MECHANICAL PROPERTIES OF HAIR 83 Fill [gmf] INDEX OF RELAXATZO J I I I I I I I I I j•JJ 0 0 t0 30 40 50 60 70 BO 90 % OF RELATI Figure 14. Hysteresis curves of fibers treated as follows: F(1) - (1 q-), and IR - (2 I-l), after 10-minute treatment in 100 glycerine and F(1) - (1 O), and IR (2 O), after 10-minute treatment in 100% propylene glycol. cycling experiments while immersed in polydimethylsiloxane oil 350 cSt. These fibers were those treated in aqueous solutions of 5% LiC1, 5% urea, and 100% glycerine. Parallel to these experiments, water absorption determinations of two groups of 17-gm tresses treated in the same manner (plus a control) were carried out (see Figures 15 and 16) the first group was immersed in polydimethylsiloxane oil while the second was not immersed. The control and 5% LiCl-treated tresses immersed in the oil absorbed only 0.1% of their total weight during a period of 70 hours after the chamber relative humidity was changed from 12% to 87% RH in fact, water diffusion into hair throughout the oil was so slow that both tresses absorbed only 4% after 30 days (see Figure 16). In contrast, those not immersed in oil and treated with 5% LiC1, glycerine, propylene glycol, and hydrolyzed wheat proteins and wheat oligosaccharides absorbed rather rapidly percent- ages of water that ranged from 5% to 20% in about 70 hours (see Figure 15). This observation is somewhat surprising since the detected changes in the hysteresis values of F(1) and IR of both fibers, i.e., those immersed and not immersed in poly- dimethylsiloxane oil, were found not to be significatively different within the 70-hour period in spite of their great differences in absorbed moisture content. This apparent contradiction might be explained if it is taken into account that the first layer absorbed onto the polar protein groups, called also the n-BET monolayer, has been reported to be of the order of 0.38 moles of water per 100 g of protein for wool (23,45). Although this monolayer might be of different dimensions in hair, it is quite possible

84 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS I OF WEIGHT VARIATION % OF RELAT•E HUMIDITY Figure 15. Weight variation percentages as a function of moisture of 17-g tresses after treatment under the following conditions: untreated fiber, (1) 10 minutes in 5% LiC1, (2) 10 minutes in 5% hydrolyzed wheat proteins and wheat oligosaccharides, (3) 10 minutes in 100% glycerine, (4 [•) and 100% propylene glycol, (4 O). 2000 t500 t000 500 o WEIBHT VARIATION {gXlO-"] TIME [HI]UP, S] Figure 16. Percentages of weight variation as a function of time of hair tresses immersed in 350 cSt polydimethylsiloxane oil after a change from 10% to 87% RH as follows: untreated control, (I) and a tress treated in 5% LiC1 during 10 minutes, (+).