Propylene Glycol (PG) USP/EP is a pharmaceutical grade of Monopropylene Glycols (PG or MPG) with a specified purity greater than 99.8%. Propylene glycol, also called propane-1,2-diol, is an organic compound with the chemical formula C3H8O2. It is a viscous colorless liquid which is nearly odorless but possesses a faintly sweet taste. Chemically it is classed as a diol and is miscible with a broad range of solvents, including water, acetone, and chloroform.
It is produced on a large scale and is primarily used in the production of polymers but also sees use in food processing as the E-number E1520.The compound is sometimes called α-propylene glycol to distinguish it from the isomer propane-1,3-diol (β-propylene glycol).
Forty-five percent of propylene glycol produced is used as chemical feedstock for the production of unsaturated polyester resins. In this regard, propylene glycol reacts with a mixture of unsaturated maleic anhydride and isophthalic acid to give a copolymer. This partially unsaturated polymer undergoes further crosslinking to yield thermoset plastics. Related to this application, propylene glycol reacts with propylene oxide to give oligomers and polymers that are used to produce polyurethanes.
Propylene glycol is used as a humectant (E1520), solvent,and preservative in food and for tobacco products. It is also one of the major ingredients (10–92%), along with vegetable glycerin, of the "e-liquid" and cartridges used in electronic cigarettes (as well as liquid nicotine), where it is aerosolized in the atomizer.Propylene glycol is also used in various edible items such as coffee-based drinks, liquid sweeteners, ice cream, whipped dairy products and soda. Vaporizers used for delivery of pharmaceuticals or personal-care products often include propylene glycol among the ingredients.Propylene glycol is used as a solvent in many pharmaceuticals, including oral, injectable and topical formulations, such as for diazepam and lorazepam which are insoluble in water.
Like ethylene glycol, propylene glycol is able to lower the freezing point of water, and so it is used as aircraft de-icing fluid.Water-propylene glycol mixtures dyed pink to indicate the mixture is relatively nontoxic are sold under the name of RV or marine antifreeze. Propylene glycol is frequently used as a substitute for ethylene glycol in low toxicity, environmentally friendly automotive antifreeze. It is also used to winterize the plumbing systems in vacant structures.The eutectic composition/temperature is 60:40 propylene glycol:water/-60 °C.The −50 °F/−45 °C commercial product is, however, water rich; a typical formulation is 40:60.
Propylene glycol is used in veterinary medicine as an oral treatment for hyperketonaemia in ruminants. Glucose, which can be used in non-ruminants for this purpose, is not effective due to its consumption by the resident microbes of the rumen. Propylene glycol is partially metabolized in the rumen to propionate which can be used as an energy source. The remainder is absorbed into the bloodstream and used by the liver for gluconeogenesis.