Hydroxyethyl methyl cellulose (HEMC) is a non-ionic cellulose ether widely used in construction, coatings, ceramics, medicine, food and other industries. HEMC has good water solubility, thickening, water retention, film-forming and bonding properties, and plays an important role in dry-mixed mortar, latex paint, detergent and other fields.
1. Production process
1.1 Raw material preparation
HEMC is mainly prepared from natural plant cellulose, methyl chloride (CH₃Cl), ethylene oxide (C₂H₄O), sodium hydroxide (NaOH) and other raw materials.
Cellulose: Wood pulp or cotton pulp is often used as the main raw material, which requires high purity and few impurities to ensure product quality.
Alkalizer (NaOH): used to activate cellulose and improve reaction activity.
Etherifying agent (CH₃Cl and C₂H₄O): provide methyl and hydroxyethyl groups respectively, so that cellulose undergoes substitution reaction, improves water solubility and functional properties.
Organic solvent (such as isopropanol): used to dissolve reactants, control reaction environment and reduce side reactions.
1.2 Alkalization treatment
After cellulose is crushed, an appropriate amount of sodium hydroxide solution is added and alkalization treatment is carried out at a certain temperature and pressure, which usually takes 30-60 minutes. The main purpose of alkalization is to expand the cellulose molecular chain and improve its reactivity with the etherifying agent. This process is usually carried out in a closed reactor with stirring to ensure that the alkali solution evenly penetrates into the cellulose.
1.3 Etherification reaction
The alkalized cellulose reacts with methylation and hydroxyethylation reagents (CH₃Cl and C₂H₄O) in a reactor to produce hydroxyethyl methyl cellulose. Reaction conditions include:
Temperature: 60-90°C
Pressure: 0.5-1.5 MPa
Time: 2-5 hours
During the reaction, methylation and hydroxyethylation reactions proceed simultaneously, so that the hydroxyl (-OH) part of the cellulose is replaced by methyl (-OCH₃) and hydroxyethyl (-OCH₂CH₂OH), thereby changing its solubility and thickening properties. In order to improve the degree of substitution (DS and MS values), it is usually necessary to optimize the order and proportion of etherification agent addition.
1.4 Neutralization and washing
After the reaction is completed, the system still contains unreacted alkali, solvent and by-products (such as NaCl). Therefore, neutralization and washing are required:
Neutralization: Use acid (such as acetic acid) to neutralize the alkali in the system and adjust the pH value to 6-8.
Washing: Use a large amount of hot water or ethanol aqueous solution to repeatedly wash the cellulose to remove unreacted substances and by-products, reduce the impurity content, and improve the purity of the product.
1.5 Drying and crushing
After washing, HEMC still contains high moisture and needs to be dried. Common drying methods are:
Airflow drying: using high-speed hot air to dry wet HEMC, with high efficiency and suitable for large-scale production.
Vacuum drying: heating and drying under low pressure environment, which can effectively prevent cellulose degradation and is suitable for high-quality products.
After drying, HEMC is crushed by a pulverizer and the particle size is controlled by screening to achieve the required fineness of the product (usually 80-120 mesh).
2. Quality control
HEMC quality control mainly includes the following indicators:
Degree of substitution (DS and MS): determines the solubility and viscosity, generally DS is between 1.1-2.0 and MS is between 0.1-0.5.
Moisture content: usually required to be ≤ 5%.
Viscosity: different viscosity grades are required for different application fields (such as 400-100,000 mPa·s).
Purity: requires low ash content, removal of residual solvents, and ensure no odor.
3. Main application areas
Building materials: used in cement mortar, putty powder, tile adhesive, to improve water retention and construction performance.
Coating industry: used in latex paint and paint, to provide good rheology and anti-sagging performance.
Medicine and food: as a thickener and emulsifier, in line with food grade or pharmacopoeia standards.
The HEMC production process includes alkalization, etherification, neutralization, washing, drying and crushing. Optimizing process parameters and improving substitution degree and product purity are the keys to improving HEMC performance. With the increasing requirements for environmental protection and green manufacturing, HEMC production will pay more attention to energy conservation and emission reduction and the application of green solvents in the future.
Post time: May-08-2025