UV DAMAGE ON GRAY HAIR 113 lOO 95 90 85 80 75 70 65 60 55 50 Control CATC OMC ,SLS 0 2 4 6 8 10 12 14 16 UV Exposure Time (days) Figure 6. Changes in dynamic contact angle after UV irradiation. hydrophobic surface, as indicated by essentially no change in the contact angle compared to those fibers that had not been exposed to UV. As a quaternized ultraviolet absorber, CATC deposited on the hair surface to protect hair from UV penetration and also modified the hair surface. Therefore, the hydrophobic surface of tress 2 even after UV irradiation could be attributed to more than one mechanism: either photoprotection of the hair surface, preventing surface damage, and/ or a conditioning effect as a result of its cationic nature. In order to differentiate between these two mechanisms, we washed a part of tress 2 with IPA to remove CATC thor- oughly from the hair surface and then remeasured the contact angles. We found no significant difference in average contact angles between extracted and un-extracted hair fibers. This clearly indicates that the hair surface is protected from UV damage by deposited CATC. As alluded to above, the CATC deposited on the hair surface not only protects hair from UV damage, but also acts as a conditioner. Studies to determine the reduction in the wet combing force were conducted to validate this conditioning effect and are discussed in the section below. REDUCTION IN WET COMBING FORCES Data on the changes in the peak load and the total work of four test gray hair tresses before and after 15 days of UV irradiation are presented in Figure 7. It is seen that the wet combing force increased more than 100% for hair tresses 3 and 4. These observed increases in hair frictional force may be related to the photochemical damages and subsequent removal of the epicuticle layer of hair lipids, such as 18-MEA, which play an important role in the surface properties of hair (5,10). This is also due in

114 JOURNAL OF COSMETIC SCIENCE 300 250 200 •5o- 100 50 [] NO UV [] CATC ß OMC I i [] SLS lOO ::::::ii!!!i :' :' :' :' :' :' 21.5 252 241 :•.:,•:: .... ===================== ß ... :-: -.-....:. ß :...-.:.:.:. • ß :: .: ...:......: ß ::.! •, ...::!i-:3-i::!ii:: ß ii:: ':• :": :'":'::: ' :" ' ' '! i• :.' :' '. :-:---:'.:: ß :•: ::'::.':!:i..:i.:'..' •.• .:.:..,:...: :.:..... .:.:• •:. ,...::: :¾:,:.::. . 1oo Peak Load Total Work Figure 7. Changes in wet combing force after UV irradiation. part to the oxidation of cystine to cysteic acid. As a result of the increased surface hydrophilicity (wettability), the wet combing force of these hair tresses increased dra- matically. In contrast, the peak load and the total work for the hair tress treated with CATC were reduced 78.5% and 72.2%, respectively. This reduction in the wet combing forces for tress 2 clearly indicates that CATC provides a conditioning benefit in addition to its U¾ protective function. SWELLING TEST Radnapandian et aL (1) determined the extent of transverse swelling in a 0.1 N NaOH solution of Piedmont hair that had been irradiated for 300 hours at various RH levels. In a similar fashion, we determined the average increases in the center cross-sectional area of hair fibers after 15 days of U¾ irradiation. The data are summarized in Figure 8. It is seen that the hair fibers treated with CATC showed almost the same amount of transverse swelling as the hair fibers without U¾ exposure. Hair fibers treated with 10% SLS exhibited the highest amount of swelling. Swelling increases with the loss of crosslinks inside the hair fiber (13). Hence, our experimental results suggest that hair treated with CATC retains a larger number of crosslinks compared to hair treated with either SLS/OMC or SLS. This interpretation is consistent with our test results of tensile strength. Alternatively, as suggested by Ratnapandian et •1. (1), the degradation of protein in the hair fiber may cause swelling. Hair tresses treated with SLS or OMC had less U¾ protection, and the proteins may have been extensively degraded. Protein residues possessing molecular weights small enough to let them diffuse out of the fiber during immersion in 0.1 N NaOH solution may have left holes in the cortex allowing the NaOH solution to swell the hair. Hair treated with CATC experienced less protein