GELS AND SPRAYS IN TWO-POINT STIFFNESS TEST 351 Figure 9. Results of half-side test (full-grey data set: formula 1 striped-grey data set: formula 1). Gradings: 1 = best, 4 = worst. For formulas, see Table II. best stiffness (formulas 2, 5, and 8 in Figure 8), followed by octylacrylamide/acrylates/ butylaminoethyl methacrylate copolymer (formulas 1, 4, and 7 in Figure 8). The lowest stiffness was observed with VP/VA copolymer (formulas 3 and 6 in Figure 8). The stiffness increased with increasing polymer content (striped grey and checkered grey: 3%, full-grey: 5%). The differences between the different polymers are more signifi cant at higher polymer content. However, it was not possible to differentiate the different polymers at 5% solids content in the subjective test by hand grading. Due to the insolubility of VP/ VA copolymer in propane/butane, the stiffness of this formulation could not be measured. The subjective evaluation of the fl at hair strains treated with hair spray formulations was less sensitive compared to the evaluation of the gel formulations (see Figures 5 and 7). Only formulas 1 and 3 were subjectively rated with a 2 grading (Figure 7, good setting). All other formulas were subjectively assessed with a 1 grading (very good set- ting). It was only possible to fi nd subjective differences at 3% polymer content with DME as propellant. Acrylates/t-butylacrylamide copolymer performed best (see formulas 2, 5, and 8 in Figure 7). The spray formulas 1 and 2 (see Table II) were further investigated in a half-side test (5). The results of the half-side test are depicted in Figure 9. Apart from stiffness (setting), further parameters were characterized. The setting effect is characterized by grading 3+ (good–satisfactory) for both formulas. The half-side test shows no signifi cant differences between formulas 1 and 2. We postulate that the different polymer distribution on hair is responsible for the lack of correlation between the stiffness test on fl at hair strands and the half-side test on model heads. The preparation device (Figure 1) with a comb aligns the hair. This was found out to

JOURNAL OF COSMETIC SCIENCE 352 be necessary for reproducible stiffness test results. After combing the hair in the preparation device, the polymer/hair composite is seam-welded after drying of the polymer fi lm. The model heads for the half-side tests are sprayed and dried without combing and without any mechanical impact. Therefore the polymer/hair composite is mainly spot-welded. The different polymer/hair architecture leads to different styling grades that overcome the infl uence of the different polymers. More subjective data like salon tests and panel tests will be necessary to prove if there are differences in setting behavior that have been observed by means of the new two-point stiffness test on fl at hair strands. SUMMARY The presented two-point bending stiffness test method on fl at hair strands is a new test for measuring the bending stiffness of hair styling products. The test can be used to assess the bending stiffness of hair gels as well as hair sprays. A preparation device is used to align the hair fi bers to get reproducible results. In addition, this preparation device min- imizes the infl uence of individual processors. Results obtained with the two-point bending method on fl at hair strands are in good agreement with sensorial and consumer tests for styling gels. The correlation between the stiffness test and subjective evaluations are much closer on fl at hair strands compared to round-shaped hair strands. The best results by means of the two-point method on fl at hair strains are achieved with the combination of acrylates/beheneth-25 methacrylate copoly- mer and VP/methacrylamide/vinyl imidazole copolymer in hair styling gels. This corre- lates very well with the subjective tests on those strains. Stiffness tests on fl at hair strands after spray application using different styling polymers did not correlate with practical relevant assessments. We postulate that different poly- mer/hair composites are responsible for these discrepancies. Hairs are seam-welded in the stiffness tests after alignment of the single hairs and are spot-welded in the half-side tests on model heads after spray application without mechanical impact before the assessment of the styling performance. REFERENCES (1) F. Frosch and F. Vogel, Une méthode simple pur mesurer la fi xation des cheveux, Parfums, Cosmétiques, Arômes, 89, 71–72 (1989). (2) J. Jachowicz and R. McMullen, Mechanical analysis of elasticity and fl exibility of virgin and polymer- treated hair fi ber assemblies, J. Cosmet. Sci., 53, 345–361 (2002). (3) C. Wood and P. Hoessel, A new dimension in hairstyling—VP/methacrylamide/vinylimidazole copolymer, Cosmet. Toiletr., 119(2), 59–66 (2004). (4) P. Hoessel, J. Basilan, M. Laubender, S. Nguyen-Kim, D. Patwardhan, and B. dePotzolli, Poly- quaternium-86: Advanced styling in hair gels, SÖFW J., English Ed., 135(6), 2–10 (2009). (5) E. Pfrommer and P. Hoessel, Polyurethane-1 for VOC 55 hairsprays, Cosmet. Toiletr., 114(8), 53–60 (1999).