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Characteristics and Synthesis of Hydroxypropyl Methyl Cellulose
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2022-07-25
Hydroxypropyl methyl cellulose is refined from cotton after alkalization, using propylene oxide and methyl chloride as etherifying agents, through a series of reactions to make non-ionic cellulose mixed ether. Hydroxypropyl methylcellulose is a non-ionic cellulose ether, white in appearance, odorless and tasteless. The degree of substitution is generally 1.2-2.0. Its properties vary depending on the ratio of methoxyl content and hydroxypropyl content.
Hydroxypropyl methyl cellulose is refined from cotton after alkalization, using propylene oxide and methyl chloride as etherifying agents, through a series of reactions to make non-ionic cellulose mixed ether. Hydroxypropyl methylcellulose is a non-ionic cellulose ether, white in appearance, odorless and tasteless. The degree of substitution is generally 1.2-2.0. Its properties vary depending on the ratio of methoxyl content and hydroxypropyl content.
First of all, first look at the synthesis of hydroxypropyl methylcellulose:
The refined cotton cellulose is treated with alkali solution at 35-40°C for half an hour, pressed, and the cellulose is pulverized and properly aged at 35°C, so that the average degree of polymerization of the obtained alkali fibers is within the required range. Put the alkali fiber into the etherification tank, add propylene oxide and methyl chloride in turn, and etherify at 50-80℃ for 5 hours, the maximum pressure is about 1.8MPa. Then add appropriate amount of hydrochloric acid and oxalic acid washing in hot water at 90°C to expand the volume. Dehydrate with a centrifuge. When the moisture content of the material is below 60%, it is rinsed to neutrality, and then dried to below 5% with a hot air flow at 130°C. Finally, a 20-mesh sieve was smashed to obtain a finished product. Second, hydroxypropyl methylcellulose product features:
1. Hydroxypropyl methylcellulose is easily soluble in cold water, but will dissolve in hot water. However, its gelation temperature in hot water is significantly higher than that of methylcellulose. Dissolution in cold water is also a great improvement over methylcellulose.
2. The viscosity of hydroxypropyl methylcellulose is related to the size of the molecular weight, and the viscosity is high when the molecular weight is large. Temperature also affects its viscosity, as the temperature increases, the viscosity decreases. But its high viscosity is lower than methyl cellulose. Its solutions are stable at room temperature.
As shown in Figure 3, the water retention capacity of hydroxypropyl methylcellulose depends on its addition amount, viscosity, etc., and its water retention rate is higher than that of methylcellulose.
4. Hydroxypropyl methylcellulose is stable to acid and alkali, and its aqueous solution is stable in the range of pH = 2~12. Caustic soda and lime water have little effect on its performance, but alkali can accelerate its dissolution and slightly increase its viscosity. Hydroxypropyl methylcellulose has stability to common 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 to form a solution with a uniform and high viscosity. Such as polyvinyl alcohol, lake powder ether, vegetable glue, etc.
As shown in Figure 6, hydroxypropyl methylcellulose is more resistant to enzymes than methylcellulose, and its solution enzymatic degradation potential is lower than that of methylcellulose.
7. The adhesion between hydroxypropyl methylcellulose and the mortar structure is higher than that of methylcellulose.
The above is a basic introduction to cellulose synthesis methods and product characteristics. Later Cellulose will bring you a more detailed explanation of hydroxypropyl methylcellulose. Stay tuned!
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