Background and Overview

Cellulose ether is a widely used polymer fine chemical material made from natural polymer cellulose through chemical treatment. After the manufacture of cellulose nitrate and cellulose acetate in the 19th century, chemists have developed a series of cellulose derivatives of many cellulose ethers, and new application fields have been discovered continuously, involving many industrial sectors. Cellulose ether products such as sodium carboxymethyl cellulose (CMC), ethyl cellulose (EC), hydroxyethyl cellulose (HEC), hydroxypropyl cellulose (HPC), methyl hydroxyethyl cellulose (MHEC) and methyl hydroxypropyl cellulose (MHPC) and other cellulose ethers are known as “industrial monosodium glutamate” and have been widely used in oil drilling, construction, coatings, food, medicine and daily chemicals.

Hydroxyethyl methyl cellulose (MHPC) is an odorless, tasteless, non-toxic white powder that can be dissolved in cold water to form a transparent viscous solution. It has the characteristics of thickening, binding, dispersing, emulsifying, film-forming, suspending, adsorbing, gelling, surface active, maintaining moisture and protecting colloid. Due to the surfaces active function of the aqueous solution, it can be used as a colloidal protective agent, emulsifier and dispersant. Hydroxyethyl methylcellulose aqueous solution has good hydrophilicity and is an efficient water retention agent. Because hydroxyethyl methylcellulose contains hydroxyethyl groups, it has good anti-mildew ability, good viscosity stability and mildew resistance during long-term storage.

Hydroxyethyl methylcellulose (HEMC) is prepared by introducing ethylene oxide substituents (MS 0.3~0.4) into methylcellulose (MC), and its salt resistance is better than that of unmodified polymers. The gelation temperature of methylcellulose is also higher than that of MC.

Structure

Feature

The main characteristics of hydroxyethyl methylcellulose (HEMC) are:

1. Solubility: Soluble in water and some organic solvents. HEMC can be dissolved in cold water. Its highest concentration is only determined by viscosity. Solubility varies with viscosity. The lower the viscosity, the greater the solubility.

2. Salt resistance: HEMC products are non-ionic cellulose ethers and are not polyelectrolytes, so they are relatively stable in aqueous solutions when metal salts or organic electrolytes exist, but excessive addition of electrolytes can cause gelation and precipitation.

3. Surface activity: Due to the surface active function of the aqueous solution, it can be used as a colloidal protective agent, emulsifier and dispersant.

4. Thermal gel: When the aqueous solution of HEMC products is heated to a certain temperature, it becomes opaque, gels, and precipitates, but when it is continuously cooled, it returns to the original solution state, and the temperature at which this gel and precipitation occurs is mainly Depending on them lubricants, suspending aids, protective colloids, emulsifiers etc.

5. Metabolic inertness and low odor and fragrance: HEMC is widely used in food and medicine because it will not be metabolized and has low odor and fragrance.

6. Mildew resistance: HEMC has relatively good mildew resistance and good viscosity stability during long-term storage.

7. PH stability: The viscosity of the aqueous solution of HEMC products is hardly affected by acid or alkali, and the pH value is relatively stable within the range of 3.0 to 11.0.

Application

Hydroxyethyl methylcellulose can be used as a colloidal protective agent, emulsifier and dispersant due to its surface-active function in aqueous solution. Its application examples are as follows:

1. Effect of hydroxyethyl methylcellulose on cement performance. Hydroxyethyl methylcellulose is an odorless, tasteless, non-toxic white powder that can be dissolved in cold water to form a transparent viscous solution. It has the characteristics of thickening, binding, dispersing, emulsifying, film-forming, suspending, adsorbing, gelling, surface active, maintaining moisture and protecting colloid. Since the aqueous solution has a surfaces active function, it can be used as a colloidal protective agent, emulsifier and dispersant. Hydroxyethyl methylcellulose aqueous solution has good hydrophilicity and is an efficient water retention agent.

2. A highly flexible relief paint is prepared, which is made of the following raw materials in parts by weight: 150-200 g of deionized water; 60-70 g of pure acrylic emulsion; 550-650 g of heavy calcium; 70-90 g of talcum powder; Base cellulose aqueous solution 30-40g; lignocellulose aqueous solution 10-20g; film-forming aid 4-6g; antiseptic and fungicide 1.5-2.5g; dispersant 1.8-2.2g; wetting agent 1.8-2.2g; 3.5-4.5g; Ethylene glycol 9-11g; The hydroxyethyl methylcellulose aqueous solution is made by dissolving 2-4% hydroxyethyl methylcellulose in water; The lignocellulose aqueous solution is made of 1-3 % Lignocellulose is made by dissolving in water.

Preparation

A preparation method of hydroxyethyl methyl cellulose, the method is that refined cotton is used as raw material, and ethylene oxide is used as an etherification agent to prepare hydroxyethyl methyl cellulose. The weight parts of raw materials for preparing hydroxyethyl methylcellulose are as follows: 700-800 parts of toluene and isopropanol mixture as solvent, 30-40 parts of water, 70-80 parts of sodium hydroxide, 80-85 parts of refined cotton, ring 20-28 parts of oxy ethane, 80-90 parts of methyl chloride, 16-19 parts of glacial acetic acid; the specific steps are:

The first step, in the reaction kettle, add toluene and isopropanol mixture, water, and sodium hydroxide, heat up to 60-80 ° C, keep warm for 20-40 minutes;

The second step, alkalization: cool the above materials to 30-50°C, add refined cotton, spray the toluene and isopropanol mixture solvent, vacuumize to 0.006Mpa, fill nitrogen for 3 replacements, and carry out after the replacement Alkalinization, the alkalization conditions are: the alkalization time is 2 hours, and the alkalization temperature is 30°C to 50°C;

The third step, etherification: after the alkalization is completed, the reactor is evacuated to 0.05-0.07MPa, and ethylene oxide and methyl chloride are added for 30-50 minutes; the first stage of etherification: 40-60°C, 1.0-2.0 Hours, the pressure is controlled between 0.15 and 0.3Mpa; the second stage of etherification: 60～90℃, 2.0～2.5 hours, the pressure is controlled between 0.4 and 0.8Mpa;

The fourth step, neutralization: add the measured glacial acetic acid in advance to the precipitation kettle, press into the etherified material for neutralization, raise the temperature to 75-80°C for precipitation, the temperature rises to 102°C, and the pH value is detected to be 6 At 8 o’clock, the desolventization is completed; the desolventization tank is filled with tap water treated by a reverse osmosis device at 90 ° C to 100 ° C;

The fifth step, centrifugal washing: the material in the fourth step is centrifuged through a horizontal screw centrifuge, and the separated material is transferred to a washing tank filled with hot water in advance for washing of the material;

The sixth step, centrifugal drying: the washed material is conveyed into the dryer through a horizontal screw centrifuge, and the material is dried at 150-170°C, and the dried material is crushed and packaged.

Compared with the existing cellulose ether production technology, the present invention uses ethylene oxide as an etherification agent to prepare hydroxyethyl methyl cellulose, which has good mildew resistance because of containing hydroxyethyl groups. It has good viscosity stability and mildew resistance during long-term storage. It can be used instead of other cellulose ethers.