190 JOURNAL OF COSMETIC SCIENCE THERMAL DEGREDATION AND PROTECTION OF HAIR Roger L. McMullen, Jr. and Janusz Jachowicz, Ph.D. International Specialty Products, Wayne, NJ 07470 Introduction The literature reflects a limited amount of research focusing on the irreversible chemical and physico chemical changes occurring in hair as a result of thermal treatment, which is applied to hair in conjunction with the use of curling irons or hair-dryers, i.e. in the temperature range from 100 øC to 170 øC [1-5]. The present study concentrates on the effects of thermal treatments on human hair induced by conventional curling irons, operating in the temperature range from 130 øC to 164 øC. The extent of hair degradation was probed by using a tryptophan assay, Hunter colorimetry, texture analysis, and mechanical combing measurements for detecting changes in the inter-fiber frictional properties. The thermal protection of hair against structural damage was investigated by employing PVP/DMAPA Actylates Copolymer and Quatermum 70. Materials & Methods In order to examine the thermal effects on different types of hair, several experiments were performed on bleached and Piedmont hair purchased from DeMeo Brothers, Inc., as well as Asian, light brown, and unpigmented (white) hair from International Hair Importers, Inc. Hair samples, in the form of 6.5" x 1.25" tresses, were precleaned with 3% w/w ammonium lauryl sulfate solution and thoroughly rinsed prior to experimentation. Thermal treatment of hair was performed using a commercial curling iron, operating in the temperature range from 130 øC to 165 øC. In order to maintain uniformity of the experimental conditions and to assure repmducibility of the obtained data, the thermal treatment to each hair tress was administered in the same position. For thermal protection, the hair tress treatments were administered with 1% solutions of the indicated active in which 3.46 mg of active was applied per each gram of hair. The treated tress was then air- o Figure 1 o Bie/½h0d, k-.04 [] Piedmont, k•.05 •x .t•ien, k-.OS X Light Brown, k•.04 ß White, k-.03 Time dried (23 øC) with an Elchim Professional hair clsyer (Model EC 35227) distributed by Elchim - USA. The treatments described above (PVP/DMAPA Acrylates Copolymer and Quatemium 70) are commercial products sold under the trade names of Styleze CC-10 (ISP) and Ceraphy170 (ISP), respectively. Fluorescence measurements were performed using a Fluomlog-2 spectrophotometer (Spex Industries) equipped with a fiber-optic sample accessory. The experimental procedures were similar to those described in reference [6]. The combing measurements of hair tresses were performed by employing a Diastron Miniature Tensile Tester operated by MTrWIN software. In order to quantfly the degree of color changes resulting from heat treatment in various types of hair, we used a HunterLab ColorQUEST Sphere Spectrocolorimeter marefractured by Hunter Associates Laboratory, Inc., Reston, VA, USA. The use of the spectrocolorimeter enables us to obtain the tristimulus (L, a, b) values, which were utilized to calculate discoloration parameters as a result of thermal treatment. Results & Discussion The effects of thermal treatments on human hair induced by conventional curling irons, operating in the temperature range from 130øC to 164øC, have been investigated. The fibers were thermally exposed by continuous heating for extended periods of time (3-15 ram) or by short (15 seconds) intermittent heating cycles. The model calculations of heat transfer through a fibrous assembly, based on heat

PREPRINTS OF THE 1998 ANNUAL SCIENTIFIC SEMINAR 191 conduction through a semi-infinite solid, were performed. The calculated data have shown that near-uniform temperature distributions are ,reached in the hair samples within a few seconds of thermal exposure, suggesting that continuous and intermittent modes of treatment are equivalent. The resulting damage to the fibers has been investigated and quantified by the use of fluorescence spectrophotometry, Hunter colofimetry, and combing analysis. The fluorescence analysis analysis has shown that thermal treatment results in a decomposition of hair chromophores, specifically tryptophan (Trp) and its oxidation products (kynurenines). The calculated first-order rate coefficients of Trp decomposition were in the range from 0.03 to 0.12 (rain -I) with an estimated activation energy of 6.6 kcal/mol. Figure 1 illustrates the decomposition of Trp as a function of the thermal treatment time for various types of hair at 164 øC. At this temperature, the extent of Trp decomposition is very high reaching nearly 80% conversion after 30 minutes. In addition to this, we have employed Hunter colorimetry to quantify the thermally induced color changes in hair, such as an increase in the yellowhess of white and Piedmont hair, or simultaneous yellowing and darkening of bleached it 1o o o Hair Thermal Damage Figure 2 ,m•. ] Reg•n .o, f Curling iron , 4O 0O stun !Oe 120 140 toe Di ce (ram) 2O • PVP•DMAPA Ac•ate* CopoJym or ß •uatemlmu 70 x unb•eated 7o. aeoo 4 0 8( !0 '$2 ?line rain) Figure 3 hair. Surface damage, resulting from thermal treatment, was quantified by using combing analysis, which revealed a gradual increase in combing forces that were measured in the tress section exposed to the curling iron. Figure 2 provides a representative example of the combing force increases resulting from thermal exposure at 152 øC for light brown hair. Force difference curves were determined by subtracting the curve obtained after thermal degradation from the curve obtained prior to any thermal treatments. A possible method for preventing thermal damage to hair has been tested by pre-treating fibers with PVP/DMAPA Acrylates Copolymer and Quatemium 70. The decomposition of Trp in fibers pretreated with the indicated actives, followed by thermal exposure, was monitored. Figure 3 presents the Trp degradation at 152 øC as a function of the thermal treatment time for light brown hair. As indicated by the data in Figure 3, depositing a layer of surfactant on the surface of hair appears to provide some degree of Trp protection. We also monitored the surface modifications of the fibers, resulting from thermal treatment at 152 øC, by combing analysis. Figure 4 pertrays combing work difference as a function of time for hair treated with the indicated actives and for untreated hair. The combing work difference values were determined by integrating the area of the combing curve where thermal treatment was administered and subtracting this value from the similarly obtained value prior to thermal exposure. Similar studies were conducted at 132 øC and provided comparable data with respect to the possible thermal protection properties of the tested compounds. x tMiJ. elfod x Figure 4 o o lO 12 Time (rain) References [1] P. Milczarek, M. ZieLinski, and M. Garcia, Colloid Polym. Sci., 270, 1106 (1992). [2] R. Crawford, C. Robbins, and K. Chesney, J. $oc. Cosmet. Chem., 32, 27 (1981). [3] L. Rebenfeld, H. Weigmann, and C. Dansizer, o r. $oc. Cosmet. Chem., 17, 525 (1966). [4] W. Humphties, D. Miller, and R. Wildnauer, or. Soc. Cosmet. Chem., 23, 359 (1972). [5] R. Amaud, G. Perbet, A. DeFlandre, and G. Lang, Int. J. Cosmet. Sci., 6, 71 (1984). [6] C. Pande and J. Jachowicz, or. $oc. Cosmet. Chem., 44, 109 (1993).