meo Brothers, New York, N.Y. ]'Instron Corp., Canton, MA. •Phoenix Instrument Co. ß

HYDROPHOBIC BONDS AND HAIR TREATMENTS 233 the liquid retained by the hair after a 30 min equilibration in water or other specified solvent. 6. Setting.' One gram (7 in.) tresses were set on one-half in. rollers with water or aqueous alcohol as specified in the text. The set tresses were allowed to dry overnight at ambient temperature and humidity. After removing the tress from the roller, the hair was combed, being careful to maintain the alignment of the hair fibers. The set stability of treated hair was assessed by measuring the hanging length of the tresses after various relaxation times, while exposing them to maintained conditions of humidity and temperature (85 per cent RH, 85øF). B. RESULTS AND DISCUSSION 1. The reaction of reduced hair with alkyI iodides.' Earlier investigations conducted by Harris (2) on wool suggested that the wet mechanical properties of reduced wool could be restored following alkylation with long chain alkyl halides. Both the magnitude of the restorative effect and the simplicity of the alkylation step suggested this approach as being particularly attractive for application to hair. An attempt was, therefore, made to evaluate the efficacy of the alkylation reaction. Calibrated hair fibers were treated with 0.25 N potassium thioglycolate at pH 5 (3 h at 50øC, 25:1 bath ratio) to cleave approximately 50 per cent of the disulfide bonds. Sam- ples of the reduced fibers were then alkylated with 0.02 M alkylating agent suspended in 0.1 M pH 8 phosphate buffer utilizing 100:]_ bath ratio. The alkyl halides used as blocking agents were methyl, hexyl, and decyl iodides, respectively. After 20 h, at 35øC, the fibers were thoroughly rinsed with running tap water and dried. Bulk sam- ples were treated simultaneously in order to determine the weight changes following alkylation. A small weight increase (1.9 per cent) was observed only in the case of the sample treated with decyl iodide. This weight increase corresponded to less than 20 per cent yield of the alkylation reaction. The alkylation treatment also had a negligible effect on the mechanical properties of the reduced hair (Table I). These results were in sharp contrast with the data reported for wool by Harris (2). To ascertain whether the reactivity of the substrate (hair versus wool) contributes to these large differences in behavior, it was decided to re-examine the reaction system using wool fibers. The reduction-alkylation cycle was run under conditions identical to those described by Harris. 2. AIkylation of wool with alkyl iodides.' New Zealand wool samples were reduced with 0.2 N potassium thioglycolate at ph 4.5 for 2]_ h at 35øC (25:]_ bath ratio). The subsequent alkylation was performed using 0.02 M alkylating agent, methyl, hexyl, or decyl iodides suspended in ]_ M, pH 8 phosphate buffer, 35øC at 100:1 bath ratio. The alkylation proceeded very slowly in the presence of the longer chain halides, as was evident by the persistence of thioglycolic acid after ]_8 h reaction time. To insure that an excess of alkylation agent was present, fresh solutions of the hexyl and decyl io- dides, respectively, were added to the wool samples, and the alkylation continued for an additional 7 h. These reactions were monitored by measuring the weight changes, as well as examining the properties of the treated wool.