What is the viscosity of HPMC?

Hydroxypropyl methylcellulose (HPMC) is a common water-soluble polymer widely used in building materials, pharmaceuticals, food, coatings, and daily chemicals. One of its most prominent properties is viscosity, which not only affects the rheological properties of the solution but also directly impacts the product's application performance, film-forming properties, and user experience. So, what exactly is the viscosity of HPMC?

HPMC Viscosity Range

The viscosity of hydroxypropyl methylcellulose is typically expressed as millipascals-seconds (mPa·s) of a 2% aqueous solution at 20°C. Depending on the type, the viscosity range varies greatly, ranging from tens to hundreds of thousands of mPa·s:

Low-viscosity HPMC: approximately 20–100 mPa·s, is often used in applications requiring rapid dissolution and good fluidity, such as sprays and surface treatment fluids.

Medium-viscosity HPMC: Approximately 400–6,000 mPa·s. It is commonly used in construction mortars, putty powders, coatings, and other applications to improve water retention and leveling.

High-viscosity HPMC: 20,000–200,000 mPa·s, and even exceeding 300,000 mPa·s. It is primarily used in products requiring stronger viscosity and thickening properties, such as tile adhesives, pharmaceutical sustained-release tablet bases, and food thickeners.

Therefore, HPMC does not have a fixed "viscosity value," but rather a range. Users must select the appropriate grade based on the application.

Factors Affecting HPMC Viscosity

Degree of Substitution (DS/MS Value): Different degrees of substitution with methoxy and hydroxypropoxy groups on the HPMC molecule affect both water solubility and viscosity. A high degree of methoxy substitution results in better solubility but relatively lower viscosity; an increase in the hydroxypropoxy group content enhances the thickening effect of the solution.

Solution Concentration: For the same HPMC grade, higher concentrations increase the viscosity. The general test standard is 2%, but in actual application, this often varies depending on the formulation ratio.

Dissolution Temperature and Method: HPMC has thermogel properties and is easily dispersed in cold water, but complete dissolution requires an appropriate temperature and time. If dissolution is incomplete, the measured viscosity will be lower.

Molecular Weight: The larger the molecular weight, the longer the chain segments, the stronger the entanglement, and the higher the apparent viscosity.

Shear Rate: HPMC solutions generally behave as pseudoplastic fluids, meaning that the apparent viscosity decreases with increasing shear rate, which is very beneficial during construction.

The Significance of Viscosity in Applications

3.1. Construction and Building Materials

In putty powders and dry-mix mortars, medium- to high-viscosity HPMC can significantly improve water retention, fully hydrating the cement and preventing cracking caused by rapid water loss.

In tile adhesives, high-viscosity grades can enhance adhesion and anti-slip properties.

3.2. Pharmaceuticals

Low- to medium-viscosity HPMC is often used in capsule shells or film coatings to ensure transparency and uniformity. High-viscosity HPMC is used in sustained-release formulations to form a gel barrier and delay drug release.

3.3. Food and Daily Chemicals

In food, HPMC acts as a thickener and stabilizer to adjust mouthfeel.

In shampoos and skincare products, medium-viscosity HPMC improves flow and emulsion stability.

Principles for Selecting the Appropriate Viscosity

If you are looking for flow and easy dispersibility, choose low-viscosity HPMC.

If you require a balance between workability and water retention, choose medium-viscosity HPMC.

If you need thickening, film-forming, and sustained-release properties, choose high-viscosity HPMC.

The viscosity of HPMC is not a single value; it varies depending on the type, application, and concentration, typically ranging from 20–300,000 mPa·s. This wide viscosity range explains the diversity of HPMC applications across different industries. In construction, pharmaceuticals, food, and daily chemicals, selecting the right HPMC grade helps achieve specific functions such as adhesion, controlled release, stabilization, and water retention. Understanding viscosity differences and the factors that influence them allows users to better formulate products and improve overall performance.