Propylene glycol is a colorless, transparent, and viscous liquid; viscosity is a key physical parameter reflecting its flow characteristics. The dynamic viscosity of commonly used 1,2-propylene glycol is approximately 52 mPa·s at 20°C and about 43 mPa·s at 25°C. Compared to water, propylene glycol has a significantly higher viscosity, resulting in a relatively slower flow rate at room temperature; however, it retains sufficient fluidity to meet the requirements of standard production and experimental operations.
The viscosity of propylene glycol is notably temperature-dependent, generally decreasing as the temperature rises. As the temperature increases, intermolecular forces weaken and internal flow resistance drops, making the liquid easier to transport and mix. For instance, at approximately 40°C, the viscosity can fall to around 20 mPa·s. Consequently, in practical production, if it is necessary to enhance transport efficiency or improve mixing with other raw materials, the system's viscosity can be reduced by appropriately raising the temperature.
In the production of polyesters, polyurethanes, and other chemicals, the viscosity of propylene glycol affects raw material metering, transport, and mixing. Temperature-induced viscosity fluctuations must be taken into account, particularly in continuous production processes or operations requiring precise control of raw material ratios. In practice, viscosity values should be determined based on specific product purity, temperature, and testing conditions; furthermore, appropriate transport and mixing parameters should be selected in conjunction with the production process to ensure the material enters subsequent reaction stages in a stable and uniform manner.