What is the appropriate viscosity of hydroxypropyl methylcellulose (HPMC)?

The viscosity of hydroxypropyl methylcellulose (HPMC) depends on the specific application scenario and performance requirements. HPMC is a commonly used non-ionic cellulose ether with good thickening, film-forming, stabilizing and water-retaining properties, so it is widely used in building materials, pharmaceuticals, food and cosmetics.

1. Definition and unit of viscosity of HPMC
The viscosity of HPMC is usually based on the measured value of 2% aqueous solution, and the unit is mPa·s (millipascals·seconds). The methods for measuring viscosity include capillary method, rotation method and falling ball method. Different test methods will result in different viscosity values, but the measurement results of Brookfield rotational viscometer are usually used.

2. Principles for selecting HPMC viscosity
2.1 Building materials field
Putty powder, mortar and tile adhesive
HPMC is used in building materials mainly to thicken, resist sagging and improve construction performance.
Viscosity range: usually 4000-200000 mPa·s.
Low viscosity (4000-20000 mPa·s): Improves material fluidity and is suitable for spraying products.
Medium-high viscosity (20000-100000 mPa·s): Improves the water retention and anti-slip properties of the material and is suitable for manual construction.
Ultra-high viscosity (>100000 mPa·s): Suitable for scenes with extremely high requirements for water retention, such as construction under high temperature environments.

2.2 Pharmaceutical field
Tablet coating, sustained-release agents and capsules
HPMC is a drug excipient, mainly used for film formation, thickening of tablets and substrates for controlled-release preparations.
Viscosity range: 3-100000 mPa·s.
Low viscosity (3-50 mPa·s): Used for tablet coating, uniform film formation and fast drying.
Medium viscosity (50-4000 mPa·s): Used as a thickener or sustained-release agent to improve the drug release stability.
High viscosity (>4000 mPa·s): used for capsule molding or special controlled release matrix.

2.3 Food and cosmetics field
Thickener, emulsion stabilizer
In the food industry, HPMC is mainly used as a thickener and emulsion stabilizer; in cosmetics, it can be used to improve the stability of emulsions and pastes.
Viscosity range: 5-5000 mPa·s.
Low viscosity (5-100 mPa·s): used for emulsions or transparent beverages to maintain the fluidity of the product.
Medium-high viscosity (1000-5000 mPa·s): used for paste cosmetics and high-viscosity foods such as jams or creams.

3. Factors affecting HPMC viscosity
The viscosity of HPMC is affected by the following factors:

Molecular weight: The higher the molecular weight of HPMC, the greater its viscosity.
Concentration: As the concentration of the solution increases, the viscosity will also increase.
Temperature: High temperature will reduce the viscosity, so it is necessary to choose a higher viscosity product when applying at high temperature.
pH value of solution: HPMC exhibits a relatively stable viscosity in the pH range of 3-11.

4. Optimization suggestions for viscosity selection
In practical applications, comprehensive considerations should be taken when selecting the viscosity of HPMC:

Process requirements: Spraying process requires lower viscosity, and manual construction is suitable for medium and high viscosity.

Performance balance: Low viscosity is easier to disperse, but high viscosity has better water retention and anti-slip properties.

Environmental conditions: Environmental factors such as temperature and humidity will directly affect the construction performance.

The choice of HPMC viscosity should be flexibly adjusted according to specific needs and application scenarios to ensure the best cost-effectiveness and effect while meeting basic functions.