J. Cosmet. Sci., 62, 265–282 (March/April 2011) 265 The effect of various cosmetic pretreatments on protecting hair from thermal damage by hot fl at ironing Y. ZHOU, R. RIGOLETTO, D. KOELMEL, G. ZHANG, T.W. GILLECE, L. FOLTIS, D. J. MOORE, X. QU, and C. SUN, International Specialty Products, Wayne NJ (Y.Z., R.R., D.K., G.Z., T.W.G., L.F.), and ISP Shanghai Global R&D, Shanghai, China (X.Q., C.S.). Synopsis Hot fl at irons are used to create straight hair styles. As these devices operate at temperatures over 200 °C they can cause signifi cant damage to hair keratin. In this study, hair thermal damage and the effect of various polymeric pretreatments were investigated using FTIR imaging spectroscopy, DSC, dynamic vapor sorption (DVS), AFM, SEM, and thermal image analysis. FTIR imaging spectroscopy of hair cross sections provides spatially resolved molecular information such as protein distribution and structure. This approach was used to monitor thermally induced modifi cation of hair protein, including the conversion of α-helix to β-sheet and protein degradation. DSC measurements of thermally treated hair also demonstrated degradation of hair keratin. DVS of thermally treated hair shows the reduced water regain and lower water retention, compared to the non-thermally treated hair, which might be attributed to the protein conformation changes due to heat damage. The protection of native protein structure associated with selected polymer pretreatments leads to improved moisture restoration and water retention of hair. This contributes to heat control on repeated hot fl at ironing. Thermally stressing hair led to signifi cantly increased hair breakage when subjected to combing. These studies indicate that hair breakage can be reduced signifi cantly when hair is pretreated with selected polymers such as VP/acrylates/lauryl methacrylate copolymer, polyquaternium-55, and a polyelectrolyte complex of PVM/MA copolymer and polyquaternium-28. In addition, polymeric pretreatments provide thermal protection against thermal degradation of keratin in the cortex as well as hair surface damage. The morphological improvement in cuticle integrity and smoothness with the polymer pretreatment plays an important role in their anti-breakage effect. Insights into structure-property relationships necessary to pro- vide thermal protection to hair are presented. INTRODUCTION Hair damage from thermal treatment with styling appliances such as hot fl at irons, blow dryers and curling irons has become an increasing concern in hair care. This is especially true with hot fl at irons that can exceed temperatures of 200°C. Because of the growing popularity of using high temperature thermal styling appliances, there is a need for ther- mal protective ingredients/products and test methods to show their effi cacy. To meet this challenge, understanding and assessing hair damage from thermal treatment is needed. In recent decades, thermal damage of hair by curling irons has been discussed by several publications (1–3) that have studied various effects on hair thermal damage, such as

JOURNAL OF COSMETIC SCIENCE 266 moisture content, conditioners, polymers and heating modes. Changes in hair mechanical properties, combing force and tryptophan by curling ironing treatment at 120–160°C were demonstrated in the literature as well. High-temperature decomposition of hair keratin has been studied by using DSC (4,5). On the other hand, the literature refl ects limited amount of research on hair damage and protection from using hot fl at ironing at a temperature over 200°C. In this work, hair damage from thermal treatment was studied in different aspects by several techniques towards understanding hair thermal damage and the protective effect by cosmetic pretreatment. It is also our objective to understand the thermal protection mechanism, such as the role of moisture regain of hair on controlling hair temperature from repeated heating. Also, the alleviation of weakening of hair and the consequent re- duction in hair breakage through combing using polymers with different functional groups highlights the structure-property relationships important for thermal protection effi cacy. MATERIALS AND METHODS POLYMERS VP/acrylates/lauryl methacrylate copolymer, PEC (polyelectrolyte complex of methylvi- nylether/maleic acid copolymer and polyquaternium-28 (6,7)), polyquaternium-55, co- polymer of VP and DMAPA acrylates, and other polymers used in this study were supplied by International Specialty Products (ISP). Hydroxyethylcellulose (HEC) was supplied by Aqualon. These ingredients are used as supplied and not purifi ed and modi- fi ed in any way. HAIR SAMPLES European dark brown hair was purchased from International Hair Importers. Each hair tress was 1.5” wide, 3.5 g in weight and 6.5” in length of loose hair. Asian hair tresses were supplied from a local commercial source in China made with the same specifi cations. THERMAL TREATMENT OF HAIR Hair tresses were hot fl at ironed by a controlled 12-minute treatment schedule. The tem- perature of hot iron used in this work was 232°C unless specifi ed elsewhere. First, the hair tresses were washed with 10% sodium lauryl ether sulfate (SLES) and dried with a hair blow dryer set on hot. Then hair tresses were thermally exposed for a short (12 seconds) intermittent heating cycle separated with SLES washing every 4 minutes for a total of 12 minutes thermal treatment. If a protective agent was tested, tresses were pretreated with 0.5 g of a 1% polymer solution for Asian hair or 0.5 g of a 1% polymer solution made into 0.5% hydroxyethyl cellulose (HEC), after the SLES wash, then dried and followed with hot fl at ironing. At the end of the 12-minute hot ironing, the tresses were washed with 10% SLES again and dried for subsequent combing to quantify hair breakage. The polyelectrolyte complex (PEC) was supplied and tested at 2%, unless specifi ed.