332 JOURNAL OF COSMETIC SCIENCE DIFFERENTIAL SCANNING CALORIMETRY (DSC) STUDY OF HAIR DAMAGE AND HAIR RESTRUCTURING BY PROTEIN DERIVATIVES Tao Gao, Ph.D., and Ann Bedell Croda, Inc., 180 Northfield Avenue, Edison, NJ 08837 INTRODUCTION Extensive DSC studies have been carried out to investigate the structural changes in the microfibril- matrix complex of extended and thermally treated (annealed) keratin samples (1-4). An endothermic peak in the temperature range of 230 ø - 250øC of DSC curves of ct-keratins has been indexed as the ct-helix peak and the area under the peak represents a measure of the Relative Helix Content (RHC) of the sample (2). Recently, Wortmann (5) reported their studies on cosmetically treated hair by High-Pressure DSC in water. They concluded that the area of the helix peak depends on the structural integrity of the ct-helical material in the intermediate filaments (IFs). The cross-link density of the matrix, in which the intermediate filaments are embedded, kinetically controls the helix peak temperature. In this paper we present our studies on effects of weathering, bleaching, and relaxing on ct-helix peaks of virgin brown and Afro-American hair. The effects of cosmetic treatments of bleached and relaxed hair with protein derivatives on the recovery of deformed ct-helix peaks are also discussed. EXPERIMENTAL ß Materials: Virgin brown, bleached blond, and virgin Afro black hair samples were purchased from International Hair Importers & Products Inc., Bellerose, NY. Protein derivatives were commercial samples from Croda Inc, Parsippany, NJ. ß Sample Preparation: The hair was immersed in 1.5% active aqueous solution or in tested formulas for three minutes, rinsed (for rinse-off products)), air-dried, and chopped into small pieces having lengths less than 1.0 min. ß Moisture Content: Hair samples were equilibrated in a chamber at 23øC and 50% relative humidity for 48 hours. The moisture content of the equilibrated hair was determined as 11.48% and 10.15% for the bleached and the virgin brown hair samples, respectively. ß Instrument: A DSC 2010 (TA Instruments, New Castle, DE) was used for measurements. 5 - 7 mg of hair sample were placed in an open aluminum pan at a nitrogen environment (N2 flow rate = 50 ml/min). The sample was heated to 70øC and kept at that temperature for 30 minutes to remove moisture and then cooled to 25øC. The hair sample was re-heated this time to 270øC at a rate of 10ø/min. Three trials were conducted for each hair sample and the average peak temperature and peak area were calculated. RESULTS AND DISCUSSION ß Data Analysis A typical DSC curve of a virgin hair sample is presented in Figure I. The peak temperature is defined as the temperature of denaturation (Td) of the e-helix in the IFs. The denaturation includes phas. e transition and protein degradation. The area of the peak represents the denaturation enthalpy ZXHa, which is the energy required for denaturation of the ct-helix and expressed by the heat of absorption per gram of dry hair (J/g). zXHa is used to determine RHC. RHC = 100 X (zXHa/zSHaø)%, where zXHa ø is the average denaturation enthalpy of the untreated hair. ß Weathering Effects Helix peaks with different intensities and positions were observed along the fiber axis of a virgin brown hair sample having a length of 18 cm. Data are summarized in Table I. Table I Weathering Effects on ct-Helix Peak of Hair [ Hair components Tip I •oot l z•Ha (J/g) 3.44 (85.6% RHC) 3.77 (93.9% PdqC) 4.02 (100% PdqC) Ta (øC) 234.4 233.9 Middle 233.6 It can be seen that AHa decreases and Ta increases from the tip to the root of the hair, The R_I-IC in the tip of the hair is 85.6% of that in the root end. This is a clear indication of the weathering effect. ß Bleaching and Relaxing Effects Figure 2 depicts the effects of bleaching time on the Ta and RHC of virgin hair, The Pd-IC decreases with the increase in bleaching time. The Z•Hd is 3,85 J/g and 1.07 J/g for the virgin and bleached hair,

