It is common practice in cosmetic chemistry to be interested in achieving different types of aesthetics. As natural personal care products rise in demand, altering feels and physical properties of natural oils and fats through cosmetic chemistry become paramount.
A popular approach has been altering the physical properties of natural oils or fats to achieve butters that are spreadable on skin. These butters posses attributes that are different from traditional solids and liquids in that they are solid when applied but liquefy under pressure. Butters have become more and more important in personal care products, especially when the formulator desires materials that incorporate natural oils in a formulation requiring a solid form. Typically, butters are either natural or chemically altered oils or fats. The most common chemical alteration is a simple process called hydrogenation.
Natural butters are materials that are produced from a natural source and are not chemically modified. Natural butters are extracted and refined by chemists; however, unlike hydrogenation, no chemical modification is made to the molecule. There are a number of naturally occurring butters including shea butter and cocoa butter. These materials are butters by virtue of their fatty compositions. Shea butter, a natural fat extracted from the nut of the African shea tree, is widely used in the cosmetic field as a moisturizer, salve or lotion. There are many natural oils that have a wide composition of materials and are liquids. These materials have a degree of unsaturation in the alkyl group of the triglyceride. Natural oils can be monosaturated or polysaturated, meaning they have one or many degrees of unsaturation. The steric hindrance of the double bond or bonds prevents the molecules from packing closely together and becoming solid.
The most common way to solve the problem of natural “unrefined” oils is for a chemist to chemically alter the oil by hydrogenation. Hydrogenation changes the chemical structure of the materials in the oil and results in the conversion of liquid oil to a solid or semi-solid fat. The most common example of this margarine. Changing the fat's degree of saturation alters some important physical properties such as the melting range, which is why liquid oils become semi-solid. The hydrogenation process was considered a mild reaction that adds two hydrogens and left the molecule “unchanged." Karabulut et al. found that hydrogenation produced a large amount of trans fats. Trans fats are produced by chemical modification and have been found to be unhealthy in diets.
Another approach to making butters is to add gelation agents. These additives will provide structure to natural oils and make them into butters. The gelation agents are generally added at low concentrations (below 10%) and allow for alteration of the butter's spread properties. These materials will be addressed in a subsequent "Comparatively Speaking" column.
Butters in Formulation
In the cosmetic field, formulation chemists have a tricky task ahead of them. The overall goal is to find a product that has the correct physical characteristics but is green. Natural oils like olive and soybean are used as solvents and natural additives in cosmetic products. The major advantage in using natural oils is that they are renewable and generally mild. Conversely, their rheological properties are typically weak, and the product has to be refined to improve its rheological properties. When these oils are added into a chemical formulation, they will weaken the structural integrity of the product. This is not a major problem when formulating a cream or liquid product, but it becomes a problem in lipstick, where the lack of structural integrity will lead to the product failing. There are a couple of ways to fix this problem. The first is to refine the hydrocarbons from the liquid oil. Refining or concentrating oils will produce a solid and does not chemically alter the chemical structure of the material. The second solution is to hydrogenate or chemically modify the chemical structure of the oil.
3. I Karabulut, M Kayahan and S Yaprak, Determination of changes in some physical and chemical properties of soybean oil during hydrogenation, Food Chemistry, 81(3) 453–456 (2003)