4O4 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS 7 in Table I), which adds 8% to the weight of the fiber, causes only small changes in W20 and//20. Ninhydrin (treatment 2 in Table I), which increases the weight of the fiber by 15%, changes Woo drastically at temperatures between 0 øC and 25 øC. tt2o is also markedly altered at low temperatures but approaches the value of the control fibers at higher temperatures. This may be interpreted by assuming that Ruhemann's Purple, which is formed by the reaction of ninhydrin with the amino groups of the fiber, is deposited near sites normally occupied by water. The interaction of Ruhemann's Purple with the molecules of the matrix could effect an increase in viscosity by mechanical rubbing during defor- mation. This effect is analogous to one in polycrystalline textile fibers (16), in which the crystallites may rub against each other to produce a fiber with a high internal viscosity. At higher temperatures, especially above Tt, the viscosity of the deaminated (due to reaction with ninhy- drin) matrix becomes low enough to flow around these large obstructing molecules or aggregates. After reaction with phenyl isocyanate (treat- ment 6a in Table I), which increases fiber weight by 2•3%, the matrix apparently becomes so viscous (due to steric interferences between bulky groups) that there is no observable transition point, at least up to 80 øC. Hydrophobie bonding (30) may be used similarly to explain the observed experimental facts. The formation of new hydrophobie bonds in the fiber in effect squeezes water out of the fiber and would be expected to alter the equilibrium water content (20). At the same time, the presence of such bonds would be expected to make fibers more difficult to stretch, i.e., increase viscosity. Main Chain and Oxidative Scission W20 is lowered by treatment with 0.01N HC1 for one or for 24 hours (treatments 3a and 3b in Table I) but only in the case of the 24-hour treatment is this weakening appreciable. On the other hand, the hysteresis ratios remain the same as those of control fibers. This observation suggests that the viscosity of the matrix (the dashpot in Fig. 3) remains constant, while the fibrillar portion of the fiber is changing. This conclusion is similar to the one reached by Feughelman and Watt (9) from torsional measurements of a ratio which is a function of the viscosity of the matrix, i.e., •wet/•dry- They indicate that "bond scission apparently causes little change in the effective viscosity of the wool structure maintaining the stress."

MECHANICAL HYSTERESIS OF CHEMICALLY MODIFIED HAIR 405 Strain Strain 0 ø C 250 C Strain Strain 650 C 800 C Figure 4. Hysteresis curves of PFO-treated human hair at various temperatures Repeated bleachings (treatments la-e in Table I) seem to cause changes which, at times, correspond to those from hydrolysis with HCI: The hysteresis ratio at constant temperature seems to be independent of the number of bleach treatments but the absolute value of W20 decreases as much as 35% with an increasing number of bleachings. Bleaching increases the temperature of the second order phase transition from 46 øC to 56 øC. The surprising lack of dependence of H20, T•, and HE of the number of bleach treatments indicates that oxidation (of disulfide bonds) has produced changes in the fiber after the first treatment which are not significantly magnified by further bleaching. It must be assumed that disulfide bonds scission under the bleaching conditions employed here was slight. This is in accord with Zahn's (31) observation that the cystine content does not change appreciably during the first six hours of hydrogen peroxide oxidation even at 50 øC. Helix Disruption and Crosslinking Feughelman and Haly (23) observed the disappearance of the Hookean region of the load-extension curve of wool treated with perfluorooctanoic acid (PFO)for 30 days. The data obtained here (with human hair, treatment 8 in Table I) are somewhat different (Fig. 4), but fibers treated with PFO show a marked change of slope of the yield region. The most interesting property exhibited by fibers treated with PFO is that their hysteresis ratio is a linear function of temperature (up to 80 øC) and has the same slope as that of control fibers in the pretransition area (Fig. 5). Feughelman and Haly suggest that "the PFO has disorganized the a-helices probably by taking part in the inter- and intra-chain hydrogen bonding." They also proved that PFO completely penetrates