2001 ANNUAL SCIENTIFIC SEMINAR 333 respectively. The RHC of the bleached hair decreased 72.8% compared with that of the virgin hair. Such a decrease indicates the severity of damage sustained by the bleached hair. SEM inspection found many visible holes and severe cuticle abrasion on the surface of bleached hair. Ta increases with an increase in bleaching time. Since Ta depends on the cross-link density of the matrix, the higher the cross-link density is, the higher their viscosity will be, and the more hindered the helix/coil transition will be in the IFs. It is known that the content of cysteic acid (the product of oxidation of cystinc during bleaching) increases with bleaching time. The increase in Ta with the bleaching time may reflect the increased amount of cysteic acid being produced in bleached hair and the stronger ionic interactions that result. It is also observed that the AHa decreases and Ta increases with an increase in relaxation time for Afro-American hair. ß Helix Peak Recovery - Hair Restructuring Data on AHa and Ta of bleached hair before and after treatemnts with a selection of protein derivatives are presented in Table II. Table II Effects of Protein Treatments on Helix Peak of Bleached Hair Hair None Hydrolyzed Cystinc Hydrolyzed Wheat Protein and Treatment Wheat Protein Polysiloxane Hydroxypr0pyl Polysiloxane AHa (J/g) 1.07 (100%) 1.90 (177.5%) 1.84 (172.0%) 2.02 (188.8%) Ta (øC) 247.0 242.2 241.5 242.2 The RHC increased 77.5%, 72.0%, and 88.8%, respectively, for hair samples treated with Hydrolyzed Wheat Protein, Cystinc Polysiloxane, and Hydrolyzed Wheat Protein and Hydroxypropyi Polysiloxane. The Ta decreases dramatically after treatment with the proteins. Previous studies (6) have shown that hydrolyzed wheat protein and cystinc polysiloxane are both able to penetrate the hair where they undergo disulphide bond interchange reactions with cystinc residues in the hair. These reactions change the amount and structure of helix in the hair, as reflected by an increase in AHa and decrease in Ta. It is found that the leave-on products showed better peak recovery effects than the rinse-off products. Generally speaking, high molecular weight protein derivatives like hydrolyzed wheat protein and hydroxypropyi polysiloxane cannot penetrate into the hair because of their large size. As mentioned before, the bleached hair sample was severely damaged and very porous. The porosity of the hair may have made it possible for the polymer to penetrate into hair and react with the hair. The partial penetration may account for the significant increase in the AHa of hair sample treated with the polymer. An increase in AHa and decrease in Ta are also observed for the relaxed hair samples treated with the protein derivatives. 2.5 o • 1.5 0.5 210 230 250 T Figure I DSC curve of human hair References i. 2. 3. 4. 5. 6. 105 100 95 90 85 80 242 "'' ' ø ' 240 238 234 2•2 0 15 30 45 60 Bleaching Time (min.) Figure 2 Changes in RHC and Ta with bleaching time M. Spei and R. Holzem, Thermoanalytical investigation of extended and annealed keratins, Colloid & Polymer Sci., 265,965- 970 (1987). M. Spei and R. Holzem, Thermoanalytical determination of the relative helix content of keratins, Colloid & Polymer Sci., 267, 549-551 (1989). P. Milczarek, M. Zielinski and M.L. Garcia, The mechanism and stability of thermal transition in hair keratin, Colloid & PolymerSci., 270, i 106-1 i 15 (1992). J. Cao, Melting study of the a-form crystallites in human hair keratin by DSC, Therm. Acta, 335, 5-9 (1999). F.J. Wortmann, C. Springob and G. Sendeibach, Investigation of cosmetically treated hair by DSC in water, Proceedings of XXl IFSCC, 293-298, 2000. • J.A. Swift, S.P. Chahal, N.A. Chalioner, and J.E. Paefrey, Investigations on the penetration of hydrolyzed wheat proteins into human hair by confocal laser-scanning fluorescence microscopy, J Cosmet_ Sci., 5 i (3), 193-203 (2000).