Synthesis and product properties of hydroxypropyl methyl cellulose
Hydroxypropyl methyl cellulose HPMC is a nonionic cellulose ether made by a series of reactions after refined cotton is alkalized with propylene oxide and methane chloride as etherifying agent. Hydroxypropyl methyl cellulose for non-ionic cellulose ether, the appearance of white powder, odorless tasteless. The degree of substitution is generally 1.2~2.0. Its properties vary with the proportion of methoxy and hydroxypropyl content.
A, hydroxypropyl methyl cellulose HPMC product characteristics:
1, hydroxypropyl methyl cellulose HPMC is easily soluble in cold water, hot water will encounter difficulties in dissolution. However, its gelation temperature in hot water is obviously higher than that of methyl cellulose. The solubility of methyl cellulose in cold water was also improved greatly.
2. The viscosity of hydroxypropyl methyl cellulose is related to its molecular weight, and the larger the molecular weight, the higher the viscosity. Temperature will also affect its viscosity, temperature increases, viscosity decreases. But its high viscosity temperature effect is lower than that of methyl cellulose. The solution is stable when stored at room temperature.
3. The water retention of hydroxypropyl methyl cellulose depends on its addition amount and viscosity, etc. The water retention rate of hydroxypropyl methyl cellulose is higher than that of methyl cellulose under the same addition amount.
4. Hydroxypropyl methyl cellulose HPMC is stable to acid and base, and its aqueous solution is very stable in the range of pH=2~12. Caustic soda and lime water had little effect on its properties, but alkali could accelerate its dissolution rate and slightly increase its viscosity. Hydroxypropyl methyl cellulose is stable to general salts, but when the concentration of salt solution is high, the viscosity of hydroxypropyl methyl cellulose solution tends to increase.
5, hydroxypropyl methyl cellulose can be mixed with water-soluble polymer compounds to become a uniform, higher viscosity solution. Such as polyvinyl alcohol, starch ether, vegetable glue and so on.
6. Hydroxypropyl methyl cellulose has better enzyme resistance than methyl cellulose, and its solution enzyme degradation possibility is lower than methyl cellulose.
7, hydroxypropyl methyl cellulose on mortar construction bonding is higher than methyl cellulose.
B, hydroxypropyl methyl cellulose HPMC synthesis method:
The refined cotton cellulose is treated with lye at 35-40℃ for half an hour, pressed, the cellulose is crushed and aged at 35℃, so that the average polymerization degree of the alkali fiber obtained is within the required range. Put the alkali fiber into the etherification kettle, add propylene oxide and methane chloride successively, etherize at 50-80℃ for 5h, the highest pressure is about 1.8mpa. Then add proper amount of hydrochloric acid and oxalic acid washing materials in 90℃ hot water to enlarge the volume. Dehydrate with a centrifuge. Wash to neutral, when the water content of the material is less than 60%, dry to less than 5% with hot air flow at 130℃. Finally crushed through 20 mesh sieve finished product.