j. Soc. Cosmet. Chem., 28, 231-241 (May 1977) Application of the theory of hydrophobic bonds to hair treatments KATHLEEN E. HALL and LESZEKJ. WOLFRAM The Gillette Company, Personal Care Division, Boston, MA 02I 06. Received July 16, 1976. Presented Ninth IFSCC Congress, June 1976, Boston, MA. Synopsis A novel technique of HAIR TREATMENT via introduction of nonpolar residues into hair structure in HYDROALCOHOLIC MEDIA is described. HaJr modified in this manner exhibits greatly ENHANCED SETTABILITY and HIGH SET RETENTION, even at high levels of ambient humidity. The setting be-. havior can be manipulated by uulizing the differential swelling response of treated hair to water and aqueous alcohols. I. INTRODUCTION Conformational stability of a protein, and thus, its response to external mechanical or chemical forces, depends on the type and number of stabilizing bonds present within the protein structure. In the case of o•-keratin, this stability is primarily derived from covalent crosslinking by cystine and intrachain hydrogen bonding. Some contribution also comes from the electrostatic interaction of basic and acidic sidechains, as well as from the hydrophobic bonding of nonpolar residues such as proline, leucine, and valine (1). However, the contribution of the latter is small, and in the intact fiber, the covalent and polar interactions greatly overshadow the nonpolar ones. In an earlier work reported by Harris (2), it was shown that the wet mechanical properties of reduced keratin fibers could be restored without crosslinking by alkylat- ing the fibers with high molecular weight monohalides. Alkylation with alkyl halides of low molecular weight produced permanently weakened fibers. Successful mechanical recovery of the alkylated fibers was ascribed to the interaction of secondary forces, arising from the high molecular weight residues incorporated into the fiber structure during alkylation. In this respect, it is of particular interest to note that the introduction of apolar residues creates an environment favoring the formation of hy- drophobic bonds, and that the strength of these bonds depends on the size and shape of the introduced alkyl groups.