Hydroxypropyl methyl cellulose is a non-ionic cellulose mixed ether made from refined cotton after alkalization, using propylene oxide and methyl chloride as etherification agents, through a series of reactions. Hydroxypropyl methylcellulose is a non-ionic cellulose ether, white powder in appearance, odorless and tasteless. The degree of substitution is generally 1.2 to 2.0. Its properties are different by the ratio of methoxy content and hydroxypropyl content.
1. Product characteristics of hydroxypropyl methylcellulose:
1. Hydroxypropyl methylcellulose is easy to dissolve in cold water, and 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.
2. The viscosity of hydroxypropyl methyl cellulose is related to its molecular weight. The higher the molecular weight, the higher the viscosity. Temperature also affects its viscosity, as the temperature increases, the viscosity decreases. But its high viscosity has a lower temperature effect than methyl cellulose. The solution is stable when stored at room temperature.
3. The water retention of hydroxypropyl methyl cellulose depends on its addition amount, viscosity, etc. The water retention rate under the same addition amount is higher than that of methyl cellulose.
4. 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 impact on its performance, but alkali can speed up its dissolution and slightly increase its viscosity. Hydroxypropyl methylcellulose is stable to general salts, but when the concentration of the salt solution is high, the viscosity of the hydroxypropyl methylcellulose solution tends to increase.
5. Hydroxypropyl methylcellulose can be mixed with water-soluble polymer compounds to form a uniform and higher viscosity solution. Such as polyvinyl alcohol, starch ether, vegetable glue, etc.
6. Hydroxypropyl methyl cellulose has better enzyme resistance than methyl cellulose, and the possibility of enzymatic degradation in solution is lower than that of methyl cellulose.
7. The adhesion of hydroxypropyl methyl cellulose to mortar construction is higher than that of methyl cellulose.
2. Synthesis method of hydroxypropyl methylcellulose:
The refined cotton cellulose is treated with lye at 35-40°C for half an hour, pressed, the cellulose is crushed, and appropriately aged at 35°C, so that the obtained alkali fiber average degree of polymerization is within the required range. Put the alkali fiber into the etherification kettle, add propylene oxide and methyl chloride successively, and etherify at 50-80℃ for 5h, the maximum pressure is about 1.8MPa. Then add proper amount of hydrochloric acid and oxalic acid to wash the materials in hot water at 90°C to increase the volume. Dehydrate with a centrifuge. Wash to neutral. When the water content in the material is less than 60%, dry it with a stream of hot air at 130°C to less than 5%. Finally, it is crushed through a 20-mesh sieve to obtain the finished product.