46 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Table IV Effect of Water Content on Hardness of Emulsion Lipsticks Additional ingredients Hardness Formula (parts by weight) (compression by 0.1 mm) 1-1 5 H20 5 Span 60 140 + 13 g 1-2 10 H20 5 Span 60 223 + 23 g 1-3 15 H20 5 Span 60 270 + 28 g 2-1 5 H20 5 Span 80 190 + 18 g 2-2 10 H20 5 Span 80 263 -+ 27 g 2-3 15 H•O 5 Span 80 273 + 26 g An emulsion lipstick is usually a W/O-type emulsion because of high oil and wax contents. A selection of lipophilic emulsifiers is therefore preferable. However, it is interesting to examine the effect of a hydrophilic emulsifier. Tween 20 with an HLB value of 16.7 was used to prepare an emulsion lipstick. Examples are given in Table III. The hardness of emulsion lipsticks prepared with a hydrophilic emulsifier also decreased when compared with a conventional lipstick. The hardness of Formulae 2 and 3 in Table III is similar to that of Formulae 2 and 3 in Table II, which shows that a hydrophilic emulsifier can also give a stable W/O emulsion lipstick. The reason is not understood. o o x 1.1.1 First run , Second run 4O i I I ' 60 70 80 90 TEMPE R-AT U R E(øG) Figure 3. DSC curves of a conventional lipstick. lOO

HARDNESS OF EMULSION LIPSTICKS 47 The effect of water content on the hardness of emulsion lipsticks is shown in Table IV. Hardness increases with the water content, using both Span 60 and Span 80. This is unexpected because water is a liquid, and more water in the formulation should decrease the hardness. However, a large enough amount of water is needed to form W/O emulsion droplets, which make an important contribution to hardness. That is thought to be the reason why the higher the water content the higher the value of hardness. MEASUREMENT OF CRYSTALLIZATION DSC is sensitive to thermal changes in materials. Therefore, DSC was used to study the effect of formulation on crystallization of lipsticks. Usually the degree of crystallization is proportional to the heat of transition of the melting point peak, measured by DSC. Thus the heat of transition was used as an indicator of the degree of crystallization of the lipsticks. The crystallization of lipsticks depends on the individual ingredients. Only microcrys- talline wax, carnauba wax, candelilla wax, and beeswax are able to crystallize in the basic lipstick formula in Table I. The melting point of microcrystalline wax is reported to be approximately 80øC, of carnauba wax 85øC, of candelilla wax 70øC, and of beeswax 61-66øC in Williams and Schmitt's book (! 1% Figure 3 is a DSC curve of a conventional lipstick (Table I or Formula ! of Table II) and shows a broad thermal peak range from 60øC to about 73øC. This broad peak is due to the absorption of heat when the mixture of different waxes is melted. I Formula 1 Formula 2 Formula 3 40 50 60 70 80 90 TFJvIp1= RATURF(øO) Figure 4. DSC curves of a conventional lipstick and two types of emulsion lipstick. 100