1. Alkaline cellulose is a kind of natural polymer. Each fiber base ring contains three hydroxyl groups. The most active hydroxyl group reacts to form hydroxyethyl cellulose. Soak the raw cotton linter or refined pulp in 30% liquid alkali, and take it out for pressing after half an hour. Press until the ratio of alkaline water reaches 1:2.8, and then crush. The crushed alkali cellulose is put into the reactor, sealed, vacuumized, filled with nitrogen, and repeatedly vacuumized and filled with nitrogen to completely replace the air in the reactor. Pre-cooled ethylene oxide liquid is pressed in, cooling water is injected into the jacket of the reaction kettle, and the reaction is controlled at 25 ℃ for about 2h to obtain crude hydroxyethyl cellulose. The crude product is washed with alcohol, neutralized with acetic acid to pH4-6, and then cross-linked and aged with glyoxal. Then wash with water, centrifuge, dry and grind to obtain hydroxyethyl cellulose. Raw material consumption (kg/t): cotton linter or low pulp: 730-780, liquid alkali (30%): 2400, ethylene oxide: 900, alcohol (95%): 4500, acetic acid: 240, glyoxal (40%): 100-300.
2. Gas phase method: gas phase method is to add additives or diluents during the reaction process, and alkali fiber and EO react in the gas phase. The cotton fiber is soaked and activated in 18.5% NaOH solution, and then pressed and crushed into a reactor. Vacuum the reactor, fill it with nitrogen twice, add EO, and react for 3~3.5h at a vacuum of 90.64kPa and 27~32 ℃.
3. Liquid phase method: liquid phase method is etherification reaction in the presence of diluent. After the cotton linter is alkalized and pressed, it reacts with EO at 20~60 ℃ for 1~3h in the presence of diluent to obtain the crude hydroxyethyl cellulose. Commonly used diluents include acetone, isopropanol, tert-butanol or their mixture. The product remains insoluble in the diluent.
The two production processes of gas-phase method and liquid-phase method need to prepare alkali cellulose in advance, that is, the cellulose is immersed in 18% NaOH solution at about 20 ℃ for degreasing, and the final product is obtained after the etherification reaction, neutralization, washing, drying and crushing.
