DPG - Dipropylene Glycol

About This Product

Dipropylene glycol, DPG (CAS 25265-71-8, EC 246-770-3, formula C6H14O3), is a co-product of propylene glycol manufacture, formed when propylene oxide reacts with propylene glycol instead of water. It is not a single compound but a mixture of three structural isomers, which is why it is identified by one mixture CAS number. It is a clear, colourless, slightly viscous, hygroscopic liquid, boiling at about 230 °C, with very low volatility and complete miscibility with water and many organic solvents. Two qualities are commonly traded. Industrial grade is used in resins, plasticiser manufacture and as a chemical intermediate. Fragrance or cosmetic grade, sometimes described as low-odour, is refined further to remove trace impurities that affect odour, and is tested by odour panels as well as by chemical analysis. The distinction matters because a fragrance with a faint off-note from its solvent cannot be corrected later in the formulation. In perfumery, DPG is the most widely used diluent for fragrance concentrates, because it dissolves most perfume materials, has almost no odour of its own, evaporates slowly and is mild to skin. The same properties make it a solvent and humectant in air fresheners, reed diffusers, deodorants, creams and hair products. In industry, DPG is a diol for unsaturated polyester and alkyd resins, where its longer chain gives more flexibility than MPG, and it is a raw material for dipropylene glycol dibenzoate plasticisers and acrylate monomers. It is also used in some inks, cutting fluids and textile auxiliaries. The parameters buyers agree are purity (sum of isomers), water, colour on the Pt-Co scale, acidity, density and, for fragrance grades, odour against an agreed standard. Some buyers also specify residual MPG and tripropylene glycol. Agree the limits and grade in writing and check each certificate of analysis. DPG is not classified as hazardous under CLP and is not regulated as dangerous goods for transport, but check sections 2 and 14 of the safety data sheet. An importer into the EU or Great Britain should confirm which REACH or UK REACH registration covers the substance and the intended use. Cosmetic formulators should file the grade documents with the product information file. Store DPG in closed stainless steel, aluminium or lined containers in a cool, dry area, because it absorbs water from the air and odour-sensitive grades can pick up taints from dirty or previously used equipment. Keep it away from strong oxidisers and ignition sources; its flash point is well above ambient, at around 124–138 °C depending on the isomer mix. When you enquire, state fragrance or industrial grade, the application, the purity and water limits, any odour standard, the pack format (drum, IBC or ISO tank), your volumes and your destination.