Propylene glycol (1,2-propanediol) is a clear, colorless, viscous, and practically odorless synthetic organic compound with a slightly sweet taste. This versatile chemical serves as a solvent, humectant, preservative, and vehicle across pharmaceuticals, cosmetics, food products, and industrial applications.

Liquid medications rely on propylene glycol to dissolve active ingredients that won't mix with water alone. Baked goods stay fresh longer because propylene glycol holds moisture inside. Skin lotions feel smooth and hydrating thanks to propylene glycol drawing water to the skin surface. Aircraft wings shed dangerous ice through propylene glycol-based de-icing fluids. Theater productions create dramatic fog effects by heating propylene glycol into visible vapor.

The remarkable aspect of propylene glycol isn't just versatility but safety. Few solvents can claim FDA approval for direct food contact, pharmaceutical injection, and cosmetic application simultaneously. This compound achieves that rare combination of powerful functionality with remarkably low toxicity. The oral LD50 of 20 g/kg classifies it as practically non-toxic, yet it performs as effectively as many hazardous industrial solvents.

Understanding propylene glycol means recognizing how grade selection impacts regulatory compliance. A pharmaceutical formulator needs USP grade meeting strict purity standards. A food manufacturer requires an FCC grade with GRAS certification. An industrial plant selecting antifreeze can use technical grade at a lower cost. Each application demands appropriate specifications, and substituting grades creates regulatory violations alongside potential safety issues.

• Compound Name: Propylene Glycol

• Synonyms: 1,2-Propanediol, PG, Propane-1,2-diol, Methylethylene glycol, Methyl glycol, α-Propylene glycol

• Chemical Formula: C₃H₈O₂ or CH₃CH(OH)CH₂OH

• CAS Number: 57-55-6

• RTECS Number: TY2000000

• Molecular Weight: 76.09 g/mol

• Appearance: Clear, colorless, viscous liquid; practically odorless; slightly sweet taste

Propylene glycol weighs 1.036 g/cm³ at 20°C, denser than water with a specific gravity of 1.04. This extra weight matters when designing pumping systems and calculating storage tank capacities. The boiling point of 188.2°C (370.8°F) sits far above water's 100°C threshold, preventing evaporation losses during normal use. The freezing point drops to -59°C (-74°F), maintaining a liquid state through extreme cold. Aircraft de-icing and antifreeze applications depend on this low freezing point.

Flash point measurements show 99°C (210°F) closed cup and 107°C (225°F) open cup. These values classify propylene glycol as combustible rather than flammable. Compare this to ethanol's 13°C flash point, where vapors ignite from minor sparks. Propylene glycol requires sustained heating well above room temperature for ignition. Autoignition occurs at 371°C (700°F).

Complete miscibility with water means propylene glycol blends uniformly at any concentration. This unlimited compatibility distinguishes propylene glycol from many organic solvents, showing limited aqueous solubility. Beyond water, propylene glycol mixes completely with ethanol, acetone, and chloroform.

The ability to dissolve essential oils, resins, and flavor compounds makes propylene glycol invaluable when compounds resist water solubility. The hygroscopic character means atmospheric moisture gets absorbed continuously. Leave a container open and volume increases as water accumulates from humid air.

Propylene glycol is a synthetic, odorless, and colorless liquid widely used across industrial, pharmaceutical, and consumer applications. In its pure form, it appears as a clear, viscous fluid with low toxicity and strong hygroscopic properties, making it effective at retaining moisture and stabilizing formulations. The compound functions as a solvent, humectant, and carrier in pharmaceuticals, food products, cosmetics, and industrial processes. It supports product consistency, enhances ingredient delivery, and extends shelf life in formulations ranging from medicines and personal care products to food and antifreeze systems. U.S. laboratories and manufacturers sourcing propylene glycol by grade and purity contact Lab Alley at 512-668-9918 for product selection and ordering support.

A neutral pH of 6.0 to 8.0 eliminates corrosion concerns with metal equipment and prevents tissue irritation. The viscosity of 40.4 mPa·s at 25°C creates noticeable thickness compared to water. This moderate viscosity provides substantivity in topical products. Refractive index is 1.432 at 20°C, enabling quick verification of purity.

Stability under normal conditions allows years of storage without decomposition. No polymerization occurs, eliminating concerns about solidification during storage. Strong oxidizing agents, strong acids, and strong bases represent incompatibilities requiring physical separation. Container material selection matters: stainless steel, aluminum, polyethylene, and polypropylene all work well. Avoid copper and copper alloys for extended contact, as these metals catalyze unwanted oxidation.

Multiple grades serve different regulatory requirements and application needs, from pharmaceutical through industrial uses.

United States Pharmacopeia and National Formulary standards define pharmaceutical-quality propylene glycol. Purity reaches 99.5% minimum with strictly controlled impurity levels, particularly diethylene glycol, which poses significant toxicity risks. Pharmaceutical formulations from oral medications through injectable solutions require this grade.

Food Chemicals Codex standards govern food-grade specifications. GRAS (Generally Recognized As Safe) designation reflects decades of consumption history without adverse effects at approved levels. Purity matches USP grade but specifications target food industry requirements specifically.

Lower purity creates cost advantages for applications not involving human consumption. Antifreeze, coolants, de-icing fluids, and general industrial processes use technical-grade material. High-volume consumption benefits from reduced pricing.

Religious dietary compliance requires certification beyond chemical purity. Manufacturing processes must meet Islamic and Jewish dietary law requirements. Documentation accompanies certified products proving compliance.

Analytical applications demand minimal impurities. Reagent-grade material includes detailed certificates of analysis. Laboratory research and precision analytical chemistry justify premium costs.

Propylene glycol from Lab Alley is available as a high-purity, clear, colorless liquid meeting USP/FCC and food-grade standards, suitable for food, beverage, pharmaceutical, cosmetic, and industrial applications. Packaging ranges from small laboratory containers to bulk drums and totes to support laboratory, manufacturing, and commercial supply needs.