Development of a three‐point cantilever bending technique to study the mechanical properties of hair styling ingredients

BACKGROUND: The mechanical properties of hair treated with styling ingredients is an important aspect to determine if products will be efficacious when used by the consumer. Measurement techniques have been proposed in earlier work; however, these are mostly aimed at hairspray systems and not the myriad of styling products available to the modern‐day consumer. AIM: In this article, experimental and data analysis guidelines are proposed for the evaluation of styling ingredients using a three‐point cantilever bending technique. Most of the experiments were carried out on polysaccharide‐based ingredients—guar hydroxypropyltrimonium chloride (Guar HPTC) and cassia hydroxypropyltrimonium chloride (Cassia HPTC)—to establish basic characterization concepts of the polymer‐fiber assemblies. METHODS: A three‐point cantilever bending technique was developed using a texture analyzer housed in a temperature and humidity‐controlled chamber. Scanning electron microscopy (SEM) studies were conducted to monitor the fracture mechanics of polymer‐fiber assemblies. RESULTS: Fundamental studies were carried out to determine the effect of concentration, molecular weight (MW), and chemistry of the polysaccharides on the calculated indices, which characterize the stiffness, flexibility, elasticity, and plasticity of the treated hair. Experiments were conducted in a controlled temperature and humidity environment, which allowed us to monitor the behavior of the polymer‐treated hair from 40–90% RH. Studies were also conducted on polymer blends and conventional styling polymers to provide guidance of the performance of naturally‐derived polymers to their synthetic counterparts. CONCLUSIONS: A detailed description is provided for a user‐friendly, quick method to measure the mechanical properties of styling ingredients on hair. We provide guidelines for three‐point cantilever bending tests of straight hair tresses treated with conventional and naturally‐derived styling polymers. Indices were developed to characterize the force‐distance curves and were designated as E1, F1, position of F1, post‐fracture gradient, toughness, E10/E1, and F10/F1. These indices provide an overall characterization of the stiffness, flexibility, elasticity, and plasticity of polymer‐treated hair.