MECHANICAL PROPERTIES OF HAIR 77 I OF LON$IIUDINAL S#EI_LING 2.õ' 1.5 0.5 % OF PTIVE Figure 7. Longitudinal swelling as a function of moisture after 10 minutes of fiber treatment in de-ionized water, (5) 5% MgC12, (4) 5% NaCI, (3) 5% CaCI 2, (2) and 5% LiC1, (1). Other salts that fell in this same category and led to decay and recovery patterns of F(1) similar to those produced by de-ionized water were NaNO 3 and Na2CO 3. Changes in the F(1)s or hair upon immersion in urea solutions were observed to depend also on the conditioning history of hair and on the urea concentration. The dependence of F(1) on concentration presented, however, peculiar characteristics at concentrations lower than 10%, F(1) decreased monotonically with time and then leveled off at equi- librium values lower than that observed in the case of pure de-ionized water (see Figure 10). In contrast, at urea concentrations higher than 10%, up to saturation, F(1) showed increases, always accompanied by fiber length contractions that lasted only for a short period of time, after which F(1) started to decrease to a level lower than that observed for de-ionized water. Also, the fiber swelled 2% more in length than when immersed in pure water. An inspection of the hysteresis cycle of IR values in Figure 6 indicates that hair treated with a 5% urea solution is slightly more plasticized than before treatment. No changes in the behavior of F(1) were, however, detected after treatment (see Figure 5). The effects of urea were seen to be totally reversible, in that upon thoroughly rinsing the fiber with de-ionized water, the hair recovered its typical normal untreated behavior. Immersion of hair in aqueous solutions of lysine resulted in variations of F(1)s that were dependent on the lysine concentration and hair conditioning history. Upon de- immersion from a 5% lysine solution, it was seen that the time for F(1) and IR to attain equilibrium at any moisture level was slightly longer than that presented by the agents described so far (see Figures 2 and 3). Equilibration of the fiber through the hysteresis

78 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS OF F[1} VARTATTON -too o t 2 ] 4 5 6 7 I{ 9 t0 tt i2 t3 t4 t5 t6 i7 t8 i.q a{ TIME [MINUTES) Figure 8. Percentages of F(1) variation as a function of time of hair fibers conditioned at 87% RH after immersion, (i), and de-immersion, (d), in LiC1 solutions as follows: at saturation, (i) - (1), (d) - (2) 35%, (i) - (3) of hair fibers conditioned at 5% RH at saturation, (i) - (4) and 35%, (i) - (5). cycle showed that the presence of lysine on the fiber causes decreases and increases in the equilibrium values of F(1) and IRs, respectively (see Figure 11). Hence, it seems that this amino acid confers an overall plasticization to the fiber. The behavior of hair fibers immersed in silk amino acids, and in hydrolyzed wheat proteins and wheat oligosaccharides, presented substantial differences when compared to any of the immersion systems already described above. For instance, the behavior of F(1)s and length upon immersion in these systems was always unidirectional and inde- pendent of the amino acid and oligosaccharide concentrations. Equilibration of the F(1)s and IRs after de-immersion from these solutions also took more time than with any of the other immersion systems (see Figure 2). The above results can be explained by considering that when these proteins are absorbed onto the hair, they retard the desorption of water, thereby causing a delay in the turning point that exists between viscoelastic and Fickean diffusion (29,32). It is important to note here that similar modifications in the water absorption isotherm of wool have been induced by the physical and chemical treatment of these fibers (42). The hysteresis behavior of F(1)s and IRs of fibers treated with a 5% silk amino acids solution shows that they have been greatly plasticized (see Figure 12). The effects of a 5 % solution of hydrolyzed wheat proteins and wheat oligosaccharides seems, in contrast, to render the fiber stiffer, although its rate of relaxation as measured by the IR seems to increase at low humidities and to decrease at high levels of moisture (see Figure 12).