Creating improved lipstick formulations

There is little information known about how different waxes commonly found in lipsticks solidify different oils. The objective of the investigation described in this article was to fill in this gap in knowledge with regard to a selection of oils commonly used in lipstick formulas. Castor oil is commonly used as the fluid oil part of a lipstick with properties associated with its unique triglyceride structure well liked by formulators. It was therefore chosen as a benchmark oil type ingredient in this study. One advantage of castor oil is its capability to function as a bridge between non-polar waxes and polar oils. Wax swelling is one of the three main functional needs of oils in lipstick alongside pigment wetting and gloss. Structure and mechanical properties of the stick are provided by the appropriate interactions between waxes and oils. This gives rise to stable shape and easy application, two contradictory requirements.1 The chosen waxes are carnauba, a complex mixture of esters and polyesters of mono and di hydroxy acids and fatty alcohols; ceresin, which is a hydrocarbon wax; and candelilla which is a mixture of ester and hydrocarbon waxes. To develop a realistic lipstick a combination of these three waxes are used. In the case of a lipstick, the product is expected to transfer easily from the stick to the lips. If this is not accomplished, the coverage on the lips may be uneven and unacceptable. A lipstick is also expected to retain its shape, even under very hot conditions.2 Important rheological concerns of a lipstick that this investigation covers include spreadability, firmness/hardness, break resistance and payoff.

 Materials and methods

For this investigation a number of oils were assessed, all of which are used in lipstick formulas. The waxes used in the assessment were: Candelilla Wax 7454 (congealing point ASTMD938 65-70°C); Yellow Carnuba Wax T1 (melting point capillary rise method 80-88°C); Ceresin Wax 7068 (congealing point ASTMD938 59-63°C). Supplied by Poth Hille & Co Ltd.