COMBING FORCE MEASUREMENT 123 combing force curves obtained at 0.12 and 0.18 ks. This end-peak force must be due to a rather unusual tangle and therefore has been ignored. The variation of midlength and end-peak forces during the drying of the tress is shown in Figure 11 as a function of drying time. As can be seen from Figure 11, the levelling off of the midlength force and the maximum in the end-peak force occur almost at the same time (--0.4 ks), corresponding to the removal of extraneous moisture from the tress. Further drying has very little effect on midlength force, whereas the end-peak force continues to decrease at a slow rate, presumably reflecting a continuous improve- ment in fiber alignment during successive combings. This again suggests the contribu- tion of surface tension forces of the liquid to the midlength combing force. Their con- tribution to the end-peak force is indirect in that the surface tension forces prevent fiber entanglement, thus leading to a lower end-peak force or complete elimination of the end-peak force (as in this case) depending upon the method used to measure combing forces. CONCLUSIONS Results reported in this paper and the observations of earlier workers in this field clearly indicate that interfiber interactions make major contributions to midlength and end- peak combing forces in hair tresses. The contribution of comb-hair friction to the mid- length force has been shown to be relatively small. An increase in humidity seems to result in a small decrease in midlength force due to the lubricating effect of surface moisture. On the other hand, wetting the tress increases the midlength force as a result COMBING FORCE (raN) 160 - 120 8( 4O 0 •-o-• x I I I 0.8 1.2 1.6 EP-2 (End-peek) o ML-2 {Mid length} I x---x I I I XX4'x--I 2.0 2.4 2.8 3.2 :3.6 TIME (ks) Figure 11. Variation of end-peak (EP-2) and midlength (ML-2) forces during the drying of a hair tress at 60øC.

124 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS of swelling of the fibers, which makes the compression of fiber bundles between the teeth of the comb more difficult, and also increases the force required to overcome the surface tension forces of the liquid film which hold the fibers together. Wetting the hair assembly results in alignment of the fibers by the surface tension forces of the liquid film after elimination of entanglements. This leads to a drastic reduction in end-peak force to which entanglements make a major contribution. The reduction in wet combing forces with surfactant solutions suggests that the surface tension forces of the liquid make a definite contribution to the midlength force. These effects are further confirmed by the observed decrease in midlength force and increase in end-peak force as a result of removing capillary moisture from a wet tress combed during the process of drying. ACKNOWLEDGMENTS These studies comprised one aspect of work on the Textile Research Institute project "Studies of the Modification of Human Hair Properties by Surface Treatments," sup- ported by a group of Corporate TRI Participants. The authors would like to thank Ms. Margaret Ann Rogers and Ms. Hannelore Mark for their careful experimental work. REFERENCES (1) W. Newman, G. L. Cohen, and C. Hayes, A quantitative characterization of combing force, J. Soc. Cosmet. Chem., 24, 773-782 (1973). (2) W. C. Waggoner and G. V. Scott, Instrumental method for the determination of hair raspiness, J. Soc. Cosmet. Chem., 17, 171-179 (1966). (3) W. S. Tolgyesi, E. Cottington, and A. Fookson, Mechanics of hair combing, presented at the Sympo- siam on Mechanics ofFibroas Stractares, Fiber Society, Inc., Atlanta, Ga., May 14, 1975. (4) M. L. Garcia and J. Diaz, Combability measurements on human hair, J, Soc, Cosmet. Chem,, 27, 379 (1976). (5) A. C. Lunn and R. E. Evans, The electrostatic properties of human hair, J. Soc. Cosmet. Chem., 28, 549 (1977). (6) J. A. Epps and L. J. Wolfram, Combing differences between caucasian and black hair, J. Soc. Cosmet, Chem., 34, 213 (1983). (7) G. F. Scott and C. R. Robbins, The effects of surfactant solutions on hair fiber friction,J. Soc. Cosmet. Chem,, 31, 179 (1980).