j. Cosmet. sci., 54, 63-83 (January/February 2003) The role of cationic conditioning compounds in reinforcement of the cuticula SIGRID B. RUETSCH, Y. K. KAMATH, and H.-D. WEIGMANN, TRI/Princeton, P.O. Box 625, Princeton, NJ 08542. Accepted for publication April 3, 2002. INTRODUCTION Everyday grooming practices result in ablation of the cuticula. This ablation is directly associated with the ease of scale lifting that occurs during the imposition of stresses on individual hair fibers during grooming, especially when encountering a snag. During extension, the cuticle cells release the stress of extension by moving relative to one another. This relative movement is accommodated by the deformation and fracture of intracuticular (endocuticle) and intercuticular (CMC) structures in the cuticular sheath. At high strains, failure of these intra- and intercuticular domains occurs, causing lifting of the edge of the exposed cuticle cell (1). In the cosmetic industry, conditioners are believed to be beneficial in preventing or at least significantly reducing long-term grooming damage to the hair fiber. This has been confirmed by various test methods developed at TRI. Principal among these are methods involving prolonged combing and fiber fatigue experiments. In addition to reducing stresses by friction reduction, the efficacy of these compounds can be attributed to the reinforcement of the cuticular sheath by strengthening the endocuticle, improvements in intercuticular adhesion, and subsequent prevention of scale lifting and scale chipping. Therefore, the core of this work investigates the effects of model cationic conditioning compounds of different molecular weight on the reinforcement of the cuticula, that is, on improvement of cuticular cohesion and prevention of scale lifting during extension. We have, therefore, attempted to quantify the scale-lifting behavior that occurs during longitudinal extension of unaltered hair fibers and hair fibers that have been exposed to treatments with high- and low-molecular-weight conditioners. Our results clearly in- dicate that treatment of hair with cationic polymeric and monomeric quaternary am- monium compounds improved cuticular cohesion and improved resistance to scale lift- ing. Comparison of the effects and performance of the compounds will be made. Mi- crofiuorometry and scanning electron microscopy (SEM) have been used in this work. In an associated study, we demonstrate improved cuticular cohesion by cationic corn- 63

64 JOURNAL OF COSMETIC SCIENCE pounds using another technique. We investigate changes in hair fiber creep as a result of cationic treatments. We are able to show that creep (under special conditions) is significantly inhibited in hair fibers treated with cationic compounds, which corrobo- rates the results of the scale-lifting study. THE ROLE OF CATIONIC CONDITIONING COMPOUNDS ON SCALE LIFTING DURING EXTENSION EXPERIMENTAL MATERIALS Hair fibers. Four 1.2-g skeins of root sections of 14-inch-long, dark brown, unaltered European hair from DeMeo Brothers were prepared for this study. One skein of unaltered hair served as control. Cationic conditioning compounds. The following model cationic compounds (MCCs) were investigated: 1. Polyquaternium 10 (PQ-10) (polymeric) 2. Quaternized hydroxy propyl guar derivative (HPG) (polymeric) 3. A monomeric, low-molecular-weight, cationic quaternary compound, cetyl trimethyl ammonium bromide (CETAB) Aqueous solutions (0.5%) of the three MCCs were prepared by moderate stirring at 35øC. APPLICATION OF MCCs TO HAIR The prepared microskeins were moistened in deionized water (40øC), blotted, treated for two minutes with 2 ml of the 0.5% solutions of the MCCs (well stirred prior to application to provide homogeneity), and rinsed three times for 20 seconds in 200 ml of deionized water at 40øC while actively swirling the microskein and sometimes stroking the fibers in the "with-scale" direction. This was followed by blow-drying at moderate temperature. A total of ten such applications were carried out. An appropriate number of hair fibers was taken after the first and tenth application for scale-lifting studies. METHODOLOGIES Microfluorometry. Unaltered hair fibers, and hair fibers treated once and ten times with the respective MCCs were mounted individually on a small metal frame and gradually extended in steps at -45% RH at room temperature. The ongoing extension of the individual hair fibers was observed in autofluorescence in the UV excitation beam of a Leitz MPV 1.1 microspectrophotometer with a vertical Ploem illuminator. (These ob- servations can also be carried out in the brightfield in complete white light in the incident beam.) The specific extensions at which certain levels (types) of scale lifting occur were recorded. The appearance of the surface cuticle cell as it lifts was classified in four different categories, (A-D). Category (A) denotes the surface cuticle cells of the