358 JOURNAL OF COSMETIC SCIENCE 800 700 600 500 o•400 3O0 2OO 100 0 1000 (a) 1. o8 (b) O45 04 035 O3 025 02 015 01 (c) .... 1 o9 3: o 85 10000 100000 1000000 MW (Daltons) 10000000 2.00% [35.71% 10000 100000 100o000 MW (Daltons) ß 2,00% E] 5.71% 100oo 1 ooooo 10000o0 MW (Daltons) o 8 ß 2.00% E]5.71% 075 lOOO 10000 100oo0 10o0000 10000o00 (d) MW (Daltons) Figure 12. (a) F• and F•o, (b) F•o/F •, (c) E•o/E•, and (d) H•o/H • as a function of molecular weight for PVP.

ELASTICITY AND FLEXIBILITY OF HAIR FIBERS 359 (a) (b) 600 600 1 F•ø = 0.49 H'ø = 0.87 S00 J • • il =0. 400 m = 0.73 200 100 0.95 0 , 0 I 2 3 4 5 o • 2 3 4 s Dis•n ce (m m) o•=ne (mm) Figure 13. Mechanical characteristics of hair treated with (a) IEHC (5.71%) and (b) IEHC plasticized with oleth-10 (5.71% IEHC + 4% oleth-10). within ten seconds of the relaxation time (the time span between consecutive deforma- tion cycles). Another observation concerns the variation in the ratios of Flo/F • and Elo/E • for brittle and plasticized polymers. In general, one could expect an increase in both parameters for more flexible polymers, as was reported for a series of materials presented in Figures 9a-9e. In contrast to this, for both plasticized IEHC and ethyl ester of PVM/MA copolymer (Figures 12b and 13b), a decrease in the ratios Flo/F 1 and Elo/E • is evident. This result indicates that a significant energy loss in such systems occurs through plastic flow, which is facilitated by the presence of a low-molecular-weight additive at a high concentration that decreases the Tg below room temperature. Further details concerning the dependence of F•o/F•, Elo/E l, and Hlo/H 1 as a function of composition were in- vestigated for systems comprised of dimethicone copolyols and oleth-10. The results, not shown in this paper, confirmed a decrease in the values of all three parameters for both blends in the concentration range from 2% to 4% of the plasticizer. CONCLUSIONS Mechanical properties of hair fiber assemblies have been measured by (a) compression of omega loops and (b) three-point bending of hair tresses. The results from both experi- mental procedures were found to be qualitatively similar for both untreated and poly- mer-treated hair tresses. For untreated tresses, humidity was found to significantly affect the properties of hair in terms of bending forces after multiple deformations. The