Monopropylene glycol (MPG) is a highly versatile organic compound that has various industrial and commercial applications. In fact, it’s found in everything from cosmetics and pharmaceutical products to food and e-cigarettes.
MPG is available in different purity grades, each of which has an impact on the respective applications.
- USP Grade – With the highest purity level, USP grade MPG contains at least 99.8% monopropylene glycol. As well as being used as a food flavouring, it has applications across the pharmaceutical, cosmetic, and e-cigarette industries.
- Technical Grade – This grade of monopropylene glycol is most commonly used as an antifreeze for car engines. It’s also used for cooling and de-icing purposes.
- Feed Grade – Mainly used for livestock feed, this grade meets European quality standards. It’s registered under the Feed Materials Assurance Scheme (FEMAS).
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What is monopropylene glycol?
Monopropylene glycol (also spelt ‘mono propylene glycol’) is a colourless and odour-free organic solvent with a higher viscosity than water. Its hygroscopic properties mean it attracts and easily absorbs moisture from the air. MPG is also highly miscible with other solvent-liquids such as water, alcohols, esters, and ketones.
As a solvent, MPG can connect and stabilise some insoluble fluids. When used as an antifreeze, it reduces the freezing point of water. It can also stabilise volatile, flammable liquids like alcohol and ketones by increasing their flash points and boiling points. MPG itself is chemically stable and relatively unreactive with other chemicals.
Is monopropylene glycol the same as propylene glycol?
Chemically, propylene glycol is the same as monopropylene glycol; the main difference is its purity level. For example, pharmaceutical grade MPG has a purity level of more than 99.8%.
The chemical formula for MPG is C3H8O2. This can also be written as CH3CH(OH)CH2OH. Its two hydroxyl groups make it a diol, meaning two alcohols are present. MPG has a molar mass of 76.095 g·mol−1 and a viscosity of 0.042 Pa·s. The molecular structure consists of two hydroxyl groups, as shown below.
What are the uses of monopropylene glycol?
Its versatility means monopropylene glycol has a wide range of household, commercial, and industrial applications.
Antifreeze
The normal freezing point of pure water is 0°C at 1 atm (101.325 kPa). 
Adding MPG to water lowers the freezing point to a certain temperature, depending on the percentage of MPG used. The table below shows how the freezing point of water decreases proportionally as the percentage of antifreeze increases.
Antifreeze is commonly added to the water in car radiators to prevent it from freezing in cold weather. It’s also used to treat the fuselage, wings and tail surfaces of aircrafts to prevent ice accretion before take-off.
Coolant
MPG is a non-volatile and non-flammable liquid. Although it’s a very good conductor of heat, it also releases heat easily. This makes it an excellent refrigerant. Unsurprisingly, MPG is used in air conditioning systems, as well as a coolant liquid in household fridges.
Lubricant
MPG has a viscosity and consistency similar to oil. It’s therefore suitable as a lubricant for moving machine parts such as those in car engines and industrial machinery. It prevents damage to moving parts by reducing friction and minimising expansion due to heat.
MPG is also used as a non-toxic, hypoallergenic lubricant in condoms. Various flavours can even be added to it.
Pharmaceutical Industry
Monopropylene glycol’s hygroscopic properties make it a useful ingredient in various topical medicines. Not only does it improve the adherence and hydration of medicinal creams, but it helps to maintain the product’s chemical integrity.
Topical medicines containing MPG can also be stored at low temperatures, thereby improving their shelf life. Aside from the pleasant cooling effect when applied to the skin, MPG aids the healing and regeneration process.
Cosmetic products
Thanks to its ability to retain and prevent moisture from evaporating, MPG is widely used in moisturisers and other cosmetic products. It’s now an active ingredient in products such as shaving lotions, deodorants, shampoos, conditioners, repairing masks, and beard soaps.
Food processing
In the food processing industry, MPG is used as an additive and preservative. It’s therefore present in many processed foods and beverages, including carbonated drinks. It also acts as a moisturiser and anticoagulant for food products such as ice cream and pastry.
Is monopropylene glycol harmful?
Monopropylene is non-toxic and hypoallergenic. It’s safe enough to be added to food as an ingredient and consumed by humans.
Where to buy monopropylene glycol in the UK
You can buy monopropylene glycol in bulk or retail quantities directly from a chemical manufacturer, but you typically need to be a business to order it in these quantities. You can also order it online. 
