FRAGRANCE RETENTION IN HAIR 367 FRAGRANCE RETENTION Hair fragrance release rate was evaluated by normalizing to 100% the peak chromato- graphic area of the most abundant fragrance compound. Consequently, the values ob- tained for the amount of fragrance transferred to hair after washing and retained after different periods of drying are expressed in percentage. The fragrance compounds bar graph (Figure 1) shows that more compounds are trapped by bleached than by virgin hair thus, more fragrance material is sorbed on hair by wash- ing with shampoo. Compared with virgin hair, bleaching for 40 min showed at least 40.0% more abundance for ethyl 2-methylbutanoate, 16.9% for linalool, 20.2% for ben- zyl acetate, and 24.6% for Mintonat. Bleaching for 10 and 20 min analyzed immediately after washing showed amounts of fragrance materials with intermediate values, between virgin hair and hair bleached for 40 min. Oxidative bleaching under alkaline condition causes the oxidation of melanin (in the cortex) and other hair components, generating a structural hair modifi cation. Richena et al. (6) proved by transmission electron microscopy that gray Caucasian hair bleached with the same reactants used in this work presented hole formation in the cortex, where melanin granules used to be located. The same structural transformation can be seen in the scanning electron micrography in the work of Ruetsch et al. (12) using the hair treated with 6% hydrogen peroxide for 4 h. This hair internal morphologic transformation leads to a surface increase and consequently more fragrance compounds retention on hair washing. Therefore, the longer the hair bleaching process, the greater is the hair structural damage and, conse- quently, the higher is the surface of interaction between fragrance compounds and hair. Another consequence of hair bleaching is the oxidation of cystine disulfi de bond in the cortical matrix, the A-layer and the exocuticle inside cuticle cells (3,13). The chemical transformation by bleaching converts the virgin hair fi ber, especially the surface from a hydrophobic material with little surface charge to a more hydrophilic, more polar, and more negatively charged surface (3). This change in the polarity of the protein groups of hair increases its capacity to interact and attach chemical compounds as water, fragrance compounds, and rhodamine B as demonstrated with the results previously mentioned. Robbins and Kelly (14) observed large amounts of cysteic acid in hydrolyzated bleached hair when analyzing amino acids in cosmetically modifi ed hair and the quantities in- creased with increased bleaching. Therefore, longer bleaching processes produce larger amounts of cysteic acid and the higher is the polarity of the fi ber. This explains why Figure 1. Amount of fragrance released from bleached Caucasian hair using a 4.5% wt. hydrogen peroxide solution in pH 9.5 at 55°C as a function of time of bleaching: 2-methylbutanoate (blue fi lled square), linalool (orange fi lled square), benzyl acetate (green fi lled square), and Mintonat (violet fi lled square).
JOURNAL OF COSMETIC SCIENCE 368 bleached hair for 40 min showed higher capacity of fragrance deposition on hair by wash- ing with shampoo. The hair damages caused by the chemical bleaching must also be taken into consideration with regard to the transference of fragrance compounds to the hair interior. Chemical bleaches weakens cell membrane complex by oxidizing thioester groups between cuticle cells, leading to the breakdown of the membrane complex, and also dissolving proteins in endocuticle and in the cortex. Moreover, chemical bleaching promotes the cuticle scale lifting, cracks, and split formation (3). As a consequence, large molecules and other sub- stances can penetrate easier from the inside to the outside of the fi bers through the inter- cellular diffusion path in the low cross-link density regions. The results obtained for the hair analyzed after 2 h of drying showed that analogous to the results for wet hair, the amount of fragrance of bleached hair for 40 min was higher than that of virgin hair: at least 8.8% more for ethyl 2-methylbutanoate, 1.2% for linalool, 10.3% for benzyl acetate, and 17.1% for Mintonat. Despite this, a signifi cant reduction in this difference of amount of fragrance between virgin and bleached hair can be observed. It proves that the fragrance liberation from bleached hair is faster than that from virgin hair besides its greater capacity of embody fragrances right after washing with shampoo, as it was observed for the results of wet hair. The period of 4 h of drying follows the same tendency of reduction and this fact is very evident for the period of 6 h of drying: at least 1.8% more for linalool, 1.2% for benzyl acetate, and 5.0% for Mintonat. In both 4 and 6 h of drying, no difference in the amount of ethyl 2-methylbutanoate in virgin hair and hair bleached for 40 min can be observed. In addition, the faster fragrance decrease rates of the bleached compared with virgin hair during drying process are assigned to hair surface damages caused by the oxidation reac- tions of the structural protein of hair. The damage of the barriers that prevent intercel- lular diffusion and penetration of substances into the fi ber increases the transference of fragrance compounds from the inside to the outside of the bleached hair when compared with virgin hair. DESORPTION OF WATER The higher capacity of sorption of substances on bleached hair compared with virgin hair was demonstrated by water sorption tests. The results for water desorption shows that bleached hair for 40 min sorbed at least 28.1 mgwater.ghair-1 more water than virgin hair after 20 d at 98–99% RU (time: 0 h on abscise coordinate of the graphic in Figure 2). When submitted at 0% RU, both virgin and bleached hair show a decrease in water, and bleached hair showed a higher content of water until at least 19 h of exposition to the drying agent P2O5 at 21°C. After this period, no difference in water content between virgin and bleached hair can be observed. These results correlate with fragrance uptake: bleached hair can sorb a higher amount of substances (fragrances compounds and water). The moisture decrease rate for bleached hair is higher in comparison with virgin hair and this can also be attributed to the fi ber surface damage caused by bleaching that increases the ability of hair to retain and release water. This explanation is in accordance with the work of Pauling (15), which verifi ed that the polar side chains of amino acid residues of proteins provide much of the attrac- tion for the adsorbed water molecules.
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