Hydroxypropyl methyl cellulose (HPMC), also known as hypromellose, cellulose hydroxypropyl methyl ether, is made by using highly pure cotton cellulose as raw material and specially etherified under alkaline conditions. Got.
Hydroxypropyl methyl cellulose has thermal gel properties and is easily soluble in cold water, but it will be difficult to dissolve in hot water. But its gelation temperature in hot water is significantly higher than that of methyl cellulose. The dissolution in cold water is also greatly improved compared to methyl cellulose.
After the aqueous solution is heated, it forms a gel and precipitates, and then dissolves after cooling. The gel temperature of products of different specifications is different. The solubility changes with the viscosity. The lower the viscosity, the greater the solubility. There are certain differences in the properties of different specifications of HPMC. The dissolution of HPMC in water is not affected by the pH value. Bulk density: 0.25-0.70g/(usually about 0.4g/), specific gravity 1.26-1.31. Discoloration temperature: 180-200℃, carbonization temperature: 280-300℃. The methoxy value is 19.0% to 30.0%, and the hydroxypropyl value is 4% to 12%. Viscosity (22℃, 2%) 5～200,000mPa.s. Gel temperature (0.2%) 50-90℃. HPMC has the characteristics of thickening ability, salt discharge, pH stability, water retention, dimensional stability, excellent film-forming properties, and wide range of enzyme resistance, dispersibility and adhesion.
Hydroxypropyl methylcellulose is stable to acid and alkali, and its aqueous solution is very stable in the range of pH=2~12. Caustic soda and lime water do not have much effect on its performance, but alkali can speed up its dissolution rate and increase viscosity. Hydroxypropyl methyl cellulose is stable to general salts, but when the concentration of the salt solution is high, the viscosity of the hydroxypropyl methyl cellulose solution tends to increase.