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Surface Science and Adhesion in Cosmetics


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F/m.

       2.4.2.3 Hardness of Lipsticks

      A simple lipstick containing polyethylene wax and oil was prepared by heating the mixture above 95°C until it melted completely. Then the hot mixture was poured into a lipstick mold and cooled down in a refrigerator for 20 min. The lipstick was molded and placed in a 12mm diameter bullet shape container. The lipstick was then stored at 20°C for 24 hours before measuring its hardness.

      The hardness of the lipstick samples was measured using a DFGS2 dynamometer (Indelco-Chatillon). The hardness corresponds to the maximal shear force exerted by a rigid tungsten wire of diameter 250 μm, advancing at a speed of 100 mm/min.

      The technique above is normally described as the “butter- cutting wire” method. The hardness value from this method is expressed in grams as the shear force required to cut a lipstick under the above conditions.

       2.4.2.4 Amount and Thickness of Lipstick Deposit on Bioskin

       2.4.2.5 Wax Crystallization Study

      The relative crystallinity Xc (%) from cooling or from melting is calculated via either equation:

Graph depicts the DSC thermogram of an oil-wax gel system.

      where ΔHc0 and ΔHm0 are the enthalpies of crystallization and melting for 100% PE wax, respectively and w is the weight fraction of the PE wax in the oil-wax system.

       2.4.2.6 Morphology of Wax Structure by SEM

      The morphology of the wax-oil systems was studied using a HITACHI Ultra-High Resolution Scanning Electron Microscope model S-4800 at an accelerating voltage of 5 kV.

       2.5.1 Factors Affecting Lipstick Structure: Oil Viscosity