Synthesis method of hydroxypropyl methylcellulose

Synthesis method of hydroxypropyl methylcellulose

Generally, in the synthesis of hydroxypropyl methylcellulose, the refined cotton cellulose is treated with alkali solution at 35-40°C for half an hour, squeezed, the cellulose is crushed, and appropriately aged at 35°C, so that the resulting alkali fiber is averagely polymerized The degree is within the required range. Put the alkali fiber into the etherification kettle, add propylene oxide and methyl chloride in sequence, and etherify at 50-80°C for 5 hours to a high pressure of 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%.
Alkalization: The powdered refined cotton after opening the cotton is added to an inert solvent and activated with alkali and soft water to swell the crystal lattice of the refined cotton to facilitate the penetration of etherifying agent molecules and improve the uniformity of the etherification reaction. The alkali used for alkalization is a metal hydroxide or an organic base. The amount of alkali added (by mass, the same below) is 0.1-0.6 times that of refined cotton, the amount of soft water added is 0.3-1.0 times that of refined cotton; the inert solvent is a mixture of alcohol and hydrocarbon, and the amount of inert solvent added is refined cotton 7-15 times: the inert solvent can also be alcohols with 3-5 carbon atoms (such as alcohol, propanol), acetone. It can also be aliphatic hydrocarbons and aromatic hydrocarbons; the temperature during alkalization should be controlled within 0-35℃; the alkalization time is about 1hr. The temperature and time can be adjusted according to the requirements of the post-materials and products.
Etherification: After alkalization, under vacuum conditions, add etherification agent for etherification, etherification agent is propylene oxide. In order to reduce the consumption of the etherifying agent, the etherifying agent is added in two times during the etherification process.