J. Cosmet. Sci., 61, 343–352 (September/October 2010) 343 Assessment of styling performance in hair gels and hair sprays by means of a new two-point stiffness test PETER HOESSEL, SOLVEIG RIEMANN, ROBERT KNEBL, JENS SCHROEDER, GERD SCHUH, and CATALINA CASTILLO*, BASF SE, 67056 Ludwigshafen, Germany. Accepted for publication June 15, 2010. Synopsis A new two-point bending stiffness method on fl at hair strands was developed and validated after application of hair styling gels and hair styling sprays. A special mold was used to align single hair fi bers after applying the formulations to the hair. The styling gels used contain different commercially available thickeners and styling polymers, e.g., car- bomer, acrylates/beheneth-25 methacrylate copolymer, Polyquaternium-86, PVP, VP/VA copolymers, and VP/methacrylamide/vinylimidazole copolymer. Evaluation of hair sprays was performed after spray applica- tion on fl at hair strands. Commercially available hair styling resins were used, e.g. acrylates/t-butylacrylamide copolymer, octylacrylamide/acrylates/butylaminoethyl methacrylate copolymer, and VP/VA copolymer (30:70). The new stiffness test method provided the best correlation with practically relevant sensory assessments on hair strands and a panel test in which styling gels were evaluated. However, we did not observe a correlation between the new stiffness method on fl at hair strands and practical assessments in hair spray application. We postulate that different polymer/hair composites are responsible for these discrepancies. Hairs on model heads for half-side testing are spot-welded after spray application, while hairs are seam-welded in the stiffness test after alignment of single hair fi bers. This alignment is necessary to achieve reproducible results. INTRODUCTION Hair gels and sprays have a high rank among styling products. Gels are favored for short hair styles and are particularly used by men, while sprays are used by women with long hair. However, styling products differ in composition, especially in the polymers used. In order to tailor properties such as fi xative power, wash-out, and elasticity, polymers are developed by a smart choice of monomer composition and process technology. A tempo- rary hold is achieved by means of a composition of hair fi ber and polymer at the hair surface. For characterization of the polymer fi lm, bending stiffness is the most important parameter. There are several methods to evaluate stiffness: sensorial tests on hair strains, half-side tests on model heads, salon tests, and panel tests. The objective test, fi rst *Trainee from March to July 2009. Address all correspondence to Peter Hoessel.
JOURNAL OF COSMETIC SCIENCE 344 evaluated by Frosch and Vogel (1), is the three-point bending stiffness test. Alternatively, the omega-loop method (2) can be used. Depending on the application and type of formulation, the correlation of the objective stiffness test with the subjective consumer relevant tests is limited. OBJECTIVE OF THE STUDY The objective test, e.g., the three-point stiffness test on round-shaped hair strains (1), has limited correlation with the afore-mentioned consumer-relevant tests. This is especially a problem for the assessment of the styling performance of hair gels. There is a need for improved objective tests and a closer correlation with practically relevant tests. Tests on hair gels with combinations of different thickeners and styling polymers will be investigated by means of a new two-point bending stiffness test on fl at hair strains. The results will be correlated with the subjective tests on these hair strains and by means of a panel test for selected formulations. In conventional stiffness tests for hair sprays, multiple application procedures are often applied, e.g., by means of a syringe or by dip- ping the hair strains into the hair spray solution without a propellant (1). Any infl uence of these factors, such as propellants, solvents, water, and valve cannot be considered in the conventional bending test after dipping. In our new approach we use a two-point bending stiffness test in which fl at hair strains are used after practically relevant spray application. EXPERIMENTAL MATERIALS Round- shaped (2.9–3.3 g, 26 cm) and fl at (2.9–3.3 g, 20cm) hair strains from Kerling (Caucasian, virgin brown hair, Art- Nr. 826550) were used. Model heads (Caucasian dark brown hair) from Wernesgruen, Germany, were used for half-side tests. All hair strains and model heads were washed twice with a solution of 27–28% sodium laureth sulfate. FORMULATIONS Gel and spray formulations tested for bending stiffness are listed in Tables I and II. BENDING STIFFNESS METHOD: THREE-POINT ROUND Hair strains (2.9–3.3 g, 26-cm round shape) were dipped repeatedly into the diluted gel (50 g of gel and 140 g of water) or in the spray solution without propellant. Excess gel or spray was wiped off and the hair strains were lightly compressed on fi lter paper. After- wards the hair strains were formed with fi ngers until they were round-shaped. The strains were dried overnight at 20°C and 65% relative humidity. The measurement of the bending stiffness was performed on a Karg tensile tester (TT 27025E6). The spacing between
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