Glycerol is generally stable under sunlight, but after long-term exposure or intense radiation, it will be oxidized by air, especially in the presence of metals such as iron or copper, the oxidation will accelerate, and the presence of water will also accelerate the oxidation. Intense ultraviolet radiation causes glycerol to produce carbon dioxide, aldehydes and acids. But the weaker radiation produces glycerol sugar. A small amount of hydrogen peroxide can greatly accelerate the oxidation reaction. Glycerol is exposed to ultraviolet radiation and air, and glyceraldehyde is formed in neutral solution at 25 ℃.
The apparent and true proportions of 99% glycerol at 25 ℃ are about 1.25945 and 1.25970 respectively. The proportion of glycerol increases with the increase of glycerol content and decreases with the increase of temperature.
The density of 99% glycerol is about 1.25546 at 25 ℃. The density of glycerol increases with the increase of glycerol content and decreases with the increase of temperature.
Glycerol expands when heated, and the extent of its expansion can be determined by its volume and density.
When glycerol and water are mixed, the total volume decreases slightly and the temperature rises slightly.
The boiling point of pure glycerol increases with the increase of pressure. The boiling point of pure glycerol is about 290 ℃at 760 mm mercury column pressure.
Glycerol has a strong hygroscopicity. Even if the moisture content in the air is very small, anhydrous glycerol will still absorb moisture from the air. Any concentration of glycerol exposed to the air will release or absorb moisture until the concentration is in equilibrium with the humidity of the air. Within the normal range of pressure change, if the relative humidity remains unchanged, the change of temperature has no significant effect on the equilibrium concentration. When glycerol is placed in the air or distributed on certain substances, such as colloids, the time to reach equilibrium with the relative humidity of the air may be extended to many days. If glycerol is coated in a thin film, such as fibers or paper, the equilibrium can be achieved in a few seconds. When glycerol is distributed on fiberglass to form a thin layer, it can adjust its relative humidity from 76% to 16% within 35 minutes. When it changes from low humidity to high humidity, the same result will be achieved.
The viscosity of 99% glycerol is about 775 CP at 20 ℃. The viscosity of glycerol increases with the increase of glycerol content and with the decrease of temperature. Glycerol viscosity varies in a wide range. The viscosity of 99% glycerol at 0 ℃ is about 9420 cp, while that of 235 CP at 40 ℃ is about 235 CP. Electrolyte dissolution in anhydrous glycerol and glycerol solution usually increases the viscosity of glycerol, but there are a few exceptions. The higher the concentration of these salts, the higher the glycerol concentration and the higher the temperature, the more the viscosity decreases.
