Introduction and production process of hydroxypropyl methylcellulose (HPMC)

1. Introduction to HPMC

Hydroxypropyl methylcellulose (HPMC) is a non-ionic cellulose ether made from natural polymer materials such as refined cotton or wood pulp through chemical treatments such as alkalization, etherification, and neutralization. HPMC has good water solubility, thickening, emulsification, film-forming, adhesion, water retention, and thermal gelation, and is widely used in building materials, medicine, food, cosmetics, coatings, ceramics, daily chemicals and other industries.

2. Main properties of HPMC

Water solubility: HPMC can be quickly dispersed and dissolved in cold water to form a transparent or translucent viscous solution.

Thickening: It has a good thickening effect and can be used in coatings, building materials and other fields.

Water retention: In cement mortar and putty powder, it can effectively reduce water loss and improve construction performance.

Lubricity: Reduce friction and improve construction smoothness.

Film-forming property: HPMC can form a flexible transparent film, which is used in the fields of medicine, food and coatings.

Thermal gelation: When the temperature rises, the HPMC solution will form a gel, and after cooling, it will return to a dissolved state. This property has important applications in the fields of food and medicine.

3. Production process of HPMC

The production process of HPMC mainly includes raw material preparation, alkalization treatment, etherification reaction, neutralization washing, drying, crushing and packaging. The specific process is as follows:

Raw material preparation

The main raw material is refined cotton or wood pulp, and its main component is cellulose. Refined cotton needs to be degreased, bleached, dried and other treatments to ensure its purity and reactivity.

Alkalization treatment

The refined cotton or wood pulp is mixed with sodium hydroxide (NaOH) solution to make the cellulose molecules swell in an alkaline environment and form alkali cellulose, which increases its reactivity with the etherifying agent. This process is generally carried out in a closed reactor with a temperature controlled at 25-40℃.

Etherification reaction

Add methyl etherification agent (such as methyl chloride) and hydroxypropylation agent (such as propylene oxide) to the alkalized cellulose, and carry out etherification reaction at a certain temperature and pressure to partially replace the hydroxyl groups of cellulose and generate hydroxypropyl methylcellulose.

Methyl etherification reaction: methyl chloride (CH3Cl) reacts with alkali cellulose to generate methyl cellulose.

Hydroxypropylation reaction: propylene oxide (C3H6O) reacts with alkali cellulose to generate hydroxypropyl substituents.

Neutralization washing

After the reaction, the system still contains unreacted alkali and by-products (such as salts). Neutralization treatment is carried out by adding acidic solution (such as acetic acid or hydrochloric acid), followed by repeated washing with hot water to remove impurities and unreacted products to obtain purer HPMC.

Drying and crushing

After the wet HPMC is dehydrated by centrifugation, it is sent to a drying device (such as an air flow dryer or a drum dryer) for drying treatment to control the appropriate moisture content (generally ≤5%). After drying, HPMC is crushed and sieved to obtain products of different fineness.

Packaging and storage

After quality inspection, HPMC is packaged according to customer needs, generally in 25kg paper-plastic composite bags or kraft paper bags to avoid moisture absorption. The storage environment requires dryness, coolness, ventilation, and avoid high temperature and humidity.

4. Application fields of HPMC

Construction industry: used in cement mortar, tile adhesive, putty powder, etc. to improve construction performance and adhesion.

Pharmaceutical industry: used as tablet coating, sustained-release material, gel, etc., in accordance with USP and EP standards.

Food industry: used as thickener, emulsifier, stabilizer, such as in ice cream, bread and other foods.

Coating industry: improve the rheological properties of coatings, improve the water resistance and adhesion of coatings.

Daily chemical industry: used in shampoo, shower gel, toothpaste, etc. to improve viscosity and stability.

As an important cellulose derivative, HPMC is widely used in many industries due to its excellent water solubility, thickening, water retention and biocompatibility. Its production process involves key steps such as alkalization, etherification, neutralization, washing, and drying, which require strict control of process conditions to ensure product quality. With the advancement of technology and the growth of market demand, the application field of HPMC will be further expanded, and its development prospects are broad.