694 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS REFERENCES (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (ll) (12) (13) S. D. Gershon, and Morton Pader, in Cosmetics, Science, and Technology, 2nd Ed., Dentifrices, Vol. 1, Chap. XIV, Wiley-Interscience, New York, 1972. J. J. Hefferren, Laboratory analysis of toothpastes containing anticaries agents, J. Soc. Cosmet. Chem. 18, 135 (1967). J. J. Hefferren, Interfaces of laboratory and clinical assessment of therapeutic dentifrices, J. Soc. Cosmet. Chem., 24, 815 (1973). W. E. Cooley, Applied research in the development of anticaries dentifrices, J. Chem. Educ., 47, 177 (1970). S. D. Gershon, O. W. Neiditch, and R. H. C. Lee, The effect of fluorides on solubility of powdered enamel, Proc. Sci. Sect. Toilet Goods Ass., 28, 14 (1957). K. G. K6nig, T. M. Marthaler, and H. R. Michlemann, Methodik der kurtzfristig erzengten rattenka- ries, Deutsche Zahn. Mund. IO'eferheilk. 29, 99 (1958). F. Brudevold, H. G. McCann, and P. Gr0n, An enamel biopsy method for determination of fluoride in human teeth, Arch. Oral Bio., 13,877 (1968). Accepted Dental Therapeutics, 36th Ed., American Dental Association. M. W. Reed, Clinical evaluation of three concentrations of sodium fluoride in dentifrices, J. Amer. Dent. Ass., 87, 1401 (1973). S. G. Finn and H. C. Jamison, A comparative clinical study of three dentifrices. J. Dent. Child., 30, 17 (1963). J. Peterson, L. Williamson and A. Casad, Caries inhibition with MFP calcium carbonate in a fluoridated area, Abstract No. L-338, Int. Ass. Den. Res., Preprinted Abstracts, 1975. R. J. Andlaw, and G. J. Tucker, A dentifrice containing 0.8 per cent sodium monofluorophosphate in an aluminum oxide trihydrate base: A three-year clinical trial, Brit. Dent. J, 138, 426 (1975). F. Brudevold and N. W. Chilton, Comparative study of a fluoride dentifrice containing soluble phos- phate and a calcium-free abrasive: Second year report, J. Amer. Dent. Ass., 72,889 (1966).

J. Soc. Cosmet. Chem., 28,695-704 (November 1977) The tensile properties of hair fibers in 1-propanol water mixtures D. LU g and M. M. BREUERt Personal Care Division, The Gillette Company, Gillette Park Boston, MA 02i 06. Received January 3, 1977. Synopsis The stress-strain curves of intact hair fibers immersed in aqueous 1-propanol solutions were measured as functions of 1-propanol concentration, pH and temperature. Plots of the tensile forces at given extensions against the propanol concentrations show minima at about 50 per cent propanol these become more pronounced at low pH values and at higher temperatures. The experimental results can be interpreted by assuming that two additive molecular processes are responsi- ble for the elasticity of hair: conformational changes of the polypeptide chains and electrostatic interactions between the various ionic side chains. The presence of Dpropanol in low concentrations accentuates the im- portance of the latter process by diminishing the value of the effective dielectric constant inside the hair structure. At high propanol concentrations, however, the dehydration of the fibers increases the relative contribution of the conformational changes and brings about a strengthening of the hair. I. INTRODUCTION Alcohols are extensively used in the formulation of hair care products. Although many of the technologically important properties of keratin fibers have been known to be af- fected by exposure to alcohols (1, 2) (e.g., the elastic modulus and the temperature of supercontraction both change when hair is immersed in aqueous alcoholic solutions (3)), the mechanisms responsible for these processes are still unclear. Essentially, two hypotheses have been formulated to account for these phenomena. Blankenberg and Zahn (2) suggested that the alcohols break hydrophobic bonds and thus, weaken the keratin structure. Breuer (4), on the other hand, postulated that the presence of al- cohols in the keratin fiber alters the transition equilibrium between the organized and amorphous regions of keratin and, therefore, affects the stress-strain characteristics of the fibers. Neither of these hypotheses allowed for the possibility that the absorption of alcohols by hair might also affect the electrostatic interactions within the fibers and, thus, could affect their mechanical properties. 26133 Hughes Aircraft Co., ! 1940 West Jefferson Blvd., Culver City, CA 90230. tGillette Research Institute, ! 4 ! 3 Research Blvd., Rockville Md. 20850. 695