Formulation of personal care products containing siloxane and natural lipids（I）


Natural lipids have been used for personal care for thousands of years. Olive oil was used to care for skin and hair in ancient Rome. This may be the first natural lipid widely used as emollient. For some time, natural lipids have been replaced by synthetic esters and oils derived from petroleum in many modern personal care formulations. However, with the increase of consumers'preference for natural ingredients, there is a new tendency to use natural lipids in various personal care formulations. Siloxane is a synthetic emollient that has been used in personal care formulations for more than 50 years. Because of its special aesthetic properties, it is now used in almost all personal care formulations.


Natural lipids and siloxanes have many beneficial properties and complement each other in personal care formulations, thus creating conditions for the diversification of formulations.


Natural lipids and siloxane chemical natural lipids are oily substances from plants or animals. These substances contain various chemical constituents. However, most of the natural lipids used in personal care products are a mixture of plant lipids, the main component of which is triglycerides. In plant lipids rich in triglycerides, there are also non-triglyceride components, which are called unsaponifiable compounds. This part is generally composed of tocopherols, sterols, free fatty alcohols and triterpenes.


The natural lipids described in this paper are triglyceride fractions extracted mechanically from seeds of different plants. Triglycerides are long-chain carboxylic acid alkyl chains consisting of a glycerol molecule bonded with three fatty acid molecules, which generally have 10 or more carbon atoms.


The chain length of three fatty acid molecules can be the same or different; the base carbon chain can be saturated or unsaturated. The fatty acid composition of triglycerides is determined by the source of triglycerides. For example, triglycerides from coconut fruits are rich in lauric acid (C12 saturated fatty acid). In many cases, surfactants produced from coconut oil, such as sodium lauryl sulfate, retain a slight coconut oil odor.


Triglycerides can be classified according to their melting point. Melting point is a property related to the type of fatty acid bonded by triglycerides. Natural triglyceride oils are liquid at room temperature, while natural lipids are soft solids. Mango fat extracted from Mango seeds is solid because its dominant fatty acid is hard acid; on the contrary, triglycerides extracted from evening primrose seeds are rich in polyunsaturated fatty acids (such as linoleic acid), which have low melting point and are an oil.


In the International Naming of Cosmetic Components (INCI), natural lipids are named according to the species of plants. If plants have common names, they can also be used in INCI. Because the common name of INCl is Mangifera indica or mango butter, and the common name of INCI is oenomera biennis or evening primrose oil. Triglyceride is a mixture of plant extracts called vegetable oil.


Siloxane is a polymer synthesized from quartz (a natural crystalline silica) and methanol. Most of the siloxanes used in personal care products are polydimethylsiloxane-like. The INCI name of polydimethylsiloxane is Dimethicone. Polydimethylsiloxane is a linear polymer with molecular weight in a certain range. For a particular kind of polydimethylsiloxane, its molecular weight determines its viscosity. Low molecular weight polydimethylsiloxane has low viscosity, and its viscosity increases with the increase of molecular weight. Another commonly used siloxane is phenyltrimethylsiloxane, which is a multi-branched benzene functional siloxane.


From Cosmetics Science