What are the physical properties of propylene glycol?

Propylene glycol is a colorless, odorless, viscous, transparent liquid, an aliphatic mixture containing two hydroxyl groups. Propylene glycol is further divided into 1,2-propanediol (also known as 1,2-PDO) and 1,3-propanediol (1,3-PDO). Since both hydroxyl groups in the propylene glycol molecule can undergo chemical reactions, propylene glycol is an important chemical intermediate and has a wide range of applications in plastics, clothing, synthetic resins, cosmetics, food, and many other fields. As antifreeze, deicer, heat transfer medium, liquid detergent, etc. 

Propylene glycol is mainly used as a solvent for various spices, pigments, and preservatives, and as an extraction solvent for vanilla beans, roasted coffee granules, and natural flavors. Moisturizer and softener for candy, bread, packaged meat, cheese, etc. It can also be used as an anti-mildew additive for noodles and stuffing cores. Adding 0.006% to soymilk can make the flavor unchanged when heated, and making white and shiny packaged tofu while frying will increase the volume. 

Propylene glycol is an intermediate for the fungicide difenoconazole. Propylene glycol can be used as a solvent to dissolve food additives that are insoluble in water such as preservatives, pigments, antioxidants, etc., and then add food; it has strong hygroscopicity and has moisturizing and anti-freezing effects on food. Can be used in pastries, the maximum usage is 3.0g/kg.  

In the field of food, propylene glycol can be used as a high-efficiency solvent for flavors and food colorings, and can also be used as a mildew inhibitor and fruit ripening preservative. 

In addition, some antifreeze, food machinery lubricants, and other products often use propylene glycol as the main raw material. Propylene glycol is a legal food additive, which is allowed to be added to raw and wet flour products, Chinese pastries, Western pastries, moon cakes, etc. 

(1) Freezing point Add a certain amount of water to the diol, and the freezing point of the resulting solution is lower than 0 °C. This characteristic makes aqueous glycol solution widely used as a refrigeration medium. Different from the fast solidification characteristics of some solutions, in the process of gradually decreasing the temperature, the glycol aqueous solution gradually becomes viscous until it is no longer fluid. 

(2) Antifreeze protection During the cooling process, many fluids experience volume expansion. Pipelines and other closed systems containing fluids, when exposed to lower temperature conditions, may rupture or explode due to the volume expansion of the fluid. Therefore, it is necessary to protect against the sudden accident of the explosion of the pipeline or other closed systems caused by the expansion of the fluid volume due to the low temperature. Glycol-based fluids are often used as protective fluids due to their low freezing point. 

(3) Solubility is the same as that of other low molecular weight alcohols. Propylene glycol can be miscible with water in any proportion, and after adding a certain amount of glycol to water, many water-insoluble substances can be dissolved in the alcohol-water mixture.  Propylene glycol is also an organic solvent, and its dissolution effect is better than that of ethylene glycol. 

(4) Water absorption Propylene glycol has strong water absorption and is non-toxic. Therefore, propylene glycol is widely used in the food industry as a moisturizing agent. 

(5) Viscosity The viscosity of propylene glycol is inversely proportional to temperature. When the temperature increases, the viscosity of propylene glycol decreases. When the temperature reaches a certain temperature, propylene glycol can flow freely. On the contrary, the viscosity of propylene glycol gradually increases with the decrease in temperature until it loses flow. sex. Compared with other high-boiling solvents and plasticizers, propylene glycol has higher fluidity at the same temperature, so propylene glycol is often used as an additive to reduce the viscosity of other components. 

(6) Specific heat refers to the amount of heat absorbed by a unit weight of a substance to raise 1°C. Adding a certain amount of water to propylene glycol can increase the specific heat of propylene glycol. Taking advantage of this characteristic, propylene glycol is widely used as an important heat transfer medium on many occasions. 

(7) Toxicity Propylene glycol is widely used in food additives because of its non-toxicity. The harm of propylene glycol to humans and animals is extremely low. Studies have shown that after 140 days of feeding mice with water containing 10% propylene glycol, the mice did not show any abnormality; studies have shown that adding 4.9% to the daily diet of mice % propylene glycol, after 24 months, all the activities of the mice were still normal.