j. Cosmet. Sci., 49, 245-256 (July/August 1998) Thermal degradation of hair. II. Effect of selected polymers and surfactants R. McMULLEN and J. JACHOWICZ, International Specialty Products, Wayne, NJ 07470. Accepted for publication July 15, 1998. Synopsis Fluorescence spectroscopy, combing analysis, and texture analysis with a dual-cantilever bending accessory have been employed to study the effect of pretreatments on the thermal damage of hair. The pretreatments, applied to hair as 1% aqueous solutions, included a cationic polymer (PVP/DMAPA acrylates copolymer), a protein hydrolyzate (hydrolyzed wheat protein), and a cationic surfactant (quaternium 70). Fluorescence spectroscopy was used to probe the content of tryptophan (Trp) in hair, which is gradually destroyed by the application of curling irons at 132 øC and 152 øC. All pretreatment materials were found to reduce the extent of Trp decomposition by 10-20% as a result of 4-12 min of thermal exposure. Surface damage has been quantified by combing analysis and has shown that the use of PVP/DMAPA acrylates copolymers or a cationic surfactant can suppress an increase in combing forces, which is observed in unmodified hair subjected to thermal exposure. The variation in stiffness of hair tresses has been studied by texture analysis with a dual-cantilever bending accessory. From the texture analysis, an increase in the stiffness ratio of the fiber assemblies was evident for polymer-modified and intact (unmodified) hair. INTRODUCTION The thermal degradation of hair has been discussed in several publications (1-5) that have demonstrated various aspects of hair damage. Changes in hair coloration, decom- position of hair chromophores, and damage to the fiber surface were found to be typical manifestations of hair damage after exposure to temperatures greater than 130øC. The changes in fiber structure and properties, as a result of the use of milder thermal conditions ( 100øC) that accompany drying by hair dryers, have also been discussed (6). On the other hand, the thermal protection of hair keratin has not been a topic of scientific inquiry, with only patent literature reflecting several studies pertaining to this subject. Currently, there are several commercial products sold on the retail market that claim to protect hair from thermal styling appliances. These formulations often contain a wide range of actives, including protein hydrolyzates, enzyme cofactors, fatty acids, saccha- rides, surfactants, and various polymers. It has been suggested that hydrolyzed wheat protein, wheat oligosaccharides, wheat amino acids, and panthenol, formulated together, increase the strength and moisture retention of hair fibers when used in conjunction with 245

246 JOURNAL OF COSMETIC SCIENCE a thermal styling appliance (7). Several patents specifically identify the compound or formulation as a protectant against thermal hair dryers or hot irons. For hair dryer protection, the following systems were identified as effective: high-molecular-weight silicone and fatty acid alkanolamide(s) (8) mono-N-acyl basic amino acid lower-alkyl- ester salt and/or cationic surfactant, liquid oil, and heme iron compound (9) quaternary ammounium salt(s), fruit extracts, and a water-soluble cationic polymer (10) and con- ditioners containing stearyltrimethyl-ammonium chloride and polyethylene-polypropyl- ene glycol butyl ether as its actives (11). For patents that strictly apply to protecting hair from hot irons, one formulation includes a two-phase system and a surfactant in which the oil phase contains hydrocarbon or silicone oils, an aqueous phase comprised of glycerol, propylene glycol, and polyethylene glycol, and a surfactant possessing nonionic or ionic character (12). Another composition, consisting of polyoxyethylene sorbitol tetraoleate, polyoxyethylene castor oils, fatty acids (from animal or vegetable sources), and a nonionic surfactant, has also been suggested to protect hair from hot irons (13). Several compounds have also been used as thermal setting agents, in which the active is applied to hair prior to or during thermal treatment. Specifically, the application of a thermoplastic polyester fixative resin used in conjunction with a thermal styling appli- ance has been described in the patent literature (14). The objective of this study was to compare the thermally induced interactions of hair with selected materials including a cationic polymer, cationic surfactant, and a protein hydrolyzate. The thermal protection potential of these materials has been evaluated by previously developed methodology, i.e., combing analysis to detect hair surface modi- fication, fluorescence spectroscopy to analyze the decomposition of tryptophan (Trp), and texture analysis to provide information about the mechanical properties of the fiber assemblies. EXPERIMENTAL INSTRUMENTATION The instrumentation used to quantify thermally induced changes of hair, in terms of combing forces and fluorescence, has been described in the first publication of this series (5). Additionally, we have conducted experiments in which the mechanical properties of hair tresses, before and after thermal treatment, could be quantified. This was achieved using a texture analyzer (Model TA-XT2, Texture Technologies Corp.) equipped with a custom-made attachment in order to perform dual-cantilever bending measurements (15). The texture analyzer had a load sensitivity of 0.1 g and was operated using XTRA dimension software 3.7 from Stable Micro Systems. The bending measurements were performed by placing a hair tress on cantilevers separated by a distance of 1.25 in. and fastening it to a clamp from one side. During the test, a blade-shaped probe attached to the texture analyzer produces a deformation in the hair tress of 3.0 mm after detection of a 2.0 G trigger force. The ratio of the forces recorded at the 3.0-mm deformation, for modified and unmodified hair, is defined as the stiffness ratio and is discussed further in the context of various treatments in this paper. MATERIALS AND METHODS The thermal treatment of hair was performed using a Soft Sheen, Optimum Styling