DPG - Dipropylene Glycol — Frequently Asked Questions

DPG dissolves most perfume materials, has almost no odour of its own, evaporates slowly so it does not flash off before the fragrance, and is mild to the skin. It also mixes with water and alcohol, so it works in fine fragrance, air care and personal care. Few other solvents combine all of these properties at a comparable cost.

Fragrance-grade DPG is refined further than industrial grade to remove trace impurities that carry odour. It is tested by odour panels against a reference standard as well as by chemical analysis. Use it for perfumes, air fresheners and cosmetics; industrial grade is suitable for resins and chemical manufacture, where a faint odour does not matter.

DPG forms as a mixture of three structural isomers when propylene oxide reacts with propylene glycol. The isomers are not separated commercially, so the product is registered and traded as one mixture under CAS 25265-71-8. The isomer distribution is fairly constant between producers, which is why DPG from different sources usually performs similarly.

DPG is a longer molecule than MPG, so it is less volatile, more viscous and gives more flexibility when used in resins. It is also a better solvent for many fragrance materials, with less odour. MPG is cheaper and more widely used as a humectant, antifreeze and pharmaceutical excipient. Formulators often use both, depending on solubility and cost.

Store it in closed, clean stainless steel, aluminium or lined containers in a cool, dry place. DPG absorbs moisture from the air, and it readily picks up odours from previously used drums, hoses and tanks. Use dedicated equipment where possible, keep containers sealed and use stock in rotation to protect the odour quality.