392 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS small change in both birefringence and Young's Modulus. However, from a 6M to 7M concentration of lithium bromide the optical birefringence drops drastically to a value less than 0.2 of the value for the fiber in water. Completely concomittant with this rapid drop of birefringence, the Young's modulus of the fiber as indicated previously drops by a factor in excess of 20 to a value corresponding to a material in the elastomeric state. The c•-helices have been transformed to random coils and no longer form crystalline structures. Crystallinity within the c•-keratin structure, which involves the ordering of the c•-helices within that structure, appears to be the main factor contributing to the stiffness of the fiber in water at extensions within the Hookean region. INFRA RED ANALYSIS The infra-red absorption of c•-keratin fibers (35) exhibits the characteristics found in protein spectra generally, such as the amide A, I, and II bands. By the application of polarized infra-red and the measurement of absorption with the planes of polarization parallel and perpendicular to the fiber direction (dichroism), it has been shown that the amide NH and CO groups in keratin are preferentially ordered in the fiber direction (36). Further, when the fibers were immersed in heavy water (D20) within 24 hours about 70% of the amide hydrogens were replaced by deuterium (37). The remaining amide -NH groups were highly dichroic, the dichroic ratio for -NH groups increasing by the deuteration from about 1.5 to 5.5. This means that the undeuterated NH groups remaining correspond to highly oriented structures. A theoretic estimate from the dichroic ratio (38) shows that the 30% undeuterated groups could be accounted for by 80% perfectly aligned c•-helical material with about 20% randomly oriented undeuter- ated -NH groups. Further, the infra-red data means that this highly organized 30% of the structure of c•-keratin fibers in the time range of 24 hours exhibits negligible association with water as far as the amide --NH groups are concerned. Again the evidence points strongly to the lack of interaction of water with the organized c•-helical structure within the keratin fibers. ELECTRICAL CONDUCTIVITY AND THE DIELECTRIC PROPERTIES The electrical conductivity of an c•-keratin fiber is very dependent on the water content of the fiber. The keratin-water system acts as a protonic semi-conductor in which the mechanism of transfer of the proton is similar to that proposed in ice, consisting of a rotation of water molecules and proton jumps between two equilibrium positions between the oxygen atoms of neighboring water molecules. 39 The conductivity requires a continuous hydrogen bonded network of water molecules, and it is the sensitivity to the number of protonic pathways throughout this network that results in an increase of electrical resistivity of wool fibers at 25øC from 6 x 106 ohm-cm at 25% water content to 3 x 1012 ohm-cm at 7% water content based on the mass of dry keratin. The conductivity also depends on the freedom of rotation of the water molecules. The temperature coefficient of the conductivity corresponds to an activation energy barrier of 30K.cal./g. mole for a nearly dry fiber reducing to 15K.cal./g. mole at 25% water content, indicating a freeing within the structure of the movement of protons as the water content of the fiber is increased (40). With the small extensions corresponding to strain in the "Hookean" region the electrical conductivity of the fibers exhibits an insignificant drop. The network of water

PHYSICAL PROPERTIES OF ALPHA-KERATIN FIBERS 393 molecules coming under this low level of strain is little affected in terms of its conductivity pathways. Conduction associated with the water present within the keratin structure is essentially a property of the non-ordered component of the structure. The dielectric properties of the keratin water system (41) are dependent on frequency of' the measurement as well as the water content. At high water contents, which correspond to the state of the fibers in a high humidity environment, the dipolaf orientational polarization of large segments of the keratin structure is plasticized that is, it is freed in its movement by water and is responsible for the major component of the total polarization. A contribution is also made by water molecules free to align with the applied field. Because dielectric and dynamic mechanical data are essentially dependent on the mobility of the same elements within the keratin structure, comparison can be made between the mechnical relaxation spectra obtained for fibers extended within the "Hookean" region and the dielectric relaxation spectrum for fibers at the same water content and temperature. THE TWO-PHASE MODEL For small distortions of a keratin fiber that exist in the "Hookean" region the fiber's behavior with changes of water content on the basis of much of the foregoing data has been expressed in terms of a two-phase model (42) consisting of a water impenetrable phase of cylindrical rods oriented parallel to the fiber direction embedded in a water penetrable matrix-phase. The matrix-phase is mechanically plasticized and weakened by the presence of water, whereas no mechanical change is expected in the cylindrical rods with water uptake by the fiber. Torsional mechanical data shows that the modulus of rigidity of a dry fiber (,• 0% relative humidity) is about 1.7 x 10 9 pascals, falling by a factor of 10-20 to a value of 1-2 x 108 pascals for a wet fiber (43,44). This major change in torsional rigidity for the fiber as the environment is changed from dry to wet occurs in parallel with a much smaller change in the longitudinal stiffness of the fiber by a factor of 3-4. In longitudinal extension in terms of the two-phase model the two phases act in parallel with both equally deformed. This means that in the wet state the unweakened cylindrical rods contribute considerably to the longitudinal stiffness of the fiber. When the structure undergoes twist about the fiber axis, however, if the matrix is weakened by the presence of water the distortion is nearly completely confined to the matrix, and the torsional stiffness depends mainly on the matrix opposition to the torsional distortion. The result would be that on the basis of the proposed model the presence of water in the structure should cause a much greater reduction in torsional rigidity than in longitudinal stiffness of the fiber going from a dry to wet environment, a result borne out by the experimental data. Ample evidence exists for the presence of a highly ordered structure of low water penetrability within the keratin fibers, containing the organized c•-helical material (11). Chemical evidence (45) based on the extraction of proteins from c•-keratin fibers after the breaking of the disulphide bonds shows that two major fractions of proteins are obtained, a high and a low sulphur component. The low sulphur component is made up'of about 50% c•-helical material, and the high sulphur protein extract has no helices. In line with the physical evidence, the microfibrils within the cortex of the c•-keratin fibers have been identified with the water impenetrable cylindrical rods of the tw$-phase model. The microfibrils contain the crystalline c•-helical material and hence are the source of the low sulphur protein extracts. However, as has been pointed out by Bendit (46), the low sulphur protein is not completely confined to the microfibrils and