The Different Grades of Glycerin
Feb 13, 2016
Glycerine or glycerin as it is also termed is one of the most commonly used humectants in cosmetics. Physically, glycerine is a water-soluble, clear, almost colorless, odorless, viscous, hygroscopic liquid with a high boiling point. Chemically, glycerine is a trihydric alcohol, capable of being reacted as an alcohol yet stable under most conditions. Glycerine has over 1500 known end uses. About 300 million pounds of glycerine are used annually in the United States.
The origin, chemical structure, and utility of glycerine have been known for little more than two centuries. Glycerine was accidentally discovered in 1779 by K.W. Scheele, the Swedish chemist, while he was heating a mixture of olive oil and litharge (lead monoxide). Scheele called glycerine the "sweet principle of fat." [1] Scheele later established that other metals and glycerides produce the same chemical reaction which yields glycerine and soap and, in 1783, he published a description of his method of preparation in the Transactions of the Royal Academy of Sweden.
The immense potential of glycerine went largely untapped until M. E. Chevreul, the French pioneer investigator of fats and oils, studied it early in the 19th Century. Chevreul named Scheele's "sweet principle of fat" glycerine in 1811 after the Greek word, glykys, meaning sweet." In 1823 Chevreul obtained the first patent for a new way to produce fatty acids from fats treated with an alkali, which included the recovery of glycerine released during the process.
Glycerine did not become economically or industrially significant until Alfred Nobel invented dynamite in 1866 after twenty years of experimentation. Nobel's invention successfully stabilized trinitroglycerin, a highly explosive compound, by absorption on kieselguhr, which permitted safe handling and transportation.
Chemically there are Five Grades of Glycerine
USP GLYCERIN(E) is a clear, almost colorless product for uses requiring glycerine of high purity with taste and odor characteristics desirable for pharmaceutical and food purposes. The designation USP is an abbreviation of U.S. Pharmacopeia and signifies that the glycerine thus designated meets or exceeds the standards established in U.S. Pharmacopeia (USP XXII, 1990) monograph, Glycerin. The USP designation has official legal status in the United States since the U.S. Pharmacopeia has been incorporated by reference in various statutes and regulations governing drug and medical practices, of which the federal Food, Drug, and Cosmetic Act is the most significant. USP glycerine is commonly available commercially at anhydrous glycerol content levels of 96%. 99.0% and 99.5%. Concentrations above 99.5% are also available commercially.
CP GLYCERINE or chemically pure glycerine is generally understood to be of the same quality or grade as USP glycerine, but this term is considered generic in the United States because it does not reflect compliance with any official quality requirements or specifications a s does the USP designation.
FOOD GRADE GLYCERINE in the United States meets the requirements outlined in the monograph Glycerin contained in the Food Chemicals Codex prepared by the Committee on Food Protection of the National Research Council. Food grade requirements are similar to USP standards. Within the European Economic Community, glycerine for use in food products must comply with Council Directive 78/663/EEC which specifies the standards of purity for emulsifiers, stabilizers, thickeners, and gelling agents for use in foods.
HIGH GRAVITY GLYCERINE is a designation used in the United States for a commercial grade of glycerine that is clear, almost colorless and conforms to Federal Specification 0-G-491C issued November 14, 1983 by the General Services Administration. This product also conforms to Standard Specification for High-Gravity Glycerin, D-1257, issued by the American Society for Testing and Materials (ASTM). This grade must contain not less than 98.7% glycerol. It is commonly supplied at not less than 99.0% concentration.
DYNAMITE GLYCERINE in the United States meets all the High Gravity grade specifications except color, but it cannot be darker than the Federal Color Standard. In Europe, glycerine for use in explosives is defined by Specification 21D for dynamite glycerine issued by the Nobel Explosives Company Ltd. The British Standards Institution has also issued a standard specification for this grade of glycerine as British Standard Specification for Dynamite Glycerol.
Glycerine is still a valuable ingredient for skin care. Recently there seems to be a backlash against the use of it, with claims saying that it dehydrates the skin and should not be used. Ironically the founder of Corneotherapy Albert Kligman endorsed the use of Glycerine.
In our next post we will delve into the benefits of Glycerine and expose the myths and controversy surrounding its denigration as no more than marketing tactics designed to put the products that use glycerine in a poor light.
References:
1. Miner, C. S. and Dalton, N. N., Editors. Glycerol, American Chemical Society Monograph Series. Reinhold Publishing Company, New York. 1953. p. 1.
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