GELS AND SPRAYS IN TWO-POINT STIFFNESS TEST 349 The new two-point stiffness test on fl at hair strands after application of styling gels (see Table I) was developed to overcome those discrepancies between hand grading and the stiffness test (see Figure 6). The two-point stiffness test on fl at hair strands gives lower stiffness values than the three-point measurement. Especially for formula 7 the difference is obvious. The stiffness measured on fl at hair strands shows a much better correlation with hand grading. Now the gel with the highest stiffness values (formula 1, 160 cN) was rated to have the highest setting effect by hand grading (-1). Gels with lower stiffness values (for- mula 3–7) were consequently rated lower by hand grading (2). The accuracy of the new two-point method is very good with standard deviations less than 20%. A confi dence interval of 95 % could be achieved by measuring each hair strain four times at different positions (see Figure 3). Signifi cant differences between the stiffness values at these different positions could not be detected. Therefore, it was pos- sible to calculate confi dence intervals with data of 4 ´ 10 = 40 single measurements. Gel formulas 3 (1.0% cationic thickener Polyquaternium-86, 2.5% polyvinylpyrroli- done) and 4 (0.5% anionic thickener carbomer, 3.0% polyvinylpyrrolidone) were further investigated in a panel test (4). Apart from stiffness (setting), further parameters were characterized. The panel test results are depicted in Figure 7. Fifty percent of the panel- ists could confi rm a higher setting effect with formula 3 compared to formula 4. This correlates with the two-point and three-point stiffness results in Figures 4 and 5. The new two-point bending stiffness test was also implemented to spray application. The focus was on fi xative polymers in European water-free spray formulas based on dimethyl- ether (DME) rsp propane/butane (P/B), a liquid pressure gas, as propellant (see Table II). Figure 8 depicts the results of the stiffness test and the hand grading after spray application. The striped-grey and full-grey data sets (formulas 1 to 6 in Figure 8) are formulations Figure 6. Result of the two-point stiffness test after gel application (striped-grey-data set: BASF formula- tions full-grey data set: market products). Hand grading: 1 = highest, 4 = lowest. Breaking of the strains by hand. For formulas, see Table I.
JOURNAL OF COSMETIC SCIENCE 350 with dimethylether (DME) as propellant, while the checkered-grey data sets (formulas 7 and 8 in Figure 8) are the same formulations with propane/butane (P/B) as propellant. In each set of formulations the polymer acrylates/t-butylacrylamide copolymer provides the Figure 8. Result of the two-point stiffness test after spray application (striped-grey data set: formulations with 3% polymer content and DME full-grey data set: formulations with 5% polymer content and DME checkered-grey data set: formulations with 3% polymer content and P/B). Hand grading: 1 = highest, 4 = lowest. For formulas, see Table II. Figure 7. Result of panel test: Comparison of gels based of Polyquaternium-86 with polyvinylpyrrolidone and carbomer with polyvinylpyrrolidone 28 answers.
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