]. Cosmet. Sci., 58, 319-327 Quly/August 2007) Investigations of cosmetic treatments on high-pressure differential scanning calorimetry J.M. MARSH, C. J. CLARKE, K. MEINERT, and R. M DAHLGREN, Procter & Gamble Technical Centres, Rusham Park, Egham Surrey, TW20 9NW U.M.M., C.j.C., R.M.D), and Wella Service GmbH, Berliner Allee 65, D-64274, Darmstadt, Germany (K.M.). Synopsis High Pressure Differential Scanning Calorimetry (HPDSC) can be used to gain information on both the degree of crystallinity in the intermediate filaments (IFs) and the structural rigidity of the surrounding matrix or intermediate filament associated proteins (IF AP) of the hair cortex. We have used HPDSC to measure changes in denaturation temperature (T 0) and enthalpy (OH0) of the crystalline components after treatment with bleach products. Literature reports suggest that a decrease in peak denaturation temperature is indicative of permanent damage to the hair. However, changing the rigidity of the matrix surrounding the IFs, by temporarily changing electrostatic interactions, should also result in a similar decrease in peak tern perature. The complex nature of bleach formulations including oxidants, alkalizers and salts suggests that several of the components could have a non-permanent affect on salt bridges and hydrogen bonds and hence rigidity or viscosity of the matrix. We have compared the denaturation temperature with levels of lightening (dL) and tensile properties of the fiber after treatment both before and after removal of actives from the fiber. It is evident that the HPDSC results are strongly influenced by formulation components and that these changes are reversible with extensive washing or dialysis. Combined with tensile data, it is proposed that a decrease in T0 and OHn following treatment with bleach products can be due to both permanent and reversible changes to either the intermediate filaments or intermediate filament associated proteins of the hair fiber. INTRODUCTION Cosmetic treatments such as bleaching, perming and the use of permanent colorants have been shown to cause changes to the fibre structure of the hair (1-4). These changes are often seen by the consumer as damage such as increased hair breakage, reduced shine and a poor hair feel in both the wet and dry state. It is important to relate these consumer noticeable effects to measurable changes in the fibre structure. One technique that has been used to measure structural changes to hair is High Pressure Differential Scanning Calorimetry (HPDSC) (5-7). The technique records the thermal behaviour of a sample, such as hair, under controlled heating and in a sealed vessel with a known amount of water. The thermal transition observed is in the range 130-180°C and has been related to the denaturation of the hair's keratin structure. The hair 1s a 319

320 JOURNAL OF COSMETIC SCIENCE complex morphological structure composed of three components: the cuticle, the cortex, and the medulla (8). It is proposed that it is the cortex that is the significant contributor to the thermal stability of the fiber. The cortical structure has been described as being composed of the intermediate filaments (IFs), which have an a-helical structure, em- bedded inside an amorphous matrix containing the intermediate filament associated proteins (IFAPs) (9,10). As measured by the HPDSC technique, the denaturation en- thalpy (0HD) is proposed by Wortmann et al. (11) as being dependent on the structural rigidity of the a-helical material in the intermediate filaments. The peak temperature (TD) is controlled by the cross-link density and viscosity of the matrix in which the intermediate filaments are embedded. Several authors have specifically investigated the effect of multiple bleaching treatments on the HPDSC peak temperature and enthalpy. Wortmann et al. (12) showed a steady decrease in both BHD and TD with an increasing number of treatment cycles. Monteiro et al. (13) observed a similar trend. In both cases the decrease in 3HD and TD was linked to the oxidative cleavage of the cystine protein to form cysteic acid, with a decrease in inter-protein cross-linkage. In this present study we also look at the effect of multiple bleaching treatments on the HPDSC peak temperature and enthalpy, but we have also considered the role of the chassis formulation and its components on influencing the HPDSC results. Specifically, we studied treatments with the alkalizer alone (either ammonia or ethanolamine) buff- ered at pH 10, the same pH as a typical bleach product. The results from the HPDSC experiment were also compared to tensile strength measures such as plateau load and break force. The tensile strength method has also been reported to indicate the oxidative damage caused by bleach products (14-16). EXPERIMENT AL Caucasian untreated mixed hair (medium brown), obtained from a commercial source (IHIP, New York), was formed into swatches (16 cm, 1.5 g). The hair swatches were subjected to a number of repeat wash cycles between each treatment. One wash cycle consisted of two shampoo plus rinses in tap water with a commercial clarifying shampoo. The following products were used: • Bleach product A-alkaline solution of hydrogen peroxide, ammonium persulfate and ethanolamine (pH 10) in a gel formulation • Bleach product B-alkaline solution of hydrogen peroxide, ammonium persulfate and ammonium hydroxide (pH 10) in a gel formulation • Bleach product C-alkaline solution of hydrogen peroxide, ammonium persulfate and ammonium hydroxide (pH 10) in a cream formulation Dialysis of the hair was achieved by soaking in repeated changes of lliter deionised water for a total of 25 liters. The pH of the dialysed water was monitored for each change of deionised water. For treatment with the alkalizers two swatches were soaked in 100 ml of the alkalizer solution (1.27M) for 30 minutes at 30°C. The hair was washed twice with a clarifying shampoo before HPDSC analysis. HPDSC investigations were carried out using either: • A Dynamic Difference Calorimeter DSC 204 Phoenix supplied by the Netzsch Com- pany. The heating range was 90-l 70°C at a rate of 5 ° C I minute. Hair tresses were