Synthetic oils

Synthetic oils
Synthetic oils are esters, usually obtained by direct reaction of fatty acids with alcohols. Common fatty acids are caprylic. caprinic. lauric, myristic. palmitic, stearic, oleic, linoleic and behenic acid, and also adipic acid, a dicarboxylic acid. Alcohols can be, for example, isopropyl, butyl, ethylhexyl, myristyl or oleyl alcohol, as well as polyvalent alcohols such as ethylene glycol, propylene glycol and glycerol. A wide range of combinations to produce different synthetic esters is possible, and the list of synthetic oils available to the cosmetic industry is long.
In addition to products obtained via normal esterification using chemical catalysts, esters obtained by enzymatic catalysis are now also available]. Possibly advantages can be found in the case of oleic acid derivatives, because esterification can be obtained under milder conditions. Consequently, a light color and weak odor can be expected.
- Isopropyl esters
The most important synthetic ester for cosmetics is isopropy myristate. It has a very dry character and shows good spreading on the skin. It can open films of mineral oil or other fatty oils in order to let water evaporate, and it is an excellent solvent for perfumes, ultraviolet filters, etc.
A disadvantage of isopropyl myristate is its high comedogenicity.
Due to their good solvent properties, the isopropyl esters can cause difficulties when used in formulation that are filled into polystyrene or polyethylene containers.
- Ethylhexyl esters
Other alternatives to isopropyl myristate are the ethylhexyl esters of palmitic acid or stearic acid. These have become important products for the cosmetic industry. Compared with isopropyl esters, the molecular weight is higher, but spreading properties are similar.

- Oleic acid esters

The two most important oleates are decyl oleate and oleyl oleate. The character of these esters is relatively fatty and, as with unsaturated esters, they can become rancid. The advantage of the oleates is that, even at high molecular weight, the esters are liquid.
Interesting alternatives to the oleates are the isostearates. Esters of branched isostearic acid are also liquid and present no oxidation problem. The limiting factor for use is the price, which is much higher than that of the oleates.

- Caprylic/capric acid esters

The most important caprylic/capric esters are the triglyceride and the propylene glycol diester. The glycerol ester is mainly used as a replacement for natural triglycerides, with the advantage that it is stable against oxidation. Like the natural triglycerides, the products are relatively difficult to emulsify. Due to the typical odor of short chain fatty acids, caprylic/capric esters must be produced in very pure form. Following long-term storage, hydrolysis, which leads to changes in the odor of cosmetic products, can take place.